Glutathione affects the transport activity of Rhizobium leguminosarum 3841 and is essential for efficient nodulation

Abstract

As glutathione (GSH) plays an essential role in growth and symbiotic capacity of rhizobia, a glutathione synthetase (gshB) mutant of Rhizobium leguminosarum biovar viciae 3841 (Rlv3841) was characterised. It fails to efficiently utilise various compounds as a sole carbon source, including glucose, succinate, glutamine and histidine, and shows 60%–69% reduction in uptake rates of glucose, succinate and the non-metabolisable substrate α-amino isobutyric acid. The defect in glucose uptake can be overcome by addition of exogenous GSH, indicating GSH, but not its bacterial synthesis, is required for efficient transport. GSH is not involved in the regulation of the activity of Rlv3841's transporters via the global regulator of transport, PtsNTR. Although lack of GSH reduces transcription of the branched amino acid transporter, this was not the case for all uptake transport systems, for example, the amino acid permease. This suggests GSH alters activity and/or assembly of transport systems by an unknown mechanism. In interaction with plants, the gshB mutant is not only severely impaired in rhizosphere colonisation, but also shows a 50% reduction in dry weight of plants and nitrogen-fixation ability. This reveals that changes in GSH metabolism affect the bacterial–plant interactions required for symbiosis.

A GMC Oxidoreductase GmcA Is Required for Symbiotic Nitrogen Fixation in Rhizobium leguminosarum bv. viciae

“…Plants were incubated in a controlled-environment chamber with an 18h photoperiod (day/night temperature, 22 and 20 • C). For dry weight determination, plants were grown in a 2-L beaker filled with sterile vermiculite, watered with nitrogen-free nutrient solution and harvested at 7 weeks (Cheng et al, 2017). The shoot was removed from the root and dried at 70 • C in a dry-heat incubator for 3 days before being weighed.…”

“…Rhizosphere colonization assays were performed as previously described (Cheng et al, 2017). Pea seedlings were grown for 7 days, as described above, for acetylene reduction, and inoculated with RLgmcA and RL3841 in the cfu ratios 1000:0, 0:1000, 1000:1000, and 10000:1000.…”

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

“…This deficiency in nutrient transport also detected in R. leguminosarum 3841, which fails to efficiently use various carbon sources such as glucose, succinate, glutamine and histidine, may trigger an early nodule senescence. 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 symbiotic interaction established between legumes and bacteria allows the plant to satisfy its needs in nitrogen. The use of a bacterial strain deficient in GSH production alters significantly the biological nitrogen fixation and the growth of M. sativa, P. vulgaris, and P. sativum during NFS (Harrison et al, 2005;Muglia et al, 2008;Taté et al, 2012;Cheng et al, 2017). Moreover, the electronic microscopy analyses suggested that SmgshB mutant strain is partially impaired in the bacteroid differentiation (Harrison et al, 2005).…”

“…On the bacterial side, the use of mutants deficient in the GSHS-encoding gene (gshB) impairs the BNF efficiency during the symbiosis between Medicago sativa/S. meliloti strain 1021, Phaseolus vulgaris/Rhizobium tropici, P. vulgaris/Rhizobium etli, and Pisum sativum/Rhizobium leguminosarum (Harrison et al, 2005;Muglia et al, 2008;Taté et al, 2012;Cheng et al, 2017). 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).…”