Always prepared: priming of the defense response by trichomes (Nature Comms)

Rain contributes to plant disease.  Rain can contain high concentrations of pathogens (like Pseudomonas, Xanthomonas, Alternaria, Fusarium sp., etc.), and high humidity associated with rain antagonizes stomatal closure, leaving open entry points for some pathogens. Matsumura and colleagues have demonstrated a novel function of Arabidopsis mechanosensory cells present in the leaves, the trichomes. The authors showed that raindrops can create a mechanosensation sensed by the trichomes and perceived as an emergency signal, which triggers an immune response. Upon mechanostimulation by rain, trichomes initiate an intercellular  Ca²⁺ wave, resulting in (a) the activation of CALMODULIN-BINDING TRANSCRIPTION ACTIVATOR 3 (CAMTA3) and CAMTA3-dependent gene expression, and (b) phosphorylation of MITOGEN -ACTIVATED PROTEIN KINASE3 (MAPK3) and MAPK6 resulting in the phosphorylation of WRKY DNA-binding protein and WRKY-dependent gene expression; these are canonoical defense pathways. This work demonstrates a central role played by trichomes in mechanosensation and activation of plant defense responses for priming against an impending pathogen attack. (Summary by Sibaji K Sanyal @SibajiSanyal) Nature Comms.  10.1038/s41467-022-28813-8