Laboratory of Plant Molecular Genetics, Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan.
Cell Host Microbe. 2013 Apr 17;13(4):465-76. doi: 10.1016/j.chom.2013.03.007.
OsCEBiP, a chitin-binding protein, and OsCERK1, a receptor-like kinase, are plasma membrane (PM) proteins that form a receptor complex essential for fungal chitin-driven immune responses in rice. The signaling events immediately following chitin perception are unclear. Investigating the spatiotemporal regulation of the rice small GTPase OsRac1, we find that chitin induces rapid activation of OsRac1 at the PM. Searching for OsRac1 interactors, we identified OsRacGEF1 as a guanine nucleotide exchange factor for OsRac1. OsRacGEF1 interacts with OsCERK1 and is activated when its C-terminal S549 is phosphorylated by the cytoplasmic domain of OsCERK1 in response to chitin. Activated OsRacGEF1 is required for chitin-driven immune responses and resistance to rice blast fungus infection. Further, a protein complex including OsCERK1 and OsRacGEF1 is transported from the endoplasmic reticulum to the PM. Collectively, our results suggest that OsCEBiP, OsCERK1, OsRacGEF1, and OsRac1 function as key components of a "defensome" critically engaged early during chitin-induced immunity.
OsCEBiP，一种几丁质结合蛋白，和 OsCERK1，一种受体样激酶，是质膜（PM）蛋白，它们形成一个受体复合物，对于水稻中真菌几丁质驱动的免疫反应是必需的。几丁质感知后立即发生的信号事件尚不清楚。研究水稻小分子 GTP 酶 OsRac1 的时空调控，我们发现几丁质诱导 OsRac1 在 PM 上的快速激活。在寻找 OsRac1 相互作用蛋白时，我们鉴定出 OsRacGEF1 是 OsRac1 的鸟嘌呤核苷酸交换因子。OsRacGEF1 与 OsCERK1 相互作用，并且当其 C 末端 S549 被细胞质结构域 OsCERK1 磷酸化时被激活，响应几丁质。激活的 OsRacGEF1 是几丁质驱动的免疫反应和对稻瘟病菌感染的抗性所必需的。此外，包括 OsCERK1 和 OsRacGEF1 的蛋白质复合物从内质网运输到 PM。总之，我们的结果表明，OsCEBiP、OsCERK1、OsRacGEF1 和 OsRac1 作为一个“防御体”的关键组成部分，在几丁质诱导的免疫中早期起关键作用。
