Patent Grant
11859196
This application contains a sequence listing in ASCII format, which is being submitted as a text file via EFS-Web with the file name “2014-108-07_SL_ST25.txt” (created Aug. 13, 2021; size 313,032 bytes) and which is hereby incorporated by reference in its entirety.
The present invention relates to abiotic stress-resistant plants and processes for obtaining them, including flowering plants and seeds thereof.
Abiotic stress is a major challenge facing the agricultural industry (see Yang et al., 2010). Abiotic stresses such as drought and heat not only cause a reduction in crop yield, but also cause high variation in crop yield. Improving crop tolerance to abiotic stresses such as heat and drought is essential for maintaining a stable yield under the continued threat of climate change. It is also a key factor for sustaining and expanding arable land areas for crop production.
Plants have evolved various mechanisms to cope with abiotic stress at both the physiological and biochemical levels. Many stress-induced genes have been identified, including those encoding key enzymes for abscisic acid (ABA) biosynthesis and signaling transduction components such as protein kinases, protein phosphatases and transcription factors. In recent years, several stress-regulated miRNAs have also been identified in model plants under biotic and abiotic stress conditions. Plants respond differently to drought and heat stress (Rizhsky et al., 2004).
Methods are provided for modulating an abiotic stress response to drought or heat in a plant, for example by introducing a heritable change to the plant, which alters the expression in the plant of an endogenous or exogenous Kanghan protein. Similarly, plants and plant cells having such heritable changes are provided.
Plants having enhanced drought tolerance are accordingly provided, for example by altering selected quantitative trait loci (QTL) associated with the family of Kanghan genes. Suppression of Kanghan genes, for example in null mutations, confers drought tolerance.
Methods are accordingly provided for modulating an abiotic stress response to drought in a plant, comprising introducing a heritable change to the plant which alters the expression in the plant of an endogenous or exogenous Kanghan protein. The Kanghan protein may for example be at least 35% identical to, or at least 49% positively aligned with, a protein encoded by the nucleotide sequence set forth in SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, and/or SEQ ID NO: 13; and this alignment may for example be over an alignment length of at least 90 amino acids, with BLOSUM or PAM substitution matrix, with gaps permitted. Alternative degrees of sequence similarity are contemplated in alternative embodiments, for example 50%, 75%, 90% or 95% identical to, or at least 75%, 90% or 100% positively aligned with, the protein encoded by the nucleotide sequence set forth in SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, or SEQ ID NO: 13; over an alignment length of at least 90, 100 or 110 amino acids, with BLOSUM or PAM substitution matrix, and with gaps permitted.
The Kanghan protein includes a variety conserved domains, such as domains: identical to hTVKDChphAhp (SEQ ID NO: 6); and/or, at least 80% identical to LTVKDCLEhAhK-G (SEQ ID NO: 7); and/or, at least 70% identical to LTVKDCLEhAFKKG (SEQ ID NO: 8); and/or at least 80% identical to VshKGpVlEstshpEs.chhhpQs-huA+LHlFpPph (SEQ ID NO: 9); and/or, at least 70% identical to VsMKGEVIEspsh-EAhcLllcQP-lGA+LHlFoPcl (SEQ ID NO: 10); and/or, at least 80% identical to cppDYDtStpAAhVAlpLISSARlhLKlDuhhTEYSsQaLhDpsutpp (SEQ ID NO: 11); and/or, at least 70% identical to spphhpShupscGhCHPDC-KAssEpEDYDASQpAAhVAVsLISSARlhLKLDusaTEYSAQYLVDNAGpccs (SEQ ID NO: 12).
In alternative embodiments, the plant may lack an endogenous Kanghan protein, such as a protein that has the sequence characteristics of Kanghan proteins described above, such as being at least 35% identical to, or at least 49% positively aligned with, a protein encoded by the nucleotide sequence set forth in SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, or SEQ ID NO: 13; over an alignment length of at least 90 amino acids, with BLOSUM or PAM substitution matrix.
The plant may be an angiosperm, and may for example belong to the family of Brassicaceae, Fabaceae, Poaceae, or Asteraceae plants. The plant may for example be a Caspsella rubella, Brassica rapa, Brassica napus, Brassica carinata, Eutrema salsugineum, Thellugiella parvula, Camelina sativa, Glycine max, Triticum, Zea maize, Oryza sativa or Helianthus annuus plant.
The heritable change may be one that sufficiently decreases the expression of the Kanghan protein so as to enhance drought tolerance relative to an unmodified plant, for example improving drought tolerance by an objective measure by 10% to 100% or more.
The heritable change may for example involve expressing in the plant an inhibitory polynucleotide that down-regulates the expression of the Kanghan protein, such as an inhibitory RNA, for example an anti-sense oligonucleotide, an RNAi oligonucleotide (including a small interfering RNA), a microRNA, or a CRISPR guide RNA. Alternatively, the heritable change may be an alteration of a Kanghan gene sequence encoding the Kanghan protein, for example by transformation with an exogenous Kanghan gene encoding the exogenous Kanghan protein, or by editing or mutation of an endogenous Kanghan gene encoding the endogenous Kanghan protein. The editing or mutation may for example introduce a change to a coding sequence of the Kanghan gene which changes (renders) the amino acid sequence of the Kanghan protein (non-functional?).
In accordance with the foregoing methods, there are also provided parental plants or plant cells that are produced by these processes. Similarly, plant lines, varieties or cultivars are provided that include the parental plant or plant cell, and the plant line, variety or cultivar may for example be characterized by an improved drought tolerance characteristic. Seeds and plant parts are provided, for example from foregoing plant lines, varieties or cultivars.
Seeds in turn may be used to provide progeny plants, such as progeny plants that are genetically derived from the plant line, variety or cultivar so as to retain the improved drought tolerance characteristic.
Methods of marker assisted selection may for example be used to introduce the heritable change, with subsequent screening of the plant or plant cell or progeny for the desired modulation of the abiotic stress response to drought.
A further embodiment is a method for producing a plant having increased tolerance to heat stress, comprising introducing into a plant cell an expression construct comprising a nucleic acid molecule encoding a polypeptide with at least 80% identity to SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 18, and/or SEQ ID NO: 19 over an alignment length of at least 90 amino acids, operatively linked to at least one regulatory element, said at least one regulatory element being effective to direct expression of said nucleic acid molecule in the plant; and growing the plant cell into the plant. In another embodiment, the nucleic acid molecule encodes a polypeptide with at least 80%, at least 81%, at least 82%, at least 83%, at least 84%, at least 85%, at least 86%, at least 87%, at least 88%, at least 89%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity to SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 18, and/or SEQ ID NO: 19 over an alignment length of at least 90 amino acids, at least 100 amino acids, at least 110 amino acids, or over the full length of the amino acid sequence set forth in SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 18, or SEQ ID NO: 19. The polypeptide encoded by the nucleic acid molecule will preferably have the same biological activity as the polypeptide set forth in SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 18, or SEQ ID NO: 19. In an embodiment, at least one regulatory element comprises a promoter, for example a constitutive promoter. In a further embodiment, the regulatory element is a regulatory element that is not naturally in operative linkage with the nucleic acid molecule. For example, the regulatory element may be a synthetic regulatory element, a regulatory element derived from a different species than the nucleic acid molecule, or a regulatory element derived from a different gene within the same species as the nucleic acid molecule. In an embodiment, the nucleic acid molecule is derived from a different species than the plant cell into which the expression construct is introduced. In a further embodiment, the nucleic acid molecule is derived from Arabidopsis and the plant cell is a Triticum cell.
