The tomato receptor-like cytoplasmic kinase Fir1 is involved in flagellin signaling and pre-invasion immunity
2Bioinformatics Unit, G.S. Wise Faculty of Life Science, Tel Aviv University, Israel
3Boyce Thompson Institute for Plant Research and Plant Pathology and Plant-Microbe Biology Section, School of Integrative Plant Science, Cornell University, USA
Detection of bacterial flagellin by the tomato (Solanum lycopersicum) receptors Flagellin sensing 2 (Fls2) and Fls3 triggers activation of pattern-triggered immunity (PTI). We identified the tomato Fls2/Fls3-interacting receptor-like cytoplasmic kinase 1 (Fir1) protein as a component of PTI signaling triggered by flagellin perception. Fir1 interacted with Fls2 and Fls3 in planta and CRISPR/Cas9-generated tomato fir1 mutants were impaired in flagellin-mediated resistance to Pseudomonas syringae pv. tomato (Pst) DC3000. fir1 mutants failed to close stomata when infected with Pst DC3000 and were more susceptible to Pst DC3000 than wild-type plants when inoculated by dipping, but not by vacuum-infiltration, indicating involvement of Fir1 in pre-invasion immunity. RNA-seq analysis detected fewer differentially expressed genes in fir1 mutants and altered expression of jasmonic acid (JA)-related genes. In support of JA response deregulation in fir1 mutants, these plants were similarly susceptible to Pst DC3000 and to the Pst DC3118 strain that is unable to synthesize coronatine, a JA-mimicking bacterial toxin. These results indicate that tomato Fir1 is required for a subset of flagellin-triggered PTI responses and support a model in which Fir1 negatively regulates JA signaling during PTI activation.