Anion channel SLAH3 is a regulatory target of chitin receptor-associated kinase PBL27 in microbial stomatal closure.

In plants, antimicrobial immune responses involve the cellular release of anions and are responsible for the closure of stomatal pores. Detection of microbe-associated molecular patterns (MAMPs) by pattern recognition receptors (PRRs) induces currents mediated via slow-type (S-type) anion channels by a yet not understood mechanism. Here, we show that stomatal closure to fungal chitin is conferred by the major PRRs for chitin recognition, LYK5 and CERK1, the receptor-like cytoplasmic kinase PBL27, and the SLAH3 anion channel. PBL27 has the capacity to phosphorylate SLAH3, of which S127 and S189 are required to activate SLAH3. Full activation of the channel entails CERK1, depending on PBL27. Importantly, both S127 and S189 residues of SLAH3 are required for chitin-induced stomatal closure and anti-fungal immunity at the whole leaf level. Our results demonstrate a short signal transduction module from MAMP recognition to anion channel activation, and independent of ABA-induced SLAH3 activation.

Regulation of pattern recognition receptor signalling by phosphorylation and ubiquitination.

Our understanding of how plant innate immunity is triggered and regulated has seen tremendous progress over the last decade, with many important players identified in the model systems Arabidopsis thaliana and Oryza sativa (rice). Identification of these components has come from both genetic screens as well as from proteomics approaches. While genetic approaches are powerful tools of discovery to identify key components in a signalling pathway, the application of genetics is limited when dealing with redundancy or when mutations cause lethal phenotypes. This is where the complementary strength of proteomics has brought major advances. With the advancement in technology in the field of proteomics, not only the proteins involved in innate immune signalling and responses have been identified, but also the posttranslational modifications (PTMs) that these proteins carry have been mapped in more intricate detail and shown to be functionally relevant in both genetic and biochemical terms. Here we discuss the most recent progress in pattern recognition receptor (PRR) signalling with a focus on phosphorylation and ubiquitination.