Deciphering small molecules as virulence factors by the bacterial sugarcane pathogen Xanthomonas albilineans (ALBILINEANS)

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In order to successfully colonize plants, plant pathogenic bacteria have evolved a variety of virulence factors to subvert host defences or to obtain nutrients. The understanding of the pathogenicity of these processes is of particular importance for all crop plants, since they cause enormous economic losses. Both fungal and bacterial pathogens produce secondary metabolites that play a role in plant disease. Xanthomonas albilineans (Xa) is a systemic, xylem-invading pathogen that causes leaf scald disease of sugarcane (Saccharum interspecific hybrids). The Xa-sugarcane pathosystem is an original model in plant pathology because: (i) Xa is constrained within the xylem, but disease symptoms result from changes in chlorenchyma cells; (ii) the Xa infection can be latent for many weeks or months before occurrence of acute disease; (iii) Xa produces albicidin, a unique and specific toxin that causes foliar leaf scald symptoms. Albicidin is a gyrase inhibitor and might constitute a lead structure for a novel and potent antibiotic. The genome of Xa contains 12 large unique genes with a modular architecture characteristic of NRPSs clustered in four genomic regions covering 4% of the whole genome. One of these genomic regions corresponds to previously identified albicidin biosynthesis gene cluster. In addition, our recent functional analyses strongly suggest the three other NRPS genomic regions also being involved in the pathogenicity of X. albilineans.