Patent Application
20070174933
The present invention relates to methods of altering anti-nutrient factors within plants, and plants with altered levels of anti-nutrient factors.
Oil seeds are well known for their high value associated with oil and oil-related products. Proteins obtained from plants, including plant oil seeds for example Canola, are known for their good nutritional qualities. These nutritional properties include, a good balance of essential amino acids, including sulfur binding amino acids, as compared to other plant-based proteins; a low molecular weight of major storage proteins (a characteristic that is usually associated with low antigenicity); and the protein efficiency ratio that in some cases, for example with canola protein, is similar to those of known high quality proteins, such as beef and milk, and better than those of other plant proteins, such as soybean. Despite these high quality characteristics, some plant proteins obtained from oil seeds, including canola protein, are considered a by-product of oil processing, and are used as a low-grade protein source and on a limited scale within livestock feed. Despite the high potential value of canola meal, its market share trails those of other oil seeds, such as soybean. The low value of the canola seed meal is attributed mainly to the high levels of anti-nutritional factors that remain in the seed. These factors include sinapine, fiber and phytate.
Sinapine is found almost exclusively in the seeds of crucifers. Canola seeds contain sinapine at levels ranging from 0.7% to 3%, with about 90% of it present in the embryo (non-hull) fraction. It is the cause for an unpleasant flavour in the meat and milk in animals fed on the canola meal, and the bitter flavor of sinapine results in poor palatability for livestock and fish. Moreover, consumption of sinapine in canola meal by brown-shelled egg layers that are deficient in trimethylamine oxidase imparts a fishy odour on the eggs. Upon consumption of larger amounts, sinapine can also cause serious growth and reproduction problems.
Attempts have been made to reduce sinapine levels via metabolic engineering and plant breeding. A 40% sinapine reduction in seeds of Brassica napus (the main canola species) was achieved by antisense RNA down regulation of ferulic acid 5-hydroxylase (F5H; Nair et al., 2000, Plant Physiol. 123: 1623-1634), and 76% reduction was achieved when sinapate glucosyltransferase (SGT) gene was silenced by RNAi (Husken et al., 2005, Theor. Appl. Genet. 111: 1553-1562). Efforts have also been made towards the identification of low sinapine Brassica germplasm to generate low sinapine varieties by classical plant breeding (Velasco and Möllers, 1998, Crop Sci. 38: 1650-1654).
U.S. Pat. No. 6,501,004 discloses the expression of sense and antisense constructs of ferulate 5-hydroxylase (F5H) in B. napus. Expression of either sense or antisense constructs resulted in a reduction of sinapine levels.
Dietery fiber may represent a significant portion of the meal of seed, for example about a third of canola meal is comprised of dietary fiber. High fiber content can have adverse effects on meal quality, diet digestibility and feed efficiency. Lignin comprises a considerable portion of dietary fiber in the meal, and high levels of it can have adverse effects on meal quality, particularly for fish feed. Fish are very sensitive to high dietary fiber levels. For example, dietary fiber levels of over 10% have a negative impact on growth, diet digestibility, and feed efficiency in trout. Furthermore, high levels of lignin in trees is undesirable for pulp and paper processing where the lignin must be separated from the cellulose fiber used for the production of paper.
Yellow-seeded cultivars of Brassica napus have been developed at Agriculture and Agri-Food Canada's Research Centre in Saskatoon that have lower fibre content of the seed due to the thinner hull of the yellow-seeded types (Relf-Eckstein et al., 2003, In Proceedings of the 11th International Rapeseed Congress, BP9.36 pp. 458-460). Several mutants deficient in the fibre component lignin have been identified in several plant species, including maize and Arabidopsis. In maize, the bm3 mutant has about 12% less lignin than the wild type plant (Grand et al., 1985, Physiol. Veg., 23: 905-911). This mutant is caused by a knockout of the gene coding for caffeic acid o-methyltransferase (COMT; Vignols et al. 1995, Plant Cell, 7: 407-416). In Arabidopsis, the fah1 mutant, caused by T-DNA insertion in the F5H gene (Chapple et al., 1994, Secondary metabolism in Arabidopsis, In Meyerowitz E M and Somerville C R (eds.) Arabidopsis, Cold Spring Harbor Laboratory, Cold Spring harbor, N.Y., pp. 989-1030), has a modified lignin composition (Chapple et al., 1992, Plant Cell. 4: 1413-1424).
Several genes in the phenylpropanoid pathway, including COMT, hydroxycinnamyl alcohol dehydrogenase (CAD) and phenylalanine ammonia lyase (PAL), have been targets for downregulation to reduce lignin content in plants, among which COMT and PAL appeared to be the most promising genes. Transgenic tobacco plants expressing an antisense construct of the alfalfa COMT had a significantly lower lignin content (Ni et al., 1994, Transgen Res., 3: 120-126). Sense suppression of the tobacco PAL gene resulted in up to 3- to 4-fold decrease in lignin content as compared to the wild type (Bate et al., 1994, Proc Natl Acad Sci USA. 91: 7608-7612). On the other hand, repression of CAD expression in tobacco had a negligible impact on lignin content and composition (Haplin et al., 1994, Plant J., 6, 339).
U.S. Pat. No. 6,653,528 discloses the modification of lignin biosynthesis by expressing either a sense and antisense construct of each of O-methyl transferase (OMT), 4-coumarate:CoA lyase (4CL), coumarate 3 hydroxylase (C3H), ferulate 5 hydroxylase (F5H), cinnamoyl-CoA reductase (CCR), PAL, phenylalanine ammonia lyase (PAL), cinnamic acid 4 hydroxylase (C4H). A decrease in lignin concentration (determined by methanol-thioglycoic acid extraction), from 6 to 34% of the control value with was noted with the expression of the antisense construct of OMT. Interestingly, a greater decrease, from 25-45% of the control value, was noted with expression of the sense construct for OMT. Expression of the sense or antisense constructs for the other genes resulted in less of a decrease in lignin concentration when compared to OMT.
U.S. Pat. No. 6,066,780 describes the expression of cinnamyl alcohol dehydrogenase (CAD), CCR, or catechol-O-methyl transferase (COMT), and the effect of their expression on lignin concentration. Expression of the antisense construct of each of these genes resulted in an increase, rather than a decrease, of the TGA extractable products. U.S. Pat. No. 6,465,229 teaches the isolation of caffeoyl-CoA O methylase (CCOMT), however, the effect of expression of this gene in plants was not determined
Phytate is present in canola at levels ranging from 2.0-4.0% in the whole plant, 2.0-5.0% in the oil-free meal and 5.0-7.0% in protein concentrates. Fish and monogastric animals, such as swine and poultry, are unable to digest phytate. The release of phytate increases phosphate in animal waste, and leads to pollution of water systems. Increasing phosphate effluent is a major environmental problem in fresh water aquaculture. Phytate also binds mineral nutrients lowering their bioavailability in the diet, and reducing the nutritional value of the meal.
Several strategies have been used to reduce phytate levels in plant-derived feed. Phytate levels have been reduced by producing low phytate crop varieties, such as rice, maize and barley using mutant selection (Raboy et al. 2001, J. Plant Physiol. 158, 489-497), reducing phytate levels in Arabidopsis seeds through disruption of inositol polyphosphate kinase (Stevenson-Paulik, 2005, Proc. Natl. Acad. Sci. USA 102, 12612-1261), or treating feed with microbial phytases (Cromwell et al. 1995, J. Anim. Sci., 73: 2000-2008). WO 2005/014794 discloses the reduction of phytate levels in plants by modifying inositol phosphate kinase (Ipk1 and Ipk2) expression. Reduction of phosphorous manure has been obtained by engineering transgenic animals to produce heterologous phytases in their salivary glands (Golovan et al., 2001, Nat. Biotech, 19: 741-745). However, treatment of feed with microbial phytases is an expensive process, and is cost-effective only in regions where high penalties for disposing manure with high phosphorus content exist. Engineering animals to produce phytase in salivary glands is currently impractical with most animals. Other strategies, such as mutant screening and genetic engineering, have yet to yield B. napus varieties with substantially reduced levels of phytate.
The present invention relates to methods of altering anti-nutrient factors within plants, and plants with altered levels of anti-nutrient factors.
According to the present invention there is provided a method (A) for reducing the level of one or more than one protein in a plant or a tissue within the plant comprising,
i) introducing a nucleic acid sequence into the plant, the nucleic acid sequence comprising a regulatory region operatively associated with a silencing nucleotide sequence, wherein expression of the silencing nucleotide sequence reduces or eliminates the expression of two or more than two enzymes involved in the synthesis of the one or more than one protein, and
ii) expressing the silencing nucleotide sequence within the plant or a tissue within the plant, to reduce the level of the one or more than one protein in the plant or within a tissue of the plant, the reduced level of the one or more than one protein is determined by comparing the level of the one or more than one protein in the plant, or a tissue of the plant, with a level of the one ore more than one protein in a second plant, or the tissue from the second plant, that does not express the silencing nucleic acid sequence.
The present invention also provides the method as just defined (Method A), wherein in the step of introducing, the nucleotide sequence is introduced into the plant by transformation. Alternatively, the nucleotide sequence may be introduced into the plant by crossing the plant with a second plant, the second plant comprising the nucleotide sequence.
The present invention also provides the method as described above (method A) wherein the regulatory region is selected from the group consisting of a constitutive regulatory region, an inducible regulatory region, a developmentally regulated regulatory region, and a tissue specific regulatory region. The regulatory region is preferably a tissues specific regulatory region.
The present invention pertains to the method described above (method A), wherein the silencing nucleotide sequence is selected from the group consisting of an antisense RNA encoding nucleotide sequence, a ribozyme encoding sequence, and an RNAi encoding nucleotide sequence. Preferably, the silencing nucleotide sequence is a gene fusion. Furthermore, the gene fusion may comprise nucleic acid sequences encoding from two to five gene sequences.
