Structural insights into ligand recognition and receptor activation of plant leucine-rich repeat (LRR) transmembrane receptors

Higher plants must coordinate their own growth and development by responding to a myriad of internal signals. Simultaneously, confronted with external signals such as pathogen invasion, drought and so on, they must constantly adjust themselves to adapt. These signals can be specifically recognized by transmembrane receptors on the cytoplasmic membrane, comprising receptor kinases (RKs) and receptor-like proteins (RLPs). Among these, leucine-rich repeat receptor kinases (LRR-RKs) and leucine-rich repeat receptor-like proteins (LRR-RLPs) form the largest category. By using X-ray crystallography and cryo-electron microscopy (cryo-EM) single-particle analysis, the ligand recognition and receptor activation mechanisms of some LRR-RKs/RLPs have been elucidated at the atomic scale. This deepens our understanding of the roles played by LRR-RKs/RLPs in the plant growth, development, responses to pathogen invasion and other environmental stresses. Moreover, it provides clues for precise genetic improvement aimed at improving yield, quality and stress resistance in economic crops. This review summarizes the recent progress in structural research on LRR-RKs/RLPs concerning plant growth, development, immune responses and other environmental stress responses. Additionally, this paper discusses how these receptors recognize their respective ligands and how ligand recognition triggers receptor activation from a structural biology perspective, offering new insights for crop improvement.