title: Regulation of seed germination and seedling growth by an Arabidopsis phytocystatin isoform, AtCYS6.
abstract: Phytocystatins are cysteine proteinase inhibitors in plants that are implicated in the endogenous regulation of protein turnover and defense mechanisms against insects and pathogens. A cDNA encoding a phytocystatin called AtCYS6 (Arabidopsis thaliana phytocystatin6) has been isolated. We show that AtCYS6 is highly expressed in dry seeds and seedlings and that it also accumulates in flowers. The persistence of AtCYS6 protein expression in seedlings was promoted by abscisic acid (ABA), a seed germination and post-germination inhibitory phytohormone. This finding was made in transgenic plants bearing an AtCYS6 promoter-beta-glucuronidase (GUS) reporter construct, where we found that expression from the AtCYS6 promoter persisted after ABA treatment but was reduced under control conditions and by gibberellin(4+7) (GA(4+7)) treatment during the germination and post-germinative periods. In addition, constitutive over-expression of AtCYS6 retarded germination and seedling growth, whereas these were enhanced in an AtCYS6 knock-out mutant (cys6-2). Additionally, cysteine proteinase activities stored in seeds were inhibited by AtCYS6 in transgenic Arabidopsis. From these data, we propose that AtCYS6 expression is enhanced by the germination inhibitory phytohormone ABA and that it participates in the control of germination rate and seedling growth by inhibiting the activity of stored cysteine proteinases.
authors.affiliation: Environmental Biotechnology National Core Research Center and PMBBRC, Graduate School of Gyeongsang National University, Jinju, Korea.
authors.forename: Jung Eun
authors.initials: JE
authors.lastname: Hwang
authors.forename: Joon Ki
authors.initials: JK
authors.lastname: Hong
authors.forename: Ji Hyun
authors.initials: JH
authors.lastname: Je
authors.forename: Kyun Oh
authors.initials: KO
authors.lastname: Lee
authors.forename: Dool Yi
authors.initials: DY
authors.lastname: Kim
authors.forename: Sang Yeol
authors.initials: SY
authors.lastname: Lee
authors.forename: Chae Oh
authors.initials: CO
authors.lastname: Lim
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D015891:Cystatins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D018525:Germination; D008969:Molecular Sequence Data; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D036226:Seedlings / Q000254:growth & development* / Q000378:metabolism*; D012639:Seeds / Q000254:growth & development / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C548131:CYS6 protein, Arabidopsis; D015891:Cystatins; D020033:Protein Isoforms
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