Understanding the enzymatic system involved in the degradation and utilization of xyloglucans from the plant pathogen Xanthomonas axonopodis pv. citri

Abstract

The plant cell wall is mainly composed of cellulose, hemicellulose, pectin and lignin. Although the primary interest in the bioconversion of cellulose, the economic sustainability of the use of plant biomass depends, among other factors, on the development of new technologies for the use of hemicellulose, in which the xyloglucan is the most abundant in the majority of land plants. A number of microbial enzymes belonging to the superfamily of glycoside hydrolases (GHs) are involved in depolymerization of xyloglucan. Among the organisms that possess such GHs to infect and colonize plants, the genus Xanthomonas arouses great interest because its wide repertoire of these enzymes, which is comparable to that of filamentous fungi and other organisms specialized in plant biomass maceration. In these organisms, the genes encoding xyloglucanases are clustered in one operon and their possible biological roles and potential biotechnological uses have not been determined yet. The elucidation of the strategies used by microorganisms in the cell wall degradation is important not only for its potential use in the industry, but also to reveal their distinct molecular mechanisms adopted by nature in plant-pathogen interactions, still poorly understood. Therefore, the primary objective of this project is the mechanistic understanding of the constituent enzymes of this system from Xanthomonas axonopodis pv. citri (Xac) through a multidisciplinary approach involving X-ray crystallography, SAXS, spectroscopic techniques, enzymology, in vivo assays (knockout gene and RT-PCR) and recombinant DNA techniques (mutagenesis and chimerogenesis when applicable). (AU)