Proteomics shed light on the brassinosteroid signaling mechanisms

Large numbers of receptor-like kinases (RLKs) play key roles in plant development and defense by perceiving extracellular signals. The mechanisms of ligand-induced kinase activation and downstream signal transduction have been studied for only a few RLK pathways, among which the brassinosteroid (BR) pathway is the best characterized. Recently, proteomics studies identified new components that bridge the last gap in the genetically defined BR-signaling pathway, establishing the first complete pathway from an RLK to transcription factors in plants. Furthermore, analyses of phosphorylation events, mostly by mass spectrometry, provided insights into the mechanistic details of receptor kinase activation and regulation of downstream components by phosphorylation. This review focuses on recent progress in understanding BR signal transduction made by proteomics studies.