Abstract
Legumes establish symbiosis with rhizobia, forming nitrogen-fixing nodules. The central role of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in nodule biology has been clearly established. Recently, hydrogen sulfide (H2S) and other reactive sulfur species (RSS) have emerged as novel signaling molecules in animals and plants. A major mechanism by which ROS, RNS, and RSS fulfil their signaling role is the post-translational modification of proteins. To identify possible functions of H2S in nodule development and senescence, we used the tag-switch method to quantify changes in the persulfidation profile of common bean (Phaseolus vulgaris) nodules at different developmental stages. Proteomic analyses indicate that persulfidation plays a regulatory role in plant and bacteroid metabolism and senescence. The effect of a H2S donor on nodule functioning and on several proteins involved in ROS and RNS homeostasis was also investigated. Our results using recombinant proteins and nodulated plants support a crosstalk among H2S, ROS, and RNS, a protective function of persulfidation on redox-sensitive enzymes, and a beneficial effect of H2S on symbiotic nitrogen fixation. We conclude that the general decrease of persulfidation levels observed in plant proteins of aging nodules is one of the mechanisms that disrupt redox homeostasis leading to senescence.