The present invention also pertains to the method as described above (method A) wherein the protein is involved in the synthesis of an anti-nutrient factor in seed tissue. The anti-nutrient factor may be selected from the group consisting of sinapine, phytate, fiber, and lignin. Furthermore, the two or more than two enzymes are involved in a pathway of phenylpropanoid biosynthesis leading to sinapine synthesis, a pathway of phenylpropanoid biosynthesis leading to lignin synthesis, a pathway of phytate biosynthesis, or a combination thereof.
According to the present invention there is provided a method (B) for reducing the level of one or more than one protein involved in the synthesis of an anti-nutrient factor in a plant or a tissue within the plant comprising,
i) introducing a nucleic acid sequence into the plant, the nucleic acid sequence comprising a regulatory region operatively associated with a silencing nucleotide sequence, wherein expression of the silencing nucleotide sequence reduces or eliminates the expression of two or more than two enzymes involved in the synthesis of the one or more than one protein, and
ii) expressing the silencing nucleotide sequence within the plant or a tissue within the plant, to reduce the level of the one or more than one protein in the plant or within a tissue of the plant, the reduced level of the one or more than one protein is determine by comparing the level of the one or more than one protein in the plant, or a tissue of the plant, with a level of the one ore more than one protein in a second plant, or the tissue from the second plant, that does not express the nucleic acid sequence,
wherein the anti-nutrient factor is sinapine, and the two or more than two enzymes are involved in a pathway of phenylpropanoid biosynthesis.
The present invention also provides the method as described above (method B), wherein the two or more than two enzymes are selected from the group consisting of phenylalanine ammonia lyase (PAL), cinnamate 4 hydroxylase (C4H), coumarate 3 hydroxylase (C3H), caffeic acid-/5-hydroxyferulic acid O-methyltransferase (COMT; also referred to as O-methyl transferase, OMT), ferulic acid hydroxylase (FAH), sinapate:UDP-glucose sinapoyltransferase (SGT), sinapoylglucose:malate sinapoyltransferase (SMT), sinapoylglucose:choline sinapoyltransferase (SCT), S-adenosylmethionine synthase (SAMS).
Preferably, the two or more than two enzymes (in Method B) are FAH and SCT. Furthermore, the silencing nucleotide sequence is selected from the group consisting of an antisense RNA nucleotide sequence encoding sequence, a ribozyme encoding sequence, and an RNAi encoding nucleotide sequence.
According to the present invention there is provided a method (C) for reducing the level of one or more than one protein involved in the synthesis of an anti-nutrient factor in a plant or a tissue within the plant comprising,
i) introducing a nucleic acid sequence into the plant, the nucleic acid sequence comprising a regulatory region operatively associated with a silencing nucleotide sequence, wherein expression of the silencing nucleotide sequence reduces or eliminates the expression of two or more than two enzymes involved in the synthesis of the one or more than one protein, and
ii) expressing the silencing nucleotide sequence within the plant or a tissue within the plant, to reduce the level of the one or more than one protein in the plant or within a tissue of the plant, the reduced level of the one or more than one protein is determine by comparing the level of the one or more than one protein in the plant, or a tissue of the plant, with a level of the one ore more than one protein in a second plant, or the tissue from the second plant, that does not express the nucleic acid sequence,
wherein the anti-nutrient factor is lignin, and the two or more than two enzymes are involved in a pathway of phenylpropanoid biosynthesis.
The present invention also provides the method as described above (method C), wherein the two or more than two enzymes are selected from the group consisting of cinnamic acid 4 hydroxylase (C4H), coumaric acid 3 hydroxylase (C3H), caffeic acid O-methyl transferase (COMT), ferulic acid hydroxylase (FAH), S-adenosylmethionine synthase (SAMS), 4-coumarate:CoA lyase (4CL), and cinnamoyl-CoA reductase (CCR).
Preferably, the two or more than two enzymes (in Method C) are selected from the group consisting of FAH-COMT, C3H-C4H, and 4CL-CCR. Furthermore, the silencing nucleotide sequence is selected from the group consisting of an antisense RNA nucleotide sequence encoding sequence, a ribozyme encoding sequence, and an RNAi encoding nucleotide sequence.
According to the present invention there is provided a method (D) for reducing the level of one or more than one protein involved in the synthesis of an anti-nutrient factor in a plant or a tissue within the plant comprising,
i) introducing a nucleic acid sequence into the plant, the nucleic acid sequence comprising a regulatory region operatively associated with a silencing nucleotide sequence, wherein expression of the silencing nucleotide sequence reduces or eliminates the expression of two or more than two enzymes involved in the synthesis of the one or more than one protein, and
ii) expressing the silencing nucleotide sequence within the plant or a tissue within the plant, to reduce the level of the one or more than one protein in the plant or within a tissue of the plant, the reduced level of the one or more than one protein is determine by comparing the level of the one or more than one protein in the plant, or a tissue of the plant, with a level of the one or more than one protein in a second plant, or the tissue from the second plant, that does not express the nucleic acid sequence, wherein the anti-nutrient factor is phytate, and the two or more than two enzymes are involved in a pathway of phytate biosynthesis.
The present invention also provides the method as described above (method D), wherein the two or more than two enzymes are selected from the group consisting of inositol 1,3,4-trisphosphate 5/6-kinase (IP3K), IP6K, myo-inositol hexaphosphate kinase, 1-phosphatidylinositol-4,5-bisphosphate phosphodiesterase (PIBP PDE), phosphatidylinositol phophatidylcholine transfer protein (PI/PC TP), inositol polyphosphate 5-phosphatase II (IPP), phosphatidylinositol-4-phosphate 5-kinase (PIKa), CDP-diacylglycerol-inositol 3-phosphatidyltransferase (phosphatidylinositol synthase, PIS), inositol polyphosphate 6-/3-/5-kinase 2b (IPK2a & IPK2b), inositol polyphosphate 5′-phosphatase I (IPP), Myo-inositol-1-phosphate synthase (MIP), phosphatidylinositol kinase (PIPK), phosphatidylinositol 3-kinase (PI3K), Myo-inositol monophosphatase (MIM), and phosphatidylinositol 3- and 4-kinase (PIKb).
Preferably, the two or more than two enzymes (in Method D) are selected from the group consisting of IP3K-IP6K and PIKa-PIKb. Furthermore, the silencing nucleotide sequence is selected from the group consisting of an antisense RNA nucleotide sequence encoding sequence, a ribozyme encoding sequence, and an RNAi encoding nucleotide sequence.
The present invention also provides a construct comprising a silencing nucleotide sequence, the silencing nucleotide sequence encoding two or more than two sequences that reduce or inhibit the expression of two or more that two enzymes involved in the synthesis of the one or more than one protein leading to sinapine biosynthesis, lignin biosynthesis, phytate biosynthesis, or a combination thereof.
The present invention also pertains to a plant comprising a nucleic acid sequence comprising a regulatory region operatively associated with a silencing nucleotide sequence, the silencing nucleotide sequence reducing or eliminating the expression of two or more than two enzymes involved in the synthesis of the one or more than one protein leading to sinapine biosynthesis, lignin biosynthesis, phytate biosynthesis, or a combination thereof.
The present invention also provides a seed that is characterized as having reduced levels of one or more than one anti-nutrient compounds. Examples of an anti-nutrient compound include intermediates within the phenylpropanoid pathway, or products of the phenylpropanoid pathway including sinapine and lignin, the phytate biosynthetic pathway, including phytate. The level of the anti-nutrient compound may be reduced by about 10% to about 100%, or any amount therebetween, when compared to the level of the same anti-nutrient compound obtained from a second plant that does not express a silencing nucleotide sequence. For example, the anti-nutrient compound may be reduced by from about 10% to about 60% or any amount therebetween, about 10% to about 50% or any amount therebetween, about 10% to about 40% or any amount therebetween, or from about 10% to about 30%, or any amount therebetween, or about 10% to about 20% or any amount therebetween.
The present invention also provides a method (Method E) for reducing the level of one or more than one protein within a plant or a tissue within the plant comprising, expressing a nucleotide sequence within the plant or a tissue within the plant, the nucleic acid sequence comprising a regulatory region operatively associated with a silencing nucleotide sequence, where expression of the silencing nucleotide sequence reduces or eliminates the expression of two or more than two enzymes involved in the synthesis of the one or more than one protein leading to sinapine biosynthesis, lignin biosynthesis, phytate biosynthesis, or a combination thereof, the reduced level of the one or more than one protein determined by comparing the level of the protein in the plant, or a tissue of the plant, with a level of the protein in a second plant, or the tissue from the second plant, that does not express the nucleic acid sequence.
The present invention also provides a method (Method F) for reducing the level of one or more than one protein in a plant or a tissue within the plant comprising,
i) providing a plant comprising a nucleic acid sequence, the nucleic acid sequence comprising a regulatory region operatively associated with a silencing nucleotide sequence, wherein expression of the silencing nucleotide sequence reduces or eliminates the expression of two or more than two enzymes involved in the synthesis of the one or more than one protein, and
ii) expressing the silencing nucleotide sequence within the plant or a tissue within the plant, to reduce the level of the one or more than one protein in the plant or within a tissue of the plant, the reduced level of the one or more than one protein is determine by comparing the level of the one or more than one protein in the plant, or a tissue of the plant, with a level of the one ore more than one protein in a second plant, or the tissue from the second plant, that does not express the silencing nucleic acid sequence.
Unlike the limited scope of conventional breeding, molecular approaches to reduce lignin have much wider applications in plant biotechnology. Silencing of COMT, SAMS, C3H and C4H can alter lignin levels not only in Brassica oilseeds, but also potentially in other plants where high levels of lignin are undesirable, e.g. woody plants for the pulp and paper applications.
