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Two Sinorhizobium meliloti glutaredoxins regulate iron metabolism and symbiotic bacteroid differentiation

Authors

  • Sofiane M. Benyamina,

    1. UMR ‘Institut Sophia Agrobiotech’ INRA 1355-CNRS 7254 – Université de Nice-Sophia Antipolis, 400 routes des Chappes, 06903 Sophia-Antipolis cedex, France
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  • Fabien Baldacci-Cresp,

    1. UMR ‘Institut Sophia Agrobiotech’ INRA 1355-CNRS 7254 – Université de Nice-Sophia Antipolis, 400 routes des Chappes, 06903 Sophia-Antipolis cedex, France
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  • Jérémy Couturier,

    1. UMR INRA UHP 1136, Interactions Arbres Microorganismes, IFR 110 EFABA, Université de Lorraine, Faculté des Sciences, BP 70239, 54506 Vandoeuvre cedex, France
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  • Kamel Chibani,

    1. UMR INRA UHP 1136, Interactions Arbres Microorganismes, IFR 110 EFABA, Université de Lorraine, Faculté des Sciences, BP 70239, 54506 Vandoeuvre cedex, France
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  • Julie Hopkins,

    1. UMR ‘Institut Sophia Agrobiotech’ INRA 1355-CNRS 7254 – Université de Nice-Sophia Antipolis, 400 routes des Chappes, 06903 Sophia-Antipolis cedex, France
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  • Abdelkader Bekki,

    1. Laboratoire de Biotechnologie des Rhizobiums et Amélioration des Plantes, Département de Biotechnologie, Université d'Oran Es Senia, Oran, Algeria
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  • Philippe de Lajudie,

    1. UMR ‘Laboratoire des Symbioses Tropicales et Méditerranéennes’ IRD – Université de Montpellier, 34398 Montpellier cedex 5, France
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  • Nicolas Rouhier,

    1. UMR INRA UHP 1136, Interactions Arbres Microorganismes, IFR 110 EFABA, Université de Lorraine, Faculté des Sciences, BP 70239, 54506 Vandoeuvre cedex, France
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  • Jean-Pierre Jacquot,

    1. UMR INRA UHP 1136, Interactions Arbres Microorganismes, IFR 110 EFABA, Université de Lorraine, Faculté des Sciences, BP 70239, 54506 Vandoeuvre cedex, France
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  • Geneviève Alloing,

    1. UMR ‘Institut Sophia Agrobiotech’ INRA 1355-CNRS 7254 – Université de Nice-Sophia Antipolis, 400 routes des Chappes, 06903 Sophia-Antipolis cedex, France
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  • Alain Puppo,

    Corresponding author
    1. UMR ‘Institut Sophia Agrobiotech’ INRA 1355-CNRS 7254 – Université de Nice-Sophia Antipolis, 400 routes des Chappes, 06903 Sophia-Antipolis cedex, France
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  • Pierre Frendo

    1. UMR ‘Institut Sophia Agrobiotech’ INRA 1355-CNRS 7254 – Université de Nice-Sophia Antipolis, 400 routes des Chappes, 06903 Sophia-Antipolis cedex, France
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E-mail puppo@unice.fr; Tel. (+33) 492 386631; Fax (+33) 492 386587.

Summary

Legumes interact symbiotically with bacteria of the Rhizobiaceae to form nitrogen-fixing root nodules. We investigated the contribution of the three glutaredoxin (Grx)-encoding genes present in the Sinorhizobium meliloti genome to this symbiosis. SmGRX1 (CGYC active site) and SmGRX3 (CPYG) recombinant proteins displayed deglutathionylation activity in the 2-hydroethyldisulfide assay, whereas SmGRX2 (CGFS) did not. Mutation of SmGRX3 did not affect S. meliloti growth or symbiotic capacities. In contrast, SmGRX1 and SmGRX2 mutations decreased the growth of free-living bacteria and the nitrogen fixation capacity of bacteroids. Mutation of SmGRX1 led to nodule abortion and an absence of bacteroid differentiation, whereas SmGRX2 mutation decreased nodule development without modifying bacteroid development. The higher sensitivity of the Smgrx1 mutant strain as compared with wild-type strain to oxidative stress was associated with larger amounts of glutathionylated proteins. The Smgrx2 mutant strain displayed significantly lower levels of activity than the wild type for two iron-sulfur-containing enzymes, aconitase and succinate dehydrogenase. This lower level of activity could be associated with deregulation of the transcriptional activity of the RirA iron regulator and higher intracellular iron content. Thus, two S. meliloti Grx proteins are essential for symbiotic nitrogen fixation, playing independent roles in bacterial differentiation and the regulation of iron metabolism.

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