Verslues Paul E, Guo Yan, Dong Chun-Hai, Ma Wujun, Zhu Jian-Kang
Institute for Integrative Genome Biology and Department of Botany and Plant Sciences, University of California, Riverside, CA 92521, USA.
Plant J. 2006 Sep;47(5):776-87. doi: 10.1111/j.1365-313X.2006.02833.x. Epub 2006 Aug 2.
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.
许多蛋白质和RNA加工突变体已被证明会影响脱落酸（ABA）敏感性。从RD29A:LUC植物的T-DNA诱变群体中分离出一个新的突变体sad2-1，经证明在ABA、盐、冷或聚乙二醇处理后其发光增强。该突变体中几个ABA和胁迫响应基因的表达高于野生型。sad2-1在种子萌发和幼苗生长方面也表现出对ABA的超敏感性。发现SAD2编码一种可能参与核转运的输入蛋白β结构域家族蛋白。除花外，在所有检测的组织中SAD2表达水平都很低，但SAD2的表达不受ABA或胁迫诱导。绿色荧光蛋白（GFP）标记的SAD2的亚细胞定位显示主要定位于细胞核，这与SAD2在核转运中的作用一致。敲除拟南芥中与SAD2最接近的输入蛋白β同源物并没有重现sad2的表型，这表明SAD2在ABA信号传导中起特定作用。对sad2-1与sad1或abh1-7（同样在RD29A:LUC背景下新分离的ABH1等位基因）的双突变体中RD29A:LUC的发光以及ABA和胁迫敏感性的分析表明，SAD2在这两个基因的上游起作用或与它们有累加效应。这些结果表明核转运在ABA信号转导中起作用，并讨论了SAD2相对于SAD1和ABH1可能的作用。
