Glutathione plays a fundamental role in growth and symbiotic capacity of Sinorhizobium meliloti

Rhizobia form a symbiotic relationship with plants of the legume family to produce nitrogen-fixing root nodules under nitrogen-limiting conditions. We have examined the importance of glutathione (GSH) during free-living growth and symbiosis of Sinorhizobium meliloti. An S. meliloti mutant strain (SmgshA) which is unable to synthesize GSH due to a gene disruption in gshA, encoding the enzyme for the first step in the biosynthesis of GSH, was unable to grow under nonstress conditions, precluding any nodulation. In contrast, an S. meliloti strain (SmgshB) with gshB, encoding the enzyme involved in the second step in GSH synthesis, deleted was able to grow, indicating that γ- glutamylcysteine, the dipeptide intermediate, can partially substitute for GSH. However, the SmgshB strain showed a delayed-nodulation phenotype coupled to a 75% reduction in the nitrogen fixation capacity. This phenotype was linked to abnormal nodule development. Both the SmgshA and SmgshB mutant strains exhibited higher catalase activity than the wild-type S. meliloti strain, suggesting that both mutant strains are under oxidative stress. Taken together, these results show that GSH plays a critical role in the growth of S. meliloti and during its interaction with the plant partner.Facultad de Ciencias ExactasInstituto de Biotecnologia y Biologia Molecula

Glutathione plays a fundamental role in growth and symbiotic capacity of Sinorhizobium meliloti

Rhizobia form a symbiotic relationship with plants of the legume family to produce nitrogen-fixing root nodules under nitrogen-limiting conditions. We have examined the importance of glutathione (GSH) during free-living growth and symbiosis of Sinorhizobium meliloti. An S. meliloti mutant strain (SmgshA) which is unable to synthesize GSH due to a gene disruption in gshA, encoding the enzyme for the first step in the biosynthesis of GSH, was unable to grow under nonstress conditions, precluding any nodulation. In contrast, an S. meliloti strain (SmgshB) with gshB, encoding the enzyme involved in the second step in GSH synthesis, deleted was able to grow, indicating that γ- glutamylcysteine, the dipeptide intermediate, can partially substitute for GSH. However, the SmgshB strain showed a delayed-nodulation phenotype coupled to a 75% reduction in the nitrogen fixation capacity. This phenotype was linked to abnormal nodule development. Both the SmgshA and SmgshB mutant strains exhibited higher catalase activity than the wild-type S. meliloti strain, suggesting that both mutant strains are under oxidative stress. Taken together, these results show that GSH plays a critical role in the growth of S. meliloti and during its interaction with the plant partner.Facultad de Ciencias ExactasInstituto de Biotecnologia y Biologia Molecula

(Homo)glutathione Deficiency Impairs Root-knot Nematode Development in Medicago truncatula

Root-knot nematodes (RKN) are obligatory plant parasitic worms that establish and maintain an intimate relationship with their host plants. During a compatible interaction, RKN induce the redifferentiation of root cells into multinucleate and hypertrophied giant cells essential for nematode growth and reproduction. These metabolically active feeding cells constitute the exclusive source of nutrients for the nematode. Detailed analysis of glutathione (GSH) and homoglutathione (hGSH) metabolism demonstrated the importance of these compounds for the success of nematode infection in Medicago truncatula. We reported quantification of GSH and hGSH and gene expression analysis showing that (h)GSH metabolism in neoformed gall organs differs from that in uninfected roots. Depletion of (h)GSH content impaired nematode egg mass formation and modified the sex ratio. In addition, gene expression and metabolomic analyses showed a substantial modification of starch and γ-aminobutyrate metabolism and of malate and glucose content in (h)GSH-depleted galls. Interestingly, these modifications did not occur in (h)GSH-depleted roots. These various results suggest that (h)GSH have a key role in the regulation of giant cell metabolism. The discovery of these specific plant regulatory elements could lead to the development of new pest management strategies against nematodes

Regulation of differentiation of nitrogen-fixing bacteria by microsymbiont targeting of plant thioredoxin s1

Legumes associate with rhizobia to form nitrogen (N2)-fixing nodules, which is important for plant fitness [1, 2]. Medicago truncatula controls the terminal differentiation of Sinorhizobium meliloti into N2-fixing bacteroids by producing defensin-like nodule-specific cysteine-rich peptides (NCRs) [3, 4]. The redox state of NCRs influences some biological activities in free-living bacteria, but the relevance of redox regulation of NCRs in planta is unknown [5, 6], although redox regulation plays a crucial role in symbiotic nitrogen fixation [7, 8]. Two thioredoxins (Trx), Trx s1 and s2, define a new type of Trx and are expressed principally in nodules [9]. Here, we show that there are four Trx s genes, two of which, Trx s1 and s3, are induced in the nodule infection zone where bacterial differentiation occurs. Trx s1 is targeted to the symbiosomes, the N2-fixing organelles. Trx s1 interacted with NCR247 and NCR335 and increased the cytotoxic effect of NCR335 in S. meliloti. We show that Trx s silencing impairs bacteroid growth and endoreduplication, two features of terminal bacteroid differentiation, and that the ectopic expression of Trx s1 in S. meliloti partially complements the silencing phenotype. Thus, our findings show that Trx s1 is targeted to the bacterial endosymbiont, where it controls NCR activity and bacteroid terminal differentiation. Similarly, Trxs are critical for the activation of defensins produced against infectious microbes in mammalian hosts. Therefore, our results suggest the Trx-mediated regulation of host peptides as a conserved mechanism among symbiotic and pathogenic interactions

