Lack of the Flavin-Containing Monooxygenase FmoA Partially Impairs the Symbiotic Interaction of Mesorhizobium Huakuii with Astragalus Sinicus

Background: Flavin-containing monooxygenases (FMOs) catalyze the NADPH-dependent N- or S- oxygenation of numerous foreign chemicals, and thus may mediate interactions between microorganisms and their chemical environment. The aim of this study was to investigate the role of FMO in symbiotic nitrogen fixation of Mesorhizobium huakuii and its host plant Astragalus sinicus.Results: A mutation in M. huakuii fmoA gene was generated by homologous recombination. The fmoA mutant grew more slowly than its parental strain, and displayed decreased antioxidative capacity under higher concentration of H2O2 and cumene hydroperoxide (CUOOH), indicating that FmoA plays an important role in response to the peroxides. The fmoA mutant strain displayed no difference of peroxidase activity and glutathione reductase activity, but significantly lower level of glutathione and hydrogen peroxide content than the wild type. Real-time quantitative PCR showed that the fmoA gene expression is significantly up-regulated in three different stages of nodule development. The fmoA mutant was severely impaired in its rhizosphere colonization, and its symbiotic properties in Astragalus sinicus were drastically affected. Transcriptomes in root-nodule bacteroids were analyzed and compared. A total of 1233 genes were differentially expressed, of which 560 were up-regulated and 673 were down-regulated in HKfmoA bacteroids compared with that in 7653R bacteroids. The transcriptomic data allowed us to determine additional target genes, whose differential expression was able to explain the observed the changes of symbiotic phenotype in the mutant-infected nodules.Conclusions: The fmoA gene is essential for antioxidant capacity and symbiotic nitrogen fixation. Furthermore, RNA-Seq based global transcriptomic analysis provided a comprehensive view of M. huakuii fmoA gene involved in nodule senescence and symbiotic nitrogen fixation.

Nodulation of Thermopsis lupinoides by a Mesorhizobium huakuii Strain with a UniquenodAGene in Kamtchatka, Russia

ABSTRACTVery little is known about rhizobia that form nodules onThermopsisspp. We report the isolation of aMesorhizobium huakuiistrain with a uniquenodAgene that form nodules onThermopsis lupinoidesin Kamtchatka, Russia. The isolate did not form nodules onThermopsis chinensisorThermopsis caroliniana, which suggests it may be host specific.