Cyprosulfamide mitigates nicosulfuron phytotoxicity in maize through activation of GST ‐associated phase II detoxification involving ZmGST24

BACKGROUND: Nicosulfuron is an acetolactate synthase (ALS)-inhibiting herbicide widely used in maize production. However, under unfavorable environmental conditions, its phytotoxicity to maize remains a practical concern. Cyprosulfamide (CSA) is an effective safener for maize, yet the contribution of glutathione S-transferases (GST)-associated phase II detoxification to CSA-conferred protection against nicosulfuron injury remains poorly understood. RESULTS: CSA markedly alleviated nicosulfuron-induced growth inhibition in maize seedlings and effectively reduced herbicide injury under field conditions. Inhibitor assays showed that both cytochrome P450-mediated phase I metabolism and GST-associated phase II detoxification contribute to maize tolerance to nicosulfuron. Proteomic analysis further revealed that, relative to nicosulfuron treatment alone, co-application of nicosulfuron and CSA significantly enriched the glutathione metabolism pathway in maize leaves. Among the induced GST candidate genes, ZmGST24 showed the strongest transcriptional response. Phylogenetic and conserved motif analyses supported its functional similarity to previously reported GSTs involved in herbicide detoxification. Molecular docking suggested favorable binding of ZmGST24 to nicosulfuron, and heterologous expression in yeast demonstrated that ZmGST24 not only enhanced tolerance to nicosulfuron, but also increased tolerance to several herbicides commonly used in maize fields. CONCLUSION: These findings indicate that the protective effect of CSA against nicosulfuron phytotoxicity in maize is associated with activation of GST-associated phase II detoxification. The pronounced response of the glutathione metabolism pathway, together with the functional characterization of ZmGST24, identifies this gene as a promising candidate involved in CSA-induced herbicide tolerance and as a potential target for improving herbicide safety in maize.