Function of WAKs in Regulating Cell Wall Development and Responses to Abiotic Stress

Receptor-like kinases (RLKs) are instrumental in regulating plant cell surface sensing and vascular tissue differentiation. Wall-associated kinases (WAKs) are a unique group of RLKs that have been identified as key cell wall integrity (CWI) sensors. WAK signaling is suggested to be activated during growth in response to cell expansion or when the cell wall is damaged, for example, during pathogen attack. WAKs are proposed to interact with pectins or pectin fragments that are enriched in primary walls. Secondary walls have low levels of pectins, yet recent studies have shown important functions of WAKs during secondary wall development. Several wak mutants show defects in secondary wall thickening of the xylem vessels and fibers or the development of vascular bundles. This review will discuss the recent advances in our understanding of WAK functions during plant development and responses to abiotic stresses and the regulation of vascular tissue secondary wall development.