Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2007
Publication Date: 4/18/2007
Citation: Johnson, E.T., Berhow, M.A., Dowd, P.F. 2007. Expression of a maize Myb transcription factor driven by a putative silk-specific promoter significantly enhances resistance to Helicoverpa zea in transgenic maize. Journal of Agricultural and Food Chemistry. 55(8):2998-3003. Interpretive Summary: The problem of ear mold toxins/carcinogens (mycotoxins) in corn causes hundreds of millions of dollars of losses to the U.S. each year and limits the exportability of U.S. corn. Insects can carry mycotoxin-producing fungi and damage corn so that these fungi may more readily colonize corn. The commercial Bt corn hybrids are effective against some ear feeding pests, but better control of others is needed. Using natural genes from corn, a novel gene combination directing the synthesis of corn earworm resistance compounds only to corn silks was evaluated in transgenic plants for activity against corn earworms. Successful synthesis of the resistance compounds was able to increase mortality in a corn earworm susceptible line to a level similar to a more resistant line. Proper introduction of the gene could result in more resistant corn which would have less insect damage and lower levels of mycotoxins, which would be safer for consumers and more acceptable to importers.
Technical Abstract: Hi II maize (Zea mays) plants were engineered to express maize p1 cDNA, a Myb transcription factor, controlled by a putative silk specific promoter, for secondary metabolite production and corn earworm resistance. Transgene expression did not enhance silk color, but about half of the transformed plant silks displayed browning when cut, which indicated the presence of p1-produced secondary metabolites. Levels of maysin, a secondary metabolite with insect toxicity, were highest in newly emerged browning silks. Insect resistance of transgenic silks, regardless of a visible browning reaction, was highest at emergence and declined with maturity. Mean survivor weights of corn earworm larvae fed mature browning transgenic silks were significantly lower than weights of those fed mature non-browning transgenic silks. Some transgenic pericarps browned with drying and contained similar molecules found in pericarps expressing a dominant p1 allele, suggesting the promoter may not be silk specific.