DisplayTitle

<div>Hydathodes are water pores found on leaves of a wide range of vascular plants and are the sites of guttation. They are found in direct contact with vascular discontinuities and represent one of the entry pathways for vascular pathogens. <i>Xanthomonas campestris </i>pv. <i>campestris </i>(<i>Xcc</i>), an epiphytic bacterium, is able to naturally enter inside hydathodes and spread within plants xylem, causing black rot disease of <i>Brassicaceae</i>. <i>Xcc</i> infects economically important crops such as cabbage but also the model plant <i>Arabidopsis thaliana</i>. Understanding bacterial behavior at hydathodes and immune responses in this tissue is essential to design knowledge-informed control strategies against this pathogen. We report here the detailed anatomy of cauliflower and Arabidopsis hydathodes and describe their infection by <i>Xcc</i>, thus recapitulating natural infection and black rot disease symptoms. Pre-invasive immune mechanisms were investigated by studying the ability of hydathode pores to respond to stimuli such as ABA, light or the flg22 flagellin peptide, a well-characterized elicitor of plant basal immunity. Results showed that hydathode pores respond to ABA and light but not to flg22. Post-invasive immunity was shown to limit pathogen growth in the epithem and is actively suppressed by the type III secretion system and its effector proteins. Altogether, these results give a detailed anatomic description of <i>Brassicaceae</i> hydathodes and advance our understanding of hydathode immunity.</div>