Hydrogen Sulfide Promotes Nodulation and Nitrogen Fixation in Soybean-Rhizobia Symbiotic System

The rhizobium-legume symbiotic system is crucial for nitrogen cycle balance in agriculture. Hydrogen sulfide (H S), a gaseous signaling molecule, may regulate various physiological processes in plants. However, whether H S has regulatory effect in this symbiotic system remains unknown. Herein, we investigated the possible role of H S in the symbiosis between soybean ( ) and rhizobium ( ). Our results demonstrated that an exogenous H S donor (sodium hydrosulfide [NaHS]) treatment promoted soybean growth, nodulation, and nitrogenase (Nase) activity. Western blotting analysis revealed that the abundance of Nase component nifH was increased by NaHS treatment in nodules. Quantitative real-time polymerase chain reaction data showed that NaHS treatment upregulated the expressions of symbiosis-related genes , , and of . In addition, expression of soybean nodulation marker genes, including early nodulin 40 ( ), ERF required for nodulation ( ), nodulation signaling pathway 2b ( ), and nodulation inception genes ( , , and ), were upregulated. Moreover, the expressions of glutamate synthase ( ), asparagine synthase ( ), nitrite reductase ( ), ammonia transporter ( ), leghemoglobin ( ), and involved in nitrogen metabolism were upregulated in NaHS-treated soybean roots and nodules. Together, our results suggested that H S may act as a positive signaling molecule in the soybean-rhizobia symbiotic system and enhance the system's nitrogen fixation ability.