title: ABA-Hypersensitive Germination1 encodes a protein phosphatase 2C, an essential component of abscisic acid signaling in Arabidopsis seed.
abstract: The phytohormone abscisic acid (ABA) regulates physiologically important stress and developmental responses in plants. To reveal the mechanism of response to ABA, we isolated several novel ABA-hypersensitive Arabidopsis thaliana mutants, named ahg (ABA-hypersensitive germination). ahg1-1 mutants showed hypersensitivity to ABA, NaCl, KCl, mannitol, glucose and sucrose during germination and post-germination growth, but did not display any significant phenotypes in adult plants. ahg1-1 seeds accumulated slightly more ABA before stratification and showed increased seed dormancy. Map-based cloning of AHG1 revealed that ahg1-1 has a nonsense mutation in a gene encoding a novel protein phosphatase 2C (PP2C). We previously showed that the ahg3-1 mutant has a point mutation in the AtPP2CA gene, which encodes another PP2C that has a major role in the ABA response in seeds (Yoshida et al., 2006b). The levels of AHG1 mRNA were higher in dry seeds and increased during late seed maturation--an expression pattern similar to that of ABI5. Transcriptome analysis revealed that, in ABA-treated germinating seeds, many seed-specific genes and ABA-inducible genes were highly expressed in ahg1-1 and ahg3-1 mutants compared with the wild-type. Detailed analysis suggested differences between the functions of AHG1 and AHG3. Dozens of genes were expressed more strongly in the ahg1-1 mutant than in ahg3-1. Promoter-GUS analyses demonstrated both overlapping and distinct expression patterns in seed. In addition, the ahg1-1 ahg3-1 double mutant was more hypersensitive than either monogenic mutant. These results suggest that AHG1 has specific functions in seed development and germination, shared partly with AHG3.
authors.affiliation: Laboratory of Environmental Molecular Biology, RIKEN Wako Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Nishimura
authors.forename: Tomo
authors.initials: T
authors.lastname: Yoshida
authors.forename: Nobutaka
authors.initials: N
authors.lastname: Kitahata
authors.forename: Tadao
authors.initials: T
authors.lastname: Asami
authors.forename: Kazuo
authors.initials: K
authors.lastname: Shinozaki
authors.forename: Takashi
authors.initials: T
authors.lastname: Hirayama
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000378:metabolism; D003001:Cloning, Molecular; D015870:Gene Expression; D018525:Germination / Q000502:physiology*; D009154:Mutation; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D000071636:Protein Phosphatase 2C; D012639:Seeds / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; D000040:Abscisic Acid; C463465:AHG3 protein, Arabidopsis; D010749:Phosphoprotein Phosphatases; D000071636:Protein Phosphatase 2C