By Hijacking a Host Chaperone, the Bacterial Effector XopAE Disarms Cassava Immunity

Cassava (Manihot esculenta Crantz) is a vital staple crop for over 800 million people, particularly across sub-Saharan Africa, Asia, and Latin America.It plays a role as a subsistence crop and a commercial commodity, contributing significantly to food security and rural livelihoods (Zrate-Chaves et al. 2021).Despite its importance, cassava production is severely threatened by cassava bacterial blight, the most devastating bacterial disease affecting this crop.Cassava bacterial blight is caused by Xanthomonas phaseoli pv.manihotis (Xpm), a vascular pathogen capable of inducing severe yield losses ranging from 30 to 100% under favorable environmental conditions (Zrate-Chaves et al. 2021).Xpm enters cassava plants primarily through stomata, hydathodes, or wounds, subsequently colonizing the vascular tissue and spreading systemically.Typical disease symptoms include angular leaf spots, stem cankers, exudation of bacterial gum, leaf wilting, and plant death (Zrate-Chaves et al. 2021).Research has traditionally focused on the population structure and epidemiology of Xpm (Arrieta-Ortiz et al. 2013; Bernal-Galeano et al. 2018; Botero et al. 2020), but there remains a critical knowledge gap on the molecular mechanisms of Xpm virulence, particularly the role of type III effectors in subverting host immunity.Plant pathogens such as Xpm deploy type III secretion systems to translocate effector proteins into host cells.These type III effectors manipulate host cellular processes to suppress immunity and facilitate infection.In this issue of Molecular Plant-Microbe Interactions, Gmez De La Cruz et al. (2025) present the functional characterization of a native Xpm effector, XopAE, using both homologous and heterologous systems.The researchers first used a Pseudomonas fluorescens type III secretion system to deliver XopAE into the model plants Arabidopsis thaliana and Nicotiana tabacum and observed that XopAE suppresses pattern-triggered immunity (PTI), a frontline defense pathway that detects microbial patterns and activates immune responses, such as callose deposition and reactive oxygen species production.Importantly, XopAE did not interfere with effector-