Molecular basis of carbohydrate degradation and utilization systems from the phytopathogen "Xanthomonas citri" pv. "citri"

This work has been divided into five chapters.The Chapter 1 contains a general introduction about the complex structure and composition of the plant cell wall, the basic structure of bacterial systems for polysaccharide utilization reported so far, an overview of the key pathogenicity factors of Xanthomonas spp., and the biological and biotechnological relevance of CAZymes.Chapter 2 presents a manuscript (in preparation) compiling the results of a genome-wide transcriptomic analysis showing the global gene expression profile of X. citri in response to several plant carbohydrates, unraveling the systems dedicated to the degradation and uptake of β-glucans, heteroxylans, galactomannan and starch, as well the role of their degradation products on modulating several aspects of the bacterial physiology, such as the transition between sessile and motile states.The Chapter 3 displays a manuscript 1 in which this work contributed on revealing how the products of xyloglucan hydrolysis can activate the expression of a key virulence factor of Xanthomonas spp.: the type III secretion system (T3SS).The Chapter 4 presents a manuscript (in preparation) about the biochemical characterization and main structural features of the β-mannanase XagD, which belongs to a cluster of biosynthesis of exopolysaccharide (EPS), providing clues for the unknown structure of the Xag-EPS and expanding the knowledge of the untapped GH113 family.