The method may further comprise a step of assessing the heat tolerance of the plant relative to a control plant of the same variety or genetic background that does not comprise the expression construct and identifying the plant as having increased tolerance to heat stress if it exhibits increased heat tolerance relative to the control plant. Tests for heat tolerance are known and will be understood by one skilled in the art (for example, see Kumar et al., 2013; Hatfield et al., 2015). In wheat, heat tolerance may be assessed by, for example, subjecting newly germinated seedlings, seedlings, or plants to heat stress at a temperature of about 27 or higher of about 30° C. or higher (e.g. conditions such as 36° C., 42/38° C. (day/night), or 40/38° C. (day/night)) for a period of time (typically days or weeks, for example two or three weeks) then allowing them to recover at a standard growth temperature between about 13-25° C. (e.g. growth conditions such as 25° C., 25/20° C. (day/night), 24/16° C. (day/night), or 18/13° C. (day/night)) for a period of time (e.g. 3-10 weeks) and then measuring viability or another indicator of heat stress, such as yield, biomass, or canopy temperature.
Further provided is a plant cell, plant, seed, or plant tissue comprising an expression construct as described above. In an embodiment, the plant cell, plant, seed, or plant tissue is a Poaceae cell, plant, seed, or tissue. In a further embodiment, the plant cell, plant, seed, or plant tissue is a cereal plant cell, plant, seed, or tissue. Cereal plants include commercially important grain crops such as rice (Oryza sativa), wheat/spelt (Triticum), corn/maize (Zea mays), barley (Hordeum vulgare), Sorghum, oat (Avena sativa), rye (Secale cereale), and Triticale. In a further embodiment, the plant cell, plant, seed, or plant tissue is Triticum. In accordance with the foregoing methods, there are also provided parental plants or plant cells that are produced by these processes. Seeds in turn may be used to provide progeny plants, such as progeny plants that are genetically derived from the plant line, variety or cultivar so as to retain the improved drought tolerance characteristic. Seeds and plant parts that are derived from the foregoing plant lines may be characterized by improved drought tolerance characteristics, for example they may be subjected to RNAseq analyses to identify transcripts that exhibit contrasting differential expression patterns when compared with their respective wild type controls. The combinatory profile of these genes can be an evaluation benchmark for drought tolerance.
Methods of marker assisted selection may for example be used to introduce the heritable change, with subsequent screening of the plant or plant cell or progeny for the desired modulation of the abiotic stress response to drought.
Another aspect of the disclosure is a transgenic Brassicaceae plant or plant cell comprising a recombinant nucleic acid construct encoding at least one inhibitory polynucleotide that targets an endogenous Kanghan gene in the transgenic Brassicaceae plant or plant cell to reduce or eliminate expression of a Kanghan protein encoded by the Kanghan gene, wherein:
In an embodiment of the transgenic Brassicaceae plant or plant cell, the at least one inhibitory polynucleotide comprises an anti-sense oligonucleotide, an RNAi oligonucleotide, or a CRISPR guide RNA.
In an embodiment of the transgenic Brassicaceae plant or plant cell, the Kanghan protein has at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence set forth in SEQ ID NO: 127 and further has at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence set forth in SEQ ID NO: 126.
In an embodiment of the transgenic Brassicaceae plant or plant cell, the Kanghan protein has at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence set forth in SEQ ID NO: 79, SEQ ID NO: 86, SEQ ID NO: 72, SEQ ID NO: 84, SEQ ID NO: 78, SEQ ID NO: 85, or SEQ ID NO: 95. In an embodiment, the Kanghan protein comprises SEQ ID NO: 79, SEQ ID NO: 86, SEQ ID NO: 72, SEQ ID NO: 84, SEQ ID NO: 78, SEQ ID NO: 85, or SEQ ID NO: 95.
In an embodiment of the transgenic Brassicaceae plant or plant cell, the Kanghan protein has at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence set forth in SEQ ID NO: 63, SEQ ID NO: 77, or SEQ ID NO: 121. In an embodiment, the Kanghan protein comprises SEQ ID NO: 63, SEQ ID NO: 77, or SEQ ID NO: 121.
In an embodiment of the transgenic Brassicaceae plant or plant cell, the at least one inhibitory polynucleotide targets two or more endogenous Kanghan genes in the transgenic Brassicaceae plant or plant cell to reduce or eliminate the expression of the Kanghan proteins encoded by the two or more Kanghan genes. In a further embodiment, each of the Kanghan proteins encoded by the two or more Kanghan genes has at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence set forth in SEQ ID NO: 79, SEQ ID NO: 86, SEQ ID NO: 72, SEQ ID NO: 84, SEQ ID NO: 78, SEQ ID NO: 85, or SEQ ID NO: 95. In an embodiment, each of the Kanghan proteins encoded by the two or more Kanghan genes comprises the amino acid sequence set forth in SEQ ID NO: 79, SEQ ID NO: 86, SEQ ID NO: 72, SEQ ID NO: 84, SEQ ID NO: 78, SEQ ID NO: 85, or SEQ ID NO: 95.
Another aspect is a transgenic seed obtained from a transgenic Brassicaceae plant as defined herein, wherein the transgenic seed comprises the recombinant nucleic acid construct.
In an embodiment, the transgenic Brassicaceae plant, plant cell, or seed is a Brassica napus plant or plant cell.
A further aspect of the disclosure is a method of obtaining a Brassicaceae plant having increased drought tolerance, the method comprising:
In embodiments of the method, the Kanghan protein has at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence set forth in SEQ ID NO: 127 or SEQ ID NO: 128.
In embodiments of the method, the Kanghan protein has at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence set forth in SEQ ID NO: 79, SEQ ID NO: 86, SEQ ID NO: 72, SEQ ID NO: 84, SEQ ID NO: 78, SEQ ID NO: 85, or SEQ ID NO: 95.
In embodiments of the method, the Kanghan protein has at least has at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence set forth in SEQ ID NO: 63, SEQ ID NO: 77, or SEQ ID NO: 121.
Another aspect of the disclosure is a method of obtaining a Brassicaceae plant having increased drought tolerance, the method comprising:
In an embodiment of the method, the Kanghan protein has at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence set forth in SEQ ID NO: 127 and further has at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence set forth in SEQ ID NO: 126; or
the Kanghan protein has at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence set forth in SEQ ID NO: 128 and further has at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence set forth in SEQ ID NO: 129.
In an embodiment of the method, the Kanghan protein has at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence set forth in SEQ ID NO: 79, SEQ ID NO: 86, SEQ ID NO: 72, SEQ ID NO: 84, SEQ ID NO: 78, SEQ ID NO: 85, or SEQ ID NO: 95.
In an embodiment of the method, the Kanghan protein has at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence set forth in SEQ ID NO: 63, SEQ ID NO: 77, or SEQ ID NO: 121.
In an embodiment of the method, the inhibitory polynucleotide comprises an anti-sense oligonucleotide, an RNAi oligonucleotide, or a CRISPR guide RNA.
Another aspect of the disclosure is a Brassicaceae plant, plant cell, or seed produced by the method described in the preceding paragraphs, wherein the Brassicaceae plant, plant cell, or seed comprises at least one non-naturally occurring heritable genetic change in the endogenous Kanghan gene that was induced by the inhibitory polynucleotide. In an embodiment, the plant, plant cell, or seed is a Brassica napus plant, plant cell, or seed.
In order that the invention may be more clearly understood, embodiments thereof will now be described in detail by way of example, with reference to the accompanying drawings, in which:
The following is a list of sequences appearing in this document:
In the following detailed description, various non-limiting examples are set out of particular embodiments, together with experimental procedures that may be used to implement a wide variety of modifications and variations in the practice of the present invention. For clarity, a variety of technical terms are used herein in accordance with what is understood to be the commonly understood meaning, as reflected in definitions set out below.
