Studies of the molecular basis of mannan degradation and utilization system from the phytopathogen Xanthomonas axonopodis pv. citri

Abstract

Plant cell wall consists of a complex and dynamic structure composed essentially by cellulose, hemicellulose, lignin and pectins. The deconstruction of the vegetal fiber by chemical or enzymatic hydrolysis releases fermentable sugars, which can be used in the production of biofuels or compounds with higher added value. However, the use of plant biomass still requires both a better understanding of its molecular architecture and the development of more efficient technologies for its depolymerization. Several enzymes produced by microorganisms are key components in this process, such as Glycosyl Hydrolases (GHs). Nevertheless, the functional and mechanistic diversity of these enzymes is still poorly understood; of the more than 300,000 proteins classified as GHs in the CAZy database, only 2% were biochemically characterized and still less from the structural point of view. In some species that present a large repertoire of GHs, such as the phytopathogenic bacteria of the genus Xanthomonas, the biological role of these enzymes as well as their molecular adaptations that contribute to mediate plant-pathogen interactions are poorly understood, in particular those related to degradation of hemicelluloses, such as mannan. The genome of these bacteria has gene clusters that encode enzymes potentially related to mannan degradation including ²-mannanases, ²-glycosidases, ²-mannosidases and ±-galactosidases. Such enzymes, although with potential industrial application and probable relevance for the pathogenicity of Xanthomonas spp., have not yet been characterized. Therefore, the aim of this project is the enzymatic, functional and structural characterization of enzymes involved in the mannan degradation pathway of the phytopathogen Xanthomonas axonopodis pv. citri, responsible for causing citrus canker in plants, a disease of great economic importance in Citriculture. (AU)