Functional Characterization of the Xanthomonas axonopodis pv citri Chromosomal Type IV Secretion System

• Grant number: 11/11472-5
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: October 01, 2011
• End date: March 31, 2013
• Field of knowledge: Biological Sciences - Genetics - Molecular Genetics and Genetics of Microorganisms
• Principal Investigator: Shaker Chuck Farah
• Grantee: Cristina Elisa Alvarez Martinez
• Host Institution: Instituto de Química (IQ). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Bacterial type IV secretion systems (T4SS) are protein complexes that span the cell envelope and mediate the translocation of DNA and protein substrates directly to target cells or to the extracellular milieu. Members of this family of secretion machines are responsible for the process of conjugation and/or also play an essential role in pathogenesis in several bacterial species. The bacterium Xanthomonas axonopodis pv citri (Xac) is the causative agent of citrus canker on a wide variety of citrus cultivars, resulting in significant losses to the agriculture in Brazil. Despite its economical importance, the mechanisms used by this bacterium to promote virulence are largely unknown. The genome of Xac encodes two T4SS, one located in the chromosome and a second one in the resident plasmid pXAC64. This project will use bacterial genetics and molecular biology approaches to functionally characterize the T4SS found in the chromosome of Xac. For that, the expression of this T4SS will be analyzed under distinct growth conditions and during growth in planta. Also, a protein translocation assay will be developed to test the secretion of putative substrates of the chromossomal T4SS directly to target cells. The phenotypes of mutant strains in this T4SS will be characterized for distinct aspects, including plant colonization, virulence, resistance to environmental stresses, motility and biofilm formation. These studies will provide important clues about the physiology and the molecular mechanisms of pathogenesis in this phytopathogenic bacterium.