Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/13/2006
Publication Date: 4/1/2007
Citation: Mittapalli, O., Neal, J.J., Shukle, R.H. 2007. Tissue and life state specificity of glutatione s-transferase expression in the Hessian fly, Mayetiola destructor: implications for resistance to host allelochemicals. Journal of Insect Science. 7(20):1-13. Interpretive Summary: The Hessian fly is a destructive pest of wheat, and in the eastern soft-winter-wheat region of the United States it is the most important insect pest. Despite its importance as a pest of wheat, little is known about the way Hessian fly larvae interact with wheat while feeding and how they detoxify various harmful chemicals produced by the wheat plant to defend itself. We are systematically analyzing genes expressed in the guts of Hessian fly larvae while they feed on susceptible and resistant wheat and have identified major digestive enzymes, detoxification/antioxidant enzymes, and immune defense peptides. Results from our study have shown that one class of major detoxification genes is important in detoxifying wheat defense compounds ingested by feeding larvae. This knowledge about the detoxification mechanisms employed by Hessian fly larvae while feeding on wheat provides a basis for understanding digestion in the pest and how the pest interacts with wheat plants. Scientists facing the challenge of devising innovative methods of pest control through genetic engineering and other contemporary approaches will benefit from this fundamental knowledge. The agricultural community (crop producers and commodity groups) will benefit from improved pest control that increases yield and quality without increasing costs.
Technical Abstract: We report the characterization and transcription profiles of Delta (MdesGST-1 and MdesGST-3) and Sigma (MdesGST-2) GSTs in the Hessian fly, Mayetiola destructor. The deduced amino acid sequences for MdesGST-1 and MdesGST-3 showed high similarity with other insect Delta GSTs including the conserved catalytic serine residue. The deduced amino acid sequence for MdesGST-2 showed high similarity with other insect Sigma GSTs including the conserved glutathione and substrate binding sites. Quantitative tissue expression analysis suggested the mRNA levels for MdesGST-1 to be predominant in fat body, whereas for MdesGST-2 and MdesGST-3 in the midgut. Spatial expression during development suggested peak mRNA levels for both the Delta GSTs during larval development, while the Sigma GST in the pupal stage. During incompatible (larvae on resistant wheat) and compatible (larvae on susceptible wheat) interactions, the mRNA levels for MdesGST-1 were significantly higher in the former interaction, while for MdesGST-3 in the later. MdesGST-2 showed an equivalent expression pattern during both interactions. These results suggest that the Hessian fly Delta GSTs are important in detoxifying wheat allelochemicals during feeding, while the Sigma GST participates in metabolism of endogenous substrates. Results in this study will glean further knowledge about the detoxification mechanism employed by the Hessian fly during its interaction with wheat.