PAMP signal elicited-stomatal condensation of SAIR1 fine-tunes translation for immunity

Plant guard cells perceive pathogens and close stomata to prevent invasion. Biomolecular condensates are central to life growth and stress adaptation, while their roles in regulating stomatal immunity remain unclear. Here, we identify a guard cell-preferential RRM-type RNA-binding protein (RBP) named SAIR1 (stomatal immune RBP 1). Upon pathogen infection and the pathogen-associated molecular pattern flg22 signaling, SAIR1 undergoes phase separation and forms condensates in guard cells to mediate stomatal immunity. Upon flg22 signals, the activated kinases MPK3/6 phosphorylate SAIR1 to initiate its condensation in guard cells. SAIR1 condensates associate with critical defense mRNAs, including those involved in salicylic acid (SA) signaling. SAIR1 interacts with pivotal immune translation regulators such as PABPs and eIFiso4G, and enhances translation of defense mRNAs, ultimately promoting stomatal closure. Our findings reveal that SAIR1 phosphorylation, condensation, and interactions with mRNAs and translation regulators link flg22-MPK3/6 signaling with SA pathways to mediate stomatal immunity. RNA-seq profiling of 3-week-old wild-type Col-0, sair1-1 and SAIR1-YFP-OX2 plants under mock or Pst DC3000 treatment for 24 h;RIP-seq of 3-week-old SAIR1-YFP-OX2 and 35S::GFP plants under flg22 treatment for 45 min; Ribo-seq profiling of 3-week-old wild-type Col-0, sair1-1 plants under mock or flg22 treatment for 45 min.