The role of reactive oxygen, nitrogen, and sulfur species in the integration of (a)biotic stress signals in legumes

Legumes are crops of considerable economic and ecological significance. They are suitable for cultivation in a variety of environments and temperatures. They are able to form a symbiotic relationship with nitrogen-fixing soil bacteria called rhizobia, contributing to the enrichment of marginal soils with this essential nutrient, and reduce artificial fertilizer use. Similarly, legumes establish a widespread mutualistic association with soil fungi, involving a reciprocal transfer of nutrients. Global warming is reshaping the interactions of plants with their environment, exerting profound effects on global agricultural systems. Plants have evolved sensing, signalling, and adaptive molecular mechanisms to respond to (a)biotic stimuli. Reactive oxygen, nitrogen, and sulfur species (RONSS) are key players in stress tolerance mechanisms, and their homeostasis, mainly accomplished by antioxidant enzymes and metabolites, is essential to allow redox signalling while preventing oxidative damage. Here, we review recent findings, highlighting metabolic pathways of RONSS and antioxidants, with emphasis on their functions in signalling and protection in response to (a)biotic constraints in legumes. Special attention is paid to the molecular crosstalk between RONSS in response to multiple stimuli and notably how redox homeostasis adjustment can increase (a)biotic stress tolerance and potentially be exploited to mitigate the negative effects of climate change.