This invention is aimed at improving seed meal, for example canola meal by reducing the levels of one or more than one antinutritional factor (ANF), including but not limited to sinapine, phytate, lignin, and a combination of sinapine, phytate and lignin. This may be achieved by impairing the expression of rate limiting genes in the biosynthesis pathways of these metabolites. Mutant plant lines with knockouts in genes affecting the metabolism of phenylpropanoids, phytate, or phenylpropanoids and phytate, were isolated and characterized, and constructs to silence key genes in these pathways were engineered The approach is exemplified using B. napus, however, other plants may also be modified using the methods as described herein, for example, but not limited to plants within the Crucifereae, tobacco, soybean, woody trees used in pulp and paper, for example, spruce, pine, Douglas fir, Alpine fir, larch, poplar, eucalyptus and the like.
This summary of the invention does not necessarily describe all features of the invention.
These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings wherein:
The present invention relates to methods of altering one or more than one anti-nutrient factor within plants, and plants with altered levels of one or more than one anti-nutrient factor. Examples of anti-nutrient factors that may be modified include sinapine, phytate, and lignin.
The following description is of an exemplary embodiment.
The present invention provides methods and plants with reduced anti-nutrient factors. These anti-nutrient factors may include, but are not limited to products of the phenylpropanoid pathway (see
The present invention therefore provides a method for reducing the level of one or more than one protein in a plant or a tissue within the plant comprising,
i) introducing a nucleic acid sequence into the plant, the nucleic acid sequence comprising a regulatory region operatively associated with a silencing nucleotide sequence, wherein expression of the silencing nucleotide sequence reduces or eliminates the expression of one, or two, or more than one, or two, enzymes involved in the synthesis of the one or more than one protein, and
ii) expressing the silencing nucleotide sequence within the plant or a tissue within the plant, to reduce the level of the one or more than one protein in the plant or within a tissue of the plant, the reduced level of the one or more than one protein is determined by comparing the level of the one or more than one protein in the plant, or a tissue of the plant, with a level of the one ore more than one protein in a second plant, or the tissue from the second plant, that does not express the nucleic acid sequence.
The level of the one or more than one protein may be reduced by about 10% to about 100%, or any amount therebetween, where compared to the level of the same one or more than one protein obtained from a second plant that does not express the nucleotide sequence. For example, the protein may be reduced by from about 10% to about 60% or any amount therebetween, about 10% to about 50% or any amount therebetween, about 10% to about 40% or any amount therebetween, or from about 10% to about 30%, or any amount therebetween, or about 10% to about 20% or any amount therebetween.
The regulatory region may be a constitutive regulatory region, an inducible regulatory region, a developmentally regulated regulatory region, and a tissue specific regulatory region.
By the term “expression” it is meant the production of a functional RNA, protein or both, from a gene or transgene.
By “reduction of gene expression” it is meant the reduction in the level of mRNA, protein, or both mRNA and protein, encoded by a gene or nucleotide sequence of interest. Reduction of gene expression may arise as a result of the lack of production of full length RNA, for example mRNA, or through cleaving the mRNA, for example with a ribozyme (e.g. see Methods in Molecular Biology, vol 74 Ribozyme Protocols, P. C. Turner, ed, 1997, Humana Press), or RNAi (e.g. see Gene Silencing by RNA Interference, Technology and Application, M. Sohail ed, 2005, CRC Press), or otherwise reducing the half-life of RNA, using antisense (e.g. see Antisense Technology, A Practical Approach, C. Lichtenstien and W. Nellen eds., 1997, Oxford University Press), ribozyme, or RNAi techniques.
A “silencing nucleotide sequence” refers to a sequence that when transcribed results in the reduction of expression of a target gene, or of two or more than two target genes, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 target genes, or any number of target genes therebetween. A silencing nucleotide sequence may involve the use of antisense RNA, a ribozyme, or RNAi, targeted to a single target gene, or the use of antisense RNA, ribozyme, or RNAi, comprising two or more than two sequences that are linked or fused together and targeted to two or more than two target genes. When transcribed the product of the silencing nucleotide sequence may target one, or it may target two or more than two, of the target genes. When two or more than two sequences are linked or fused together, these sequences may be referred to as gene fusions, or gene stacking. It is within the scope of the present invention that gene fusions may comprise 2, 3, 4, 5, 6, 7, 8, 9, 10 nucleotide sequences, or any number therebetween, that are fused or linked together. The fused or linked sequences may be immediately adjacent each other, or there may be linker fragment between the sequences.
Reduction in the expression of a target gene, or two or more than two target genes, results in the reduced synthesis of a protein encoded by the target sequence, or the two or more proteins encoded by the two or more than two target sequences. Preferably the protein is involved in the synthesis of an anti-nutrient factor in plant tissue (e.g. stem, leaf, root, flower), including seed tissue, but it may also be involved in reducing fiber content in plant tissue (e.g. stem, leaf, root). Examples of anti-nutrient factors include, but are not limited to sinapine, phytate, fiber, and lignin, and the protein may be involved in a pathway of phenylpropanoid biosynthesis leading to sinapine synthesis, a pathway of phenylpropanoid biosynthesis leading to lignin synthesis, a pathway of phytate biosynthesis, or a combination thereof.
Non-limiting examples of a silencing nucleotide sequence include the antisense sequence napin::COMT AS (e.g. p72-122, see
Nucleotide sequences used for gene fusions may comprise sequences that encode proteins, that are involved in the same biosynthetic pathway, for example two or more enzymes involved in the phenylpropanoid pathway (
Plants comprising two or more than two nucleic acids, including gene fusions, or combinations of silencing nucleic acid sequences, may be introduced into a plant using standard techniques, for example, but not limited to, by introducing one or more than one nucleic acid comprising a gene fusion into a plant by transformation, or by introducing one, two, or more than two, silencing nucleic acid sequences, each silencing nucleic acid sequence comprising a sequence directed against a target gene, into a plant by transformation. Alternatively, silencing nucleic acid sequences may be introduced into a plant by crossing a first plant with a second plant that comprises one or more than one first gene fusion, or by crossing a first plant comprising one or more than one first gene fusion with a second plant comprising one or more than one second gene fusion. Silencing nucleic acid sequences may also be introduced into a plant by crossing a first plant with a second plant that comprises one, two, or more than two, silencing nucleic acid sequences, each silencing nucleic acid sequence comprising a sequence directed at silencing a target gene, or by crossing a first plant comprising one, two, or more than two, silencing nucleic acid sequences, each silencing nucleic acid sequence comprising a sequence directed against a target gene with a second plant comprising one, two, or more than two, silencing nucleic acid sequences, each silencing nucleic acid sequence comprising a sequence directed against a target gene.
The anti-nutrient factor may be sinapine, and the one, or two or more than two, enzymes may be involved in the pathway of phenylpropanoid biosynthesis. Non-limiting examples of the one, or two or more than two, enzymes include:
phenylalanine ammonia lyase (PAL),
cinnamate 4 hydroxylase (C4H),
coumarate 3 hydroxylase (C3H),
O-methyl transferase (OMT; or COMT),
ferulic acid hydroxylase (FAH),
sinapate:UDP-glucose sinapoyltransferase (SGT),
sinapolyglucose:choline sinapoyltransferase (SCT),
S-adenosylmethionine synthase (SAMS),
SAMS catalyses the synthesis of the methyl donor SAM (S-adenosyl methionine) from methionine and affects methylation reactions catalyzed by COMT (or OMT) in the phenylpropanoid pathway.
Therefore, a silencing nucleotide sequence may be directed to one, two, three, four, five, six, seven or eight genes listed above, alone or in combination. As stated above, a silencing nucleotide sequence may comprise a gene fusion that comprises two or more that two nucleotide sequence that disrupts the synthesis of two or more than two enzymes involved in phenylpropanoid, phytate biosynthesis or both, for example, sinapine and phytate synthesis, sinapine and lignin biosynthesis, lignin and phytate biosynthesis, or sinapine, lignin and phytate biosynthesis.
The anti-nutrient factor may also be lignin, and the one, two or more than two enzymes, involved in a pathway of phenylpropanoid biosynthesis. Non-limiting examples of the one, or two or more than two, enzymes include
phenylalanine ammonia lyase (PAL),
cinnamic acid 4 hydroxylase (C4H),
coumaric acid 3 hydroxylase (C3H),
caffeic acid O-methyl transferase (COMT),
ferulic acid hydroxylase (FAH),
S-adenosylmethionine synthase (SAMS),
4-coumarate:CoA lyase (4CL),
cinnamoyl-CoA reductase (CCR),
cinnamyl alcohol dehydrogenase (CAD), and
peroxidase (POD)
Therefore, a silencing nucleotide sequence may be directed to one, two, three, four, five, six, seven or eight genes listed above, either alone or in combination. Furthermore, a silencing nucleotide sequence may comprise a gene fusion that comprises two or more that two nucleotide sequence that disrupts the synthesis of two or more than two enzymes involved in phenylpropanoid, phytate biosynthesis or both, for example, sinapine and phytate synthesis, sinapine and lignin biosynthesis, lignin and phytate biosynthesis, or sinapine, lignin and phytate biosynthesis.
The anti-nutrient factor may also be phytate, and the one, two or more than two enzymes may be involved in a pathway of phytate biosynthesis. Non-limiting examples of the one, or two or more than two, enzymes include:
inositol 1,3,4-trisphosphate 5/6-kinase (IP3K),
myo-inositol hexaphosphate kinase (IP6K),
1-phosphatidylinositol-4,5-bisphosphate phosphodiesterase (PIBP PDE),
phosphatidylinositol phophatidylcholine transfer protein (PI/PC TP),
inositol polyphosphate 5-phosphatase II (IPP),
phosphatidylinositol-4-phosphate 5-kinase (PIKa),
CDP-diacylglycerol-inositol 3-phosphatidyltransferase (phosphatidylinositol synthase, PIS),
inositol polyphosphate 6-/3-/5-kinase 2b (IPK2a & IPK2b),
inositol polyphosphate 5′-phosphatase I (IPP),
myo-inositol-1-phosphate synthase (MIP),
phosphatidylinositol kinase (PIPK),
phosphatidylinositol 3-kinase (PI3K),
myo-inositol monophosphatase (MIM), and
phosphatidylinositol 3- and 4-kinase (PIKb).
