Greenhouse gas emission from the soybean rhizosphere is mitigated by promoting nitrous oxide reductase activity in bradyrhizobia

抄録

Nitrous oxide (N₂O) is a potent greenhouse gas and the predominant ozone depleting substance. The soybean rhizosphere is a site of active nitrogen (N) transformations, including those involving N₂O. Processes that produce N₂O occur in the soybean rhizosphere during the transformation of organic N inside the nodules to mineral N and then N₂O is either emitted to the atmosphere or further reduced to N₂ by N₂O reductase (N₂OR), which is encoded by the nos gene of soybean bradyrhizobia. Mutants of Bradyrhizobium diazoefficiens USDA110 with higher N₂OR activity (Nos⁺⁺ strains) than wild strains were generated under N₂O respiration by a mutator strategy. Emission of N₂O from soybean ecosystems was mitigated at the field scale by inoculation of soybean with Nos⁺⁺ strains of B. diazoefficiens. Comparative analysis of the Nos⁺⁺ mutant genomes showed that mutation of nasS gene encoding the NO₃⁻ sensor (NasS) of the two-component NasST regulatory system, induces N₂OR activity. Further studies showed that NasS and NasT form a complex that dissociates in the presence of NO₃⁻. Once dissociated, the anti-terminator NasT is able to interact with the 5′-leader region of nosR mRNA to interfere with the formation of a terminator structure and facilitate read-through transcription to induce nos expression. This knowledge improves our understanding of N-cycle biology in the legume rhizosphere and presents better options for global mitigation of N₂O emission from soils.