The term “line” refers to a group of plants that displays very little overall variation among individuals sharing that designation. A “line” generally refers to a group of plants that display little or no genetic variation between individuals for at least one trait. Plants within a group of plants that display little or no genetic variation between individuals may also be referred to as having the same genetic background.
A “variety” or “cultivar” includes a line that is used for commercial production. In some aspects, Brassica varieties may for example be derived from “doubled haploid” (DH) lines, which refers to a line created by the process of microspore embryogenesis, in which a plant is created from an individual microspore. By this process, lines are created that are homogeneous, i.e. all plants within the line have the same genetic makeup. The original DH plant is referred to as DH1, while subsequent generations are referred to as DH2, DH3 etc. Doubled haploid procedures are well known and have been established for several crops. A procedure for B. juncea has been described by Thiagrarajah and Stringham (1993).
New lines, varieties or plants may be produced by introducing a heritable change in a parent plant. In this context, a “heritable change” is any molecular alteration, typically a genetic change, that is capable of being passed from one generation of plant to the next. This term is intended to include molecular alterations such as, but not limited to, insertions, deletions, point mutations, frame-shift mutations, inversions, rearrangements, and the introduction of transgenes. There is a wide variety of techniques available for introducing heritable changes to plants and plant cells.
Plant “mutagenesis” in the present context is a process in which an agent known to cause alterations in genetic material is applied to plant material, for example the mutagenic agent ethyl methylsulfonate (EMS). A range of molecular techniques such as recombination with foreign or heterologous nucleic acid fragments or gene editing may also be used for mutagenesis. All such methods of introducing nucleic acid sequence changes are included within the term “mutagenesis” as used herein.
Plant “regeneration” involves the selection of cells capable of regeneration (e.g. seeds, microspores, ovules, pollen, vegetative parts) from a selected plant or variety. These cells may optionally be subjected to mutagenesis, following which a plant is developed from the cells using regeneration, fertilization, and/or growing techniques based on the types of cells mutagenized. Applicable regeneration techniques are known to those skilled in the art; see, for example, Armstrong et al. (1985); and Close et al. (1987).
“Improved characteristics” of a plant means that the characteristics in question are altered in a way that is desirable or beneficial or both in comparison with a reference value or attribute, which in the absence of an express comparator relates to the equivalent characteristic of a wild type strain.
Plant “progeny” means the direct and indirect descendants, offspring and derivatives of a plant or plants and includes the first, second, third and subsequent generations and may be produced by self-crossing, crossing with plants with the same or different genotypes, and may be modified by range of suitable genetic engineering techniques.
Plant “breeding” includes all methods of developing or propagating plants and includes both intra and inter species and intra and inter line crosses as well as all suitable artificial breeding techniques. Desired traits may be transferred to other lines through conventional breeding methods and can also be transferred to other species through inter-specific crossing. Both conventional breeding methods and inter-specific crossing methods as well as all other methods of transferring genetic material between plants are included within the concept of “breeding”.
“Molecular biological techniques” means all forms of anthropomorphic manipulation of a biological molecules, such as nucleic acid sequences, for example to alter the sequence and expression thereof and includes the insertion, deletion, modification or editing of sequences or sequence fragments and the direct or indirect introduction of new sequences into the genome of an organism, for example by directed or random recombination using suitable vectors and/or techniques.
“Marker-assisted selection” (MAS) refers to the use of molecular markers to assist in phenotypic selection in the context of plant breeding. A wide variety of molecular markers, such as single nucleotide polymorphisms (SNPs), may for example be used in MAS plant breeding, including the application of next-generation sequencing (NGS) technologies.
The term “genetically derived” as used for example in the phrase “an improved characteristic genetically derived from the parent plant or cell” means that the characteristic in question is dictated wholly or in part by an aspect of the genetic makeup of the parent plant or cell, applying for example to progeny of the parent plant or cell that retain the improved characteristic of the parent plant or cell.
Various genes and nucleic acid sequences of the invention may be recombinant sequences. The term “recombinant” means that something has been recombined, so that when made in reference to a nucleic acid construct the term refers to a molecule that is comprised of nucleic acid sequences that are joined together or produced by means of molecular biological techniques. Nucleic acid “constructs” are accordingly recombinant nucleic acids, which have been generally been made by aggregating interoperable component sequencers. The term “recombinant” when made in reference to a protein or a polypeptide refers to a protein or polypeptide molecule which is expressed using a recombinant nucleic acid construct created by means of molecular biological techniques. The term “recombinant” when made in reference to the genetic composition or an organism or cell refers to a gamete or progeny with new combinations of alleles that did not occur in the parental genomes. Recombinant nucleic acid constructs may include a nucleotide sequence which is ligated to, or is manipulated to become ligated to, a nucleic acid sequence to which it is not ligated in nature, or to which it is ligated at a different location in nature. Referring to a nucleic acid construct as ‘recombinant’ therefore indicates that the nucleic acid molecule has been manipulated using genetic engineering, i.e. by human intervention. Recombinant nucleic acid constructs may for example be introduced into a host cell by transformation. Such recombinant nucleic acid constructs may include sequences derived from the same host cell species or from different host cell species, which have been isolated and reintroduced into cells of the host species. Recombinant nucleic acid construct sequences may become integrated into a host cell genome, either as a result of the original transformation of the host cells, or as the result of subsequent recombination and/or repair events.
Recombinant constructs of the invention may include a variety of functional molecular or genomic components, as required for example to mediate gene expression or suppression in a transformed plant. In this context, “DNA regulatory sequences,” “control elements,” and “regulatory elements,” refer to transcriptional and translational control sequences, such as promoters, enhancers, polyadenylation signals, terminators, and protein degradation signals that regulate gene expression. In the context of the present disclosure, “promoter” means a sequence sufficient to direct transcription of a gene when the promoter is operably linked to the gene. The promoter is accordingly the portion of a gene containing DNA sequences that provide for the binding of RNA polymerase and initiation of transcription. Promoter sequences are commonly, but not universally, located in the 5′ non-coding regions of a gene. A promoter and a gene are “operably linked” when such sequences are functionally connected so as to permit gene expression mediated by the promoter. The term “operably linked” accordingly indicates that DNA segments are arranged so that they function in concert for their intended purposes, such as initiating transcription in the promoter to proceed through the coding segment of a gene to a terminator portion of the gene. Gene expression may occur in some instances when appropriate molecules (such as transcriptional activator proteins) are bound to the promoter. Expression is the process of conversion of the information of a coding sequence of a gene into mRNA by transcription and subsequently into polypeptide (protein) by translation, as a result of which the protein is said to be expressed. As the term is used herein, a gene or nucleic acid is “expressible” if it is capable of expression under appropriate conditions in a particular host cell.
Promoters may for example be used that provide for preferential gene expression within a specific organ or tissue, or during a specific period of development. For example, promoters may be used that are specific for leaf (Dunsmuir et al., 1983), root tips (Pokalsky et al., 1989), fruit (Peat et al., 1989; U.S. Pat. No. 4,943,674 issued 24 Jul. 1990; International Patent Publication WO-A 8 809 334; U.S. Pat. No. 5,175,095 issued 29 Dec. 1992; European Patent Application EP-A 0 409 629; and European Patent Application EP-A 0 409 625) embryogenesis (U.S. Pat. No. 5,723,765 issued 3 Mar. 1998 to Oliver et al.), or young flowers (Nilsson et al. 1998). Promoters demonstrating preferential transcriptional activity in plant tissues are, for example, described in European Patent Application EP-A 0 255 378 and International Patent Publication WO-A 9 113 980. Promoters may be identified from genes which have a differential pattern of expression in a specific tissue by screening a tissue of interest, for example, using methods described in U.S. Pat. No. 4,943,674 and European Patent Application EP-A 0255378. The disclosure herein includes examples of this embodiment, showing that plant tissues and organs can be modified by transgenic expression of a Kanghan gene.
