Diverted Secondary Metabolism and Improved Resistance to European Corn Borer (Ostrinia nubilalis) in Maize (Zea mays L.) Transformed with Wheat Oxalate Oxidase

An alteration in the secondary metabolism of maize (Zea mays L.) genetically modified with the wheat oxalate oxidase (OxO) gene was observed using HPLC and fluorescence microscopy. Phenolic concentrations in the OxO lines were significantly increased, but DIMBOA synthesis was reduced due to a diversion in the shikimate pathway leading to phenolic and hydroxamic acids. Ferulic acid exhibited the largest increase and accounted for 80.4% of the total soluble phenolics. Transcription of a 13-lipoxygenase gene, coding for a key enzyme involved in the regulation of secondary metabolism, was substantially higher in the OxO line than in the null line. To test whether the high levels of soluble phenolic acids, in particular ferulic acid, contributed to the insect resistance in the OxO maize, ferulic acid was administered in meridic diets to European corn borer (ECB). A significant negative correlation between ferulic acid concentration and ECB larval growth rate was found. Field testing during 2001 showed that OxO maize was more resistant to ECB, with leaf consumption and stalk-tunneling damage significantly reduced by 28−34 and 37−39%, respectively, on all of the OxO lines tested and confirming published 2000 findings.

Keywords: Maize; oxalate oxidase; European corn borer; genetic transformation; phenolics; secondary compounds