An OsCEBiP/OsCERK1-OsRacGEF1-OsRac1 Module Is an Essential Early Component of Chitin-Induced Rice Immunity (April 18, 2013)

In plants, perception of microbe-associated molecular patterns (MAMPs) by pattern recognition receptors (PRRs) initiates immune response, MAMP-triggered immunity (MTI). 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.

Postdoc Researcher Akira Akamatsu, Professor Ko Shimamoto and their group members in the Laboratory of Plant Molecular Genetics have found that an OsCEBiP/OsCERK1-OsRacGEF1-OsRac1 module participates in early signaling for chitin-induced MTI. Investigating the spatiotemporal regulation of the rice small GTPase OsRac1, they find that chitin induces rapid activation of OsRac1 at the PM. Searching for OsRac1 interactors, they 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, their results suggest that OsCEBiP, OsCERK1, OsRacGEF1, and OsRac1 function as key components of a ''defensome'' critically engaged early during chitin-induced immunity.

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