An “isolated” nucleic acid or polynucleotide as used herein refers to a component that is removed from its original environment (for example, its natural environment if it is naturally occurring). An isolated nucleic acid or polypeptide may contain less than about 50%, less than about 75%, less than about 90%, less than about 99.9% or less than any integer value between 50 and 99.9% of the cellular or biological components with which it was originally associated. A polynucleotide amplified using PCR so that it is sufficiently distinguishable (on a gel for example) from the rest of the cellular components is, for example, thereby “isolated”. The polynucleotides of the invention may be “substantially pure,” i.e., having the high degree of isolation as achieved using a purification technique.
In the context of biological molecules “endogenous” refers to a molecule such as a nucleic acid that is naturally found in and/or produced by a given organism or cell. An “endogenous” molecule may also be referred to as a “native” molecule. Conversely, in the context of biological molecules “exogenous” refers to a molecule, such as a nucleic acid, that is not normally or naturally found in and/or produced by a given organism or cell in nature.
As used herein to describe nucleic acid or amino acid sequences the term “heterologous” refers to molecules or portions of molecules, such as DNA sequences, that are artificially introduced into a particular host cell, for example by transformation. Heterologous DNA sequences may for example be introduced into a host cell by transformation. Such heterologous molecules may include sequences derived from the host cell. Heterologous DNA sequences may become integrated into the host cell genome, either as a result of the original transformation of the host cells, or as the result of subsequent recombination events.
Transformation techniques that may be employed include plant cell membrane disruption by electroporation, microinjection and polyethylene glycol based transformation (such as are disclosed in Paszkowski et al. (1984); Fromm et al. (1985); Rogers et al. (1986); and in U.S. Pat. Nos. 4,684,611; 4,801,540; 4,743,548 and 5,231,019), biolistic transformation such as DNA particle bombardment (for example as disclosed in Klein et al. (1987); Gordon-Kamm, et al. (1990); and in U.S. Pat. Nos. 4,945,050; 5,015,580; 5,149,655 and 5,466,587); Agrobacterium-mediated transformation methods (such as those disclosed in Horsch et al. (1984); Fraley et al. (1983); and U.S. Pat. Nos. 4,940,838 and 5,464,763). Transformation systems adapted for use in Camelina sativa are for example described in US Patent Publication 20140223607. Varieties of Camelina sativa are for example described in US Patent Publication 20120124693, and the subject of seed samples deposited under ATCC Accession No. PTA-11480. Aspects of the present invention involve altering known plant varieties, such as Camelina sativa, to alter endogenous Kanghan genes.
Transformed plant cells may be cultured to regenerate whole plants having the transformed genotype and displaying a desired phenotype, as for example modified by the expression of a heterologous Kanghan gene during growth or development. A variety of plant culture techniques may be used to regenerate whole plants, such as are described in Gamborg et al. (1995); Evans et al. (1983); Binding (1985); Klee et al. (1987).
Various aspects of the present disclosure encompass nucleic acid or amino acid sequences that are homologous to other sequences. As the term is used herein, an amino acid or nucleic acid sequence is “homologous” to another sequence if the two sequences are substantially identical, as defined herein, and the functional activity of the sequences is conserved (as used herein, sequence conservation or identity does not infer evolutionary relatedness). Nucleic acid sequences may also be homologous if they encode substantially identical amino acid sequences, even if the nucleic acid sequences are not themselves substantially identical, for example as a result of the degeneracy of the genetic code.
With reference to biological sequences “substantial homology” or “substantial identity” is meant, in the alternative, a sequence identity of greater than 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% up to 100% sequence identity. Homology may refer to nucleic acid or amino acid sequences as the context dictates. In alternative embodiments, sequence identity may for example be at least 75%, at least 90% or at least 95%. Optimal alignment of sequences for comparisons of identity may be conducted using a variety of algorithms, such as the local homology algorithm of Smith and Waterman (1981), the homology alignment algorithm of Needleman and Wunsch (1970), the search for similarity method of Pearson and Lipman (1988), and the computerized implementations of these algorithms (such as GAP, BESTFIT, FASTA and TFASTA in the Wisconsin Genetics Software Package, Genetics Computer Group, Madison, Wis., U.S.A.). Sequence identity may also be determined using the BLAST algorithm, described in Altschul et al. (1990) (using the published default settings). Software for performing BLAST analysis may be available through the National Center for Biotechnology Information (NCBI) at their Internet site. The BLAST algorithm involves first identifying high scoring sequence pairs (HSPs) by identifying short words of length W in the query sequence that either match or satisfy some positive-valued threshold score T when aligned with a word of the same length in a database sequence. T is referred to as the neighborhood word score threshold. Initial neighborhood word hits act as seeds for initiating searches to find longer HSPs. The word hits are extended in both directions along each sequence for as far as the cumulative alignment score can be increased. Extension of the word hits in each direction is halted when the following parameters are met: the cumulative alignment score falls off by the quantity X from its maximum achieved value; the cumulative score goes to zero or below, due to the accumulation of one or more negative-scoring residue alignments; or the end of either sequence is reached. The BLAST algorithm parameters W, T and X determine the sensitivity and speed of the alignment. The BLAST program may use as defaults a word length (W) of 11, the BLOSUM62 scoring matrix (Henikoff et al., 1992) alignments (B) of 50, expectation (E) of 10, M=5, N=4, and a comparison of both strands. One measure of the statistical similarity between two sequences using the BLAST algorithm is the smallest sum probability (P(N)), which provides an indication of the probability by which a match between two nucleotide or amino acid sequences would occur by chance. In alternative embodiments, nucleotide or amino acid sequences are considered substantially identical if the smallest sum probability in a comparison of the test sequences is less than about 1, less than about 0.1, less than about 0.01, or less than about 0.001.
An alternative indication that two amino acid sequences are substantially identical is that one peptide is specifically immunologically reactive with antibodies that are also specifically immunoreactive against the other peptide. Antibodies are specifically immunoreactive to a peptide if the antibodies bind preferentially to the peptide and do not bind in a significant amount to other proteins present in the sample, so that the preferential binding of the antibody to the peptide is detectable in an immunoassay and distinguishable from non-specific binding to other peptides. Specific immunoreactivity of antibodies to peptides may be assessed using a variety of immunoassay formats, such as solid-phase ELISA immunoassays for selecting monoclonal antibodies specifically immunoreactive with a protein (see Harlow et al., 1988).
An alternative indication that two nucleic acid sequences are substantially identical is that the two sequences hybridize to each other under moderately stringent, or stringent, conditions. Hybridization to filter-bound sequences under moderately stringent conditions may, for example, be performed in 0.5 M NaHPO4, 7% sodium dodecyl sulfate (SDS), 1 mM EDTA at 65° C., and washing in 0.2×SSC/0.1% SDS at 42° C. (see Ausubel, et al. (eds), 1989). Alternatively, hybridization to filter-bound sequences under stringent conditions may, for example, be performed in 0.5 M NaHPO4, 7% SDS, 1 mM EDTA at 65° C., and washing in 0.1×SSC/0.1% SDS at 68° C. (see Ausubel, et al. (eds), 1989). Hybridization conditions may be modified in accordance with known methods depending on the sequence of interest (see Tijssen, 1993). Generally, stringent conditions are selected to be about 5° C. lower than the thermal melting point for the specific sequence at a defined ionic strength and pH. The term “a polynucleotide that hybridizes under stringent (low, intermediate) conditions” is intended to encompass both single and double-stranded polynucleotides although only one strand will hybridize to the complementary strand of another polynucleotide. Washing in the specified solutions may be conducted for a range of times from several minutes to several days and those skilled in the art will readily select appropriate wash times to discriminate between different levels of homology in bound sequences.
