Plants deploy a sophisticated immune system that involves small peptides and cell surface receptor kinases (RKs) to mediate defense responses against pathogens. Among these, phytocytokines-small, secreted peptides-play key roles as immunomodulatory molecules, functioning similarly to cytokines in mammals. These peptides act locally and systemically, amplifying immune responses triggered by microbial patterns and pathogen-derived effectors. In addition, phytocytokines regulate various infection processes, while some pathogens exploit mimicry to enhance infection. At the frontline of immune sensing, RKs like BAK1/SERK4 serve as coreceptors for multiple pattern recognition receptors (PRRs) involved in pattern-triggered immunity (PTI). Pathogens, however, attempt to disrupt these RK complexes to evade detection. In turn, plants activate compensatory RK pathways such as the BTL2 module, triggering danger-triggered immunity (DTI) and intracellular nucleotide-binding leucine-rich repeat receptors (NLRs) that drive immune signaling and cell death. This presentation will explore the perception and mechanisms of phytocytokine signaling through RKs, the dynamic regulation of immune responses via phosphorylation and calcium channels, and the evolutionary arms race between host and pathogen.
