Hydrogen sulfide promotes nodulation and nitrogen fixation in soybean-rhizobia symbiotic system

Abstract

The rhizobium-legume symbiotic system is crucial for nitrogen cycle balance in agriculture. Hydrogen sulfide (H₂S), a gaseous signaling molecule, may regulate various physiological processes in plants. However, whether H₂S has regulatory effect in this symbiotic system remains unknown. Herein, we investigated the possible role of H₂S in the symbiosis between soybean (Glycine max) and rhizobium (Sinorhizobium fredii). Our results demonstrated that exogenous H₂S donor (sodium hydrosulfide, NaHS) treatment promoted soybean growth, nodulation and nitrogenase (Nase) activity. Western blotting analysis revealed that the abundance of nitrogenase component nifH was increased by NaHS treatment in nodules. Quantitative real-time PCR data showed that NaHS treatment up-regulated the expressions of symbiosis-related genes nodC and nodD of S. fredii. Besides, expression of soybean nodulation marker genes including early nodulin 40 (GmENOD40), ERF required for nodulation (GmERN), nodulation signaling pathway2b (GmNSP2b) and nodulation inception genes (GmNIN1a, GmNIN2a and GmNIN2b) were up-regulated. Moreover, the expressions of glutamate synthase (GmGS), nitrite reductase (GmNiR), ammonia transporter (GmSAT1), and nifH involved in nitrogen metabolism were up-regulated in NaHS-treated soybean roots and nodules. Together, our results suggested that H₂S may act as a positive signaling molecule in soybean-rhizobia symbiotic system and enhance their nitrogen fixation ability.