Interfamily transfer of Bs2 from pepper to cassava (Manihot esculenta Crantz)

Cassava (Manihot esculenta Crantz) is the principal source of calories among root and tuber crops in tropical countries. Cassava bacterial blight (CBB) caused by Xanthomonas axonopodis pv. manihotis (Xam) is the most prevalent bacterial disease in cassava. Genome and mutagenesis analysis of Xam strains has led to the identification of an effector similar to avrBs2 from Xanthomonas euvesicatoria among a core set effectors contributing to Xam virulence. Previous studies have demonstrated that transgenic tomato plants expressing Bs2, the AvrBs2 cognate resistance protein from pepper, are resistant to Xanthomonas euvesicatoria. According to avrBs2 wide distribution and important contribution to Xam virulence, we aimed at overexpressing Bs2 in cassava plants as a strategy to control CBB. The susceptible cultivar 60444 was transformed with the Bs2 gene from pepper and transgenic cassava plants that functionally express Bs2 were regenerated. Our results show that overexpression of Bs2 in a highly susceptible cultivar leads to reactive oxygen species production. However, the overexpression of Bs2 neither leads to an HR in cassava nor reduces Xam growth on in vitro plants. These results suggest that BS2 activates defense-signaling pathways in cassava such as ROS production, although this is not sufficient to restrict Xam growth.