In alternative embodiments, the invention provides nucleic acids, such as isolated or recombinant nucleic acid molecules, comprising the sequence of a Kanghan allele of the invention. Isolated nucleic acids of the invention may include coding sequences of the invention recombined with other sequences, such as cloning vector sequences. Homology to sequences of the invention may be detectable by hybridization with appropriate nucleic acid probes, by PCR techniques with suitable primers or by other techniques. In particular embodiments there are provided nucleic acid probes which may comprise sequences homologous to portions of the alleles of the invention. Further embodiments may involve the use of suitable primer pairs to amplify or detect the presence of a sequence of the invention, for example a sequence that is associated with an abiotic stress response, such as drought or heat resistance.
In alternative embodiments, the invention provides methods for identifying plants, such as Camelina, Brassica or Triticum plants, with a desirable abiotic stress response, such as drought tolerance and/or heat resistance, or a desired genomic characteristic. Methods of the invention may for example involve determining the presence in a genome of particular Kanghan alleles. In particular embodiments the methods may comprise identifying the presence of: a nucleic acid polymorphism associated with one of the identified alleles; or an antigenic determinant associated with one of the alleles. Such a determination may for example be achieved with a range of techniques, such as PCR amplification of the relevant DNA fragment, DNA fingerprinting, RNA fingerprinting, gel blotting and RFLP analysis, nuclease protection assays, sequencing of the relevant nucleic acid fragment, the generation of antibodies (monoclonal or polyclonal), or alternative methods adapted to distinguish the protein produced by the relevant alleles from other variants or wild type forms of that protein.
In selected embodiments, a specific base pair change in a Kanghan allele may for example be used to design protocols for MAS, such as the use of allele-specific probes, markers or PCR primers. For an exemplary summary of allele-specific PCR protocols, see Myakishev et al. (2001) or Tanhuanpaa et al. (1999). In alternative embodiments, for example, various methods for detecting single nucleotide polymorphisms (SNPs) may be used for identifying Kanghan alleles of the invention. Such methods may for example include TaqMan assays or Molecular Beacon assays (Tapp et al., 2000), Invader Assays (Mein et al., 2000) or assays based on single strand conformational polymorphisms (SSCP) (Orita et al., 1989).
In alternative embodiments, the invention provides progeny of parent plant lines having altered endogenous or heterologous Kanghan genes, for example progeny of Camelina sativa parent line which is the subject of ATCC Accession number PTA-11480. Such progeny may for example be selected to have a desired alteration in an abiotic stress response compared to the parent strain, such as improved drought resistance or heat tolerance.
In alternative embodiments, a plant seed is provided, such as an Arabidopsis, Camelina, Triticum or Brassica seed. In alternative embodiments, genetically stable plants are provided, such as plants of the genus Arabidopsis, Camelina, Triticum or Brassica. In further alternative embodiments the invention provides processes of producing genetically stable plants, such as Arabidopsis, Camelina, Triticum or Brassica plants, for example plants having a desired alteration in an abiotic stress response compared to a reference strain that does not have a particular alteration in a Kanghan gene, such as improved drought resistance or heat tolerance.
In various aspects, the invention involves the modulation of the number of copies of an expressible Kanghan coding sequence in a plant genome. By “expressible” it is meant that the primary structure, i.e. sequence, of the coding sequence indicates that the sequence encodes an active protein. Expressible coding sequences may nevertheless not be expressed as an active protein in a particular cell, for example due to gene silencing. This ‘gene silencing’ may for example take place by various mechanisms of homologous transgene inactivation or epigenetic silencing in vivo. Homologous transgene inactivation and epigenetic silencing in transgenic plants has been described in plants where a transgene has been inserted in the sense orientation, with the result that both the gene and the transgene are down-regulated (Napoli et al., 1990; Rajeevkum et al., 2015). In the present invention, the expressible coding sequences in a genome may accordingly not all be expressed in a particular cell, and may in some embodiments result in suppression of Kanghan gene expression.
In other aspects, reduction of Kanghan gene expression may include the reduction, including the suppression or elimination (aka knockout), of expression of a nucleic acid sequence that encodes a Kanghan protein, such as a nucleic acid sequence of the invention. By elimination of expression, it is meant herein that a functional amino acid sequence encoded by the nucleic acid sequence is not produced at a detectable level. By suppression of expression, it is meant herein that a functional polypeptide encoded by the nucleic acid sequence is produced at a reduced level relative to the wild type level of expression of the polypeptide. Reduction of Kanghan expression may include the elimination of transcription of a nucleic acid sequence that encodes a Kanghan protein, such as a sequence of the invention encoding a Kanghan protein. By elimination of transcription it is meant herein that the mRNA sequence encoded by the nucleic acid sequence is not transcribed at detectable levels. Reduction of Kanghan activity may also include the production of a truncated amino acid sequence from a nucleic acid sequence that encodes a Kanghan protein, meaning that the amino acid sequence encoded by the nucleic acid sequence is missing one or more amino acids of the functional amino acid sequence encoded by a wild type nucleic acid sequence. In addition, reduction of Kanghan activity may include the production of a variant Kanghan amino acid sequence, meaning that the amino acid sequence has one or more amino acids that are different from the amino acid sequence encoded by a wild type nucleic acid sequence. A variety of mutations may be introduced into a nucleic acid sequence for the purpose of reducing Kanghan activity, such as frame-shift mutations, introduction of premature stop codon(s), substitutions and deletions. For example, mutations in coding sequences may be made so as to introduce substitutions within functional motifs or conserved domains in a Kanghan protein, such as conserved Kanghan protein domains A, B or C.
In an alternative aspect, the down-regulation of Kanghan genes may be used to alter a plant response to abiotic stress, for example to enhance drought tolerance. Such down-regulation may be tissue-specific. For example, anti-sense oligonucleotides may be expressed to down-regulate expression of Kanghan genes. The expression of such anti-sense constructs may be made to be tissue-specific by operably linking anti-sense encoding sequences to tissue-specific promoters. Anti-sense oligonucleotides, including anti-sense RNA molecules and anti-sense DNA molecules, act to block the translation of mRNA by binding to targeted mRNA and inhibiting protein translation from the bound mRNA. For example, anti-sense oligonucleotides complementary to regions of a DNA sequence encoding a Kanghan protein may be expressed in transformed plant cells during development to down-regulate the expression of the Kanghan gene. Alternative methods of down-regulating Kanghan gene expression may include the use of ribozymes or other enzymatic RNA molecules (such as hammerhead RNA structures) that are capable of catalyzing the cleavage of RNA (as disclosed in U.S. Pat. Nos. 4,987,071 and 5,591,610).
Aspects of the invention involve the use of gene editing to alter Kanghan gene sequences. For example, CRISPR-Cas system(s) (e.g., single or multiplexed) can be used to perform plant gene or genome interrogation or editing or manipulation. Kanghan genes may for example be edited for functional investigation and/or selection and/or interrogation and/or comparison and/or manipulation and/or transformation of plant Kanghan genes. This editing may be carried out so as to create, identify, develop, optimize, or confer trait(s) or characteristic(s) to plant(s) or to transform a plant genome, for example to alter an abiotic stress response in a plant, such as a drought or heat tolerance. Gene editing can in this way be used to provide improved production of plants, new plants with new combinations of traits or characteristics or new plants with enhanced traits. Such CRISPR-Cas system(s) can for example be used in Site-Directed Integration (SDI) or Gene Editing (GE) or any Near Reverse Breeding (NRB) or Reverse Breeding (RB) techniques (see the University of Arizona website “CRISPR-PLANT” http://www.genome.arizona.edu/crispr/). Embodiments of the invention can be used in genome editing in plants alone or in combination with other molecular biological techniques, such as RNAi or similar genome editing techniques (see, e.g., Nekrasov, 2013; Brooks, 2014; Shan, 2013; Feng, 2013; Xie, 2013; Xu, 2014; Caliando et al, 2015; U.S. Pat. Nos. 6,603,061; 7,868,149; US 2009/0100536; Morrell et al., 2011). Protocols for targeted plant genome editing via CRISPR/Cas9 are also available in Li et al, 2015.
