Monday, December 10, 2007 - 8:17 AM

A transcription factor that modulates cowpea bruchid adaptation to plant defense

Ji-Eun Ahn, ji-eun-ahn@neo.tamu.edu1, Linda A. Guarino, l-guarino@tamu.edu2, and Keyan Zhu-Salzman, ksalzman@tamu.edu1. (1) Texas A&M university, Entomology, Norman E. Borlaug Center for Southern Crop Improvement, West Campus Building 1513, College Station, TX, (2) Texas A&M university, Entomology/Biochemistry and Biophysics, 103 Biochemistry/Biophysics Building, College Station, TX

Cowpea bruchid (Callosobruchus maculatus) adapts to soybean cysteine protease inhibitor scN by specific activation of a cathepsin B-like cysteine protease CmCatB. To understand the transcriptional regulation of CmCatB, we cloned a portion of its promoter and demonstrated its activity in Drosophila cells using a chloramphenicol acetyltransferase reporter system. Gel shift assays detected differential DNA binding activity between nuclear extracts of scN-adapted and -unadapted midgut. Two tandem chicken ovalbumin upstream promoter (COUP) elements were identified in the CmCatB promoter that specifically interacted with a protein factor unique to nuclear extracts of unadapted insect guts. Seven-up (Svp) is a COUP-TF-related transcription factor that interacted with the COUP responsive element. Anti-mosquito Svp antibody abolished the specific DNA binding activity in cowpea bruchid midgut extracts, suggesting the protein factor is an Svp homolog. Subsequent cloning of a cowpea bruchid Svp (CmSvp) indicated that it shares a high degree of sequence similarity with various COUP-TF/Svp family members. The protein was more abundant in scN-unadapted insect guts than scN-adapted guts. Furthermore, CmCatB expression was repressed when CmSvp was transiently expressed in Drosophila cells. These findings indicate that CmSvp may contribute to insect counter-defense, in part by inhibiting CmCatB expression under normal growth conditions, but releasing the inhibition when insects are challenged by dietary scN.

Species 1: Coleoptera Bruchidae Callosobruchus maculatus (cowpea weevil)