Therefore, a silencing nucleotide sequence may be directed to one, two, three, four, five, six, seven or eight genes listed above, either alone or in combination. Furthermore, a silencing nucleotide sequence may comprise a gene fusion that comprises two or more that two nucleotide sequence that disrupts the synthesis of two or more than two enzymes involved in phenylpropanoid, phytate biosynthesis or both, for example, sinapine and phytate synthesis, sinapine and lignin biosynthesis, lignin and phytate biosynthesis, or sinapine, lignin and phytate biosynthesis.
Furthermore, analogues of any of the silencing nucleotide sequences encoding the above proteins may be used according to the present invention. An “analogue” or “derivative” includes any substitution, deletion, or addition to the silencing nucleotide sequence, provided that the nucleotide sequence retains the property of silencing expression of a target gene or sequence, reducing expression of a target sequence, or reducing synthesis or activity of a protein encoded by the target sequence. For example, derivatives, and analogues of nucleic acid sequences typically exhibit greater than 80% similarity with, a silencing nucleic acid sequence. Sequence similarity, may be determined by use of the BLAST algorithm (GenBank: www.ncbi.nlm.nih.gov/cgi-bin/BLAST/), using default parameters (Program: blastn; Database: nr; Expect 10; filter: low complexity; Alignment: pairwise; Word size:11). Analogs, or derivatives thereof, also include those nucleotide sequences that hybridize under stringent hybridization conditions (see Maniatis et al., in Molecular Cloning (A Laboratory Manual), Cold Spring Harbor Laboratory, 1982, p. 387-389) to any one of the sequences described herein, provided that the sequences exhibit the property of silencing expression of a target gene. An example of one such stringent hybridization conditions may be hybridization with a suitable probe, for example but not limited to, a [∀-32P]dATP labelled probe for 16-20 hrs at 65EC in 7% SDS, 1 mM EDTA, 0.5M Na2HPO4, pH 7.2. Followed by washing in 5% SDS, 1 mM EDTA 40 mM Na2HPO4, pH 7.2 for 30 min followed by washing in 1% SDS, 1 mM EDTA 40 mM Na2HPO4, pH 7.2 for 30 min. Washing in this buffer may be repeated to reduce background.
By “regulatory region” “regulatory element” or “promoter” it is meant a portion of nucleic acid typically, but not always, upstream of the protein coding region of a gene, which may be comprised of either DNA or RNA, or both DNA and RNA. When a regulatory region is active, and in operative association, or operatively linked, with a gene of interest, this may result in expression of the gene of interest. A regulatory element may be capable of mediating organ specificity, or controlling developmental or temporal gene activation. A “regulatory region” includes promoter elements, core promoter elements exhibiting a basal promoter activity, elements that are inducible in response to an external stimulus, elements that mediate promoter activity such as negative regulatory elements or transcriptional enhancers. “Regulatory region”, as used herein, also includes elements that are active following transcription, for example, regulatory elements that modulate gene expression such as translational and transcriptional enhancers, translational and transcriptional repressors, upstream activating sequences, and mRNA instability determinants. Several of these latter elements may be located proximal to the coding region.
In the context of this disclosure, the term “regulatory element” or “regulatory region” typically refers to a sequence of DNA, usually, but not always, upstream (5′) to the coding sequence of a structural gene, which controls the expression of the coding region by providing the recognition for RNA polymerase and/or other factors required for transcription to start at a particular site. However, it is to be understood that other nucleotide sequences, located within introns, or 3′ of the sequence may also contribute to the regulation of expression of a coding region of interest. An example of a regulatory element that provides for the recognition for RNA polymerase or other transcriptional factors to ensure initiation at a particular site is a promoter element. Most, but not all, eukaryotic promoter elements contain a TATA box, a conserved nucleic acid sequence comprised of adenosine and thymidine nucleotide base pairs usually situated approximately 25 base pairs upstream of a transcriptional start site. A promoter element comprises a basal promoter element, responsible for the initiation of transcription, as well as other regulatory elements (as listed above) that modify gene expression.
There are several types of regulatory regions, including those that are developmentally regulated, inducible or constitutive. A regulatory region that is developmentally regulated, or controls the differential expression of a gene under its control, is activated within certain organs or tissues of an organ at specific times during the development of that organ or tissue. However, some regulatory regions that are developmentally regulated may preferentially be active within certain organs or tissues at specific developmental stages, they may also be active in a developmentally regulated manner, or at a basal level in other organs or tissues within the plant as well. Examples of tissue-specific regulatory regions, for example see-specific a regulatory region, include the napin promoter, and the cruciferin promoter (Rask et al., 1998, J. Plant Physiol. 152: 595-599; Bilodeau et al., 1994, Plant Cell 14: 125-130).
An inducible regulatory region is one that is capable of directly or indirectly activating transcription of one or more DNA sequences or genes in response to an inducer. In the absence of an inducer the DNA sequences or genes will not be transcribed. Typically the protein factor that binds specifically to an inducible regulatory region to activate transcription may be present in an inactive form, which is then directly or indirectly converted to the active form by the inducer. However, the protein factor may also be absent. The inducer can be a chemical agent such as a protein, metabolite, growth regulator, herbicide or phenolic compound or a physiological stress imposed directly by heat, cold, salt, or toxic elements or indirectly through the action of a pathogen or disease agent such as a virus. A plant cell containing an inducible regulatory region may be exposed to an inducer by externally applying the inducer to the cell or plant such as by spraying, watering, heating or similar methods. Inducible regulatory elements may be derived from either plant or non-plant genes (e.g. Gatz, C. and Lenk, I. R. P., 1998, Trends Plant Sci. 3, 352-358; which is incorporated by reference). Examples, of potential inducible promoters include, but not limited to, tetracycline-inducible promoter (Gatz, C., 1997, Ann. Rev. Plant Physiol. Plant Mol. Biol. 48, 89-108; which is incorporated by reference), steroid inducible promoter (Aoyama, T. and Chua, N. H., 1997, Plant J. 2, 397-404; which is incorporated by reference) and ethanol-inducible promoter (Salter, M. G., et al, 1998, Plant Journal 16, 127-132; Caddick, M. X., et al,1998, Nature Biotech. 16, 177-180, which are incorporated by reference) cytokinin inducible IB6 and CKI1 genes (Brandstatter, I. and Kieber, J. J., 1998, Plant Cell 10, 1009-1019; Kakimoto, T., 1996, Science 274, 982-985; which are incorporated by reference) and the auxin inducible element, DR5 (Ulmasov, T., et al., 1997, Plant Cell 9, 1963-1971; which is incorporated by reference).
A constitutive regulatory region directs the expression of a gene throughout the various parts of a plant and continuously throughout plant development. Examples of known constitutive regulatory elements include promoters associated with the CaMV 35S transcript. (Odell et al., 1985, Nature, 313: 810-812), the rice actin 1 (Zhang et al, 1991, Plant Cell, 3: 1155-1165), actin 2 (An et al., 1996, Plant J., 10: 107-121), or tms 2 (U.S. Pat. No. 5,428,147, which is incorporated herein by reference), and triosephosphate isomerase 1 (Xu et. al., 1994, Plant Physiol. 106: 459-467) genes, the maize ubiquitin 1 gene (Cornejo et al, 1993, Plant Mol. Biol. 29: 637-646), the Arabidopsis ubiquitin 1 and 6 genes (Holtorf et al, 1995, Plant Mol. Biol. 29: 637-646), and the tobacco translational initiation factor 4A gene (Mandel et al, 1995 Plant Mol. Biol. 29: 995-1004). The term “constitutive” as used herein does not necessarily indicate that a gene under control of the constitutive regulatory region is expressed at the same level in all cell types, but that the gene is expressed in a wide range of cell types even though variation in abundance is often observed.
The silencing nucleotide sequence may be expressed in any suitable plant host that is transformed by the nucleotide sequence, or constructs, or vectors of the present invention. Examples of suitable hosts include, but are not limited to, agricultural crops including canola, Brassica spp., maize, tobacco, alfalfa, potato, ginseng, pea, oat, rice, soybean, wheat, barley, sunflower, and cotton. Any member of the Brassica-family can be transformed with one or more genetic constructs of the present invention including, but not limited to, canola, Brassica napus, B. carinata, B. nigra, B. oleracea, B. chinensis, B. cretica, B. incana, B. insularis, B. japonica, B. atlantica, B. bourgeaui, B. narinosa, B. juncea, B. rapa, Arabidopsis. Additionally, woody plants and trees may be transformed with a silencing nucleotide sequence or construct of the present invention to reduce fiber content.
The one or more chimeric genetic constructs of the present invention can further comprise a 3′ untranslated region. A 3′ untranslated region refers to that portion of a gene comprising a DNA segment that contains a polyadenylation signal and any other regulatory signals capable of effecting mRNA processing or gene expression. The polyadenylation signal is usually characterized by effecting the addition of polyadenylic acid tracks to the 3′ end of the mRNA precursor. Polyadenylation signals are commonly recognized by the presence of homology to the canonical form 5′ AATAAA-3′ although variations are not uncommon. One or more of the chimeric genetic constructs of the present invention can also include further enhancers, either translation or transcription enhancers, as may be required. These enhancer regions are well known to persons skilled in the art, and can include the ATG initiation codon and adjacent sequences. The initiation codon must be in phase with the reading frame of the coding sequence to ensure translation of the entire sequence.
