Maintaining sulfur supply to the symbiosome delays nodule senescence in soybean

Symbiotic nitrogen fixation (SNF) in legume-rhizobia represents a sustainable and eco-friendly alternative to chemical nitrogen fertilizers in agriculture. Identifying key factors involved in nodule senescence, is crucial for enhancing SNF by effectively extending the lifespan of nodules. Here, we reveal that sulfur (S), an essential element for SNF, plays a major regulatory role in the senescence of soybean (Glycine max) nodules. Blocking S input into the symbiosome by knocking out either S transporter genes SULTR2;1 or SULTR3;5, resulted in a significant decrease in glutathione levels. This reduction impairs the capacity for reactive nitrogen species scavenging, thereby accelerating nodule senescence. Notably, reducing reactive nitrogen species (RNS) production in rhizobia or increasing S input in soybean nodules through genetic manipulation, can effectively mitigate high nitrogen-induced nodule senescence. Our findings demonstrate that SULTR-mediated S input is a pivotal step in regulating nodule senescence, and provide insights for developing strategies to enhance SNF in legumes by delaying nodule senescence.