In some embodiments, the invention provides new Kanghan polypeptide sequences, which may be produced from wild type Kanghan proteins by a variety of molecular biological techniques. It is well known in the art that some modifications and changes can be made in the structure of a polypeptide without substantially altering the biological function of that peptide, to obtain a biologically equivalent polypeptide. As used herein, the term “conserved amino acid substitutions” refers to the substitution of one amino acid for another at a given location in the peptide, where the substitution can be made without any appreciable loss or gain of function, to obtain a biologically equivalent polypeptide. In making such changes, substitutions of like amino acid residues can be made on the basis of relative similarity of side-chain substituents, for example, their size, charge, hydrophobicity, hydrophilicity, and the like, and such substitutions may be assayed for their effect on the function of the peptide by routine testing. Conversely, as used herein, the term “non-conserved amino acid substitutions” refers to the substitution of one amino acid for another at a given location in the peptide, where the substitution causes an appreciable loss or gain of function of the peptide, to obtain a polypeptide that is not biologically equivalent.
In some embodiments, conserved amino acid substitutions may be made where an amino acid residue is substituted for another having a similar hydrophilicity value (e.g., within a value of plus or minus 2.0), where the following hydrophilicity values are assigned to amino acid residues (as detailed in U.S. Pat. No. 4,554,101): Arg (+3.0); Lys (+3.0); Asp (+3.0); Glu (+3.0); Ser (+0.3); Asn (+0.2); Gln (+0.2); Gly (0); Pro (−0.5); Thr (−0.4); Ala (−0.5); His (−0.5); Cys (−1.0); Met (−1.3); Val (−1.5); Leu (−1.8); Ile (−1.8); Tyr (−2.3); Phe (−2.5); and Trp (−3.4). Non-conserved amino acid substitutions may be made were the hydrophilicity value of the residues is significantly different, e.g. differing by more than 2.0.
In alternative embodiments, conserved amino acid substitutions may be made where an amino acid residue is substituted for another having a similar hydropathic index (e.g., within a value of plus or minus 2.0). In such embodiments, each amino acid residue may be assigned a hydropathic index on the basis of its hydrophobicity and charge characteristics, as follows: Ile (+4.5); Val (+4.2); Leu (+3.8); Phe (+2.8); Cys (+2.5); Met (+1.9); Ala (+1.8); Gly (−0.4); Thr (−0.7); Ser (−0.8); Trp (−0.9); Tyr (−1.3); Pro (−1.6); His (−3.2); Glu (−3.5); Gln (−3.5); Asp (−3.5); Asn (−3.5); Lys (−3.9); and Arg (−4.5). Non-conserved amino acid substitutions may be made were the hydropathic index of the residues is significantly different, e.g. differing by more than 2.0.
In alternative embodiments, conserved amino acid substitutions may be made where an amino acid residue is substituted for another in the same class, where the amino acids are divided into non-polar, acidic, basic and neutral classes, as follows: non-polar: Ala, Val, Leu, Ile, Phe, Trp, Pro, Met; acidic: Asp, Glu; basic: Lys, Arg, His; neutral: Gly, Ser, Thr, Cys, Asn, Gln, Tyr. Non-conserved amino acid substitutions may be made were the residues do not fall into the same class, for example substitution of a basic amino acid for a neutral or non-polar amino acid.
This Example illustrates that drought tolerance in Arabidopsis is conferred by novel QTLs located on three different chromosomes. These genes were identified in an extremely drought tolerant Arabidopsis ecotype, designated herein as #95. The #95 ecotype was isolated during a series of drought treatment experiments, and assessed as follows.
In one assay, 36 plants of ecotype Col and 36 plants of ecotype #95 were used for drought sensitivity testing. At the outset, soil for each pot was dried and weighed to ensure that each pot had the same amount of soil, after which water was added to maintain moisture.
Seeds from Col and #95 were first germinated, then sown one seedling per pot separately. The plants were grown in a controlled environment under long-day conditions (16-h-light/8-h-dark cycle) at 23° C., light intensity of 50 gmol m−2 s−1 and 70% relative humidity (rH). Watering was stopped for both Col and #95 plants three weeks after germination, and all pots were then weighed again, and additional water was supplied to keep every pot at the same weight. Thereafter, drought treatment was initiated and survival days were recorded for both ecotypes. After a period of 15 days without watering, all 36 plants of ecotype Col had died. In contrast, the plants of ecotype #95 retained considerable vigor, and fully recovered to maturity when water supply was resumed.
The extreme drought tolerance Arabidopsis ecotype #95 was particularly evident after withdrawing water for 38 days. Plants of the ecotype Col were all severely wilted due to drought. Ecotype #95, in contrast, still exhibited clear vigor. The F1 progeny between Col and #95 were also sensitive to drought, indicating the recessive nature of the #95 drought resistant trait. In one assay, 27 days after water was withdrawn, the plants were segregated into two groups, those that had died, and those that maintained vigor and were recoverable to full maturity when watering was resumed. In alternative drought tolerance tests of F2 progeny derived from a cross between Col and #95, segregation of F2 population plants after drought treatment (50 days after water withdrawal) was much lower than 3:1. This segregation is consistent with the involvement of major QTL in controlling the drought tolerance trait.
Map based cloning through crossing with ecotype Col, revealed that the drought-related trait was governed by three major QTLs distributed on three different chromosomes. To delineate the underlying genetic components, an F1 generation was developed from the seeds of a cross between Col and #95. The F1 seeds were then used to develop a large F2 population of 5000 lines. The F2 populations showed significant segregation of the drought tolerance trait, with some plants showing significant drought tolerance, and others showing no drought tolerance, which indicated that the drought tolerance trait of #95 was controlled by several QTLs.
A fine mapping of the genes was further pursued using 500 lines of this population from which 20 extremely drought tolerant individuals and 20 extremely drought sensitive individuals were selected to conduct a Bulk Segregate Analysis (BSA) with 106 molecular markers which cover all 5 chromosomes of Arabidopsis. Based on this analysis, three major QTLs distributed on three different chromosomes were identified. Specifically, QTL's were identified on chromosomes 1, 4 and 5 of the Arabidopsis genome. The contribution rates of these 3 loci to the observed drought tolerance trait were 13.8%, 29.3%, 37.7%, respectively, explaining in the aggregate more than 80% of the drought tolerance variation between ecotype #95 and Col.
Fine mapping was first focused on loci on Chr.4 and Chr.5, which was carried out using 700 extremely drought tolerant individuals from a total of 5000 F2 plants. The candidate genes were narrowed down to two regions of 540 kb on Chr.4 and 189 kb on Chr.5. Single nucleotide polymorphism (SNP) and insertion/deletion (In/del) analysis, as well as expression level analysis based on the TAIR database, was carried out for all of the genes identified in these two regions on Chr.4 and 5.
The full genome sequence of ecotype #95 was compared with the full genome sequence of Arabidopsis ecotype Columbia (ecotype Col. The three major QTL's associated with drought tolerance on Chr. 1, Chr. 4 and Chr. 5 of ecotype #95 were revealed to harbor members of a protein coding gene family: At1g51670 (also referred to as Kanghan3 or KH3), At4g29760 (also referred to as Kanghan4 or KH4), At4g29770 (also referred to as Kanghan2 or KH2), At5g18065 (also referred to as Kanghan5 or KH5) and At5g18040 (also referred to as Kanghan1 or KH1). An additional member of the gene family was recognized by sequence similarity: At1g48180 (also referred to as Kanghan6 or KH6). This gene family is designated herein as the Kanghan gene family, the first 5 of which have very strong roles in drought tolerance (a GenBank database accession number for a protein encoded by each of the native Arabidopsis genes is given after the gene name in brackets): Kanghan1 (At5g18040; NP_197305.1), Kanghan2 (At4g29770; NP 001154277.1), Kanghan3 (At1g51670; NP_175578.2), Kanghan4 (At4g29760; NP_194705.1), Kanghan5 (At5g18065; NP_680172.2), Kanghan6 (At1g48180; NP_175252.1).