Non-limiting examples of suitable 3′ regions are the 3′ transcribed non-translated regions containing a polyadenylation signal of Agrobacterium tumor inducing (Ti) plasmid genes, such as the nopaline synthase (Nos gene) and plant genes such as the soybean storage protein genes and the small subunit of the ribulose-1,5-bisphosphate carboxylase (ssRUBISCO) gene.
To aid in identification of transformed plant cells, the constructs of this invention may be further manipulated to include plant selectable markers. Useful selectable markers include enzymes that provide for resistance to chemicals such as an antibiotic for example, gentamycin, hygromycin, kanamycin, or herbicides such as phosphinothrycin, glyphosate, chlorosulfuron, and the like. Similarly, enzymes providing for production of a compound identifiable by colour change such as GUS (beta-glucuronidase), or luminescence, such as luciferase or GFP, may be used.
Also considered part of this invention are transgenic plants containing the chimeric gene construct of the present invention. Methods of regenerating whole plants from plant cells are also known in the art. In general, transformed plant cells are cultured in an appropriate medium, which may contain selective agents such as antibiotics, where selectable markers are used to facilitate identification of transformed plant cells. Once callus forms, shoot formation can be encouraged by employing the appropriate plant hormones in accordance with known methods and the shoots transferred to rooting medium for regeneration of plants. The plants may then be used to establish repetitive generations, either from seeds or using vegetative propagation techniques. Transgenic plants can also be generated without using tissue cultures.
The constructs of the present invention can be introduced into plant cells using Ti plasmids, Ri plasmids, plant virus vectors, direct DNA transformation, micro-injection, electroporation, etc. For reviews of such techniques see for example Weissbach and Weissbach, Methods for Plant Molecular Biology, Academy Press, New York VIII, pp. 421-463 (1988); Geierson and Corey, Plant Molecular Biology, 2d Ed. (1988); and Miki and Iyer, Fundamentals of Gene Transfer in Plants. In Plant Metabolism, 2d Ed. D T. Dennis, D H Turpin, D D Lefebrve, D B Layzell (eds), Addison Wesly, Langmans Ltd. London, pp. 561-579 (1997); Clough and Bent (1998)).
Reducing Anti-Nutrient Synthesis
Arabidopsis knockout mutants within the phenylpropanoid pathway were identified, and seeds obtained from the mutants analyzed (see
Homologs of genes encoding several enzymes involved in the phenylpropanoid pathway and the synthesis of sinapine were obtained and used to generate silencing nucleotide sequences (RNAi and antisense constructs). Expression of the silencing nucleotide sequences in seeds of B. napus, resulted in reduced levels of anti-nutrient factors, for example sinapine (see Example 1), in the seed. For example:
B. napus lines expressing an RNAi construct specific SCT (CaMV35S::SCT RNAi, p72-145,
B. napus lines expressing an RNAi construct specific COMT (CaMV35S::COMT RNAi, p72-115,
an antisense construct expressing the gene fusion FAH-SCT (napin::FAH-SCT, p72-148,
an antisense gene fusion, C3H-C4H, under the control of the seed-specific promoter cruciferin (Cruciferin::C3H-C4H, p72-152,
an RNAi gene fusion construct, C3H-C4H, under the control of the constitutive promoter CaMV35S (CaMV35S::C3H-C4H RNAi, p72-146,
an RNAi construct directed against SAMS, under the control of the seed-specific promoter napin caused (Napin::SAMS RNAi, p72-135,
an antisense construct directed against COMT (cruciferin::COMT, p72-14,
an RNAi gene fusion construct, FAH-COMT, under the control of the constitutive promoter CaMV35S (CaMV35S:: FAH-COMT RNAi, p72-142,
These results indicate that silencing nucleotide sequences may be used to reduce anti-nutrient factors synthesized within the phenylpropanoid pathway.
B. napus lines were also developed with silencing nucleotide sequences that interfered with the expression of genes encoding enzymes involved in lignin biosynthesis (see Example 2), including caffeic acid O-methyltransferase (COMT), ferulic acid hydroxylase (FAH), S-adenosylmethionine synthase (SAMS), cinnamic acid 4-hydroxylase (C4H) and coumaric acid 3-hydroxylase (C3H), 4-coumarate ligase (4CL), cinnamoyl CoA reductase (CCR).
Genes encoding several enzymes involved in the phenylpropanoid pathway and the synthesis of lignin were obtained and used to generate silencing nucleotide sequences (RNAi and antisense constructs). Expression of the silencing nucleotide sequences in seeds of B. napus, resulted in reduced levels of anti-nutrient factors, for example lignin, in the seed For example:
expression of a COMT RNAi construct under control of a cruciferin promoter (Cruciferin::COMT
an RNAi gene fusion construct directed against FAH-COMT (
expression of SAMS RNAi construct under the control of a napin promoter (
B. napus expressing the antisense construct napin::COMT (
expressing the RNAi construct CaMV35S::C3H-C4H (
B. napus expressing the antisense construct cruciferin::COMT (
These results additionally indicate that silencing nucleotide sequences may be used to reduce anti-nutrient factors synthesized within the phenylpropanoid pathway.
B. napus lines were also developed with silencing nucleotide sequences that interfered with the expression of genes encoding enzymes involved in phytate biosynthesis (see
Genes encoding several enzymes involved in the pathway leading to the synthesis of phytate were obtained and used to generate silencing nucleotide sequences (RNAi and antisense constructs). Expression of the silencing nucleotide sequences in seeds of B. napus, resulted in reduced levels of anti-nutrient factors, for example phytate, in the seed (see Table 4, Example 3). For example:
levels of phytate B. napus seeds expressing the gene fusion RNAi construct IP3K-IP6K (Actin2::IP3K-IP6KP, p72-535), resulted in a 19% reduction in phytate levels when compared to wild type levels;
an RNAi gene fusion construct, PIKa-PIKb (CaMV35S::PIKa-PIKb, p72-528) resulted in a reduction of seed phytate levels of about 13% when compared to wild type phytate levels.
B. napus plants expressing IP6K (Actin2::IP6K, p72-536) resulted in a reduction of seed phytate levels of about 16.5% when compared to wild type phytate levels;
the RNAi construct, PIKa under the control of an actin promoter (Actin2::PIKa, p72-537), resulted in a reduction of seed phytate levels of about 29.4% when compared to wild type phytate levels.
These results additionally show that silencing nucleotide sequences may be used to reduce anti-nutrient factors synthesized within the phytate biosynthetic pathway.
Most of the seed phytate is synthesized through the step-wise phosphorylation of myo-inositol rather than through phosphatidyl inositol. An alternate strategy to reduce phytate levels involves diverting more myo-inositol to phosphatidyl inositol biosynthesis, combined with blocking the de-esterification of the latter to myo-inositol phosphate. This is achieved by overexpressing phosphatidyl inositol synthase (PIS), by ectopically expressing PIS, and silencing phosphotidyl inositol bisphosphate phosphodiesterase (PIBP PDE), using a silencing nucleotide sequence and the methods disclosed within the present invention.
The present invention provides a construct comprising a silencing nucleotide sequence, the silencing nucleotide sequence encoding one, or two or more than two sequences that when expressed in a host reduces or inhibits the expression of one, or two or more that two enzymes involved in the synthesis of one or more than one protein leading to sinapine biosynthesis, lignin biosynthesis, phytate biosynthesis, or a combination thereof, the reduced level of the one or more than one protein determined by comparing the level of the protein in the host, or a tissue of the host, with a level of the protein in a second host, or the tissue from the second host, that does not express the nucleic acid sequence.
The silencing nucleotide sequence may comprise an RNAi construct, or an antisense construct directed against one gene, or two or more genes, for example the construct may comprise a gene fusion directed to 2, 3, 4, 5, 6, 7 or 8 different genes within one or more than one biosynthetic pathway.
The present invention also provides for a plant comprising a nucleic acid sequence comprising a regulatory region operatively associated with a silencing nucleotide sequence, the silencing nucleotide sequence encoding one, or two or more than two sequences that reduce or eliminates the expression of one, or two or more than two enzymes involved in the synthesis of the one or more than one protein leading to sinapine biosynthesis, lignin biosynthesis, phytate biosynthesis, or a combination thereof, the reduced level of the one or more than one protein determined by comparing the level of the protein in the plant, or a tissue of the plant, with a level of the protein in a second plant, or the tissue from the second plant, that does not express the nucleic acid sequence.
The silencing nucleotide sequence may comprise an RNAi construct, or an antisense construct directed against one gene, or two or more genes, for example the construct may comprise a gene fusion directed to 2, 3, 4, 5, 6, 7 or 8 different genes within one or more than one biosynthetic pathway.
The present invention also provides a seed that is characterized as having reduced levels of one or more than one anti-nutrient compounds. Examples of an anti-nutrient compound include intermediates within the phenylpropanoid pathway, or products of the phenylpropanoid pathway including sinapine and lignin, the phytate biosynthetic pathway, including phytate. The level of the anti-nutrient compound may be reduced by about 10% to about 100%, or any amount therebetween, when compared to the level of the same anti-nutrient compound obtained from a second plant that does not express a silencing nucleotide sequence. For example, the anti-nutrient compound may be reduced by from about 10% to about 60% or any amount therebetween, about 10% to about 50% or any amount therebetween, about 10% to about 40% or any amount therebetween, or from about 10% to about 30%, or any amount therebetween, or about 10% to about 20% or any amount therebetween.
The present invention also provides for a method for reducing the level of one or more than one protein within a plant or a tissue within the plant comprising, expressing a nucleotide sequence within the plant or a tissue within the plant, the nucleic acid sequence comprising a regulatory region operatively associated with a silencing nucleotide sequence, where expression of the silencing nucleotide sequence reduces or eliminates the expression of one, or two or more than two enzymes involved in the synthesis of the one or more than one protein leading to sinapine biosynthesis, lignin biosynthesis, phytate biosynthesis, or a combination thereof, the reduced level of the one or more than one protein determined by comparing the level of the protein in the plant, or a tissue of the plant, with a level of the protein in a second plant, or the tissue from the second plant, that does not express the nucleic acid sequence.
