Patent Application
20180312869
The present invention relates to method for preparing a plant from a protoplast comprising knocking-out or knocking-in one or more the endogenous gene of the protoplast, and the plant regenerated from a genome-modified protoplast prepared by the above method.
Programmable nucleases, which include zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and RNA-guided endonucleases (RGENs) repurposed from the type II clustered, regularly-interspaced palindromic repeat (CRISPR)-CRISPR-associated (Cas) adaptive immune system in bacteria and archaea have been successfully used for genome editing in cells and organisms including various plant species, paving the way for novel applications in biomedical research, medicine, and biotechnology (Kim, H. etc., Nat Rev Genet, 2014, 15: 321-334). Among these nucleases, CRISPR RGENs, the latest of the trio of nucleases, are rapidly replacing ZFNs and TALENs, owing to their ease of programmability; RGENs that consist of the Cas9 protein derived from Streptococcus pyogenes and guide RNAs (gRNAs) are customized by replacing the RNA component only, sidestepping the labor-intensive and time-consuming protein engineering required for making new TALENs and ZFNs. Programmable nucleases, delivered into plant cells via Agrobacterium or transfection of plasmids that encode them, cleave chromosomal target sites in a sequence-dependent manner, producing site-specific DNA double-strand breaks (DSBs). The repair of these DSBs by endogenous systems gives rise to targeted genome modifications.
It remains unclear whether the resulting genome-edited plants will be regulated by genetically-modified organism (GMO) legislation in the EU and other countries (Jones, H. D., Nature Plants, 2015, 1: 14011). Programmable nucleases induce small insertions and deletions (indels) or substitutions at chromosomal target sites that are indistinguishable from naturally-occurring variations. Still, these plants may be considered as GMOs by regulatory authorities in certain countries, hampering widespread use of programmable nucleases in plant biotechnology and agriculture. For example, when Agrobacterium is used, genome-edited plants will contain foreign DNA sequences, including those encoding programmable nucleases in the host genome. Removal of these Agrobacterium-derived DNA sequences by breeding is not feasible in certain plants such as grape, potato, and banana, owing to their asexual reproduction.
Alternatively, non-integrating plasmids that encode programmable nucleases can be transfected into plant cells such as protoplasts. We note, however, that transfected plasmids are degraded in cells by endogenous nucleases and that the resulting small DNA fragments can be inserted at the Cas9 on-target and off-target sites, as shown in human cells (Kim, S, etc., Genome research, 2014, 24: 1012-1019).
Delivery of preassembled Cas9 protein-gRNA ribonucleoproteins (RNPs) rather than plasmids encoding these components into plant cells could avoid the possibility of inserting recombinant DNA in the host genome. Furthermore, as shown in cultured human cells, RGEN RNPs cleave chromosomal target sites immediately after transfection and are degraded rapidly by endogenous proteases in cells, potentially reducing mosaicism and off-target effects in regenerated whole plants. Preassembled RGEN RNPs can be used broadly across plant species without prior optimization of codon usage and promoters to express Cas9 and gRNAs in each species. In addition, RGEN RNPs enable pre-screening in vitro to choose highly active gRNAs and genotyping of mutant clones via restriction fragment length polymorphism (RFLP) analysis.
To the best of our knowledge, however, RGEN RNPs have never been used in any plant species.
It is an object of the present invention to provide a method for preparing a plant from a protoplast comprising knocking-out or knocking-in one or more endogenous genes of the protoplast.
Another object of the present invention is to provide a plant regenerated from a genome-edited protoplast prepared by the method for preparing a plant from a protoplast.
Still another object of the present invention is to provide a composition for cleaving DNA encoding BIN2 gene in a plant cell, comprising: a guide RNA specific to DNA encoding Brassinosteroid Insensitive 2 (BIN2) gene, BKI1 gene, or homologs thereof, or DNA encoding the guide RNA; and a nucleic acid encoding a Cas protein, or a Cas protein.
Still another object of the present invention is to provide a composition for preparing a plant from a protoplast, comprising: a guide RNA specific to DNA encoding Brassinosteroid Insensitive 2 (BIN2) gene, BKI1 gene, or homologs thereof, or DNA encoding the guide RNA; and a nucleic acid encoding a Cas protein or a Cas protein.
Still another object of the present invention is to provide a kit for preparing a plant from a protoplast comprising the composition for preparing a plant from a protoplast.
