Virulence functions of xanthomonads

Bacteria belonging to the genus Xanthomonas cause diseases on a wide variety of plant species. They elaborate a number of virulence factors to successfully infect and cause disease on their hosts. These include surface polysaccharides, putative adhesins, various secretion systems and their effectors, toxins, functions involved in detoxification of host derived anti-microbial compounds, nutrient acquisition, etc. Over and above these are the regulatory functions that direct the expression of the various virulence factors. In addition, mutations in genes involved in the biosynthesis of certain amino acids and purines cause virulence deficiency, suggesting an inability to source these metabolites from the host. Some genes involved in sugar metabolism have been shown to be required for virulence, pointing towards the importance of these sugars as carbon sources during in planta growth. The genome sequences of several xanthomonads have been determined during the last few years. These studies have uncovered a number of candidate virulence functions whose role in virulence needs to be systematically analysed. A number of species and strain specific xanthomonad genes have also been identified, some of which may have a role in determining host range of the pathogens.