The Xa7 resistance gene guards the rice susceptibility gene SWEET14 against exploitation by the bacterial blight pathogen

Many plant disease resistance (R) genes function specifically in reaction to the presence of cognate effectors from a pathogen. Xanthomonas oryzae pathovar oryzae (Xoo) uses transcription activator-like effectors (TALes) to target specific rice genes for expression, thereby promoting host susceptibility to bacterial blight. Here, we report the molecular characterization of Xa7, the cognate R gene to the TALes AvrXa7 and PthXo3, which target the rice major susceptibility gene SWEET14. Xa7 was mapped to a unique 74-kb region. Gene expression analysis of the region revealed a candidate gene that contained a putative AvrXa7 effector binding element (EBE) in its promoter and encoded a 113-amino-acid peptide of unknown function. Genome editing at the Xa7 locus rendered the plants susceptible to avrXa7-carrying Xoo strains. Both AvrXa7 and PthXo3 activated a GUS reporter gene fused with the EBE-containing Xa7 promoter in Nicotiana benthamiana. The EBE of Xa7 is a close mimic of the EBE of SWEET14 for TALe-induced disease susceptibility. Ectopic expression of Xa7 triggers cell death in N. benthamiana. Xa7 is prevalent in indica rice accessions from 3000 rice genomes. Xa7 appears to be an adaptation that protects against pathogen exploitation of SWEET14 and disease susceptibility.