XopAC-triggered vascular immunity in plants – XOPAQUE

Type III secretion (T3S) systems found in Gram-negative bacterial pathogens of plants and animals deliver type III effector/virulence (T3E) proteins directly in the plant/animal cells where they interfere with immunity and contribute to establish favourable conditions for pathogen growth. Identifying and characterizing the effectors and their virulence targets is a major scientific challenge because it enables the identification of key components of plant immunity and provides valuable tools to study/manipulate fundamental processes of plant physiology in general (eg. gene silencing, protein post-translational modifications (PTM), cell death regulation, gene transcription,…).
Our group focuses on the dissection of infection strategies of Gram-negative phytopathogenic bacteria of the Xanthomonas family because of their economic importance and their broad host range and multiple virulence strategies. We particularly focus our studies on Xanthomonas campestris pv. campestris (Xcc), the causal agent of black rot on crucifers such as cabbage and the model plant Arabidopsis.
This proposal will be focussed on XopAC T3E because of its original features: (i) It is specific to Xcc, (ii) it contributes to aggressiveness and host range determination in Xcc (iii) it likely possesses adenylylation activity, a yet unknown protein PTM in plants and (iv) it specifically triggers vascular effector-triggered immunity in Arabidopsis vasculature.
Our studies are designed to identify XopAC direct virulence targets in planta and components of the xopAC-triggered immunity in the vascular system. Our experimental program has been organized into three work packages: (i) Structure/function analysis of XopAC to study the biological importance of xopAC in Xcc aggressiveness and the contribution of its domains to these functions. (ii) Biochemical identification of direct plant targets of XopAC which either interact with XopAC or are modified by the adenylylation activity of XopAC. In particular, we will address the existence and biological importance of adenylylation in planta which existence and functions in plants was still unsuspected few months ago. (iii) Identification of plant genetic interactors of xopAC which could encode direct or indirect interactors of the effector and signalling element of the xopAC triggered immunity in the vasculature.
Vascular immunity has hardly been studied so far and many devastating diseases are caused by bacterial or fungal diseases which enter the plant and spread trough its vascular system. We believe that manipulating vascular immunity at early steps of infection could be a very effective defence strategy, as exemplified by the xopAC-triggered immunity against Xanthomonas.