We transfected purified Cas9 protein and guide RNAs into various plant protoplasts, inducing targeted mutagenesis in regenerated plants at frequencies of up to 46%. Cas9 ribonucleoprotein delivery into protoplasts avoided the possibility of inserting foreign DNA in the host genome. The resulting plants contained germline-transmissible, small insertions or deletions at target sites, which are indistinguishable from naturally-occurring variations, possibly bypassing regulatory requirements associated with use of Agrobacterium or plasmids.
In the present invention, we showed that RGEN RNPs can be delivered into protoplasts derived from various plant species and induce targeted genome modifications in whole plants regenerated from them.
An aspect of the present invention provides a method for preparing a plant from a protoplast comprising knocking-out or knocking-in one or more the endogenous gene of the protoplast.
In one embodiment, the endogenous gene of the plant may be a gene capable of increasing stress resistance of the plant by knocking-out or knocking-in.
In another embodiment, the endogenous gene of the plant may be a gene involved in Brassinosteroid signal transduction of plants.
In still another embodiment, (i) in the knocking-out step, the endogenous gene may be one or more genes selected from the group consisting of BIN2 gene, BKI1 gene, and homolog genes thereof; and (ii) in the knocking-in step, the gene being knocked in may be one or more genes selected from the group consisting of BRI1 gene, BSU gene, BZR1 gene, DWF4 gene, CYP85A1, and homolog genes thereof.
In still another embodiment, the knocking-out of genes may be performed by knocking-out one or two alleles of the genes selected from the group consisting of BIN 2 gene, BKI1 gene, and homolog genes thereof.
In still another embodiment, the knocking-out of genes may be performed by gene knock-out and the knocking-in of genes is performed by gene knock-in.
In still another embodiment, the knocking-out of genes may be performed using an engineered nuclease specific to one or more genes selected from the group consisting of BIN2 gene, BKI1 gene, and homolog genes thereof.
In still another embodiment, the engineered nuclease may be selected from the group consisting of zinc finger nuclease (ZFN), transcription activator-like effector nuclease (TALEN), and RNA-guided engineered nuclease (RGEN).
In still another embodiment, the RGEN may comprise guide RNA, which specifically binds to a specific sequence of one or more genes selected from the group consisting of BIN2 gene, BKI1 gene, and homolog genes thereof, or DNA encoding the guide RNA; and a nucleic acid encoding a Cas protein, or a Cas protein.
In still another embodiment, the knocking-out of genes may be performed by introducing the guide RNA, which specifically binds to a specific sequence of one or more genes selected from the group consisting of BIN2 gene, BKI1 gene, and homolog genes thereof, or DNA encoding the guide RNA; and a nucleic acid encoding a Cas protein, or a Cas protein, to the protoplast.
In still another embodiment, the guide RNA may be in the form of a dual RNA or a single-chain guide RNA (sgRNA) comprising crRNA and tracrRNA.
In still another embodiment, the single-chain guide RNA may comprise a part of crRNA and tracrRNA.
In still another embodiment, the single-chain guide RNA may be in the form of isolated RNA.
In still another embodiment, the DNA encoding the guide RNA may be encoded by a vector, and the vector is virus vector, plasmid vector, or Agrobacterium vector.
In still another embodiment, the Cas protein may be a Cas9 protein or a variant thereof.
In still another embodiment, the Cas protein may recognize NGG trinucleotide.
In still another embodiment, the Cas protein may be linked to a protein transduction domain.
In still another embodiment, the variant of the Cas9 protein may be in a mutant form of Cas9 protein, wherein the catalytic aspartate residue is substituted with another amino acid.
In still another embodiment, the amino acid may be alanine.
In still another embodiment, the nucleic acid encoding a Cas protein or Cas protein may be derived from a microorganism of the genus Streptococcus.
In still another embodiment, the microorganism of the genus Streptococcus may be Streptococcus pyogenes.
In still another embodiment, the protoplast may be derived from Lactuca sativa.
In still another embodiment, the introduction may be performed by co-transfecting or serial-transfecting of a nucleic acid encoding a Cas protein or a Cas protein, and the guide DNA or DNA encoding the guide DNA into a protoplast.
In still another embodiment, the serial-transfection may be performed by firstly transfecting a Cas protein or a nucleic acid encoding a Cas protein followed by secondly transfecting a naked guide RNA.
In still another embodiment, the introduction may be performed by a method selected from the group consisting of microinjection, electroporation, DEAE-dextran treatment, lipofection, nanoparticle-mediated transfection, protein transduction domain-mediated transfection, and PEG-mediated transfection.
