Enzymatic systems for carbohydrate utilization and biosynthesis in Xanthomonas and their role in pathogenesis and tissue specificity

Abstract

Xanthomonas plant pathogens can infect hundreds of agricultural plants. These bacteria exploit sophisticated molecular strategies based on multiple secretion systems and their associated virulence factors to overcome the plant defenses, including the physical barrier imposed by the plant cell walls and the innate immune system. Xanthomonads are equipped with a broad and diverse repertoire of Carbohydrate-Active enZymes (CAZymes), which besides enabling the utilization of complex plant carbohydrates as carbon and energy source, can also play pivotal roles in virulence and bacterial lifestyle in the host. CAZymes in xanthomonads are often organized in multienzymatic systems similar to the Polysaccharide Utilization Loci (PUL) from Bacteroidetes known as CUT systems (from Carbohydrate Utilization systems associated with TonB-dependent transporters). Xanthomonas bacteria are also recognized to synthesize distinct exopolysaccharides including xanthan gum and untapped exopolysaccharides associated with biofilm formation. Here, we summarize the current knowledge on the multifaceted roles of CAZymes in xanthomonads, connecting their function with pathogenicity and tissue specificity.

Plant structural and storage glucans trigger distinct transcriptional responses that modulate the motility of Xanthomonas pathogens

“…Most pathogenic xanthomonads conserve genes encoding putative endo-β-1,4-glucanases and β-glucosidases as well as amylases and α-glucosidases, indicating their capacity to break down and utilize cellulose and starch ( 8 ). In particular, genes related to starch depolymerization usually colocalize with genes encoding for TonB-dependent transporters (TBDT) ( 9 ) and such genomic organization is known as carbohydrate utilization containing TBDT ( 10 ) systems in xanthomonads and as polysaccharide utilization loci ( 11 ) in the phylum Bacteroidota .…”