Xanthomonas axonopodis Virulence Is Promoted by a Transcription Activator-Like Effector Mediated Induction of a SWEET Sugar Transporter in Cassava

The gene-for-gene concept has historically been applied to describe a specific resistance interaction wherein single genes from the host and the pathogen dictate the outcome. These interactions have been observed across the plant kingdom and all known plant microbial pathogens. In recent years, this concept has been extended to susceptibility phenotypes in the context of transcription activator-like (TAL) effectors that target SWEET sugar transporters. However, because this interaction has only been observed in rice, it was not clear whether the gene-for-gene susceptibility was unique to that system. Here, we show, through a combined systematic analysis of the TAL effector complement of Xanthomonas axonopodis pv. manihotis and RNA sequencing to identify targets in cassava, that TAL20(Xam668) specifically induces the sugar transporter MeSWEET10a to promote virulence. Designer TAL effectors (dTALE) complement TAL20(Xam668),668 mutant phenotypes, demonstrating that MeSWEET10a is a susceptibility gene in cassava. Sucrose uptake deficient X. axonopodis pv. manihotis bacteria do not lose virulence, indicating that sucrose may be cleaved extracellularly and taken up as hexoses into X. axonopodis pv. manihotis. Together, our data suggest that pathogen hijacking of plant nutrients is not unique to rice blight but also plays a role in bacterial blight of the dicot cassava.