Submitted to: Journal of Insect Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/20/2008
Publication Date: 2/1/2009
Citation: Shukle, R.H., Mittapalli, O., Morton, P.K., Chen, M. 2009. Characterization and expression analysis of a gene encoding a secreted lipase-like protein expressed in the salivary glands of larval Hessian fly, Mayetiola destructor (Say). Journal of Insect Physiology. 55(2):104-111. Interpretive Summary: The Hessian fly is a gall midge that is present in all of the wheat producing regions of the United States and poses a significant economic threat to wheat production in terms of reduced grain yield. The most environmentally sound and cost effective control for the Hessian fly is resistant wheat. While resistant wheat is the most effective control method, the deployment of resistant wheat has led to the development within 5 to 10 years of biotypes of the pest that can overcome formerly resistant wheat. Virulent biotypes of the Hessian fly pose a continuing threat to wheat production and there is a need to identify alternative targets for resistance within the pest that could affect its ability to attack wheat. We have identified and characterized a gene that produces a secreted lipase-like protein in the salivary glands of larval Hessian fly. Lipases are enzymes that breakdown lipids and lipids are a major component of cell membranes. The attack of host cells by microbial pathogens involves penetration and damage of host cell membranes by physical or enzymatic means. Our interest in the secreted lipase-like protein was sparked because of its possible role in the interaction of Hessian fly larvae with wheat and the increased permeability and cell damage in wheat tissue near larval feeding sites. We speculate the secreted lipase-like protein is involved in feeding by larvae and may be a virulence factor in the attack of wheat by Hessian fly larvae. 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: The Hessian fly is a destructive pest of wheat particularly in the soft-winter-wheat region of the United States. In a salivary gland transcriptomics study we identified a full-length cDNA encoding a lipase-like protein expressed in the salivary glands of the larval Hessian fly, Mayetiola destructor (Say). BLASTp and conserved domain searches revealed the protein contained a lipase superfamily domain and similarity to lipases and phospholipases from other insects. A secretion signal peptide was identified at the amino terminus of the lipase-like protein indicating it was a secreted protein. Spatial analysis of transcript levels for the lipase-like protein in larval Hessian fly tissues by quantitative real-time PCR (qPCR) revealed the greatest level of transcript was in salivary gland tissue. Analysis of transcript levels during development showed the greatest level was detected in 1st-instar and early 2nd-instar larvae. Transcript levels for the lipase-like protein increased dramatically in larvae feeding on susceptible wheat but were detected at low levels in larvae feeding on resistant wheat. These data suggest the lipase-like protein is secreted into host-plant cells during larval feeding. We speculate the lipase-like protein could be involved in extra-oral digestion and changes in host-cell permeability as well as signaling in host-plant cells.