An infection assay recapitulating Xanthomonas translucens pv. translucens natural entry into barley hydathodes

Pathogenic bacteria navigate biological host landscapes to enter and establish infection. How Xanthomonas phytopathogenic bacteria enter specific plant tissues is believed to directly determine the systemic vs. local outcome of infection. Non-vascular Xanthomonas infect leaf mesophyll locally from stomatal pores, while vascular ones enter through hydathode water pores on the leaf margin before invading the xylem for systemic movement. The pathovar Xanthomonas translucens pv. translucens (Xtt) is associated with barley infection, causing both bacterial leaf streak and bacterial blight symptoms by colonizing both the mesophyll spaces through stomatal guard cells and the plant vasculature, respectively. How Xtt reaches the vasculature in barley leaves is yet to be established. In this study, we determined the anatomy of barley hydathodes. A protocol allowing efficient hydathode infection by Xtt was established and caused bacterial blight symptoms, closely mimicking the natural infection process. This study establishes Xtt as one of the few demonstrated hydathode pathogens.