In still another embodiment, the method may further comprise regenerating the protoplast having a knocked-out gene.
In still another embodiment, the regeneration may comprise culturing a protoplast having one or more knocked-out genes selected from the group consisting of BIN2 gene, BKI1 gene, and homolog genes thereof in agarose-containing medium to form callus; and culturing the callus in regeneration medium.
Another aspect of the present invention is a plant regenerated from a genome-edited protoplast prepared by the above method.
Another aspect of the present invention is a composition for cleaving DNA encoding BIN2 gene in a plant cell, comprising: a guide RNA specific to DNA encoding Brassinosteroid Insensitive 2 (BIN2) gene, BKI1 gene, or homologs thereof, or DNA encoding the guide RNA; and a nucleic acid encoding a Cas protein, or a Cas protein.
In still another embodiment, the composition may induce a targeted mutagenesis in a plant cell.
Another aspect of the present invention is a composition for preparing a plant from a protoplast, comprising: a guide RNA specific to DNA encoding Brassinosteroid Insensitive 2 (BIN2) gene, BKI1 gene, or homologs thereof, or DNA encoding the guide RNA; and a nucleic acid encoding a Cas protein or a Cas protein.
Another aspect of the present invention is a kit for preparing a plant from a protoplast comprising the above composition.
Hereinafter, the present invention will be described in further detail with reference to examples. It is to be understood, however, that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention.
Cas9 Protein and Guide RNAs.
Cas9 protein tagged with a nuclear localization signal was purchased from ToolGen, Inc. (South Korea). Templates for guide RNA transcription were generated by oligo-extension using Phusion polymerase (Table 1-4). Guide RNAs were in vitro transcribed through run-off reactions using the T7 RNA polymerase (New England Biolabs) according to the manufacturer's protocol. The reaction mixture was treated with DNase I (New England Biolabs) in 1× DNase I reaction buffer. Transcribed sgRNAs were resolved on an 8% denaturing ureapolyacryl amide gel with SYBR gold staining (Invitrogen) for quality control. Transcribed sgRNAs were purified with MG™ PCR Product Purification SV (Macrogen) and quantified by spectrometry.
GAAATTAATACGACTCACTATAG
CAAAAGACTGTCAATTCCC
TGTTTTAGAGCTAGAAATAGCAAG (SEQ ID NO: 84)
GAAATTAATACGACTCACTATAGG
CACTAGGAGCAACACCCA
ACGTTTTAGAGCTAGAAATAGCAAG (SEQ ID NO: 85)
GAAATTAATACGACTCACTATAGG
CATATAGTTGGGTCATGG
CAGTTTTAGAGCTAGAAATAGCAAG (SEQ ID NO: 86)
GAAATTAATACGACTCACTATAGG
TGCATCGTCCAAGCGCAC
AGGTTTTAGAGCTAGAAATAGCAAG (SEQ ID NO: 87)
GAAATTAATACGACTCACTATAGG
CTACGACGTCAGGTTCTA
CCGTTTTAGAGCTAGAAATAGCAAG (SEQ ID NO: 88)
GAAATTAATACGACTCACTATAGG
TTTGAAAGATGGAAGCGC
GGGTTTTAGAGCTAGAAATAGCAAG (SEQ ID NO: 89)
GAAATTAATACGACTCACTATAGG
TGAAACTAAACTGGTCCA
CAGTTTTAGAGCTAGAAATAGCAAG (SEQ ID NO: 90)
GAAATTAATACGACTCACTATAG
ATCACAGTGATGCTCGTCA
AGTTTTAGAGCTAGAAATAGCAAG (SEQ ID NO: 91)
Protoplast Culture.
