title: Mutation of SAD2, an importin beta-domain protein in Arabidopsis, alters abscisic acid sensitivity.
abstract: A number of protein and RNA-processing mutants have been shown to affect ABA sensitivity. A new mutant, sad2-1, was isolated from a T-DNA mutagenized population of RD29A:LUC plants and shown to have increased luminescence after ABA, salt, cold or polyethylene glycol treatments. Expression of several ABA- and stress-responsive genes was higher in the mutant than in the wild type. sad2-1 also exhibited ABA hypersensitivity in seed germination and seedling growth. SAD2 was found to encode an importin beta-domain family protein likely to be involved in nuclear transport. SAD2 was expressed at a low level in all tissues examined except flowers, but SAD2 expression was not inducible by ABA or stress. Subcellular localization of GFP-tagged SAD2 showed a predominantly nuclear localization, consistent with a role for SAD2 in nuclear transport. Knockout of the closest importin beta homolog of SAD2 in Arabidopsis did not duplicate the sad2 phenotype, indicating that SAD2 plays a specific role in ABA signaling. Analysis of RD29A:LUC luminescence and ABA and stress sensitivity in double mutants of sad2-1 and sad1 or abh1-7, a newly isolated allele of ABH1 also in the RD29A:LUC background, suggested that SAD2 acts upstream of or has additive effects with these two genes. The results suggest a role for nuclear transport in ABA signal transduction, and the possible roles of SAD2 in relation to that of SAD1 and ABH1 are discussed.
authors.affiliation: Institute for Integrative Genome Biology and Department of Botany and Plant Sciences, University of California, Riverside, CA 92521, USA.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Verslues
authors.forename: Yan
authors.initials: Y
authors.lastname: Guo
authors.forename: Chun-Hai
authors.initials: CH
authors.lastname: Dong
authors.forename: Wujun
authors.initials: W
authors.lastname: Ma
authors.forename: Jian-Kang
authors.initials: JK
authors.lastname: Zhu
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism / Q000494:pharmacology*; D021581:Active Transport, Cell Nucleus / Q000235:genetics; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D049452:Green Fluorescent Proteins / Q000032:analysis; D028884:Karyopherins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D009154:Mutation; D010937:Plant Growth Regulators / Q000378:metabolism / Q000494:pharmacology*; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000032:analysis; D015398:Signal Transduction; D028961:beta Karyopherins / Q000235:genetics / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D028884:Karyopherins; D010937:Plant Growth Regulators; D011993:Recombinant Fusion Proteins; C514676:SAD2 protein, Arabidopsis; D028961:beta Karyopherins; D049452:Green Fluorescent Proteins; D000040:Abscisic Acid