title: Biallelic Gene Targeting in Rice.
abstract: Sequence-specific nucleases (SSNs) have been used successfully in homology-directed repair (HDR)-mediated gene targeting (GT) in many organisms. However, break-induced GT in plants remains challenging due to inefficient delivery of HDR templates and SSNs into plant nuclei. In many plants, including rice, Agrobacterium-mediated transformation is the most practical means of transformation because this biotic transformation system can deliver longer and more intact DNA payloads with less incorporation of fragmented DNA compared with physical transformation systems such as polyethylene glycol, electroporation, or biolistics. Following infection with Agrobacterium, transfer of transfer DNA (T-DNA) to the nucleus and its integration into the plant genome occur consecutively during cocultivation, thus timing the induction of DNA double-strand breaks (DSBs) on the target gene to coincide with the delivery of the HDR template is crucial. To synchronize DSB induction and delivery of the HDR template, we transformed a Cas9 expression construct and GT vector harboring the HDR template with guide RNAs (gRNAs) targeting the rice acetolactate synthase (ALS) gene either separately or sequentially into rice calli. When gRNAs targeting ALS were transcribed transiently from double-stranded T-DNA containing the HDR template, DSBs were induced in the ALS locus by the assembled Cas9/gRNA complex and homologous recombination was stimulated. Contrary to our expectations, there was no great difference in GT efficiency between Cas9-expressing and nonexpressing cells. However, when gRNA targeting DNA ligase 4 was transformed with Cas9 prior to the GT experiment, GT efficiency increased dramatically and more than one line exhibiting biallelic GT at the ALS locus was obtained.
authors.affiliation: Plant Genome Engineering Research Unit, Agrogenomics Research Center, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki, 305-8602, Japan (M.E., M.M., S.T.);Graduate School of Nanobioscience, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama, Kanagawa, 236-0027, Japan (M.M., S.T.); andKihara Institute for Biological Research, Yokohama City University, 641-12 Maioka-cho, Yokohama, Kanagawa, 244-0813, Japan (S.T.)Plant Genome Engineering Research Unit, Agrogenomics Research Center, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki, 305-8602 Japan (M.E., M.M., S.T.); Graduate School of Nanobioscience, Yokohama City University, 22-2, Seto, Kanazawa-ku, Yokohama, Kanagawa, 236-0027, Japan (M.M., S.T.); and Kihara Institute for Biological Research, Yokohama City University, 641-12 Maioka-cho, Yokohama, Kanagawa, 244-0813, Japan (S.T.).
authors.forename: Masaki
authors.identifier: http://orcid.org/0000-0002-9199-181X
authors.initials: M
authors.lastname: Endo
authors.affiliation: Plant Genome Engineering Research Unit, Agrogenomics Research Center, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki, 305-8602, Japan (M.E., M.M., S.T.);Graduate School of Nanobioscience, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama, Kanagawa, 236-0027, Japan (M.M., S.T.); andKihara Institute for Biological Research, Yokohama City University, 641-12 Maioka-cho, Yokohama, Kanagawa, 244-0813, Japan (S.T.)Plant Genome Engineering Research Unit, Agrogenomics Research Center, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki, 305-8602 Japan (M.E., M.M., S.T.); Graduate School of Nanobioscience, Yokohama City University, 22-2, Seto, Kanazawa-ku, Yokohama, Kanagawa, 236-0027, Japan (M.M., S.T.); and Kihara Institute for Biological Research, Yokohama City University, 641-12 Maioka-cho, Yokohama, Kanagawa, 244-0813, Japan (S.T.).
authors.forename: Masafumi
authors.initials: M
authors.lastname: Mikami
authors.affiliation: Plant Genome Engineering Research Unit, Agrogenomics Research Center, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki, 305-8602, Japan (M.E., M.M., S.T.);Graduate School of Nanobioscience, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama, Kanagawa, 236-0027, Japan (M.M., S.T.); andKihara Institute for Biological Research, Yokohama City University, 641-12 Maioka-cho, Yokohama, Kanagawa, 244-0813, Japan (S.T.)Plant Genome Engineering Research Unit, Agrogenomics Research Center, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki, 305-8602 Japan (M.E., M.M., S.T.); Graduate School of Nanobioscience, Yokohama City University, 22-2, Seto, Kanazawa-ku, Yokohama, Kanagawa, 236-0027, Japan (M.M., S.T.); and Kihara Institute for Biological Research, Yokohama City University, 641-12 Maioka-cho, Yokohama, Kanagawa, 244-0813, Japan (S.T.) stoki@affrc.go.jp.
authors.forename: Seiichi
authors.identifier: http://orcid.org/0000-0003-0066-6446
authors.initials: S
authors.lastname: Toki
mesh_terms: D000095:Acetolactate Synthase / Q000235:genetics; D060054:Agrobacterium / Q000235:genetics; D064113:CRISPR-Cas Systems; D053903:DNA Breaks, Double-Stranded; D011088:DNA Ligases / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D018390:Gene Targeting / Q000379:methods*; D018745:Genome, Plant / Q000235:genetics*; D059765:Homologous Recombination; D012275:Oryza / Q000201:enzymology / Q000235:genetics*; D010940:Plant Proteins / Q000235:genetics; D014170:Transformation, Genetic
chemical_list: D004269:DNA, Bacterial; D010940:Plant Proteins; C036483:T-DNA; D000095:Acetolactate Synthase; D011088:DNA Ligases