Identify a novel MAP kinase that targets receptor-like cytoplasmic kinases to regulate plant innate immunity
Y. CHIANG (1), M. Zhang (1), T. Toruño (1), K. Yadeta (1), J. Banderas (1), G. Coaker (1) (1) University of California, Davis, U.S.A.

Plant innate immunity is mediated by surface localized and intracellular receptors that can recognize all pathogen classes and activate downstream immune signaling networks. Despite the importance of innate immune responses, the immediate targets of activated immune receptors remain largely unknown. Plant immune signaling networks heavily rely on protein phosphorylation. One class of kinases, the receptor-like cytoplasmic kinases (RLCKs), can directly associate with multiple immune receptors and are important immune regulators. Here, we identified a novel Arabidopsis MAP kinase, M4K, which interacts with multiple RLCKs. The m4k T-DNA lines exhibited developmental phenotypes with stunted growth, curled leaves and delayed flowering. The m4k mutants displayed high accumulation of salicylic acid, lesion mimic phenotype and elevated expression of the pathogenesis-related genes, marker genes for the accumulation of salicylic acid and defense responses. The m4k mutants showed enhanced resistance against virulent Pseudomonas syringae pv. tomato (Pto) DC3000.  Upon bacterial elicitor flg22 treatment, the m4k mutants showed altered Pattern-Triggered Immunity (PTI) with reduced extracellular reactive oxygen species (ROS) burst and partially phenocopied the bik1 RLCK mutant. Moreover, the m4k mutants were strongly affected in immunity mediated by the RPS5 NB-LRR receptor that monitors for perturbation of another RLCK called PBS1. Co-expressing with PBS1 enhanced M4K stability in N. benthamiana, whereas silencing NbM4K decreased PBS1 accumulation. These results indicate that M4K mediates the stability of multiple RLCKs to regulate immune responses. The role of M4K in regulating primary immune receptor signaling will be presented.    

Abstract Number: P18-663
Session Type: Poster