Expression profiles of catalase genes in the phytopathogen Xanthomonas axonopodis pv. citri

TONDO, M. LAURA; OTTADO, JORGELINA; ORELLANO, ELENA G.

Carlos Paz, Córdoba, Argentina

Congreso; XLIV Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB); 2008

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB)

Xanthomonas axonopodis pv. citri (Xac) is a Gram-negative obligate aerobic bacterium that infects citrus plants. Pathogenic bacteria are usually exposed to H2O2 produced either by normal aerobic metabolism or as a part of the plant defense response against microbial invasion. In order to survive and colonize plant tissues Xac must overcome H2O2 toxicity, and catalases are enzymes employed for its detoxification. We determined Xac catalase activity in different growth phases and observed that it was higher in stationary-phase compared to early-exponential phase. This was consistent with the capacity of cultures to resist H2O2. Semi-quantitative RT-PCR analysis showed that three catalase genes are expressed in Xac during growth in rich media. The genes srpA and katG are expressed throughout all phases of growth whereas katE transcripts are only detected as cells enter the stationary phase. We also analyzed the expression profiles of catalase genes in Xac cultures grown in standard media and in XVM2, suspected to mimic the environment of plant intercellular spaces. We found that mRNA levels of katE are significantly higher in XVM2, which could account for the higher catalase activity previously observed in this media. Our results suggest that KatE may be the major catalase induced in Xac in starvation conditions and in the environment found during plant-pathogen interactions.