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Poster

Session: Session 1 Presenting Authors at Posters (Odds)

P-225 - Water availability in leaves defines the ecological niche and proliferation of Xanthomonas

Monday, July 14, 2025
13:30 - 15:15  
Location: Confex Hall 3
Microbial infection strategies (pathogens & non-pathogens)

Plants have developed complex immune responses able of restricting the proliferation of most microbes they encounter. In the case of pathogenic microbes, disease symptoms are often linked to the formation of water-soaked lesions, resulting from the accumulation of water in the apoplast. While it is well established that humidity is a key factor in plant disease development, the molecular mechanisms behind this phenomenon remain largely unknown. Recent studies highlight the role of the pathogenic bacterium Pseudomonas syringae in manipulating water availability within the apoplast, suggesting that water may be a direct effector of plant immunity. In this work, we explore the potential link between water availability and plant immunity using the vascular pathogenic bacterium Xanthomonas campestris pv. campestris (Xcc) which infects hydathodes of Brassicaceae plants. We identified Arabidopsis mutant plants affected in their leaf development which exhibit higher levels of apoplastic water and support enhanced proliferation of Xcc within the mesophyll. In those mutants, Xcc gained the capacity to establish infection from stomata. Mechanically blocking guttation recapitulated the phenotypes, i.e. caused both watersoaking and increased proliferation of Xcc in both Arabidopsis and cauliflower. These results raise several key questions: Is water accessibility in the apoplast a key effector of plant immunity? Can Xcc favour high-humidity conditions to promote its proliferation?