Analysis of the genomic sequence of Ecotype #95 reveals that mutations within Kanghan family genes are associated with drought tolerance. Specifically, in ecotype #95, all 5 members of the Kanghan family strongly associated with drought tolerance have dramatic mutations. Specifically, four members of the Kanghan gene family (At4g29770, At5g18065, At5g18040 and At1g51670) contain a premature stop codon (see
To further illustrate the role of the Kanghan genes in drought tolerance, two full length Kanghan genes (AT5g18040 and At4g29770) from Arabidopsis ecotype Col were used to transform Arabidopsis ecotype #95, including at least 2 kb 5′UTR, 1 kb 3′UTR and CDS. The transformants lost their drought resistance, confirming that the modulation of Kanghan gene expression plays a dramatic role in drought resistance.
A further illustration of the dramatic effect of Kanghan genes on drought tolerance was provided by introducing five Kanghan gene alleles from ecotype #95 into ecotype Columbia (Col) by crossing and molecular marker based selection, generation by generation. The 7th generation of backcrossed lines was used for self-crossing to provide homozygous plants which contained the five Kanghan gene alleles from #95 strongly associated with drought tolerance. These homozygous plants were subjected to drought treatment. The result was that introduction of the #95 Kanghan gene alleles rendered ecotype Columbia drastically enhanced in its drought tolerance traits.
A further illustration of the effect of Kanghan genes on abiotic stress response was provided by measuring the canopy temperatures of Col, #95 and the backcrossed lines bearing the Kanghan alleles. Increased canopy temperature was clearly evident in #95 plants and backcrossed lines, when compared with Col ecotype plants. Further, subjecting seedlings of #95 and Col to heat treatment at 45° C. confirmed heat sensitivity in ecotype #95.
As this Example illustrates, functional expression of Kanghan gene family proteins plays a positive role in heat tolerance, and a negative role in drought tolerance. The invention accordingly provides a variety of avenues for modulating abiotic stress response in plants. In some embodiments, this involves balancing Kanghan gene expression to achieve a desired phenotype of abiotic stress response, for example balancing drought and heat tolerance.
The negative role of the Kanghan family of genes in drought tolerance serves as a basis for improving plant drought tolerance by down-regulating or silencing members of the Kanghan gene family. This may for example be achieved through a wide variety of techniques, including mutagenesis (TILLing) or targeted gene editing, as discussed above.
As set out in the tables above, which alternatively set out BLAST alignments with reference sequences that are the most divergent of the Kanghan genes (AT4G29770 and AT1G51670) the Kanghan gene family may be defined as including genes that encode proteins, that when optimally aligned, have at least 35% identity and/or at least 49% positive alignments, over a length of at least 90 amino acids, with BLOSUM or PAM substitution matrix, with gaps permitted.
This Example further illustrates the existence of conserved protein domains encoded by Kanghan family genes, as depicted in
Conserved domain A is close to the amino end of the proteins, and as shown in
Conserved domain B, as shown in
Conserved domain C, as shown in
Conserved domain A is absent in Kanghan1 (At5g18040) in Columbia (Col) due to an 82 bp deletion compared to the orthologous gene in other species of Arabidopsis. As shown in
Conserved domain B is relatively highly conserved in all members of Kanghan gene family in Columbia. In contrast, the premature stop codons of Kanghan1, Kanghan2, Kanghan3, 5 and Kanghan5 cause the loss of conserved domain B in #95. Accordingly, this absence of this domain is closely associated with the drought tolerance trait.
Conserved domain C and the tasi-RNA target site are not present in Kanghan5 (At5g18065) in both Columbia and #95.
BLAST searching reveals that Kanghan family genes are widely distributed in Brassicaceae, in addition to the six Kanghan genes in Arabidopsis thaliana, there are also 5 members in Arabidopsis lyrata, 6 members in Caspsella rubella, 5 members in Brassica rapa, 11 members in Brassica napus, 3 members in Eutrema salsugineum, 1 member in Thellugiella parvula, and at least 24 members in Camelina sativa. Most of these Kanghan genes include all three conserved domains, and all of them contain conserved domain B.
thaliana]
oleracea]
oleracea]
thaliana]
lyrata subsp. lyrata]
thaliana]
This example illustrates a genetic modification of a wild-type wheat by gene gun mediated transformation using a Kanghan gene construct, to modulate an abiotic stress response, in this case conferring heat tolerance. Transgenic constructs for overexpression of Arabidopsis Kanghan family genes in wheat were produced using monocot special overexpression vector PANIC5E. This vector was designed for stable transformation and overexpression of heterologous Kanghan genes in wheat. Over expression of Arabidopsis Kanghan1 (At5g18040) in one wheat wild type (Fielder) was achieved in this way by gene gun mediated transformation. The construct used to perform this transformation is shown in
To illustrate the heat tolerance of the wheat transgenic lines, three-week seedlings of both wild types and T1 transgenic lines were heat treated at 42/38° C. (day/night). After two weeks of heat treatment, recovery at normal growth temperature was performed, and phenotypes observed. Heat tolerance was clearly observed in T1 transformants compared to non-transgenic plants under heat treatment. Non-transgenic plants displayed wilt symptoms or died. The transformants, on the other hand, recovered after transferring to normal growth temperature conditions, and were able to grow normally and transit to reproductive growth.
To further illustrate the heat tolerance of the wheat transgenic lines, three week old seedlings of both wild-type and T1 transgenic lines were subjected to 40/38° C. (day/night) for three weeks, followed by a three week recovery period at 25° C. After this recovery period, the transgenic plants fully recovered whereas the control plants failed to recover (
Under standard growth conditions of 23° C. day/18° C. night, 16 h photoperiod (16 h light/8 h dark), and 200 μmol m−2 s−1 light intensity wild-type and transgenic plants are visually indistinguishable, however as determined by infrared thermal imaging using FLIR T640 Infrared Camera, the canopy temperature of T1 transgenic wheat plants is significantly lower (
These studies illustrate the utility of the Kanghan genes in modulating abiotic stress response in crop species such as wheat, in this case to improve heat tolerance.
A BLAST sequence search was carried out on available genome and transcript data from Brassica napus to identify potential homologues of at4g29770 (SEQ ID NOs: 2 and 15), at4g29760 (SEQ ID NOs: 1 and 14), at5g18040 (SEQ ID NOs: 4 and 17), at5g18065 (SEQ ID NOs: 3 and 16), at1g51670 (SEQ ID NOs: 5 and 18), and at1g48180 (SEQ ID NOs: 13 and 19). The potential candidates identified are provided in Table 6.
A DNA neighbor phylogenetic tree of the Brassica napus Kanghan gene candidates and their Arabidopsis thaliana counterparts is provided in
A sequence alignment of the Brassica napus homologues of at4g29770, at4g29760, at5g18040, and at5g18065 is provided in
A sequence alignment of the Brassica napus homologues of at1g51670 and at1g48180 is provided in
Primer Design
Two conserved fragments from 12 putative Brassica napus Kanghan genes, identified based on ClustalW multiple alignment, were used to design two pairs of RNAi primers. The reverse primers were designed to include a BamH1 restriction site and a Sal1 restriction site to facilitate cloning.
