RAF-Like Protein Kinases in Plants

Abstract

RAF-like protein kinases constitute a major subclass of mitogen-activated protein kinase kinase kinases (MAPKKKs) in plants and function as critical regulators of stress and hormone signaling pathways. Unlike their animal counterparts, plant RAF kinases show extensive expansion and diversification, with distinct subgroups (B and C) exhibiting both conserved and specialized functions. Recent studies have unveiled their pivotal roles in sensing environmental stresses, such as hyperosmotic stress and elevated CO₂, as well as in mediating hormonal responses, including those to abscisic acid (ABA), ethylene, and auxin. RAFs also participate in guard cell signaling, immune responses, and developmental processes, integrating diverse external and internal cues. This review summarizes the current knowledge of plant RAF kinases, emphasizing their functional diversity, mechanisms of activation, and physiological relevance in plant adaptation.