Stomatal Immunity

Abstract

Stomata have long been assumed as passive portals of entry for pathogenic microorganisms, which may cause severe crop loss and food poisoning; however, accumulating evidence suggests that stomata have an important immune function. Plants actively close their stomata upon recognition of invading pathogens to stave off pathogenesis. Stomatal immunity starts from the perception of pathogen‐associated molecular patterns by surface‐localised pattern recognition receptors and activating a signalling cascade that requires plant hormones, reactive oxygen species (ROS) production, ion flux and gene expression to trigger stomatal closure. However, the arms race between plants and pathogens has driven the pathogenic microbes to constantly evolve new strategies and effector combinations as a countermeasure to manipulate stomatal movement for their own benefit. Changes in the guard cell metabolome, circadian clock regulating genes and climate‐related factors can impact plant defence through stomatal regulation. Understanding stomatal immunity has broad applications in combating pathogens, enhancing agricultural capacity and food safety. Key Concepts Active stomatal movement is tightly regulated by plants as a general mechanism of defence against biotic and abiotic stresses. Guard cells recognise pathogen‐associated molecular patterns and trigger a signalling cascade rendering stomatal closure and a reduction of pathogen entry into the plant. Different types of pathogens can subvert or take control of the plant immune responses and re‐open stomata for enhancing pathogenicity via toxins and/or effectors. Changes in the guard cell metabolome, redox homeostasis, circadian clock regulating genes and climate‐related factors can impact plant defence through stomatal regulation. Elucidating how stomata prioritise their responses to multiple biotic and abiotic signal inputs and the epistatic relationships between various signalling pathways in the guard cells will be a next important step in understanding the regulatory mechanism of stomatal immunity.