Protoplasts were isolated as previously described from Arabidopsis, rice, and lettuce. Initially, Arabidopsis (Arabidopsis thaliana) ecotype Columbia-0, rice (Oryza sativa L.) cv. Dongjin, and lettuce (Lactuca sativa L.) cv Cheongchima seeds were sterilized in a 70% ethanol, 0.4% hypochlorite solution for 15 min, washed three times in distilled water, and sown on ½× Murashige and Skoog solid medium supplemented with 2% sucrose. The seedlings were grown under a 16 h light (150 μmol m−2 s−1) and 8 h dark cycle at 25° C. in a growth room. For protoplast isolation, the leaves of 14 d Arabidopsis seedlings, the stem and sheath of 14 d rice seedlings, and the cotyledons of 7 d lettuce seedlings were digested with enzyme solution (1.0% cellulase R10, 0.5% macerozyme R10, 0.45 M mannitol, 20 mM MES [pH 5.7], CPW solution) during incubation with shaking (40 rpm) for 12 h at 25° C. in darkness and then diluted with an equal volume of W5 solution. The mixture was filtered before protoplasts were collected by centrifugation at 100 g in a round-bottomed tube for 5 min. Re-suspended protoplasts were purified by floating on a CPW 21S (21% [w/v] sucrose in CPW solution, pH 5.8) solution followed by centrifugation at 80 g for 7 min. The purified protoplasts were washed with W5 solution and pelleted by centrifugation at 70 g for 5 min. Finally, protoplasts were re-suspended in W5 solution and counted under the microscope using a hemocytometer. Protoplasts were diluted to a density of 1×106 protoplasts/ml of MMG solution (0.4 M mannitol and 15 mM MgCl2, 4 mM MES [pH 5.7]).
Protoplast Transfection.
PEG-mediated RNP transfections were performed as previously described. Briefly, to introduce DSBs using an RNP complex, 1×105 protoplast cells were transfected with Cas9 protein (10-60 μg) premixed with in vitro transcribed sgRNA (20-120 μg). Prior to transfection, Cas9 protein in storage buffer (20 mM HEPES pH 7.5, 150 mM KCl, 1 mM DTT, and 10% glycerol) was mixed with sgRNA in 1×NEB buffer 3 and incubated for 10 min at room temperature. A mixture of 1×105 protoplasts (or 5×105 protoplasts in the case of lettuce) re-suspended in 200 μL MMG solution was gently mixed with 5-20 μL of RNP complex and 210 μL of freshly prepared PEG solution (40% [w/v] PEG 4000; Sigma No. 95904, 0.2 M mannitol and 0.1 M CaCl2)), and then incubated at 25° C. for 10 min in darkness. After incubation, 950 μL W5 solution (2 mM MES [pH 5.7], 154 mM NaCl, 125 mM CaCl2) and 5 mM KCl) were added slowly. The resulting solution was mixed well by inverting the tube. Protoplasts were pelleted by centrifugation at 100 g for 3 min and re-suspended gently in 1 ml WI solution (0.5 M mannitol, 20 mM KCl and 4 mM MES at pH 5.7). Finally, the protoplasts were transferred into multi-well plates and cultured under dark conditions at 25° C. for 24-48 h. Cells were analyzed one day after transfection.
Protoplast Regeneration.
RNP-transfected protoplasts were re-suspended in ½× B5 culture medium supplemented with 375 mg/l CaCl2.2H2O, 18.35 mg/l NaFe-EDTA, 270 mg/l sodium succinate, 103 g/l sucrose, 0.2 mg/l 2,4 dichlorophenoxyacetic acid (2,4-D), 0.3 mg/l 6-benzylaminopurine (BAP), and 0.1 g/l MES. The protoplasts were mixed with a 1:1 solution of ½× B5 medium and 2.4% agarose to a culture density of 2.5×105 protoplasts/ml. The protoplasts embedded in agarose were plated onto 6-well plates, overlaid with 2 ml of liquid ½× B5 culture medium, and cultured at 25° C. in darkness. After 7 days, the liquid medium replaced with fresh culture medium. The cultures were transferred to the light (16 h light [30 μmol m−2 s−1] and 8 h darkness) and cultured at 25° C. After 3 weeks of culture, micro-calli were grown to a few mm in diameter and transferred to MS regeneration medium supplemented with 30 g/l sucrose, 0.6% plant agar, 0.1 mg/l α-naphthalaneacetic acid (NAA), 0.5 mg/l BAP. Induction of multiple lettuce shoots was observed after about 4 weeks on regeneration medium.
Rooting, Transfer to Soil and Hardening of Lettuce.
To regenerate whole plants, proliferated and elongated adventitious shoots were transferred to a fresh regeneration medium and incubated for 4-6 weeks at 25° C. in the light (16 h light [120 μmol m−2 s−1] and 8 h darkness). For root induction, approximately 3-5 cm long plantlets were excised and transferred onto a solid hormone-free ½× MS medium in Magenta vessels. Plantlets developed from adventitious shoots were subjected to acclimation, transplanted to potting soil, and maintained in a growth chamber at 25° C. (100-150 μmol m−2 s−1 under cool-white fluorescent lamps with a 16-h photoperiod).
