ENHANCED INSECT RESISTANCE AND CROP MANAGEMENT FOR REDUCTION OF MYCOTOXINS IN MIDWEST CORN
Location: Crop Bioprotection Research
Title: Effects of elevated peroxidase levels and corn earworm feeding on gene expression in tomato
Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 24, 2012
Publication Date: December 15, 2012
Citation: Suzuki, H., Dowd, P.F., Johnson, E.T., Hum-Musser, S.M., Musser, R.O. 2012. Effects of elevated peroxidase levels and corn earworm feeding on gene expression in tomato. Journal of Chemical Ecology. v. 38(1):1247-1263.
Interpretive Summary: Insect damage causes billions of dollars in crop damage each year in the U.S., and can also contribute to the presence of fungal toxins in some crops, such as corn. Host plant resistance is a valuable tool for managing insects, but in order for effective breeding for resistance to occur, the most effective combinations of genes contributing to resistance, and how they interact, needs to be determined. Gene arrays from tomato were used to examine how pest resistance and other genes were affect by the high expression of one particular resistance gene. High expression of this gene apparently induced the increased expression of several other insect and disease defense genes, without adversely affecting other defensive genes or photosynthetic genes. This was in contrast to what was noted when insect feeding occurred, which increased several insect resistance genes, but repressed some disease resistance and photosynthetic genes. This information can lead to the more effective breeding of insect resistant plants, thereby increasing crop yields, reducing costs to consumers, and producing a healthier food supply.
Tomato gene arrays were used to investigate how high levels of transgenic peroxidase expression and feeding by the corn earworm, Helicoverpa zea, affected expression of defensive and other genes. High peroxidase activity significantly upregulated proteinase inhibitors and a few other defensive genes, as well as genes associated with iron and calcium transport and flowering. Feeding by H. zea tended to upregulate the same genes to a greater extent, whether wild type or high peroxidase plants were used, as well as some additional protease inhibitors and proteases. However, H. zea feeding also downregulated a number of genes, including lipoxygenase, disease resistance and some contributing to photosynthesis. qtPCR analysis using primers for representative defensive genes and tissue from a separate experiment run under similar conditions generally confirmed what was noted in the gene array analysis. There was some indication that multiple regulatory interactions were occurring because up or down regulation was not consistent among different treatments. Although high peroxidase plants generally upregulated defensive and other genes to a lesser extent than insect feeding, there were some examples where much higher upregulation occurred in the high peroxidase plants, or regulation was unchanged and significantly down regulated in insect damaged plants. In other cases, insect damaged high peroxidase plants had genes significantly upregulated to either a significantly greater, or lesser extent than insect damaged wild type plants. These results suggest levels of expression of a multifunctional gene, such as peroxidase and its products, can influence other expression systems apart from conventional signaling pathways, further indicating the complexity of plant defensive responses to insects.