Dual Activities of Receptor-Like Kinase OsWAKL21.2 Induce Immune Responses1

Plant pathogens secrete cell wall-degrading enzymes that degrade various components of the plant cell wall. Plants sense this cell wall damage as a mark of infection and induce immune responses. However, the plant functions that are involved in the elaboration of cell wall damage-induced immune responses remain poorly understood. Transcriptome analysis revealed that a rice (Oryza sativa) receptor-like kinase,WALL-ASSOCIATED KINASE-LIKE21(OsWAKL21.2), is up-regulated following treatment with eitherXanthomonas oryzaepvoryzae(a bacterial pathogen) or lipaseA/esterase (LipA; a cell wall-degrading enzyme ofX. oryzaepvoryzae). Overexpression ofOsWAKL21.2in rice induces immune responses similar to those activated by LipA treatment. Down-regulation ofOsWAKL21.2attenuates LipA-mediated immune responses. Heterologous expression ofOsWAKL21.2in Arabidopsis (Arabidopsis thaliana) also activates plant immune responses. OsWAKL21.2 is a dual-activity kinase that has in vitro kinase and guanylate cyclase activities. Interestingly, kinase activity of OsWAKL21.2 is necessary to activate rice immune responses, whereas in Arabidopsis, OsWAKL21.2 guanylate cyclase activity activates these responses. Our study reveals a rice receptor kinase that activates immune responses in two different species via two different mechanisms. A rice receptor-like kinase induces immune responses in rice and Arabidopsis by kinase and guanylate cyclase activities, respectively.