Sharma Gunjan, Giri Jitender, Tyagi Akhilesh K
National Institute of Plant Genome Research, Aruna Asaf Ali Road, New Delhi 110067, India.
Plant Sci. 2015 Aug;237:80-92. doi: 10.1016/j.plantsci.2015.05.011. Epub 2015 May 19.
Stress associated protein (SAP) genes in plants regulate abiotic stress responses. SAP gene family consists of 18 members in rice. Although their abiotic stress responsiveness is well established, the mechanism of their action is poorly understood. OsiSAP7 was chosen to investigate the mechanism of its action based on the dual nature of its sub-cellular localization preferentially in the nucleus or sub-nuclear speckles upon transient expression in onion epidermal cells. Its expression was down-regulated in rice seedlings under abiotic stresses. OsiSAP7 was localized evenly in the nucleus under unstressed conditions and in sub-nuclear speckles on MG132 treatment. OsiSAP7 exhibits E3 ubiquitin ligase activity in vitro. Abiotic stress responses of OsiSAP7 were assessed by its overexpression in Arabidopsis under the control of a stress inducible promoter rd29A. Stress response assessment was done at seed germination and advanced stages of development. Transgenics were ABA insensitive at seed germination stage and sensitive to water-deficit stress at advanced stage as compared to wild type (WT). They were also impaired in ABA and stress-responsive gene expression. Our study suggests that OsiSAP7 acts as a negative regulator of ABA and water-deficit stress signalling by acting as an E3 ubiquitin ligase.
植物中的胁迫相关蛋白（SAP）基因调控非生物胁迫响应。水稻中的SAP基因家族由18个成员组成。尽管它们的非生物胁迫响应性已得到充分证实，但其作用机制仍知之甚少。基于其在洋葱表皮细胞中瞬时表达时优先定位于细胞核或核内斑点的亚细胞定位的双重性质，选择了OsiSAP7来研究其作用机制。在非生物胁迫下，水稻幼苗中OsiSAP7的表达下调。在未受胁迫的条件下，OsiSAP7均匀地定位于细胞核中，而在MG132处理下则定位于核内斑点中。OsiSAP7在体外表现出E3泛素连接酶活性。通过在胁迫诱导型启动子rd29A的控制下在拟南芥中过表达OsiSAP7来评估其非生物胁迫响应。在种子萌发和发育后期进行胁迫响应评估。与野生型（WT）相比，转基因植株在种子萌发阶段对脱落酸不敏感，在发育后期对水分亏缺胁迫敏感。它们在脱落酸和胁迫响应基因表达方面也存在缺陷。我们的研究表明，OsiSAP7作为一种E3泛素连接酶，充当脱落酸和水分亏缺胁迫信号的负调节因子。
