title: A green-cotyledon/stay-green mutant exemplifies the ancient whole-genome duplications in soybean.
abstract: The recent whole-genome sequencing of soybean (Glycine max) revealed that soybean experienced whole-genome duplications 59 million and 13 million years ago, and it has an octoploid-like genome in spite of its diploid nature. We analyzed a natural green-cotyledon mutant line, Tenshin-daiseitou. The physiological analysis revealed that Tenshin-daiseitou shows a non-functional stay-green phenotype in senescent leaves, which is similar to that of the mutant of Mendel's green-cotyledon gene I, the ortholog of SGR in pea. The identification of gene mutations and genetic segregation analysis suggested that defects in GmSGR1 and GmSGR2 were responsible for the green-cotyledon/stay-green phenotype of Tenshin-daiseitou, which was confirmed by RNA interference (RNAi) transgenic soybean experiments using GmSGR genes. The characterized green-cotyledon double mutant d1d2 was found to have the same mutations, suggesting that GmSGR1 and GmSGR2 are D1 and D2. Among the examined d1d2 strains, the d1d2 strain K144a showed a lower Chl a/b ratio in mature seeds than other strains but not in senescent leaves, suggesting a seed-specific genetic factor of the Chl composition in K144a. Analysis of the soybean genome sequence revealed four genomic regions with microsynteny to the Arabidopsis SGR1 region, which included the GmSGR1 and GmSGR2 regions. The other two regions contained GmSGR3a/GmSGR3b and GmSGR4, respectively, which might be pseudogenes or genes with a function that is unrelated to Chl degradation during seed maturation and leaf senescence. These GmSGR genes were thought to be produced by the two whole-genome duplications, and they provide a good example of such whole-genome duplication events in the evolution of the soybean genome.
authors.affiliation: Graduate School of Science, Hiroshima University, Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8526 Japan These authors contributed equally to this work.
authors.forename: Michiharu
authors.initials: M
authors.lastname: Nakano
authors.affiliation: Graduate School of Agriculture, Hokkaido University, Kita, Sapporo, Hokkaido, 060-8589 Japan These authors contributed equally to this work.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Yamada
authors.affiliation: Graduate School of Science, Hiroshima University, Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8526 Japan These authors contributed equally to this work.
authors.forename: Yu
authors.initials: Y
authors.lastname: Masuda
authors.affiliation: Agrogenomics Research Center, National Institute of Agrobiological Sciences, Kannondai, Tsukuba, Ibaraki, 305-860 Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Sato
authors.affiliation: Graduate School of Agriculture, Hokkaido University, Kita, Sapporo, Hokkaido, 060-8589 Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Kobayashi
authors.affiliation: Graduate School of Science, Hiroshima University, Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8526 Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ueda
authors.affiliation: Institute of Breeding Science, National Institute of Agrobiological Sciences, Kamimurata, Hitachi-Ohmiya, 219-2293 Japan Present address: Nishina Center for Accelerator-based Science, RIKEN, Wako, 351-0198 Japan.
authors.forename: Ryouhei
authors.initials: R
authors.lastname: Morita
authors.affiliation: Institute of Breeding Science, National Institute of Agrobiological Sciences, Kamimurata, Hitachi-Ohmiya, 219-2293 Japan Present address: Faculty of Agriculture, Niigata University, Ikarashi, Nishi-ku, Niigata, 950-2181 Japan.
authors.forename: Minoru
authors.initials: M
authors.lastname: Nishimura
authors.affiliation: Graduate School of Agriculture, Hokkaido University, Kita, Sapporo, Hokkaido, 060-8589 Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Kitamura
authors.affiliation: Graduate School of Science, Hiroshima University, Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8526 Japan akusaba@hiroshima-u.ac.jp.
authors.forename: Makoto
authors.initials: M
authors.lastname: Kusaba
mesh_terms: D005075:Biological Evolution; D018548:Cotyledon / Q000502:physiology*; D020440:Gene Duplication; D018745:Genome, Plant; D009154:Mutation; D013025:Glycine max / Q000235:genetics*
keywords: Green-cotyledon; SGR; Soybean; Stay-green; Whole-genome duplication