MAP4 kinase SIK1 promotes ROS burst and antibacterial immunity in plants (Cell Host Microbe)

Cell surface pattern-recognition receptors (PRRs) such as FLS2 that recognize conserved pathogen features are important contributors to plant defenses against pathogens, triggering the so-called Pattern-Triggered Immunity (PTI) response. Pattern recognition by PRRs triggers the production of extracellular reactive oxygen species (ROS), which both promotes additional defense responses and can help to weaken or kill the pathogen. Zhang et al. identified a MAP4 kinase, SIK1, that connects the PRRs with the activation of a plasma-membrane localized NADPH oxidase that produces extracellular ROS, thus connecting two parts of the PTI pathway. Surprisingly, loss-of-function mutants of SIK1 showed more robust defense against pathogens, which the authors identified as arising due to elevated salicylic acid (SA) levels. However, when they suppressed SA accumulation (though expression of salicylate hydroxylase NahG), the sak1 mutants showed reduced PTI responsiveness. Thus, the authors have identified an important piece of the plant’s defense response. (Summary by Mary Williams) Cell Host Microbe 10.1016/j.chom.2018.08.007