P-202 - Plant infections by Xanthomonas pathogens: a lense into tissue-specific virulence and immunity

Plant pathogenic bacteria have evolved specialized infection strategies to invade distinct host tissues, exploiting natural entry points such as stomata and hydathodes. While stomatal immunity has been extensively studied, hydathode-mediated infection remains less understood. Vascular Xanthomonas pathogens infect hydathodes to access the xylem veins and spread systemically causing disease in several crops, including cabbage. Here, to identify immune mechanisms in hydathodes, we screened natural accessions of Arabidopsis thaliana against Xanthomonas campestris pv. campestris (Xcc). Interestingly, we identified an immune receptor, SUPPRESSOR OF TOPP4 1 (SUT1), which restricts Xcc in hydathodes but is ineffective in the vasculature, highlighting tissue-specific immune specialization.

To further understand what enables Xcc to infect hydathodes and cause vascular disease, we applied comparative genomics between X. campestris pathovars. This revealed that vascular-adapted strains have undergone evolutionary shifts. We demonstrate a pivotal role of the type II secretion system and a set of four plant cell wall-degrading enzymes for Xcc to escape from hydathodes into the vascular system, suggesting a physical barrier that prevents systemic infections. Collectively, our data provides new insights into the molecular mechanisms underlying Xanthomonas tissue-specific virulence and plant immunity, emphasizing the evolutionary and functional adaptations that enable vascular pathogenesis.