Submitted to: Insect Biochemistry and Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2005
Publication Date: 2/1/2006
Citation: Omprakash, M., Wise, I.L., Shukle, R.H. 2006. Characterization of a serine carboxypeptidase in the Salivary glands and fat body of the orange wheat blossom midge, Sitodiplosis mosellana (Diptera: Cecidomyiidae). Insect Biochemistry and Molecular Biology 36:154-160. Interpretive Summary: The orange blossom wheat midge (a small fly similar in appearance to mosquitoes) is the most important insect pest of wheat in western Canada and is also a pest of wheat on the north central plains of the United States. Historically, the only effective means of control of the pest was insecticide applications. Recently, a gene for resistance was characterized and incorporated into wheat cultivars. Due to the identification of only one gene for resistance there is concern about the development of biotypes of the pest capable of surviving on resistant wheat. We have provided the first molecular characterization of a gene from the wheat midge. The gene produces a protein digesting enzyme that is expressed in the salivary glands and differentially expressed between males and females in fat body (an insect organ similar to the liver in higher organisms). From our results, we propose the enzyme has two roles in the wheat midge. Secretion from the salivary glands indicates involvement in the digestion of storage proteins in the developing wheat kernel by feeding larvae. Expression in the fat body of females suggests a role like that described in female mosquitoes for a similar protein digesting enzyme that is expressed in fat body and transported to the eggs for the break down of yolk protein to provide nutrients to the developing embryo. The identification and characterization of genes that are important in the biology of the wheat midge is providing a better understanding of the pest at the molecular level. Such knowledge will provide novel approaches to the control of the pest to ensure durable resistant in wheat. This will benefit the agricultural community by providing improved pest control that increases yield and quality without increasing costs.
Technical Abstract: A full-length cDNA encoding a serine carboxypeptidase (designated SmSCP-1) was recovered from an ongoing salivary gland EST project of the wheat midge. The deduced 461-amino acid sequence had a putative signal sequence at the amino terminus, indicating it was a secreted protein. The protein shared homology with serine carboxypeptidases from other insects, mammals, plants, and yeasts. SmSCP-1 mRNA was expressed in all stages of development and detected in salivary gland and fat body tissues but not in midgut tissue. Expression analysis and quantitative real-time PCR assays in male and female wheat midges revealed the SmSCP-1 was up-regulated nearly 4-fold in the female midges compared to males. The wheat midge serine carboxypeptidase (SmSCP-1) most likely has a dual function. As a secreted digestive enzyme, it could play a role in mobilizing host-plant seed reserves for feeding larvae and as expressed in fat body could function as an exopeptidase in degradation of vitellogenin and/or in post-translational processing of other enzymes.