Arbuscular mycorrhizal fungus regulates the cysteine and methionine metabolic pathways in the roots of continuously cropped soybean by alleviating sulfur deficiency

Soybean ( Glycine max L.) is a key industrial crop extensively cultivated in northeastern China and serves as a vital raw material for both food and non-food industries, including edible oils, animal feed, and biofuels. However, continuous cropping often leads to soil sulfur deficiency, which significantly impacts soybean yield and quality, thereby affecting the production of soybean-derived products. The present work examines the potential of inoculating soybean with arbuscular mycorrhizal fungi (AMF), specifically Funneliformis mosseae ( F. mosseae ), to enhance the absorption of soil-available sulfur by soybean and improve soil sulfur utilization, thereby alleviating sulfur deficiency under continuous cropping conditions. The results showed that, compared with continuous cropping without inoculation of F. mosseae , continuous cropping with inoculation of F. mosseae for 3 years increased the sulfur content in soybean roots by 3.59 %. Additionally, cysteine (Cys) content increased by 3.01 % ( p < 0.05), glutathione (GSH) by 12.23 % ( p < 0.05), and β-thioglucoside by 7.3 % ( p < 0.05). Comprehensive analyses of transcriptomics and metabolomics deeply elucidated the regulatory mechanisms of AMF inoculation on soybean root metabolism. It was found that F. mosseae , by enriching cysteine and methionine metabolic pathways, considerably upregulated the expression of key regulatory genes such as ACO1 and Glyma.06G235900 , and boosted the content of the sulfur metabolite 5′-methylthioadenosine. These findings indicate that F. mosseae can effectively regulate sulfur metabolism in soybean roots, enhance the absorption of soil-available sulfur by the root system, and thus mitigate sulfur deficiency in continuously cropped soybean. This study clarifies AMF's role in enhancing soybean sulfur nutrition and offers insights for sustainable soybean production in continuous cropping systems. • F. mosseae upregulates ACO1 to alleviate soybean continuous-cropping obstacles. • F. mosseae elevates root sulfur by modulating 5′-methylthioadenosine level. • AMF– ACO1 –MTA network: a precise tool against soil continuous-cropping obstacles.