Antagonistic Interaction between Auxin and SA Signaling Pathways Regulates Bacterial Infection through Lateral Root in Arabidopsis

Pathogen entry into host tissues is a critical and first step in infections. In plants, the lateral roots (LRs) are a potential entry and colonization site for pathogens. Here, using a GFP-labeled pathogenic bacterium Pseudomonas syringae pv. tomato strain DC3000 (Pto DC3000), we observe that virulent Pto DC3000 invades plants through emerged LRs in Arabidopsis. Pto DC3000 strongly induced LR formation, a process that was dependent on the AUXIN RESPONSE FACTOR7 (ARF7)/ARF19-LATERAL ORGAN BOUNDARIES-DOMAIN (LBD) regulatory module. We show that salicylic acid (SA) represses LR formation, and several mutants defective in SA signaling are also involved in Pto DC3000-induced LR development. Significantly, ARF7, a well-documented positive regulator of LR development, directly represses the transcription of PR1 and PR2 to promote LR development. This study indicates that ARF7-mediated auxin signaling antagonizes with SA signaling to control bacterial infection through the regulation of LR development. [Display omitted] •Lateral roots are potential Pseudomonas syringae pv. tomato DC3000 entry sites•The ARF7-LBD module regulates Pto DC3000-triggered lateral root formation•SA-suppressed lateral root formation is partially dependent on PR1 and PR2•ARF7 regulates the expression of PR1 and PR2 in lateral root development Lateral roots (LRs) are potential entry and colonization sites for pathogens. Kong et al. show that Pto DC3000-triggered lateral root formation is dependent on the ARF7-LBD regulatory module, which represses SA responsive genes PR1 and PR2 to enhance LR emergence, thus opening the infection gates in roots.