The Cotton Wall-associated Kinase GhWAK7A Mediates Responses to Fungal Wilt Pathogens by Complexing with the Chitin Sensory Receptors.

Plant receptor-like kinases (RLKs) are important players in response to pathogen infections. Verticillium and Fusarium wilts, caused by Verticillium dahliae (Vd) and Fusarium oxysporum f. sp. vasinfectum (Fov), respectively, are among the most devastating diseases in cotton. To understand cotton response to these soil-borne fungal pathogens, we performed a genome-wide in silico characterization and functional screen of diverse RLKs for their involvements in cotton wilt diseases. We identified GhWAK7A, a wall-associated kinase, that positively regulates cotton response to both Vd and Fov infections. Chitin, the major constituent of fungal cell wall, is perceived by lysin motif-containing RLKs (LYKs/CERK1), leading to the activation of plant defense against fungal pathogens. A conserved chitin sensing and signaling system is present in cotton, including chitin-induced GhLYK5-GhCERK1 dimerization and phosphorylation, and this system is important for cotton response to Vd and Fov infections. Importantly, GhWAK7A directly interacts with both GhLYK5 and GhCERK1 and promotes chitin-induced GhLYK5-GhCERK1 dimerization. GhWAK7A phosphorylates GhLYK5, which itself does not have a kinase activity, but requires the phosphorylation for its function. Consequently, GhWAK7A plays a crucial role in chitin-induced responses. Thus, our data reveal GhWAK7A as an important component in cotton response to fungal wilt pathogens by modulating chitin receptor complex.