title: ahg12 is a dominant proteasome mutant that affects multiple regulatory systems for germination of Arabidopsis.
abstract: The ubiquitin-proteasome system is fundamentally involved in myriad biological phenomena of eukaryotes. In plants, this regulated protein degradation system has a pivotal role in the cellular response mechanisms for both internal and external stimuli, such as plant hormones and environmental stresses. Information about substrate selection by the ubiquitination machinery has accumulated, but there is very little information about selectivity for substrates at the proteasome. Here, we report characterization of a novel abscisic acid (ABA)-hypersensitive mutant named ABA hypersensitive germination12 (ahg12) in Arabidopsis. The ahg12 mutant showed a unique pleiotropic phenotype, including hypersensitivity to ABA and ethylene, and hyposensitivity to light. Map-based cloning identified the ahg12 mutation to cause an amino acid conversion in the L23 loop of RPT5a, which is predicted to form the pore structure of the 19S RP complex of the proteasome. Transient expression assays demonstrated that some plant-specific signaling components accumulated at higher levels in the ahg12 mutant. These results suggest that the ahg12 mutation led to changes in the substrate preference of the 26S proteasome. The discovery of the ahg12 mutation thus will contribute to elucidate the characteristics of the regulated protein degradation system.
authors.affiliation: Graduate School of Nanobioscience, Yokohama City University, 1-7-29 Suehiro, Tsurumi, Yokohama 230-0045, Japan.
authors.forename: Shimpei
authors.initials: S
authors.lastname: Hayashi
authors.affiliation: Institute of Plant Science and Resources, Okayama University, 2-20-1 Chuo, Kurashiki, Okayama 710-0046, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Hirayama
mesh_terms: D000040:Abscisic Acid / Q000633:toxicity; D000251:Adenosine Triphosphatases / Q000235:genetics* / Q000378:metabolism*; D019943:Amino Acid Substitution; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics* / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism*; D016000:Cluster Analysis; D018744:DNA, Plant / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D018525:Germination; D020125:Mutation, Missense; D010802:Phylogeny; D046988:Proteasome Endopeptidase Complex / Q000235:genetics* / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D029681:Arabidopsis Proteins; D018744:DNA, Plant; D004275:DNA, Ribosomal; D012335:RNA, Ribosomal; C065096:RNA, ribosomal, 26S; D000040:Abscisic Acid; D046988:Proteasome Endopeptidase Complex; D000251:Adenosine Triphosphatases; C541999:RPT5a protein, Arabidopsis