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United States Department of Agriculture

Agricultural Research Service


Location: Crop Bioprotection Research

2011 Annual Report

1a. Objectives (from AD-416)
Make publicly available a predictive computer program for mycotoxin levels in Midwest corn and adapt as necessary for a wider range of human food use corn varieties. Use molecular biological approaches to discover, introduce, and evaluate new insect resistance genes (producing bioactive proteins and secondary metabolites), alone and in combination. Use molecular biological approaches to discover, introduce, and evaluate plant-derived selectable markers for transgnic plant production.

1b. Approach (from AD-416)
As part of the process of making the program publicly available, feedback on the present state of the program will be sought and utilized as appropriate. An economic module to assist in making control decisions will be developed and incorporated. The program will be tested for utility in food grade corn by comparing actual field collected data with predicted levels and correcting as necessary empirically. Genes identified in the prior project that are potentially useful in combination will be examined in model systems and further evaluated. New genes of potential use will be identified through functional targeting of cDNA, array-based technology. Molecular evolution of genes coding for resistance proteins will be utilized to further optimize efficacy against insects, while at the same time minimizing vertebrate effects. Gene product efficacy will be examined in model systems and in regenerated corn. Plant-derived genes involved in toxin resistance will be the ultimate focus of the investigation, although genes from other sources will initially be examined if appropriate plant-derived gene sequence information is not yet sufficient for cloning. Efficacy of target gene products as selectable markers and against insects, alone and in combination with insect-active genes, will be investigated.

3. Progress Report
As part of studies to determine what structural components are important in determining protein activity against insects, plants expressing a modified peptide were evaluated for insect resistance. Increased resistance was noted for the two major insect pests tested in plants containing the gene. As part of studies to determine which genes are involved in lowering mycotoxin levels in popcorn, ears were collected from popcorn fields, rated for insect and mold damage, and analyzed for mycotoxins. Damaged ears were stored for future use in gene expression analysis. As part of studies to determine which insect resistance genes may be added or lost when breeding for higher yields, leaves were collected from corn inbred parent and progeny and found to have different levels of insect resistance. The leaves were also evaluated for differential gene expression in order to determine which genes may be involved in increased insect resistance. As part of studies to determine if previously unreported genes that code for proteins that have targets in insects may be involved in insect resistance, a clone of a gene that was upregulated in insect resistant tissue was expressed and evaluated for effects on insects. As part of studies designed to maintain effective levels of insect resistance chemicals throughout the life of the corn plant, novel regulatory sequences were identified in maize genes which may contribute to the biosynthesis of an insect-defense chemical produced primarily in seedlings. As part of studies to determine if noncrop plants may have metabolites coded for by genes that may be adaptable to crop plants, new fungal metabolites were evaluated for effects on insects, and some active against insects were found.

4. Accomplishments
1. Active structures of insect resistance chemicals determined. Insect damage and associated corn ear mold toxins cause hundreds of millions of dollars in losses each year. A series of related compounds from different plant families were tested for their ability to slow insect growth by Agricultural Research Service scientists in the Crop Bioprotection Research Unit at the National Center for Agricultural Utilization Research Center, Peoria, IL, against two major corn pests. In general, their ability to slow insect pest growth depended on whether sugars were part of the molecules or not. Chemicals from soybeans and switchgrass were discovered to slow the growth of insect pests for the first time. This knowledge can be used to guide breeding for insect resistance in crop plants, thereby enhancing yield and quality.

2. Insect resistant low lignin switchgrass identified. U.S. dependence on foreign oil causes economic hardships to consumers, businesses and manufacturing. Biomass energy crops, such as switchgrass, may help alleviate this dependence, but high lignin levels (which may be important in insect resistance) interfere with the production of ethanol. Field grown leaves from lines developed at the ARS location in Lincoln, Nebraska, were tested for resistance against fall armyworms in a three year study by ARS scientists in the Crop Bioprotection Research Unit at the National Center for Agricultural Utilization Research Center, Peoria, IL. Two of the low-lignin lines were as resistant as the high-lignin lines. This information will help guide the development of sustainable lines of switchgrass for bioenergy use, thereby reducing the dependence on foreign oil and thus reduce the trade imbalance by billions of dollars, and stabilize prices for consumers.

3. Expression levels of one insect resistance gene influences expression levels of others. Insect damage of crops causes hundreds of millions of dollars in losses each year. Although a number of insect resistance genes have been identified in plants, there is little information on how they interact. A study initiated by ARS scientists in the Crop Bioprotection Research Unit at the National Center for Agricultural Utilization Research Center, Peoria, IL, and cooperators at Western Illinois University, Macomb, IL, using tomato gene array analysis indicated when one resistance gene was overexpressed by means of biotechnology, the expression of other insect and disease resistance genes was also increased without adversely affecting genes involved in photosynthesis. When insects fed on wild type leaves, additional insect resistance genes were expressed at high levels, but some disease resistance genes and photosynthesis genes were expressed at lower levels than in non-insect damaged wild type leaves. This knowledge should lead to more effective deployment of insect resistance genes in plants, resulting in lower cost and better quality agricultural products for consumers.

Review Publications
Dowd, P.F., Berhow, M.A., Johnson, E.T. 2011. Differential activity of multiple saponins against omnivorous insects with varying feeding preferences. Journal of Chemical Ecology. 37(5):443-449.

Johnson, E.T., Dowd, P.F., Liu, Z., Musser, R.O. 2011. Comparative transcription profiling analyses of maize reveals candidate defensive genes for seedling resistance against corn earworm. Molecular Genetics and Genomics. 285(6):517-525.

Last Modified: 05/27/2017
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