MeMLO12 impairs cassava resistance to Xanthomonas axonopodis pv. manihotis by repressing ROS, callose deposition, and defense hormone pathways

Cassava (Manihot esculenta Crantz) is a vital food and energy crop in tropical regions, yet its yield is significantly threatened by cassava bacterial blight (CBB), caused by Xanthomonas axonopodis pv. manihotis (Xpm). Mildew resistance locus O (MLO) genes are known negative regulators of plant immunity, but their roles in cassava disease susceptibility remain unclear. In this study, we identified the MeMLO12 gene from cassava and investigated its function in response to Xpm infection. Subcellular localization revealed that MeMLO12 is specifically localized in the nucleus. Functional analysis via transient overexpression and virus-induced gene silencing (VIGS) demonstrated that MeMLO12 suppresses disease resistance: overexpression enhanced susceptibility to Xpm, while silencing conferred resistance. Furthermore, MeMLO12 modulated the expression of genes involved in jasmonic acid (JA) and salicylic acid (SA) signalling pathways, as well as reactive oxygen species (ROS) production and callose deposition, which are key components of plant innate immunity. These findings indicate that MeMLO12 acts as a susceptibility factor in cassava and may serve as a potential target for breeding bacterial blight-resistant varieties.