Antioxidation and symbiotic nitrogen fixation function of prxA gene in Mesorhizobium huakuii

Abstract

Peroxiredoxins (Prxs) play an essential role in the antioxidant activity and symbiotic capacity of Mesorhizobium huakuii. A mutation in the M. huakuii prxA gene (encoding a Prx5‐like peroxiredoxin) was generated by homologous recombination. The mutation of prxA did not affect M. huakuii growth, but the strain displayed decreased antioxidative capacity under organic cumene hydroperoxide (CUOOH) conditions. The higher resistance of the prxA mutant strain compared with the wild‐type strain to more than 1 mmol/L H2O2 was associated with a significantly higher level of glutathione reductase activity and a significantly lower level of intracellular hydrogen peroxide content. Real‐time quantitative PCR showed that under 1 mmol/L H2O2 conditions, expression of the stress‐responsive genes katG and katE was significantly upregulated in the prxA mutant. Although the prxA mutant can form nodules, the symbiotic ability was severely impaired, which led to an abnormal nodulation phenotype coupled to a 53.25% reduction in nitrogen fixation capacity. This phenotype was linked to an absence of bacteroid differentiation and deregulation of the transcription of the symbiotic genes nifH, nifD, and fdxN. Expression of the prxA gene was induced during symbiosis. Thus, the PrxA protein is essential for antioxidant capacity and symbiotic nitrogen fixation, playing independent roles in bacterial differentiation and cellular antioxidative systems.

Rhizobium leguminosarum Glutathione Peroxidase Is Essential for Oxidative Stress Resistance and Efficient Nodulation

“…For the dry weight plants were placed in 2 L beaker containing sterile vermiculite, watered with distilled nitrogen-free Fahraeus solution and harvested at 7 weeks from planting. The shoot was removed from the root and dried at 70°C in a warm incubator for 72 h ( Wang et al, 2019 ). Nitrogenase activity of nodules at flowering (4 weeks) was assessed by acetylene reduction assay according to the method described previously ( Allaway et al, 2000 ).…”

Redox Regulation in Diazotrophic Bacteria in Interaction with Plants

“…In Mezorhizobium huakii/A. sinikus interaction, the peroxiredoxin PrxA is important for symbiosis as a prxA mutant elicits spherical nodules displaying a considerable reduction of nitrogen fixation activity associated with bacteria that fail to differentiate [68]. Besides, R. etli contains both a catalase KatG and a 2-cys peroxiredoxin PrxS, whose inactivation gives no phenotype [67,104].…”