Interactions between hydrogen sulphide and rhizobia modulate the physiological and metabolism process during water deficiency-induced oxidative defense in soybean.

Hydrogen sulphide (H 2 S), a new gas signal molecule, participates in the regulation of various abiotic stresses in plants. However, how the tandem working of H 2 S and rhizobia affects the adaptation of soybean to water deficiency is still unclear. In this study, we investigated the adaptation mechanism of H 2 S and rhizobia in soybean to water deficiency. Our results revealed that H 2 S and rhizobia jointly enhanced the leaf chlorophyll content and relative water content in plants, and caused an increase in the biomass of soybean seedlings under water deficiency. Besides, in the absence of water, H 2 S enhanced the biomass by affecting the number of nodules and nitrogenase activity during vegetative growth. The expression of nodulation marker genes including early nodulin 40 (GmENOD40), ERF required for nodulation (GmERN) and nodulation inception genes (GmNIN1a, GmNIN2a and GmNIN2b) were upregulated by H 2 S and rhizobia in the nodules. Moreover, the combined effect of H 2 S and rhizobia was proved to affect the enzyme activities and gene expression level of antioxidants, as well as osmotic protective substance content and related gene expression levels under water deficiency in soybean seedlings. In addition, the metabolomic results suggested that the combined effect of H 2 S and rhizobia remarkably promoted the contents of lipids and lipid-like molecules. Our results indicated that H 2 S and rhizobia synergistically reduced the oxidative damage caused by water deficiency through increasing the accumulation of metabolites and strengthening the plant antioxidant capacity.