Abstract:Matamoros have contributed equally to this review.In nitrogen poor soils legumes establish a symbiotic interaction with rhizobia that results in the formation of root nodules. These are unique plant organs where bacteria differentiate into bacteroids, which express the nitrogenase enzyme complex that reduces atmospheric N 2 to ammonia. Nodule metabolism requires a tight control of the concentrations of reactive oxygen and nitrogen species (RONS) so that they can perform useful signaling roles while avoiding ni… Show more
“…Taken together, these results provide further evidence for a functional specialization of these thiols in legumes, although the specific roles of GSH and hGSH in legume nodules are yet to be defined (Frendo et al . ). In the present work, the decline in GSH can only be partially attributed to direct antioxidant functions since the levels of the oxidized form, GSSG, remained relatively constant during the experiment (Fig.…”
Symbiotic nitrogen fixation is one of the first physiological processes inhibited in legume plants under water-deficit conditions. Despite the progress made in the last decades, the molecular mechanisms behind this regulation are not fully understood yet. Recent proteomic work carried out in the model legume Medicago truncatula provided the first indications of a possible involvement of nodule methionine (Met) biosynthesis and related pathways in response to water-deficit conditions. To better understand this involvement, the drought-induced changes in expression and content of enzymes involved in the biosynthesis of Met, S-adenosyl-L-methionine (SAM) and ethylene in M. truncatula root and nodules were analyzed using targeted approaches. Nitrogen-fixing plants were subjected to a progressive water deficit and a subsequent recovery period. Besides the physiological characterization of the plants, the content of total sulphur, sulphate and main S-containing metabolites was measured. Results presented here show that S availability is not a limiting factor in the drought-induced decline of nitrogen fixation rates in M. truncatula plants and provide evidences for a down-regulation of the Met and ethylene biosynthesis pathways in roots and nodules in response to water-deficit conditions.
“…Taken together, these results provide further evidence for a functional specialization of these thiols in legumes, although the specific roles of GSH and hGSH in legume nodules are yet to be defined (Frendo et al . ). In the present work, the decline in GSH can only be partially attributed to direct antioxidant functions since the levels of the oxidized form, GSSG, remained relatively constant during the experiment (Fig.…”
Symbiotic nitrogen fixation is one of the first physiological processes inhibited in legume plants under water-deficit conditions. Despite the progress made in the last decades, the molecular mechanisms behind this regulation are not fully understood yet. Recent proteomic work carried out in the model legume Medicago truncatula provided the first indications of a possible involvement of nodule methionine (Met) biosynthesis and related pathways in response to water-deficit conditions. To better understand this involvement, the drought-induced changes in expression and content of enzymes involved in the biosynthesis of Met, S-adenosyl-L-methionine (SAM) and ethylene in M. truncatula root and nodules were analyzed using targeted approaches. Nitrogen-fixing plants were subjected to a progressive water deficit and a subsequent recovery period. Besides the physiological characterization of the plants, the content of total sulphur, sulphate and main S-containing metabolites was measured. Results presented here show that S availability is not a limiting factor in the drought-induced decline of nitrogen fixation rates in M. truncatula plants and provide evidences for a down-regulation of the Met and ethylene biosynthesis pathways in roots and nodules in response to water-deficit conditions.
“…Therefore, these two spots consisted of proteins containing cysteine residues reduced by PBZ treatment. Mass spectrometry analysis revealed that Spot 10 contained O.sativa thioredoxin (OsTRXh1), a ubiquitous redox protein that exhibits disulfide oxidoreductase activity through the reversible oxidation of two cysteine residues in a CXXC motif to a disulfide [28, 29], whereas Spot 11 contained OsRACK1A, which was detected as an oxidized protein in cultured cells expressing DN-OsRac1 (Table 1). Taken together, we identified seven potential redox proteins.Fig.…”
BackgroundReactive oxygen species (ROS) production is an early event in the immune response of plants. ROS production affects the redox-based modification of cysteine residues in redox proteins, which contribute to protein functions such as enzymatic activity, protein-protein interactions, oligomerization, and intracellular localization. Thus, the sensitivity of cysteine residues to changes in the cellular redox status is critical to the immune response of plants.MethodsWe used disulfide proteomics to identify immune response-related redox proteins. Total protein was extracted from rice cultured cells expressing constitutively active or dominant-negative OsRacl, which is a key regulator of the immune response in rice, and from rice cultured cells that were treated with probenazole, which is an activator of the plant immune response, in the presence of the thiol group-specific fluorescent probe monobromobimane (mBBr), which was a tag for reduced proteins in a differential display two-dimensional gel electrophoresis. The mBBr fluorescence was detected by using a charge-coupled device system, and total protein spots were detected using Coomassie brilliant blue staining. Both of the protein spots were analyzed by gel image software and identified using MS spectrometry. The possible disulfide bonds were identified using the disulfide bond prediction software. Subcellular localization and bimolecular fluorescence complementation analysis were performed in one of the identified proteins: Oryza sativa cold shock protein 2 (OsCSP2).ResultsWe identified seven proteins carrying potential redox-sensitive cysteine residues. Two proteins of them were oxidized in cultured cells expressing DN-OsRac1, which indicates that these two proteins would be inactivated through the inhibition of OsRac1 signaling pathway. One of the two oxidized proteins, OsCSP2, contains 197 amino acid residues and six cysteine residues. Site-directed mutagenesis of these cysteine residues revealed that a Cys140 mutation causes mislocalization of a green fluorescent protein fusion protein in the root cells of rice. Bimolecular fluorescence complementation analysis revealed that OsCSP2 is localized in the nucleus as a homo dimer in rice root cells.ConclusionsThe findings of the study indicate that redox-sensitive cysteine modification would contribute to the immune response in rice.Electronic supplementary materialThe online version of this article (doi:10.1186/s12953-017-0115-3) contains supplementary material, which is available to authorized users.
“…In this context, several studies demonstrated the importance of sulfate uptake and metabolism for the establishment and function of SNF (Matamoros et al, 1999(Matamoros et al, , 2003Abbas et al, 2002;Harrison et al, 2005;Krusell et al, 2005;Bianucci et al, 2008;Muglia et al, 2008;Chang et al, 2009;Becana et al, 2010;El Msehli et al, 2011;Frendo et al, 2013). However, little is known about the molecular and biochemical mechanisms governing S-reduction and metabolism during SNF and the impact of nodulation on the whole-plant S-metabolism.…”
We combined transcriptomic and biochemical approaches to study rhizobial and plant sulfur (S) metabolism in nitrogen (N) fixing nodules (Fix + ) of Lotus japonicus, as well as the link of S-metabolism to symbiotic nitrogen fixation and the effect of nodules on whole-plant S-partitioning and metabolism. Our data reveal that N-fixing nodules are thiol-rich organs. Their high adenosine 59-phosphosulfate reductase activity and strong 35 S-flux into cysteine and its metabolites, in combination with the transcriptional upregulation of several rhizobial and plant genes involved in S-assimilation, highlight the function of nodules as an important site of S-assimilation. The higher thiol content observed in nonsymbiotic organs of N-fixing plants in comparison to uninoculated plants could not be attributed to local biosynthesis, indicating that nodules are an important source of reduced S for the plant, which triggers whole-plant reprogramming of S-metabolism. Enhanced thiol biosynthesis in nodules and their impact on the whole-plant S-economy are dampened in plants nodulated by Fix 2 mutant rhizobia, which in most respects metabolically resemble uninoculated plants, indicating a strong interdependency between N-fixation and S-assimilation.
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