Redox regulation in the symbiotic bacterium Sinorhizobium meliloti: Characterization of the transcriptional regulator SydR and analysis of the S-glutathionyl proteome.

President of the jury :                       

• Dr. Florence WISNIEWSKI-DYE – PR, LEM, Lyon.

Rapporteurs :                     

• Dr. Benoît ALUNNI – DR, IJPB, Versailles.
• Dr. Erwan GUEGUEN – MCU, MAP, Lyon.                

Examiners

• Dr. Delphine CAPELA – DR, LIPME, Toulouse.
• Dr. Jean-Luc GATTI – DR, ISA, Sophia Antipolis.

Thesis Director :

• Dr. Geneviève ALLOING – CR, ISA, Sophia Antipolis.
• Dr. Karine MANDON – MCU, ISA, Sophia Antipolis.

Abstract :

Plant-bacteria interactions are essential for plant health and development. The establishment and maintenance of these interactions rely on the ability of bacteria to adapt to their hosts and environmental variations. In particular, Rhizobiaceae bacteria are involved in symbiotic interactions with legume plants, contributing to soil nitrogen enrichment. This symbiosis is initiated in the rhizosphere with a molecular dialogue, followed by root infection and nodule formation, where bacteria differentiate into nitrogen-fixing bacteroids. During the several steps of the symbiosis between Sinorhizobium meliloti and Medicago truncatula, Reactive Oxygen Species (ROS) are produced by the plant, and bacterial antioxidant defense is a key determinant for successful interaction. ROS can act as signal molecules, and induce reversible post-translational modifications involving redox-active cysteines of proteins that may regulate their activities. Thus, ROS produced at several steps of the interaction may activate signaling pathways regulating symbiosis. However, the mechanisms of redox regulation in S. meliloti and their importance during the symbiotic interaction remain largely unknown.

As part of their evolution, bacteria have evolved ROS-sensing proteins, such as redox-sensing-Transcriptional Regulators (TRs). TRs of the MarR family are involved in the regulation of various functions, particularly in plant-interacting bacteria. In S. meliloti, we identified SydR, whose oxidation inhibits DNA-binding activity via the formation of an intermolecular disulfide bond. Study of a ΔsydR mutant showed that SydR is crucial for infection and nodule development during symbiosis with M. truncatula. Transcriptomic analysis revealed that SydR controls a regulon of genes encoding various hydrolases, oxidoreductases and stress response proteins. Moreover, the overexpression of certain of these genes is specifically responsible for the symbiotic phenotype of the ΔsydR mutant.

We also aimed to identify S. meliloti proteins that are susceptible to S-glutathionylation. Indeed, the formation of a mixed disulfide bond between a cysteine and glutathione (GSH) is part of redox-dependent post-translational modifications that may regulate protein activities. GSH has been described as particularly important during the S. meliloti – M. truncatula symbiosis, suggesting that relevant redox-dependent signaling pathways during the interaction may involve S-glutathionylated proteins. To identify these proteins in S. meliloti, we developed a redox proteomic approach. Our experimental protocol allowed us to analyze the first S-glutathionylated proteome of S. meliloti, enabling future functional analyses to characterize the role of this modification in symbiosis. In conclusion, our work on SydR and the S-glutathionylated proteome in S. meliloti highlights the significance of redox regulation in the symbiotic bacterium, thus supporting the hypothesis of a link between ROS production detected during symbiosis and regulation of key signaling pathways involved during the symbiotic interaction.

Keywords :

Sinorhizobium meliloti, Redox signaling, Transcriptional regulation, Proteomics, S-glutathionylation.

In-class or via Zoom :

https://univ-cotedazur.zoom.us/j/86832169283?pwd=K3LzIitDYn0Mtzpd36r7hqql6ODeSL.1
ID de réunion : 868 3216 9283
Code secret : 188307