Examples of suitable plants that may be modified using the methods as described herein include, but are not limited to, agricultural crops including canola, Brassica spp., maize, tobacco, alfalfa, potato, ginseng, pea, oat, rice, soybean, wheat, barley, sunflower, cotton, and woody plants including trees. Any member of the Brassica-family can be transformed with one or more genetic constructs of the present invention including, but not limited to, Arabidopsis, Brassica amplexicaulis, Brassica atlantica, Brassica balearica, Brassica barrelieri, Brassica bourgeaui, Brassica carinata (Abyssinian mustard), Brassica chinensis, Brassica cretica, Brassica deflexa, Brassica erucastrum, Brassica hilarionis, Brassica incana, Brassica insularis, Brassica insularis subsp. insularis, Brassica juncea (Indian mustard), Brassica macrocarpa, Brassica maurorum, Brassica montana, Brassica napus (rape), Brassica napus var. napobrassica (Swedish turnip), Brassica napus var. napus (canola), Brassica narinosa, Brassica nigra (black mustard), Brassica oleracea, Brassica oleracea var. acephala (kale), Brassica oleracea var. alboglabra (Chinese kale), Brassica oleracea var. botrytis (cauliflower), Brassica oleracea var. capitata (cabbage), Brassica oleracea var. gemmifera (brussel sprouts), Brassica oleracea var. gongylodes (kohlrabi), Brassica oleracea var. italica (asparagus broccoli), Brassica oleracea var. medullosa (marrow-stem kale), Brassica oleracea var. oleracea, Brassica oleracea var. ramosa (branching bush kale), Brassica oxyrrhina, Brassica rapa (field mustard), Brassica rapa subsp. chinensis (bok-choy), Brassica rapa subsp. oleifera (biennial turnip rape), Brassica rapa subsp. pekinensis (Chinese cabbage), Brassica rapa subsp. rapa (turnip), Brassica rupestris, Brassica tournefortii, Brassica villosa.
The following sequences are included in the sequence listing:
The present invention will be further illustrated in the following examples.
Plant Material
Wild type and mutant A. thaliana, ecotype Columbia, were grown in RediEarth (W.R. Grace & Co., Ajax, Canada) soil in pots covered with window screens at 25 C, 16 h light/8 h dark cycles. Wild type and transgenic Brassica napus DH12075 plants were grown in soil prepared according to the protocol described in Stringham (1971) under conditions similar to those of A. thaliana. Seeds were collected from dry siliques of mature plants of A. thaliana and B. napus.
Arabidopsis Knockout Mutants
Arabidopsis knockout mutants were identified by searching the SALK T-DNA knockout population in the TAIR database. Gene-specific sequences were used in the search. When no knockout mutants could be identified for specific gene, a T-DNA knockout population, generated at Agriculture and Agri-Food Canada (see: brassica.ca/index e.shtml) was screened for mutants of interest using a PCR-based method (Sussman et al., 2000).
Transformation of Brassica napus
B. napus transformation was carried out following the procedures that are described in Moloney et al. (1989; which is incorporated herein by reference). The presence of transgenes in potential transformants was determined by PCR using transgene-specific primers (one primer from the promoter and the other from the coding region) and total plant genomic DNA as template using standard methods known to one of skill in the art.
Estimation of Gene Copy Numbers in Arabidopsis
Gene copy numbers were estimated using the BioVis software (see: brassica.ca), and set to a homology threshold of 80%.
ESTs and Constructs
B. napus homologs of target Arabidopsis genes were obtained from a collection of 66,960 expressed sequence tags (ESTs) derived from B. napus line DH12075 cDNA libraries generated at Agriculture and Agri-Food Canada, Saskatoon Research Centre (see: brassica.ca/index e.shtml). Where no ESTs could be identified, B. napus sequences were isolated by PCR using primers specific to conserved Arabidopsis sequences and a B. napus cDNA library as template, using techniques known to one of skill in the art.
Northern Blot Hybridization
Northern blot analysis was carried out on total RNA extracted from plant seeds to determine the level of gene expression in the wild type and transgenic lines. Hybridization with [α-32P]dCTP-labeled probes was carried out for 16-20 h at 65° C. in 7% SDS, 1 mM EDTA, 0.5 M Na2HPO4, pH 7.2. Membranes were washed once in a solution of 5% SDS, 1 mM EDTA, 40 mM Na2HPO4 (pH 7.2) for 30 min, followed by washing in 1% SDS, 1 mM EDTA, 40 mM Na2HPO4 (pH 7.2) for 30 min. The membranes were subjected to autoradiography using X-OMAT XAR5 film, and the intensity of bands measured using densitometer Quantity One Software (BioRad). The strength of the Northern blot bands was normalized by expressing it as a percentage of the density of the respective 28S rRNA band on the RNA gel.
Phenolics Extraction and Quantification
Seeds of Brassica napus and Arabidopsis thaliana were ground to a fine powder in liquid nitrogen using a pestle and a mortar. Approximately 50 mg of ground seeds were extracted with 15 volumes (w/v) of extraction buffer (50% methanol, 1.5% acetic acid), auto-vortexed for 5 minutes, stored at −80° C. for 2 hours followed by 5 min at room temperature, then auto-vortexed for 5 minutes, and centrifuged at 20 000 g for 5 minutes to pellet cellular debris. The supernatant was filtered through a 0.2 μm filter, transferred to HPLC autosampler vials and 3 μl were injected into the HPLC. HPLC was performed using a Waters Alliance 2695 instrument equipped with a Symmetry 5 μm C18 column (3 mm×150 mm). A 20 minute linear gradient was applied using a flow rate of 0.4 ml/min from 5% to 95% solvent B (methanol) in solvent A (0.05% TFA in water). The compounds were detected photometrically using a Waters 996 photodiode array detector set to 332 nm. Sinapine bisulfate (from Ian McGregor, Agriculture and Agri-Food Canada, Saskatoon), was used as a standard The percent reduction of sinapine was calculated by comparing values obtained from seeds of transgenic lines to those of the wild type. Total phenolic compounds absorbing at OD332 were measured using an Ultraspec 3000 (Pharmacia Biotech). The samples were diluted 1/50 in extraction buffer and absorbance at OD332 was read A standard curve was prepared using sinapine bisulfate. Concentrations of total phenolics absorbing at OD332, total phenolics/fresh weight (FW) and sinapine/FW were determined as follows:
Total phenolic (μg/ml)=OD332×slope of standard curve×dilution factor
Total phenolics/FW (μg/mg)=(total phenolics×μl of extraction buffer used)/seed weight/1×103
Sinapine/FW (μg/mg)=(sinapine % area/100)×total phenolics(μg/mg)
Lignin Extraction and Quantification
Approximately 50 mg of ground seed was extracted with 1 ml of protein extraction buffer (200 mM Tris pH 7.5 using acetic acid, 1% SDS, 1 ul/ml β-mercaptoethanol) vortexed for 5 minutes, iced for 20 minutes and centrifuged at 20,000 g for 5 minutes. These steps were repeated until the supernatant was clear. The pellet was resuspended in 80% methanol by vortexing and incubated at 80° C. overnight. Insoluble material was collected by centrifuging at 20 000 g for 5 minutes. After removal of the supernatant, the pellet was resuspended in a 1 ml mixture of H2O, HCl, and thioglycolic acid (75:25:1 v/v). This mixture was incubated at 80° C. for 3 hours. The insoluble material was collected by centrifuging at 20 000 g for 5 minutes. The pellet was washed with 1 ml of H2O and centrifuging as before. After removal of the supernatant the pellet was resuspended in 1 ml 1M NaOH and gently agitated at room temperature overnight. Insoluble material was collected by centrifuging at 20 000 g for 5 minutes. The supernatant was transferred to a clean tube and 200 ul of HCL was added. The tubes were vortexed and incubated at 4° C. for 4 hours. Insoluble material was collected by centrifuging at 20 000 g for 5 minutes. The pellet was dissolved in 1 ml 1M NaOH. Samples were diluted 1:20 in 1M NaOH and the absorbance read at OD280. Samples were prepared in triplicate. The average OD/mg of fresh weight of tissue was compared to that of wild-type.
Phytate Extraction and Quantification
Phytate was extracted and quantified following the protocol described in Brooks et al., (2001, which is incorporated herein by reference).
Strategy for Generating RNAi Constructs
The target DNA fragment is amplified by PCR using primers that generate products containing SpeI and AscI sites at the 5′ end and SwaI and BamHI sites at the 3′ end:
3′-SpeI-AscI-PCR PRODUCT-SwaI-BamHI-5′
The PCR product is blunt end cloned into the EcoRV site of pBluescript producing the template vector. The template vector is digested with AscI and SwaI and ligated into the backbone pGSA1252 (SEQ ID NO: 13) or pGSA1285 (SEQ ID NO: 2) RNAi vector (obtained from Dr. Richard Jorgensen, University of Arizona) cleaved with AscI and SwaI to produce the sense orientation construct. The template vector is then digested with BamHI and SpeI and ligated into the BamHI and SpeI sites of the sense orientation construct to produce the template vector in the sense as well as the anti-sense orientation (see
Strategy for Generating constructs of Gene Fusions
Template 1 and template 2 are first amplified separately using primers having the following characteristics:
The amplified template 1 and template 2 are combined and used as new templates for a new round of PCR amplification where only the forward primer 1 of template 1 and the reverse primer 2 of template 2 are used. The two separate templates are amplified to create one single in frame fusion fragment encoding template 1 and template 2 and containing restriction enzyme sites at each end. This product is then cloned into the EcoRV site of pBluescript. (see
Strategy for Generating RNAi Constructs Using the GUS Linker Cloned into pBluescript
The XhoI-SpeI GUS linker fragment from pGSA1252 was cloned into pBluescript at the XhoI-SpeI sites producing plasmid p72-515 (see
Estimation of Gene Copy Numbers in Arabidopsis
Gene copy number is an important factor that needs to be considered when analyzing knockout mutants. Our analysis revealed that, with the exception of phenylalanine ammonia lyase (PAL), all other enzymes in the phenylpropanoid pathway are encoded by single copy genes in the Arabidopsis genome. Table 1 lists names of genes, their estimated copy numbers and T-DNA insertion mutants used below.
