Liu Jinling, Park Chan Ho, He Feng, Nagano Minoru, Wang Mo, Bellizzi Maria, Zhang Kai, Zeng Xiaoshan, Liu Wende, Ning Yuese, Kawano Yoji, Wang Guo-Liang
State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China; Hunan Provincial Key Laboratory of Crop Germplasm Innovation and Utilization and College of Agronomy, Hunan Agricultural University, Changsha, Hunan, China.
Department of Plant Pathology, Ohio State University, Columbus, Ohio, United States of America.
PLoS Pathog. 2015 Feb 6;11(2):e1004629. doi: 10.1371/journal.ppat.1004629. eCollection 2015 Feb.
The ubiquitin proteasome system in plants plays important roles in plant-microbe interactions and in immune responses to pathogens. We previously demonstrated that the rice U-box E3 ligase SPL11 and its Arabidopsis ortholog PUB13 negatively regulate programmed cell death (PCD) and defense response. However, the components involved in the SPL11/PUB13-mediated PCD and immune signaling pathway remain unknown. In this study, we report that SPL11-interacting Protein 6 (SPIN6) is a Rho GTPase-activating protein (RhoGAP) that interacts with SPL11 in vitro and in vivo. SPL11 ubiquitinates SPIN6 in vitro and degrades SPIN6 in vivo via the 26S proteasome-dependent pathway. Both RNAi silencing in transgenic rice and knockout of Spin6 in a T-DNA insertion mutant lead to PCD and increased resistance to the rice blast pathogen Magnaporthe oryzae and the bacterial blight pathogen Xanthomonas oryzae pv. oryzae. The levels of reactive oxygen species and defense-related gene expression are significantly elevated in both the Spin6 RNAi and mutant plants. Strikingly, SPIN6 interacts with the small GTPase OsRac1, catalyze the GTP-bound OsRac1 into the GDP-bound state in vitro and has GAP activity towards OsRac1 in rice cells. Together, our results demonstrate that the RhoGAP SPIN6 acts as a linkage between a U-box E3 ligase-mediated ubiquitination pathway and a small GTPase-associated defensome system for plant immunity.
植物中的泛素蛋白酶体系统在植物与微生物的相互作用以及对病原体的免疫反应中发挥着重要作用。我们之前证明，水稻U-box E3连接酶SPL11及其拟南芥同源物PUB13对程序性细胞死亡（PCD）和防御反应起负调控作用。然而，参与SPL11/PUB13介导的PCD和免疫信号通路的成分仍不清楚。在本研究中，我们报道了与SPL11相互作用的蛋白6（SPIN6）是一种Rho GTP酶激活蛋白（RhoGAP），它在体外和体内均与SPL11相互作用。SPL11在体外使SPIN6泛素化，并在体内通过26S蛋白酶体依赖性途径降解SPIN6。转基因水稻中的RNA干扰沉默和T-DNA插入突变体中Spin6的敲除均导致PCD，并增强了对稻瘟病菌Magnaporthe oryzae和白叶枯病菌Xanthomonas oryzae pv. oryzae的抗性。Spin6 RNA干扰植株和突变体植株中的活性氧水平和防御相关基因表达均显著升高。引人注目的是，SPIN6与小GTP酶OsRac1相互作用，在体外将结合GTP的OsRac1催化为结合GDP的状态，并在水稻细胞中对OsRac1具有GAP活性。总之，我们的结果表明，RhoGAP SPIN6作为U-box E3连接酶介导的泛素化途径与小GTP酶相关的防御系统之间的联系，参与植物免疫。