Les symbioses et associations bénéfiques plantes-microorganismes du sol

National audienc

Le glutathion chez Medicago truncatula (étude de la régulation de sa synthèse et identification de gènes cibles lors de la symbiose avec Sinorhizobium meliloti)

La symbiose entre Medicago truncatula et Sinorhizobium meliloti conduit à la formation de nodosités racinaires capables de fixer l azote atmosphérique. Le glutathion (GSH) et l homoglutathion (hGSH) sont deux molécules antioxydantes qui participent à des fonctions essentielles pour la plante. Au cours de ce travail de thèse, la régulation de l expression des gènes de synthèse du GSH et de l hGSH par le monoxyde d azote (NO) a été analysée, et une étude transcriptomique a été réalisée afin d identifier des gènes cibles du (h)GSH lors de la symbiose. Deux donneurs chimiques de NO sont capables d augmenter la quantité d ARNm correspondant à la g-glutamylcystéine synthétase et à la glutathion synthétase, mais pas de l homoglutathion synthétase, suggérant que ces deux thiols pourraient avoir des rôles différents. L accumulation du GSH a été corrélée à l expression des gènes, montrant que le NO induit la synthèse du GSH dans les racines de Medicago truncatula. L étude transcriptomique réalisée a permis d identifier 181 gènes dont l expression est modifiée chez des plantes déficientes en (h)GSH au cours de la mise en place de la symbiose, parmi lesquels des gènes liés à la formation des méristèmes, à la transduction du signal et à la défense de la plante. L analyse du profil d expression de gènes de défense induits par l acide salicylique suggère que les mécanismes de défense liés à cette hormone affectent la nodulation des plantes déficientes en (h)GSH. Les résultats obtenus dans cette thèse ouvrent de nouvelles perspectives d étude sur les multiples rôles du h(GSH) dans les mécanismes de la nodulation, et plus généralement dans les interactions plantes-microorganismes.NICE-BU Sciences (060882101) / SudocSudocFranceF

Thiol-based redox signaling in the nitrogen-fixing symbiosis

10 Págs., 2 Figs. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CCBY). The .pdf document is protected by copyright and was first published by Frontiers.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 N2 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 nitro-oxidative damage. In nodules a thiol-dependent regulatory network that senses, transmits and responds to redox changes is starting to be elucidated. A combination of enzymatic, immunological, pharmacological and molecular analyses has allowed us to conclude that glutathione and its legume-specific homolog, homoglutathione, are abundant in meristematic and infected cells, that their spatio-temporally distribution is correlated with the corresponding (homo)glutathione synthetase activities, and that they are crucial for nodule development and function. Glutathione is at high concentrations in the bacteroids and at moderate amounts in the mitochondria, cytosol and nuclei. Less information is available on other components of the network. The expression of multiple isoforms of glutathione peroxidases, peroxiredoxins, thioredoxins, glutaredoxins and NADPH-thioredoxin reductases has been detected in nodule cells using antibodies and proteomics. Peroxiredoxins and thioredoxins are essential to regulate and in some cases to detoxify RONS in nodules. Further research is necessary to clarify the regulation of the expression and activity of thiol redox-active proteins in response to abiotic, biotic and developmental cues, their interactions with downstream targets by disulfide-exchange reactions, and their participation in signaling cascades. The availability of mutants and transgenic lines will be crucial to facilitate systematic investigations into the function of the various proteins in the legume-rhizobial symbiosis.Research from our laboratories has been funded by grants from MAE and CNRS (Envimedprogram) to Pierre Frendo and the Spanish Ministry of Economy and Competitivity (AGL2011-24524, cofunded by FEDER) to Manuel Becana.Peer reviewe

Yield management et marketing des services

International audienceLe yield management set un système d'optimisation du rendement qui connait un fort développement en Europe. Les auteurs proposent une définition et indiquent les caractéristiques communes aux situations auxquelles il s'applique. Deux aspects marketing sont étudiés : le caractère aléatoire du déplacement de la demande et l'impact du système sur la qualité du service. La conclusion met l'accent sur les enjeux stratégiques que représentent le développement et la maîtrise du yield management pour les entreprises de service. L'article s'appuie sur les témoignages de plusieurs yield managers