Transcriptomic analysis of maize uncovers putative genes involved in metabolic detoxification under four safeners...

Isoxadifen-ethyl (IDF) and cyprosulfamide (CSA) can effectively protect maize from nicosulfuron (NIC) injury, while mefenpyr-diethyl (MPR) and fenchlorazole-ethyl (FCO) did not. Their chemical diversity and requirement to use them in combination with the corresponding herbicides suggest that their elicitation of gene expression are complex and whether it is associated with the safening activity remains elusive. In this study, our first objective was to determine whether or not the ability of four safeners to enhance the metabolic rate of nicosulfuron. It was found that nicosulfuron degradation in maize was accelerated by IDF and CSA, but not by FCO and MPR. Transcriptomic analysis showed that the number of genes induced by IDF and CSA were larger than that induced by FCO and MPR. Overall, 34 genes associated with detoxification were identified, including glutathione S-transferase (GST), cytochrome P450 (CYP450), UDP-glucosyltransferase (UGT), transporter and serine. Moreover, 14 detoxification genes were screened for further verification by real-time PCR in two maize inbred lines. Two maize inbred lines exhibited high expression levels of four genes (GST31, GST39, AGXT2 and ADH) after IDF treatment. GST6, GST19, MATE, SCPL18 and UF3GT were specifically up-regulated in telerant maize inbred line under IDF and IDF + NIC treatments. Seven genes, namely GST31, GST6, GST19, UF3GT, MATE, ADH and SCPL18, are induced by IDF and CSA to play a vital role in regulating the detoxification process of NIC. Accordingly, the GST activity in maize was accelerated by IDF and CSA, but not by FCO and MPR. This result is consistent with transcriptome and metabolic data.These results indicate that the mitigation of NIC damage is associated with enhanced herbicide metabolism. IDF and CSA were more effective in protecting maize from NIC injury due to their ability to enhance the detoxification of specific types of herbicides, compared to FCO and MPR. The chemical specificity of four safeners is attributed to the up-regulated genes related to the detoxification pathway.