Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/12/2006
Publication Date: 2/6/2007
Citation: Mittapalli, O., Neal, J.J., Shukle, R.H. 2007. Antioxidant defense response in a galling insect. Proceedings of the National Academy of Sciences. 104(6):1889-1894. Interpretive Summary: Plant feeding insects are constantly faced with toxic oxygen molecules while feeding on their host plants. To deal with these ingested toxic plant chemicals, they have developed an array of defensive enzymes in their gut to detoxify the toxic oxygen molecules. While the Hessian fly is the major insect pest of wheat world-wide, little is known as to how it feeds on and parasitizes wheat plants. We have identified the genes producing the enzymes that detoxify toxic oxygen molecules Hessian fly larvae encounter while feeding on wheat and have shown the enzymes are critical to the survival of larvae on wheat. This knowledge will benefit scientists facing the challenge of devising more durable resistance in wheat to the Hessian fly through genetic engineering and other contemporary approaches. Wheat producers and commodity groups will benefit from this knowledge with improved pest control without increased cost.
Technical Abstract: Herbivorous insect species are constantly challenged with reactive oxygen species (ROS) generated from endogenous and exogenous sources. ROS produced within insects due to stress and prooxidant allelochemicals produced by host plants in response to herbivory require a complex mode of antioxidant defense during insect-plant interactions. To process the ingested toxic plant chemicals, some insect herbivores have developed a strikingly unique midgut-based strategy to defend against the suite of ROS encountered. Despite being the major insect pest of wheat world-wide, the Hessian fly (Mayetiola destructor) response to wheat at the molecular level is yet to be unraveled. We report the antioxidant defense mechanism required by the Hessian fly during compatible (larvae on susceptible wheat) and incompatible (larvae on resistant wheat) interactions. Quantitative data for two superoxide dismutases (MdesSOD-1 and MdesSOD-2), two catalases (MdesCAT-1 and MdesCAT-2) and two phospholipid glutathione peroxidases (MdesPHGPX-1 and MdesPHGPX-2) revealed high levels of all the mRNAs in larval midgut and feeding instars. Further analysis in larvae participating in compatible and incompatible interactions showed increased levels of all mRNAs except for MdesSOD-1and MdesSOD -2. We postulate MdesCAT-1, MdesCAT-2, MdesPHGPX-1 and MdesPHGPX-2 to be important in detoxifying ROS encountered by larvae while feeding on wheat seedlings and/or ROS generated endogenously due to stress. These results provide a unique opportunity to understand the cooperative antioxidant defense responses in the Hessian fly/wheat interaction and may be applicable to other insect/plant interactions.