title: Highly Sprouting-Tolerant Wheat Grain Exhibits Extreme Dormancy and Cold Imbibition-Resistant Accumulation of Abscisic Acid.
abstract: Pre-harvest sprouting (PHS) of wheat (Triticum aestivum L.) grains induces hydrolyzing enzymes such as α-amylase, which considerably decreases wheat product quality. PHS occurs when cool and wet weather conditions before harvest break dormancy and induce grain germination. In this study, we used PHS-tolerant varieties, Gifu-komugi (Gifu) and OS38, to characterize the mechanisms of both dormancy breakage and dormancy maintenance at low temperatures. Physiologically mature Gifu grains exhibited dormancy after imbibition at 20°C, but germinated at 15°C. In contrast, OS38 grains remained dormant even at temperatures as low as 5°C. Embryo half-grains cut out from the dormant Gifu grains germinated by imbibition at 20°C, similar to conventional varieties worldwide. However, OS38 embryo half-grains were still dormant. Hormonome and pharmacological analyses suggested that ABA and gibberellin metabolism are important for temperature-dependent dormancy maintenance and breakage. Imbibition at 15°C decreased ABA levels but increased gibberellin levels in embryos of freshly harvested Gifu grains. Additionally, low temperatures induced expression of the ABA catabolism genes,TaABA8' OH1 and TaABA8' OH2, and the gibberellin biosynthesis gene,TaGA3ox2, in the embryos. However, in embryos of freshly harvested OS38 grains, ABA levels were increased while gibberellin levels were suppressed at 15°C. In these dormant embryos, low temperatures induced the TaNCED ABA biosynthesis genes, but suppressed TaABA8' OH2 and TaGA3ox2.These results show that the regulatory mechanism influencing the expression of ABA and gibberellin metabolism genes may be critical for dormancy maintenance and breakage at low temperatures. Our findings should help improve PHS-resistant wheat breeding programs.
authors.affiliation: Department of Life Sciences, School of Agriculture, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, 214-8571 Japan Present address: Central Research Laboratory, Nitto Fuji Milling Co., Ltd., 6-2-1 Tokai, Ohta-ku, Tokyo, 143-0001 Japan. These authors contributed equally to this work.
authors.forename: Yu-ichi
authors.initials: Y
authors.lastname: Kashiwakura
authors.affiliation: Department of Life Sciences, School of Agriculture, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, 214-8571 Japan These authors contributed equally to this work.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kobayashi
authors.affiliation: RIKEN Center for Sustainable Resource Science, Yokohama, Kanagawa 230-0045, Japan Present address: Agilent Technologies Japan, Ltd., 9-1, Takakura-machi, Hachioji-shi, Tokyo, 192-8510 Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Jikumaru
authors.affiliation: RIKEN Center for Sustainable Resource Science, Yokohama, Kanagawa 230-0045, Japan.
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Takebayashi
authors.affiliation: Cell and Systems Biology, University of Toronto, Toronto, Ontario M5S 3B2, Canada.
authors.forename: Eiji
authors.initials: E
authors.lastname: Nambara
authors.affiliation: RIKEN Center for Sustainable Resource Science, Yokohama, Kanagawa 230-0045, Japan.
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Seo
authors.affiliation: RIKEN Center for Sustainable Resource Science, Yokohama, Kanagawa 230-0045, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kamiya
authors.affiliation: Department of Life Sciences, School of Agriculture, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, 214-8571 Japan.
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Kushiro
authors.affiliation: Department of Life Sciences, School of Agriculture, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, 214-8571 Japan kawakami@meiji.ac.jp.
authors.forename: Naoto
authors.initials: N
authors.lastname: Kawakami
mesh_terms: D000040:Abscisic Acid / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D003080:Cold Temperature; D018506:Gene Expression Regulation, Plant; D018525:Germination; D005875:Gibberellins / Q000378:metabolism; D057445:Plant Dormancy / Q000502:physiology*; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D012639:Seeds / Q000502:physiology; D014908:Triticum / Q000235:genetics / Q000254:growth & development / Q000502:physiology*
chemical_list: D005875:Gibberellins; D010940:Plant Proteins; D000040:Abscisic Acid
keywords: Abscisic acid; Gibberellin; Low temperature; Pre-harvest sprouting; Seed dormancy; Wheat