Leucine-Rich Repeat Receptor-Like Proteins in Plants: Structure, Function, and Signaling

Leucine-rich repeat receptor-like proteins (LRR-RLPs) and LRR receptor-like kinases (LRR-RLKs) are transmembrane receptors that act as critical sensors for regulating a wide variety of developmental and defense-related processes. LRR-RLPs, like LRR-RLKs, form receptor complexes with the co-receptor BAK1 on the plasma membrane to transmit ligand perception signals to intracellular signaling components. However, in contrast to LRR-RLKs, LRR-RLPs lack a cytoplasmic kinase domain and associate with the adaptor protein SUPPRESSOR OF BIR1-1 (SOBIR1) to activate downstream signal transduction. In this review, we discuss the structure of LRR-RLPs, their functions in plant immunity and development, and their ligand molecules. We also summarize the current understanding of LRR-RLP-mediated signaling mechanisms.