Sulfenylated proteins in the Medicago truncatula–Sinorhizobium meliloti symbiosis

Reactive oxygen species such as hydrogen peroxide (H2O2), play a crucial role as signaling molecules in the establishment and functioning of the nitrogen-fixing legume–Rhizobium symbiosis. The regulation of protein function through oxidative modification has emerged as an important molecular mechanism modulating various biological processes. Protein cysteine residues are known to be sensitive targets of H2O2, in a posttranslational modification called sulfenylation. We trapped and identified sulfenylated proteins in the Medicago truncatula–Sinorhizobium meliloti symbiosis, by combining the use of chemical and genetic probes with mass spectrometry analysis. We identified 44 M. truncatula proteins sulfenylated in inoculated roots (two days post infection, 2 dpi) and 65 such proteins in the functioning symbiotic organ, the nodule (four weeks post infection, 4 wpi); 18 proteins were identified at both time points. However, the largest functional groups at 2 dpi and 4 wpi were different: redox state-linked proteins early in the interaction and proteins involved in amino-acid and carbohydrate metabolism in the nodule. Twenty proteins from S. meliloti, including some directly involved in nitrogen fixation, were also identified as sulfenylated. These results suggest that sulfenylation may regulate the activity of proteins playing major roles in the development and functioning of the symbiotic interaction.

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► Hydrogen peroxide is involved in the development of the legume–Rhizobium symbiosis.
► Sulfenylated proteins were identified in inoculated roots and functioning nodules.
► They are involved in plant redox control, defense and carbon and nitrogen metabolism.
► Sulfenylation may also play a role in regulating microsymbiont metabolism.