Defining the Xanthomonas euvesicatoria type II-secreted effector arsenal: core nutritional functions and effector diversity

The type II secretion (T2S) system is conserved across the Xanthomonas lineage, yet its contributions to pathogenicity and secreted protein repertoires are poorly defined. We demonstrate that T2S systems in Xanthomonas pathovars with divergent hosts and lifestyles are required for disease.

In planta quantification of cell wall compositional changes during infection by Xanthomonas euvesicatoria ( Xe ) revealed that T2S-dependent depletion of galacturonic acid occurs during host colonization, providing experimental evidence for T2 effector (T2E)-mediated cell wall remodeling.

Using an in planta label-free proteomics approach, we identified two known and 20 new Xe T2Es from tomato apoplast, many with annotated functions in polysaccharide and protein cleavage. Growth assays on plant cell wall extracts and purified substrates revealed T2S-mediated metabolization of plant cell wall polysaccharides and proteins not only by Xe , but also by Xanthomonas axonopodis pv. glycines ( Xag ) and Xanthomonas campestris pv. campestris ( Xcc ). Interestingly, comparative sequence analysis revealed that the T2E repertoires have diversified among these pathogens, with differences in protease repertoire being the most pronounced.

Our methodology establishes a framework for T2E discovery, enabling future functional dissection of this understudied effector class and its crosstalk with other bacterial virulence factors.