Xanthomonas type III effector XopD targets SUMO‐conjugated proteins in planta

Summary Xanthomonas campestris pathovar vesicatoria (Xcv) uses the type III secretion system (TTSS) to inject effector proteins into cells of Solanaceous plants during pathogenesis. A number of Xcv TTSS effectors have been identified; however, their function in planta remains elusive. Here, we provide direct evidence for a functional role for a phytopathogenic bacterial TTSS effector in planta by demonstrating that the Xcv effector XopD encodes an active cysteine protease with plant‐specific SUMO substrate specificity. XopD is injected into plant cells by the TTSS during Xcv pathogenesis, translocated to subnuclear foci and hydrolyses SUMO‐conjugated proteins in vivo. Our studies suggest that XopD mimics endogenous plant SUMO isopeptidases to interfere with the regulation of host proteins during Xcv infection.