CYSTEINE-RICH RECEPTOR-LIKE PROTEIN KINASES - their evolution, structure and roles in stress response and development.

Abstract

Plant-specific receptor-like protein kinases (RLKs) are central components for sensing the extracellular microenvironment. CYSTEINE-RICH RLKs (CRKs) are one of the biggest subgroups of RLKs. Their physiological and molecular roles have only begun to be elucidated, but recent studies highlight the diverse types of proteins interacting with CRKs, as well as the localization of CRKs and their lateral organization within the plasma membrane. Originally proposed to act as redox sensors, the potential ligands perceived by the DOMAIN OF UNKNOWN FUNCTION 26 (DUF26)-containing extracellular region of the CRKs remain elusive. Here, we summarize the recent progress in the analysis of CRK evolution, molecular function and their roles in plant development, abiotic stress responses, plant immunity and symbiosis. The currently available information on CRKs and related proteins suggests the CRKs to be central regulators of plant signaling pathways. However, more research using classical methods and interdisciplinary approaches in various plant model species, as well as structural analyses, will not only enhance our understanding of the molecular function of CRKs, but also elucidate the contribution of other cellular components in CRK-mediated signaling pathways.