1Gene copy numbers were estimated using the BioVis software (see brassica.ca) set to a homology threshold of 80%.
2Lines obtained from the knockout population generated at the SALK institute (see http://signal.salk.edu/tabout.html);
3Lines obtained by screening AAFC's knockout population (see brassica.ca).
Profiling of Phenylpropanoids in Seeds of Arabidopsis Mutants
Chemical analysis carried out on seeds of wild type A. thaliana revealed that the main storage form of phenolics in the seed is sinapine, which represents over 50% of total extracted phenolics. A total of 10 Arabidopsis thaliana mutants with T-DNA inserts in genes affecting phenylpropanoid biosynthesis (
Analysis of homozygous mutant lines with T-DNA inserts in pal (SALK70702 and SALK92252, c4h (SK16293) and c3h (SALK36132, SALK112823) loci had only a minimal quantitative effect on the level of sinapine, and sinapine levels similar to those observed in control plants were observed. Without wishing to be bound by theory, this could be due to alternative biosynthesis pathways, or non-specific enzymatic reactions. Knockouts in gene coding for caffeic acid O-methyltransferase (COMT), ferulic acid hydroxylase (FAH), and sinapoylglucose:choline sinapoyltransferase (SCT) resulted in a dramatic decrease in sinapine levels (
Homologs of several Brassica napus genes encoding enzymes involved in the synthesis of sinapine were cloned, including caffeic acid O-methyltransferase (COMT), sinapoylglucose: choline sinapoyltransferase (SCT), S-adenosylmethionine synthase (SAMS) and ferulic acid hydroxylase (FAH). These genes were used to generate RNAi and antisense constructs for expression in B. napus. Seeds of transgenic B. napus lines expressing these constructs were harvested, and subjected to analysis of sinapine levels as described above.
Constructs
CaMV35S::COMT RNAi Construct (p72-115)
The COMT fragment was amplified by PCR from the Brassica EST, ESS2134, (SEQ ID NO:1; see: brassica.ca) using the following primers: ATTGCATTATGCTAGC
aacaaagacggtgaag
The strategy for the production of RNAi constructs outlined above was employed (see “Strategy for generating RNAi constructs”, and
CaMV35S::SCT RNAi Construct (p72-145)
A B. napus SCT (BnSCT) clone identical to the one described in Milkowski et al., (2004) (Accession # AY383718) was isolated by screening a seed-specific library of B. napus using the A. thaliana SCT as a heterologous probe. Alignment of BnSCT to members of the serine carboxypeptidase family of proteins (Shirley et al., 2001) revealed that it had a unique exon region from 876 to 1043. Therefore, the DNA fragment encoding this region was used in making a BnSCT-specific RNAi construct (
An Arabidopsis genomic DNA fragment of ˜800 bp was amplified by PCR using the following two primers:
The primers were designed based on the Arabidopsis SCT sequence (At5g09640). The PCR fragment was used as a heterologous probe to screen a seed-specific cDNA library of Brassica napus. The isolated clone, p72-505 (SEQ ID NO:4), which was similar to the Arabidopsis SCT (At5g09640), was used as a template to PCR-amplify a 170 bp SCT-specific DNA fragment using the following two primers:
The strategy for the production of RNAi constructs outlined above was employed (“Strategy for generating RNAi constructs”, and
Napin::SAMS RNAi Construct (p72-135)
A fragment encoding SAMS (S-adenosylmethionine synthase) was amplified by PCR from the Brassica EST, RL103, (SEQ ID NO:7; see brassica.ca) using the following primers: agaacgggacttgcgc
GAACACAGACAACGGC
The strategy for the production of RNAi constructs was employed using pGSA1285 as the backbone vector (see
Napin::FAH:SCT Anti-Sense Construct (p72-148)
An FAH EST, RL1627 (SEQ ID NO:3) isolated from a Brassica napus root cDNA library (see: brassica.ca) was used as template for PCR-amplification using the following two primers:
(the bold portion is identical to sequence at the 5′-end of the SCT cDNA). This PCR product generated a FAH fragment containing an overlapping 3′ end having identical sequence to the 5′ end of the SCT (see
The SCT clone 72-505 was used as template for PCR-amplification using the following two primers:
This generated a SCT fragment containing an overlapping 5′end identical to the 3′ end of the FAH. The two PCR products were used together as templates to amplify a fusion product using FAH-F7 and SCT-R8 primers. The resulting product was blunt end cloned into the EcoRV site of pBluescript, creating p72-134 (SEQ ID NO:5). The vector p72-134 was digested with BamHI and SpeI and cloned into BamHI and SpeI sites of a digested pBluescript vector containing the napin promoter in the anti-sense orientation, to generate p72-148 (
CaMV35S::C3H-C4H RNAi Construct (p72-146)
A C3H fragment was amplified by PCR from the Brassica EST, RL4992, (SEQ ID NO:9; see brassica.ca) using the following primers:
The bold portion corresponds to the 5′ end of the C4H portion (see
The C4H fragment was amplified by PCR from the Brassica EST, RL7118, (SEQ ID NO:10; see brassica.ca) using the following primers:
The products of these PCR reactions were used as templates to amplify a fusion product using C3H-F3 and C4H-R4 primers. This fusion was blunt end cloned into the EcoRV site of pBluescript to create p72-139 (SEQ ID NO:11). The strategy for the production of RNAi constructs was employed using pGSA1285 as the backbone vector generating p72-146.
Cruciferin::C3H-C4H Anti-Sense Construct (p72-152)
The cruciferin promoter (SEQ ID NO:6) was cloned into p79-103 (
CaMV35S::FAH-COMT RNAi Construct (p72-142)
A FAH EST, RL1627 (SEQ ID NO:3), isolated from a Brassica napus root cDNA library, (see: brassica.ca), was used as template for PCR-amplification using the following two primers:
in which the bold portion is identical to sequence at the 5′-end of the COMT fragment. This PCR product generated a FAH fragment containing an overlapping 3′ end having identical sequence to the 5′ end of the COMT (See
The COMT fragment was amplified by PCR from the Brassica EST, ESS2134, (SEQ ID NO:1; see brassica.ca) using the following primers: aacaaagacggtgaag
The two PCR products were used as templates for producing a FAH-COMT fusion product containing SpeI-AscI sites at the 5′ end and SwaI-BamHI sites at the 3′ end. This fusion product was blunt end cloned into the EcoRV site of pBluescript. The strategy for the production of RNAi constructs outlined above was employed (see
Cruciferin::COMT Anti-Sense Construct (p72-14)
The COMT fragment was amplified by PCR from the Brassica EST, RL4637, (SEQ ID NO:12: see brassica.ca) using the following primers:
The PCR product was blunt end cloned into the EcoRV site of pBluescript, digested with SacI and XbaI and cloned into the SacI and XbaI sites of pBI121 (Clontech) in the anti-sense orientation. The CaMV35S promoter was replaced with the cruciferin promoter (SEQ ID NO:6) via HindIII/XbaI digestion and ligation generating p72-14.
Downregulation of SCT by RNAi: Reduction of Sinapine Levels
Analysis of Arabidopsis knockout mutants indicates that silencing of SCT gene (At5g09640) resulted in over 90% reduction in sinapine content (
Sinapine levels in seeds of transgenic B. napus lines expressing an RNAi construct specific to a BnSCT (CaMV35S::SCT RNAi, p72-145) are shown in
Down Regulation of FAH-SCT by Antisense RNA: Reduction of Sinapine Levels
Previous work by Nair et al., (2000) showed that up to 40% reduction in sinapine of B. napus seeds was achieved by expressing as antisense RNA construct for FAH. As the above results with SCT revealed that downregulation of the gene encoding SCT led to a considerable reduction in sinapine, it was examined whether silencing both FAH and SCT would lead to a higher reduction in sinapine levels.
An anti-sense RNA construct for a fusion between fragments from the coding regions of the two genes was made (see
Silencing of C3H-C4H by Antisense RNA: Reduction of Sinapine Levels
Transformation of B. napus with a construct for the antisense RNA expression of a fusion between C3H and C4H gene under the control of the seed-specific promoter cruciferin (
Silencing of C3H-C4H by RNAi: Reduction of Sinapine Levels
Transformation of B. napus with an RNAi construct for a fusion between C3H and C4H genes under the control of the constitutive promoter CaMV35S (
Silencing of SAMS Gene by RNAi: Reduction of Sinapine Levels
Transformation of B. napus with a RNAi construct for the SAMS gene under the control of the seed-specific promoter napin caused (
Silencing of COMT Gene by RNAi: Reduction of Sinapine Levels
Transformation of B. napus with an RNAi construct for the COMT gene under the control of the control of the constitutive promoter CaMV35S (
Silencing of COMT by Antisense RNA: Reduction of Sinapine Levels
Transformation of B. napus with a construct for the antisense RNA expression of a COMT gene under the control of the seed-specific promoter cruciferin (
Silencing of FAH-COMT by RNAi: Reduction of Sinapine Levels
Transformation of B. napus with an RNAi construct for a fusion between FAH and COMT genes under the control of the constitutive promoter CaMV35S (
A summary of sinapine reduction data is presented in Table 2.
