Glutathione is Involved in Detoxification of Peroxide and Root Nodule Symbiosis of Mesorhizobium huakuii.

Legumes interact with symbiotic rhizobia to produce nitrogen-fixation root nodules under nitrogen-limiting conditions. The contribution of glutathione (GSH) to this symbiosis and anti-oxidative damage was investigated using the M. huakuii gshB (encoding GSH synthetase) mutant. The gshB mutant grew poorly with different monosaccharides, including glucose, sucrose, fructose, maltose, or mannitol, as sole sources of carbon. The antioxidative capacity of gshB mutant was significantly decreased by these treatments with H2O2 under the lower concentrations and cumene hydroperoxide (CUOOH) under the higher concentrations, indicating that GSH plays different roles in response to organic peroxide and inorganic peroxide. The gshB mutant strain displayed no difference in catalase activity, but significantly lower levels of the peroxidase activity and the glutathione reductase activity than the wild type. The same level of catalase activity could be associated with upregulation of the transcriptional activity of the catalase genes under H2O2-induced conditions. The nodules infected by the gshB mutant were severely impaired in abnormal nodules, and showed a nodulation phenotype coupled to a 60% reduction in the nitrogen fixation capacity. A 20-fold decrease in the expression of two nitrogenase genes, nifH and nifD, is observed in the nodules induced by gshB mutant strain. The symbiotic deficiencies were linked to bacteroid early senescence.