STRESS INDUCED FACTOR 2, a Leucine-Rich Repeat Kinase Regulates Basal Plant Pathogen Defense.

Protein kinases play fundamental roles in plant development and environmental stress responses. Here, we identified the () gene family, which encodes four leucine-rich repeat receptor-like protein kinases in Arabidopsis (). The four genes, to , are clustered in the genome and highly conserved, but they have temporally and spatially distinct expression patterns. We employed Arabidopsis knockout mutants and overexpression transgenics to examine SIF involvement during plant pathogen defense. genes are rapidly induced by biotic or abiotic stresses, and SIF proteins localize to the plasma membrane. Simultaneous knockout of and led to improved plant salt tolerance, whereas overexpression enhanced PAMP-triggered immunity and prompted basal plant defenses, significantly improving pathogen resistance. Furthermore, overexpression plants exhibited up-regulated expression of the defense-related genes and as well as enhanced MPK3/MPK6 phosphorylation upon pathogen and elicitor treatments. The expression of the calcium signaling-related gene also was enhanced in the -overexpressing lines upon pathogen inoculation but repressed in the mutants. Bimolecular fluorescence complementation demonstrates that the BRI1-ASSOCIATED RECEPTOR KINASE1 protein is a coreceptor of the SIF2 kinase in the signal transduction pathway during pathogen invasion. These findings characterize a stress-responsive protein kinase family and illustrate how SIF2 modulates signal transduction for effective plant pathogenic defense.