Arabidopsis heterotrimeric G proteins directly regulate FLS2-mediated immunity
X. LIANG (1), J. Zhou (2), J. Wang (2), M. Ma (2) (1) nstitute of Genetics and Developmental Biology,CAS, China; (2) Institute of Genetics and Developmental Biology,CAS, China

The Arabidopsis immune receptor kinase FLS2 perceives bacterial flagellar peptide flg22 to activate downstream signaling through the central cytoplasmic kinase BIK1. The heterotrimeric G proteins composed of the non-canonical Gα protein XLG2, the Gβ protein AGB1, and the Gγ proteins AGG1 and AGG2 are required for FLS2-mediated immune responses through an unknown mechanism. Here we show that in the pre-activation state, XLG2 directly interacts with FLS2 and BIK1, and it functions together with AGB1 and AGG1/2 to attenuate proteasome-mediated degradation of BIK1, allowing optimum immune activation. XLG2 also interacts with the NADPH oxidase RbohD that is essential for flg22-induced production of reactive oxygen species (ROS). Following the activation of FLS2 by flg22, XLG2 dissociates from AGB1 and the FLS2 complex. In addition, XLG2 is phosphorylated by BIK1 in the N terminus, and the phosphorylation is required for maximum production of ROS in response to flg22.  Our study demonstrates that the G proteins are directly coupled to the FLS2 receptor complex and regulate immune signaling through both pre-activation and post-activation mechanisms.  xlg2 plants were more susceptible to Pst than agb1 plants, suggesting that XLG2 regulates other effectors independent of Gβγ in the post activation state. A subfamily of cytoplasmic proteins named XAP1-XAP4 (XLG2-Associated Proteins) were identified via immunoprecipitation followed by LS-MS/MS analysis. The overexpression of XAPs showed reduced defense gene expression and resistance to Pst, suggesting that XLG2 additionally regulates immunity through XLG2-XAP interaction. Our progress on the analyses of XAPs will be presented. 

Abstract Number: P17-558
Session Type: Poster