The first primer pair was designed to target BnaC03g77540D (LOC106364365):
The second primer pair was designed to target BnaA08g12920D (LOC106424160):
Production of BnKanghan RNAi Construct and Establishment of Brassica Napus RNAi Lines
To generate a cDNA library of Brassica napus, total RNA was isolated from 3-week-old leaves of canola wild type ‘Hero’ using the Plant RNeasy Mini Kit (Qiagen). Then, RNA samples were used for library construction using the QuantiTect Reverse Transcription Kit (Qiagen). The primer pairs RNAiF1 GP438 (SEQ ID NO: 20)+RNAiR1 GP439 (SEQ ID NO: 21) and RNAiF2 (SEQ ID NO: 22)+RNAiR2 GP441 (SEQ ID NO: 23) were used separately to amplify fragments from two target BnKanghan genes from the obtained cDNA library. Each of the resulting PCR products was isolated and cloned into the pGEM®-T vector (Promega, USA). A map of the pGEM-T vector is provided in
Next, a genetic modification of canola wild type ‘Hero’ was conducted using both of these completed RNAi constructs through agrobacterium-mediated transformation aimed to obtain increased drought tolerance. Positive transformants were confirmed using a pair of hygromycin specific primers (HptF TACACAGCCATCGGTCCAGA (SEQ ID NO: 24) and HptR GTAGGAGGGCGTGGATATGTC (SEQ ID NO: 25)). A cross was carried out between T1 positive transformants from the two different constructs. In the C2 generation, lines harboring both constructs together were selected for further evaluation of silencing of BnKanghan family genes and drought tolerance traits.
To assess the expression level of BnKanghan family genes in transgenic and crossing lines, a number of primer pairs were designed for qRT-PCR assays to assess the expression levels of seven candidate Kanghan genes from Brassica napus. The targets of these primer pairs are identified in Table 7. In total, 12 lines harboring both RNAi constructs from the C2 generation were selected to detect expression level changes of BnKanghan family genes. Each line tested showed decreases in expression of at least three BnKanghan genes. The most commonly suppressed genes were: BnaA07g02270D, BnaA08g12920D, and BnaC03g77550D, followed by BnaC03g77540D and BnaC01g08490D.
Testing Canopy Temperature and Drought Tolerance of Brassica napus RNAi Lines
Individual lines C2-83-20 and C2-83-10 each showed decreased expression of six BnKanghan genes. These two lines were selected for further drought tolerance measurements. To predict the potential drought tolerance of the C2-83-20 and C2-83-10 lines, the canopy temperatures were measured using an infrared camera. In comparison to wild type plants, higher canopy temperatures were observed for the transgenic plants (
To assess the drought tolerance of the transgenic plants, four weeks-old plants of both wild type and these two transgenic lines were subjected to drought treatment. The same amount of soil and water were applied to each individual plant before treatment, and then the water supply was stopped. After two weeks of drought treatment, recovery by re-watering of the plants was performed. The resulting phenotypes are shown in
The pan-genome architecture of Brassica napus was recently released (Song et al., 2020), providing a possibility to identify all the members of Kanghan gene family in B. napus. Furthermore, through CRISPR/Cas genome editing technologies, the knock-out of designated member(s) of Kanghan gene family can used to generate non-GMO B. napus lines with high abiotic stress resistance traits.
Identifying Kanghan Homologs in Brassica napus and Other Brassicaceae Species
Genome-wide identification of Kanghan gene family numbers was performed in multiple Brassicaceae species, in which the whole genome sequence information has been released. Kanghan homologs in A. thaliana, A. lyrata, A. helleri, B. napus, B. oleracea and B. rapa were identified and a phylogenetic tree was built based on their protein sequence (
Brassica napus
Brassica rapa
Brassica oleracea
Brassica napus
Brassica napus
Brassica rapa
Brassica napus
Brassica napus
Brassica rapa
Brassica oleracea
Brassica napus
Brassica rapa
Arabidopsis halleri
Arabidopsis thaliana
Arabidopsis halleri
Arabidopsis lyrata
Arabidopsis lyrata
Arabidopsis halleri
Arabidopsis thaliana
Arabidopsis thaliana
Arabidopsis thaliana
Arabidopsis lyrata
Arabidopsis halleri
Arabidopsis thaliana
Arabidopsis lyrata
Arabidopsis halleri
Arabidopsis lyrata
Arabidopsis halleri
Arabidopsis thaliana
Arabidopsis lyrata
Arabidopsis thaliana
Arabidopsis lyrata
Arabidopsis halleri
Multiplexed Gene Editing Through an Optimized CRISPR/Cas9 Toolkit
A multiplexed toolkit (Cermak et al., 2017) has been selected and optimized for application in B. napus. This toolkit could carry up to 12 guide RNAs (gRNAs) to realize the knock-out of multiple target genes through one construct. Reducing the number of constructs will ideally reduce the cost of plant transformations and downstream molecular confirmation for gene editing. Targeted gRNA design will be performed through multiple bioinformatic tools to avoid potential off-targets and cover as many as Kanghan homologs as possible. gRNAs targeting conserved regions and specific regions of Kanghan family genes will be confirmed after a genome-wide SNP/indels screening for duplicates and homologs in different subgenomes (AA and CC). The final selected 6 gRNAs will be tandem connected with Csy-type ribonuclease 4 (Csy4) for simultaneous expression through Pol II promoter (
Generating Transgenic Plants Through Agrobacterium-Mediated Transformation
Transformation will be conducted in canola cultivar DH12075 using the generated CRISPR/Cas9 construct through agrobacterium-mediated transformation. Positive transformants will be confirmed using a pair of npt II specific primers in T0 generation transgenic lines.
High Throughput Validation for the Gene Editing
Mutations in targeted genes from T0 generation will be identified. To detect the editing on all ten KH homologs in B. napus for hundreds of T0 and T1 generation positive lines, a cost-efficient high throughput detection method is desired. A workflow using droplet digital PCR (ddPCR) assay will be established to achieve a high throughput validation. Fluorescent probes targeting gDNA-associated regions will be designed, and the corresponding primer will be selected based on SNP/Indels information obtained above. Thus, gene editing information of every Kanghan homolog in each transgenic line will be identified. The combination of different mutations in different homologs will provide transgenic materials to investigate knock-out lines of At5g18040 (KH1) homologs, At4g29770 (KH2) homologs, At5g18065 (KH3) homologs, Atg29760 (KH4) homologs, At1g51670 (KH5) homologs and knock-out lines for all Kanghan gene family members in canola, respectively. Non-GMO lines with successful gene-editing in Kanghan gene(s) but without the transformed plasmid will be identified in T1 and T2 generations.
While the present application has been described with reference to specific examples, it is to be understood that the application is not limited to the disclosed examples. To the contrary, the present application is intended to cover various modifications and equivalent arrangements encompassed by the scope of the appended claims.
All publications, patents and patent applications are herein incorporated by reference in their entirety to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety. Where a term in the present application is found to be defined differently in a document incorporated herein by reference, the definition provided herein is to serve as the definition for the term.
This application is a continuation-in-part of U.S. application Ser. No. 16/131,395, filed Sep. 14, 2018, which is a continuation-in-part of International Application No. PCT/IB2017/051474, filed Mar. 14, 2017, and further claims the benefit of U.S. Provisional Application No. 62/308,580, filed Mar. 15, 2016. The content of each of these references is hereby incorporated by reference in its entirety.
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| Number | Date | Country | |
|---|---|---|---|
| 20220090115 A1 | Mar 2022 | US |
| Number | Date | Country | |
|---|---|---|---|
| 62308580 | Mar 2016 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16131395 | Sep 2018 | US |
| Child | 17462586 | US | |
| Parent | PCT/IB2017/051474 | Mar 2017 | US |
| Child | 16131395 | US |
