Location: Corn Insects and Crop Genetics Research
Title: A cadherin-like protein influences Bacillus thuringiensis Cry1Ab toxicity in the oriental armyworm, Mythimna separata Authors
Submitted to: Environmental Microbiology Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 14, 2013
Publication Date: June 1, 2013
Citation: Wang, L., Jiang, X., Luo, L., Sappington, T.W., Stanley, D.W., Zhang, L. 2013. A cadherin-like protein influences Bacillus thuringiensis Cry1Ab toxicity in the oriental armyworm, Mythimna separata. Environmental Microbiology Reports. 5(3):438-443. Interpretive Summary: The oriental armyworm, Mythimna separata (Walker), is one of the most important pests of corn in China, but is not the main target pest of transgenic Bacillus thuringiensis (Bt) corn plants expressing the Cry1Ab toxin. Many studies focus on the molecular mechanism of how Cry toxins work to kill target organisms. Often, but not always, a protein called cadherin is what a Cry toxin binds to in the target pest insect. However, the mechanism of Cry toxin to non-target organisms (including secondary pests like M. separata) is poorly understood. Our results, using a relatively new and powerful technique called RNA interference, indicate that the cadherin-like protein of M. separata serves as a receptor of the Cry1Ab toxin. This molecular interaction is probably why Cry1Ab has good efficacy in controlling M. separata, despite it being a non-target pest of transgenic Bt corn. This information will be used by university and government scientists in China and the U.S. to better understand the mechanism of Bt toxin activity against not only M. separata, but against the many secondary pests of corn and cotton in the U.S. that are in the same insect family.
Technical Abstract: A cadherin-like gene associated with larval midgut tissues was cloned from oriental armyworm, Mythimna separata (Walker). The full-length complementary DNA (cDNA) (named Ms-CAD, GenBank accession no. JF951432) was 5642 base pairs (bp) long, with an open reading frame encoding a 1757 amino acid polypeptide, showing characteristics typical of insect cadherin proteins. As with other insects, expression of Ms-CAD is predominantly in midgut tissue, but it differs significantly among instars, with highest expression in the fourth instar and lowest in newly-hatched larvae. Knocking-down expression of Ms-CAD by RNA interference decreased Cry1Ab susceptibility of M. separata, including reduced developmental duration of 3rd instars, increased larval weight, and reduced larval mortality. These results suggest that Ms-CAD is associated with Cry1Ab toxicity in M. separata, and is probably one of its receptors. These results provide the basis for revealing the insecticidal mechanism of Bacillus thuringiensis (Bt) Cry toxins in oriental armyworm, as well as a potential resistance mechanism.