A pectase lyase that is an indirect target of a Xanthomonas TAL effector promotes susceptibility

One of the many ways that Xanthomonas bacteria manipulate their host plants is by the production of transcription activator-like (TAL) effectors, which the bacterium introduces into the host cell where they alter gene expression in the host nucleus. Schwartz et al. investigated the targets of the TAL effector AvrHah1 produced by the pathogen Xanthomonas gardneri by comparing transcriptomes of plants infected with bacteria producing the effector versus those not producing the effector. Two genes encoding bHLH transcription factors were found to be direct targets of the TAL effector, and a gene encoding a pectate lyase was found to be a target of those bHLH factors. Pectate lyase activity promotes water uptake in the apoplast, presumably through cell wall modification. As water-soaked lesions are a symptom of Xanthomonas infection and thought to contribute to an environment suitable for pathogenesis, this study links the bacterial effector with a susceptibility gene.  Proc. Natl. Acad. Sci. USA    10.1073/pnas.1620407114