Xanthomonas translucens directly induces abscisic acid biosynthesis to enhance disease susceptibility in wheat. Triticum aestivum

Plants are vulnerable to disease through pathogen manipulation of phytohormone levels, which regulate development and defense pathways. Here, we show that the bacterial wheat pathogen Xanthomonas translucens pv. undulosa, through use of a type III transcription activation-like (TAL) effector, elevates expression of a host gene, TaNCED_5BS, encoding nine-cis-epoxycarotenoid dioxygenase which catalyzes the rate-limiting step in the biosynthesis of the phytohormone abscisic acid (ABA). The induction of TaNCED_5BS results in elevated ABA levels, reduced transpiration and water loss, and enhanced bacterial growth in leaves. Low virulence field strains of the pathogen lack the effector, and introduction of TaNCED_5BS cognate TAL effectors into a low-virulence field strain resulted in elevated TaNCED_5BS expression and enhanced virulence. The results support a hypothesis that X. translucens pv. undulosa strains gain virulence by directly targeting ABA biosynthesis and illustrate the adaptive versatility of TAL effector deployment, suggestive of the appearance of TAL effectors affecting the ABA pathway in other Xanthomonas-related diseases due to the conserved function of ABA function in plants.