Sinorhizobium meliloti Glutathione Reductase Is Required for both Redox Homeostasis and Symbiosis

Abstract

Glutathione (l-γ-glutamyl-l-cysteinylglycine) (GSH), one of the key antioxidants in , is required for the development of alfalfa () nitrogen-fixing nodules. Glutathione exists as either reduced glutathione (GSH) or oxidized glutathione (GSSG), and its content is regulated by two pathways in The first pathway is the synthesis of glutathione from its constituent amino acids, namely, Glu, Cys, and Gly, catalyzed by γ-glutamylcysteine synthetase (GshA) and glutathione synthetase (GshB). The second pathway is the recycling of GSSG via glutathione reductase (GR). However, whether the GR functions similarly to GshA and GshB1 during symbiotic interactions with alfalfa remains unknown. In this study, a plasmid insertion mutation of the gene, which encodes GR, was constructed, and the mutant exhibited delayed alfalfa nodulation, with 75% reduction in nitrogen-fixing capacity. The mutant demonstrated increased accumulation of GSSG and a decreased GSH/GSSG ratio in cells. The mutant also showed defective growth in rich broth and minimal broth and was more sensitive to the oxidants HO and sodium nitroprusside. Interestingly, the expression of ,, , and was induced in the mutant. These findings reveal that the recycling of glutathione is important for to maintain redox homeostasis and to interact symbiotically with alfalfa. The antioxidant glutathione is regulated by its synthetase and reductase in cells. In the symbiotic bacterium , the synthesis of glutathione is essential for alfalfa nodulation and nitrogen fixation. In this study, we observed that the recycling of glutathione from GSSG not only was required for redox homeostasis and oxidative stress protection in cells but also contributed to alfalfa nodule development and competition capacity. Our findings demonstrate that the recycling of glutathione plays a key role in nitrogen fixation symbiosis.

Glutathione Deficiency in Sinorhizobium meliloti Does Not Impair Bacteroid Differentiation But Induces Early Senescence in the Interaction With Medicago truncatula

“…This transport deficiency in R. leguminosarum 3841 gshB mutant strain is also associated to a lower BNF (Cheng et al, 2017). The LysR-type transcriptional regulator LsrB, required for nodulation, also regulates gshA gene expression through modification of cysteine residues (Luo et al, 2005;Tang et al, 2018) and gshB gene expression (Lu et al, 2013).…”

“…The reduced BNF observed with the gshB mutant strain was correlated with nodule and bacteroid early senescence in M. sativa and P. vulgaris (Harrison et al, 2005;Muglia et al, 2008;Taté et al, 2012). In parallel, recycling of GSH by glutathione reductase was shown to be required to maintain an effective nitrogen fixation (Tang et al, 2018). Finally, a deficiency in bacteroid differentiation was observed for a S. meliloti (strain 2011) mutant for glutaredoxin 1 (Grx1), a glutaredoxin involved in the deglutathionylation of proteins using GSH as a cofactor, in the symbiotic interaction with M. truncatula (Benyamina et al, 2013).…”

Involvement of Glutaredoxin and Thioredoxin Systems in the Nitrogen-Fixing Symbiosis between Legumes and Rhizobia

“…SEMIA 6144 indeed induced functional nodules with peanut ( Arachis hypogaea L.), even though GSH depletion affects nodule occupancy capacity and growth of the free-living bacterium in normal and stressful conditions [70]. Overall, the homeostasis (both level and redox status) of GSH in bacterial cells is important for nodule development, and this is also exemplified by the symbiotic deficiency of S. meliloti gor mutant [71]. The lack of GR in gor mutants causes a decrease in the GSH/GSSG ratio, triggering oxidative stress with an increased expression of catalase genes, and an enhanced sensitivity to oxidants.…”

“…The lack of GR in gor mutants causes a decrease in the GSH/GSSG ratio, triggering oxidative stress with an increased expression of catalase genes, and an enhanced sensitivity to oxidants. In planta, the gor mutant is affected in its ability to compete for nodule occupancy and displays a reduced nitrogen-fixing phenotype [71]. Altogether, these different studies highlight the major role of rhizobial GSH in regulating the intracellular redox environment and protecting cells against ROS.…”

In Salmonella enterica, OatA (Formerly YjgM) Uses O-Acetyl-Serine and Acetyl-CoA to Synthesize N,O-Diacetylserine, Which Upregulates Cysteine Biosynthesis

“…L -Cysteine ( L -Cys) is one of the 22 proteinogenic amino acids in nature, and one of only two amino acids whose side chains contain a sulfur atom. The sulfhydryl group of L -Cys is critical to maintaining redox homeostasis in cells from all domains of life ( Hernandez et al, 2015 ; Hasan et al, 2016 ; Zhang et al, 2016 ; Cao et al, 2017 ; Liu et al, 2018 ; Tang et al, 2018 ). The biosynthesis of this important amino acid has been extensively studied ( Kredich, 2008 ).…”