Stomatal immunity: Roles of MAP kinases and cytokinin

When a pathogen is perceived, plants have the ability to induce stomatal closure to prohibit the pathogens from passing into the inner tissues; this response is known as stomatal immunity. Two new papers in The Plant Cell investigate mechanisms by which pathogen perception is transduced into stomatal closure.  Su et al. 10.1105/tpc.16.00577 show that MPK3 and MKP6 and their upstream activators are necessary for stomatal closure in response to flg22 (a peptide epitope that mimics flagellin).  They also show a role for malate (an osmotically active anion) metabolism in MPK3/MPK6-mediated stomatal immunity. Arnaud et al. 10.1105/tpc.16.00583 show that cytokinin signaling activates the production of reactive oxygen species through peroxidases, leading to stomatal closure.  Plant Cell