Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/28/2006
Publication Date: 11/30/2006
Citation: Mittapalli, O., Nagesh, S., Williams, C.E., Shukle, R.H. 2006. Expression patterns of antibacterial genes in the Hessian fly. Journal of Insect Physiology. 52:1143-1152. Interpretive Summary: The Hessian fly is the major insect pest of wheat in the eastern soft-winter-wheat production area of the United States. The most effective method of control for the pest is through the planting of resistant wheat. However, the appearance of biotypes of the pest that are able to survive and develop on formally resistant wheat is a threat to the durability of resistance and the protection of wheat. Despite its importance as a pest, there is scant knowledge at the molecular level about the Hessian fly or its interaction with wheat. This in turn limits the ability of scientists and breeders to employ new technology to enhance the durability of resistance in wheat. We have developed a program to identify genes that allow the pest to feed and develop on wheat. From this program we have identified two genes expressed in the midgut of larval Hessian fly that produce antimicrobial (bacteria killing) proteins called ‘defensins.’ These antimicrobial proteins are important in defending the larvae from bacteria they encounter while feeding on wheat plants. Knowledge about these genes and other genes important in the adaptation of Hessian fly larvae to feeding on wheat will help scientists devise innovative methods for plant resistance to ensure durable resistant wheat to prevent yield loss due to Hessian fly infestation. The agricultural community (crop producers and commodity groups) will benefit from such durable resistance through increased yield and quality without increased cost.
Technical Abstract: We report the characterization of two putative Hessian fly defensins (designated MdesDEF-I and MdesDEF-II) that were recovered from a larval midgut EST library. The deduced amino acid sequences of MdesDEF-I and MdesDEF-II contained six cysteine residues, which are highly conserved among insect defensins. Reverse transcription PCR (RT-PCR) analysis indicated that MdesDEF-I mRNA was expressed in larval midgut, salivary glands and fat body, but only in feeding instars (1st and 2nd) during development. However, MdesDEF-II was expressed constitutively in all larval tissues and stages of development examined. Quantitative real-time PCR (qPCR) and RT-PCR with different number of amplification cycles revealed that both MdesDEF-I and MdesDEF-II were up-regulated in compatible Hessian fly/wheat interactions. The MdesDEF-I and MdesDEF-II transcripts were 115- and 220-fold more abundant in four-day old virulent larvae compared to similar aged avirulent larvae. These results could provide clues to the factors that enable virulent Hessian fly larvae to successfully feed and develop in compatible interactions.