RXam2, a NLR from cassava (Manihot esculenta) contributes partially to the quantitative resistance to Xanthomonas phaseoli pv. manihotis

Key message The overexpression of RXam2, a cassava NLR (nucleotide-binding leucine-rich repeat) gene, by stable transformation and gene expression induction mediated by dTALEs, reduce cassava bacterial blight symptoms. Cassava ( Manihot esculenta ) is a tropical root crop affected by different pathogens including Xanthomonas phaseoli pv. manihotis ( Xpm ), the causal agent of cassava bacterial blight (CBB). Previous studies have reported resistance to CBB as a quantitative and polygenic character. This study sought to validate the functional role of a NLR (nucleotide-binding leucine-rich repeat) associated with a QTL to Xpm strain CIO151 called RXam2. Transgenic cassava plants overexpressing RXam2 were generated and analyzed. Plants overexpressing RXam2 showed a reduction in bacterial growth to Xpm strains CIO151, 232 and 226. In addition, designer TALEs (dTALEs) were developed to specifically bind to the RXam2 promoter region. The Xpm strain transformed with dTALEs allowed the induction of the RXam2 gene expression after inoculation in cassava plants and was associated with a diminution in CBB symptoms. These findings suggest that RXam2 contributes to the understanding of the molecular basis of quantitative disease resistance.