Transgenic B. napus lines expressing RNAi and anti-sense (AS), either as single genes or as gene fusion constructs, for several genes involved in the sinapine pathway (see
Chemical analysis of seeds of Arabidopsis mutants deficient in the phenylpropanoid pathway (
Constructs
Cruciferin::COMT RNAi (p72-123)
The cruciferin promoter was PCR amplified using forward primer: TTGGCCCTTTAATTATGC
ATTGTGTGTGTTTTGGTG
The PCR product was blunt end cloned into the EcoRV site of pBluescript digested with BglII and SacI. This cruciferin promoter fragment was used to replace the CaMV35S promoter from the CaMV35S::COMT RNAi construct (p72-115) generating p72-123 (
Napin::COMT Antisense Construct (p72-122)
The COMT fragment was amplified by PCR from the Brassica EST, ESS2134, (SEQ ID NO:1; see: brassica.ca) using the following primers:
The fragment was blunt end cloned into pBluescript. The SacI-XbaI partial fragment was cloned between the SacI and XbaI sites of pBI121 (Clontech) in the anti-sense orientation. The CaMV35S promoter was replaced with the napin promoter (sequence ID#8) via a HindIII-XbaI digest generating p72-122 (
Cruciferin::COMT Anti-Sense Construct (p72-14)
The COMT fragment was amplified by PCR from the Brassica EST, RL4637, (SEQ ID NO:12: see brassica.ca) using the following primers:
The PCR product was blunt end cloned into the EcoRV site of pBluescript, digested with SacI and XbaI and cloned into the Sad and XbaI sites of pBI121 (Clontech) in the anti-sense orientation. The CaMV35S promoter was replaced with the cruciferin promoter (SEQ ID NO:6) via HindIII/XbaI digestion and ligation generating p72-14.
Napin::SAMS RNAi Construct (p72-135)
The SAMS fragment was amplified by PCR from the Brassica EST, RL103, (SEQ ID NO:7; see brassica.ca) using the following primers: agaacgggacttgcgct
GAACACAGACAACGGCT
The strategy for the production of RNAi constructs was employed using pGSA1285 as the backbone vector. The CaMV35S promoter was replaced with the napin promoter (SEQ ID NO:8) via a BglII-SacI digest generating p72-135 (
CaMV35S::FAH-COMT RNAi Construct (p72-142)
A FAH EST, RL1627 (SEQ ID NO:3) isolated from a Brassica napus root cDNA library, (see: brassica.ca) was used as template for PCR-amplification using the following two primers:
in which the bold portion is identical to sequence at the 5′-end of the COMT fragment. This PCR product generated a FAH fragment containing an overlapping 3′ end having identical sequence to the 5′ end of the COMT (See
The COMT fragment was amplified by PCR from the Brassica EST, ESS2134, (SEQ ID NO:1; see brassica.ca) using the following primers: aacaaagacggtgaagt
The two PCR products were used as templates for producing a FAH-COMT fusion product containing SpeI-AscI sites at the 5′ end and SwaI-BamHI sites at the 3′ end. This fusion product was blunt end cloned into the EcoRV site of pBluescript. The strategy for the production of RNAi constructs outlined above was employed (see
CaMV35S::C3H-C4H RNAi Construct (p72-146)
The C3H fragment was amplified by PCR from the Brassica EST, RL4992, (SEQ ID NO:9; see brassica.ca) using the following primers:
The bold portion corresponds to the 5′ end of the C4H portion (see
The C4H fragment was amplified by PCR from the Brassica EST, RL7118, (SEQ ID NO:10; see brassica.ca) using the following primers:
The products of these PCR reactions were used as templates to amplify a fusion product using C3H-F3 and C4H-R4 primers. This fusion was blunt end cloned into the EcoRV site of pBluescript to create p72-139 (SEQ ID NO:11). The strategy for the production of RNAi constructs was employed using pGSA1285 as the backbone vector generating p72-146 (
CaMV35S::4CL RNAi Construct (p72-170)
The 4CL fragment was amplified by PCR from the Brassica EST, RL4142, (SEQ ID NO:14; see brassica.ca) using the following primers:
The PCR product was blunt-end cloned into the EcoRV site of pBluescript producing plasmid p72-165. The strategy for the production of RNAi constructs was employed using pGSA1252 as the backbone vector generating p72-170.
CaMV35S::CCR RNAi Construct (p72-174)
The CCR fragment was amplified by PCR from the Brassica EST, RL2419, (SEQ ID NO:15; see brassica.ca) using the following primers:
The PCR product was blunt end cloned into the EcoRV site of pBluescript producing plasmid p72-164. The strategy for the production of RNAi constructs was employed using pGSA1252 as the backbone vector generating p72-174.
CaMV35S::4CL-CCR RNAi Construct (p72-173)
Plasmid p72-165 was PCR amplified using:
Plasmid p72-164 was PCR amplified using:
The products of these PCR reactions were used as templates to amplify a fusion product using 4CL-F5 and CCR-R6 primers (see “Strategy for cloning fusion products,
Reduction in Lignin Levels
Transgenic B. napus lines expressing RNAi and anti-sense (AS) constructs for several genes involved in lignin biosynthesis, including caffeic acid O-methyltransferase (COMT), ferulic acid hydroxylase (FAH), S-adenosylmethionine synthase (SAMS), cinnamic acid 4-hydroxylase (C4H) and coumaric acid 3-hydroxylase (C3H), 4-coumarate ligase (4CL), cinnamoyl CoA reductase (CCR), and gene fusions of these genes, showed lignin reductions ranging from 10% to 36% (Table 3).
Silencing of COMT Using RNAi
Transforming Brassica napus with Cruciferin::COMT RNAi construct (
Silencing of FAH and COMT Expression Using RNAi
Transforming Brassica napus with CaMV35S::FAH-COMT RNAi construct (
Silencing SAMS Gene Using RNAi
Transforming Brassica napus with napin::SAMS RNAi construct (
Silencing COMT Gene Expression Using Antisense RNA
Transforming Brassica napus with napin::COMT anti-sense construct (
Silencing COMT Gene Expression Using Antisense RNA
Transforming Brassica napus with cruciferin::COMT anti-sense construct (
Silencing of C3H and C4H Genes Using RNAi
Transforming Brassica napus with a CaMV35S::C3H-C4H RNAi construct (
Analysis of seeds of Arabidopsis mutants with knockouts in genes affecting phytate biosynthesis (
B. napus homologs of candidate target genes, including inositol trisphosphate kinase (IP3K), inositol hexaphosphate kinase (IP6K), and phosphatidylinositol phosphate kinases (PIKs), were cloned and used alone or in combination as gene fusions to generate RNAi constructs for expression in B. napus, and level of phytate determined in transgenic plants.
CaMV35S::PIKa-PIKb RNA Construct (p72-528)
The PIKa fragment was amplified by PCR from the Brassica EST, CL396R (see brassica.ca; SEQ ID NO:17, which has strong homology to phosphatidylinositol-4-phosphate-5-kinase) using the following primers:
The PIKb fragment was amplified by PCR from the Brassica EST, ESS1196F (see brassica.ca; SEQ ID NO:18, which has strong homology to phosphatidylinositol 3- and 4-kinase) using the following primers:
Both of the above mentioned PCR products were used as templates for the creation of a PIKa-PIKb
Actin2::pGSA1252 Construct
The Arabidopsis actin2 promoter (SEQ ID NO:21) was PCR amplified using:
and blunt end cloned into the EcoRV site of pBluescript producing p72-518. The BamHI-XhoI fragment from p72-518 was cloned into pGSA1252 at the BglII-XhoI sites thereby replacing the CaMV35S promoter with the actin2 promoter.
Actin2::PIKa RNAi Construct (p72-537)
The PIKa fragment was amplified by PCR from the Brassica EST, CL396R, (SEQ ID NO:17, see brassica.ca) using the following primers:
and blunt end cloned into the EcoRV site of pBluescript generating p72-509 (SEQ ID NO:20). This construct was digested with either AscI-SwaI or BamHI-XbaI cloned into p72-515 AscI-SwaI or BamHI-SpeI sites in the sense and anti-sense orientation (see
Actin2::IP6K RNAi Construct (p72-536)
Brassica napus genomic DNA fragment corresponding to IP6K (myo-inositol hexaphosphate kinase) was PCR amplified using:
The PCR product was blunt end cloned into the EcoRV site of pBluescript producing p72-507 (SEQ ID NO:22). This construct was digested with AscI-SwaI and cloned into the AscI-SwaI sites of p72-515 in the sense orientation producing an IP6K sense intermediate. P72-507 was then digested with BamHI-XbaI and cloned into the BamHI-SpeI sites of the IP6K sense intermediate. (see
Actin2::IP6K-IP3K RNAi Construct (p72-535)
Plasmid p72-507 (SEQ ID NO:22) was PCR amplified using:
The IP3K fragment was amplified by PCR from the Brassica EST, RL1344R (SEQ ID NO:23, see brassica.ca, this sequence has strong homology to inositol 1,3,4-trisphosphate 5/6-kinase) using the following primers:
The two PCR products were used as templates for the generation of a fusion product (see strategy for cloning fusion products,
P72-512 was also digested with BamHI-XbaI and cloned into the BamHI-SpeI sites of the IP6K-IP3K intermediate producing the antisense intermediate (see
Using this strategy, phytate levels in B. napus seeds by up to 29.4% (Table 5). Additional reduction in phytate levels may be achieved by silencing multiple gene families through gene stacking.
Most of the seed phytate is synthesized through the step-wise phosphorylation of myo-inositol rather than through phosphatidyl inositol. An alternate strategy to reduce phytate levels involves diverting more myo-inositol to phosphatidyl inositol biosynthesis, combined with blocking the de-esterification of the latter to myo-inositol phosphate. This is achieved by overexpressing phosphatidyl inositol synthase (PIS) and silencing phosphotidyl inositol bisphosphate phosphodiesterase (PIBP PDE).
All citations are hereby incorporated by reference.
The present invention has been described with regard to one or more embodiments. However, it will be apparent to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as defined in the claims.
