Bridging sulfur assimilation to trace element homeostasis: Mechanisms and potential applications for crop improvement

Sulfur (S) assimilation directly or indirectly affects the uptake, translocation, and homeostasis of essential and beneficial micronutrients, as well as detoxification of toxic metal(loid)s in plants. This review synthesizes the multifaceted roles of S assimilation and metabolites in trace element dynamics. Sulfate transporters mediate the uptake of structurally similar oxyanions such as selenate, molybdate and chromate, while S availability modulates the biosynthesis and secretion of phytosiderophores required for iron (Fe) acquisition in gramineous plant species. S-metabolite derived ligands, notably phytochelatins (PCs), metallothioneins (MTs), and nicotianamine (NA), perform essential functions in cytosolic chelation, buffering free ion concentrations to prevent toxicity, facilitating intracellular trafficking, and delivering trace metals to enzymes and organelles. Sulfur also is indispensable for the biosynthesis of critical cofactors including the Fe-S clusters and molybdenum (Mo) cofactor (Moco). On the other hand, Fe deficiency and metal(loid) stresses modulate the uptake and homeostasis of S. This intricate interplay positions S metabolism as a key regulator of micronutrient efficiency and metal(loid) detoxification. Optimizing S assimilation pathways has the potential to biofortify micronutrients and prevent excessive accumulation of toxic metal(loid)s in food crops.