HrpG, A TRANSCRIPTIONAL REGULATOR OF PATHOGENICITY GENES DURING Xanthomonas citrus INTERACTION

FICARRA, FLORENCIA; GAROFALO, CECILIA G; GOTTIG, NATALIA; OTTADO, JORGELINA

Rosario

Congreso; IX Congreso de Microbiología General; 2013

Plant pathogens have evolved sophisticated molecular mechanisms to monitor the environment and to activate specific genes in order to invade and colonize their plant hosts. The interaction of the gram-negative bacterium Xanthomonas axonopodis pv. citri (hereafter Xac) with its host plant orange is controlled by hrp (hypersensitive reaction and pathogenicity) genes, some of which encode components of the type III protein secretion system. hrpG is a key regulatory gene and, together with hrpX, is responsible for transcriptional activation of hrp genes in Xac. HrpG is highly conserved among Xanthomonads and its C-terminal has conserved residues with members that belong to OmpR family. In this work we study the regulation of the expression of HrpG and its target genes during plant pathogen interaction. We found that HrpG represses its own expression, contributing to fine-tune HrpG levels, while activates hrpX and other hrp genes expression. We constructed an hrpG mutant which showed a typical hrp phenotype and no longer renders induction of hrp genes. Further, we identified a point mutation in hrpG sequence that allowed the interaction between HrpG with its target promoters, enabled the formation of homodimers and heterodimers with wild type HrpG but failed to complement Xac hrpG mutant phenotype. These results provide major insights into the elements that contribute to understand the mechanism of regulation of pathogenicity in Xanthomonas-citrus interaction.