Interaction of Ferulic Acid with Glutathione S-Transferase and Carboxylesterase Genes in the Brown Planthopper, Nilaparvata lugens

Plant phenolics are crucial defense phytochemicals against herbivores and glutathione S-transferase (GST) and carboxylesterase (CarE) in herbivorous insects are well-known detoxification enzymes for such xenobiotics. To understand relationship between a plant phenolic and herbivore GST or CarE genes, we evaluated the relationship between a rice phenolic ferulic acid and resistance to brown planthopper (BPH, Nilaparvata lugens), and investigated the interaction of ferulic acid with GST or CarE genes in BPH. The results indicate that ferulic acid content in tested rice varieties was highly associated with resistance to BPH. Bioassays using artificial diets show that the phenolic acid toxicity to BPH was dose dependent and the LC25 and LC50 were 5.81 and 23.30 mu g/ml at 72 hr, respectively. Activities of the enzymes BPH GST and CarE were increased at concentrations below the LC50 of ferulic acid. Moreover, low ferulic acid concentrations (< LC25) upregulated the transcriptional levels of NlGSTD1 and NlGSTE1 of the GST family and NlCE of the CarE family. By using dsRNA-induced gene silencing (DIGS) of GST or CarE, it was shown that suppressed expression levels of NlGSTD1, NlGSTE1 and NlCE were 14.6%-21.2%, 27.8%-34.2%, and 10.5%-19.8%, respectively. Combination of NlGSTD1, NlGSTE1 or NlCE knockdown with ferulic acid increased nymph mortality by 92.9%, 119.9%, or 124.6%, respectively. These results suggest that depletion of detoxification genes in herbivorous insects by plant-mediated RNAi technology might be a new potential resource for improving rice resistance to BPH.