T7E1 Assay.
Genomic DNA was isolated from protoplasts or calli using DNeasy Plant Mini Kit (Qiagen). The target DNA region was amplified and subjected to the T7E1 assay as described previously. In brief, PCR products were denatured at 95° C. and cooled down to a room temperature slowly using a thermal cycler. Annealed PCR products were incubated with T7 endonuclease I (ToolGen, Inc.) at 37° C. for 20 min and analyzed via agarose gel electrophoresis.
RGEN-RFLP.
The RGEN-RFLP assay was performed as previously described. Briefly, PCR products (300-400 ng) were incubated in 1×NEB buffer 3 for 60 min at 37° C. with Cas9 protein (1 μg) and sgRNA (750 ng) in a reaction volume of 10 μl. RNase A (4 μg) was then added to the reaction mixture and incubated at 37° C. for 30 min to remove the sgRNA. The reaction was stopped by adding 6× stop solution (30% glycerol, 1.2% SDS, 250 mM EDTA). DNA products were electrophoresed using a 2.5% agarose gel.
Targeted Deep Sequencing.
The on-target and potential off-target sites were amplified from genomic DNA. Indices and sequencing adaptors were added by additional PCR. High-throughput sequencing was performed using Illumina Miseq (v2, 300 cycle).
Purified Cas9 protein was mixed with two to 10 fold molar excess of gRNAs targeting four genes in three plant species in vitro to form preassembled RNPs. The RGEN RNPs were then incubated with protoplasts derived from Arabidopsis (A. thaliana), a wild type of tobacco (N. attenuate), and rice (O. sativa) in the presence of polyethylene glycol (PEG). We used both the T7 endonuclease I (T7E1) assay and targeted deep sequencing to measure mutation frequencies in transfected cells (
We also co-transfected two gRNAs whose target sites were separated by 201 base pairs (bps) in another gene in Arabidopsis to investigate whether the repair of two concurrent DSBs would give rise to targeted deletion of the intervening sequence, as shown in human cells. Sanger sequencing showed that 223 bp DNA sequences were deleted in the protoplasts (
Next, we investigated whether RGEN RNPs can induce off-target mutations at sites highly homologous to on-target sites. We searched for potential off-target sites of the PHYTOCHROME B (PHYB) and BRASSINOSTEROID INSENSITIVE 1 (BRI1) gene-specific sgRNAs in the Arabidopsis genome using the Cas-OFFinder program and used targeted deep sequencing to measure mutation frequencies (
We designed an RGEN target site (SEQ ID NO: 93) to disrupt the BRASSINOSTEROID INSENSITIVE 2 (BIN2) gene, which encodes a negative regulator in a bras sinosteroid (BR) signaling pathway (
We performed the regeneration process to produce whole plants which contain the BIN2 mutant alleles from RGEN-RNP treated protoplasts. Only a fraction (<0.5%) of protoplasts could be cultured to form calli. Among these, 35 of fast-growing lines were used to perform further analyses (
BIN2 gene disruption showed no morphological changes but, some stress-tolerant phenotypes in rice. We propose that up-regulation of BR signaling caused by knocking out the BIN2 gene may facilitate the overall rate of cell proliferation and growth and give advantages to calli standing the stressful regeneration process.
Finally, we transfected an RGEN RNP to disrupt the lettuce (Lactuca sativa) homolog of Arabidopsis BRASSINOSTEROID INSENSITIVE 2 (BIN2) gene (
We then determined whether the BIN2-specific RGEN induced collateral damage in the lettuce genome using high-throughput sequencing. No off-target mutations were induced at 91 homologous sites that differed by one to 5 nucleotides from the on-target site in three BIN2-mutated plantlets (Tables 5-8), consistent with our findings in human cells: Off-target mutations induced by CRISPR RGENs are rarely found in a single cell-derived clone.
Subsequently, whole plants were successfully regenerated from these genome-edited calli and grown in soil (
In summary, RGEN RNPs were successfully delivered into plant protoplasts and induced targeted genome modifications in 6 genes in 4 different plant species. Importantly, RGEN-induced mutations were stably maintained in whole plants regenerated from the protoplasts and transmitted to germlines. Because no recombinant DNA is used in this process, the resulting genome-edited plants could be exempted from current GMO regulations, paving the way for the widespread use of RNA-guided genome editing in plant biotechnology and agriculture.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2015-0140314 | Oct 2015 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2016/011217 | 10/6/2016 | WO | 00 |
