Describing the roles of the Type 6 Secretion System in Xanthomonas citri subsp citri physiology: a gene expression analysis approach

Describing the roles of the Type 6 Secretion System in Xanthomonas citri subsp citri physiology: a gene expression analysis approach Lucas de Moraes Ceseti (IC), Lidia dos Passos Lima (PG), Cristina Elisa Alv arez-Martinez (PQ) Abstract The phytopathogen Xanthomonas citri subsp citri (Xac) is responsible for big economic losses in agriculture. Several important processes to bacteria’s survival are mediated by the translocation of macromolecules to the extracellular milieu or to the target cells. The type 6 Secretion System (T6SS) is a recently described mechanism to secrete proteins and is usually associated to interbacterial competition, but in Xac this function is known to be dependent of another type of secretion system, the type 4 (T4SS). In this work, we have analyzed the gene expression patterns of some T6SS core protein genes during epiphytic growth and infection process in Xac in order to gain further insights in T6SS function in this bacterium. Our results show that these genes are induced during epiphytic growth but tightly repressed when Xac is growing inside plant leaf tissue and promoting the disease. These results demonstrate that the T6SS is not involved in pathogenesis, but may be required in some important aspects of Xac lifestyle, such as biofilm formation, adhesion to biotic surfaces/or interbacterial competition.