Glutathione deficiency induces a pleiotropic response in Rhizobium tropici CIAT899.

MUGLIA, C. I.; LODEIRO, A.; AGUILAR, O. M.

San Carlos de Bariloche, Argentina

Congreso; ARGENTINE SOCIETY FOR BIOCHEMISTRY AND MOLECULAR BIOLOGY XXXIX ANNUAL MEETING; 2003

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Glutathione is involved in many cellular functions including stress tolerance. In the common bean symbiont R. tropici it is essential for protection against environmental stresses, such as acidity,salinity and oxidative stress. We have previously cloned the gshB R. tropici wild type gene (which encodes glutathione synthetase) and demonstrated that its transcription is transiently activated when shifted to acidic conditions. We have now mapped the transcription initiation of gshB gene by primer extension analysis, and found it to be located 71 bp upstream from the predicted start codon. Centered at position –40 we have found a palindromic sequence of the general form TTGN13CAA, similar to the TTGN11CAA palindromic sequence found in the Rhizobium etli, Sinorhizobium meliloti and Agrobacterium tumefaciens recA promotor, known as the SOS box. recA gene is activated in response to DNA damage,suggesting that gshB gene should be regulated by a SOS type response. We also show that catalase activation by oxidative stress is impaired in glutathione deficient mutant, which we propose occurs in an OxyR mediated manner. We have also studied the effects of glutathione deficiency in symbiosis. We have found that, although gshB deficient mutant is able to nodulate Phaseolus vulgaris, the resulting nodules are small and in a higher number compared to plants inoculated with the wild type. We have also found that bacterial glutathione is necessary to maintain an efficient symbiosis, since lack of rhizobial glutathione is associated to premature nodule senescence.