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United States Department of Agriculture

Agricultural Research Service


Location: Crop Bioprotection Research

2013 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:
This report documents progress for the bridging Project 3620-42000-041-00D and continues research from Project 3620-42000-040-00D which terminated in October of 2010. ARS Crop Bioprotection Research Unit scientists at the National Center for Agricultural Utilization Research (NCAUR), Peoria, Illinois, are working to discover new insect resistance mechanisms that can be integrated into corn to control corn ear insect pests and associated fungi that produce toxins. 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. Ribonucleic acid (RNA) was extracted from ears, and relative gene expression was determined using gene microarray analysis. Expression changes in some resistance genes were associated with differences in mycotoxin production. As part of studies to determine which insect resistance genes may be added or lost when breeding for higher yields, leaves were collected from a second series of corn inbred parent and progeny and found to have different levels of insect resistance. Changes in expression of a few resistance genes were associated with increased insect resistance. In studies designed to determine which of a number of similar proteins may be involved in insect defense, the relative expression of different protease inhibitors in different sorghum tissues were determined. Relevant inhibitory proteins produced from sorghum DNA or RNA will be tested for activity against insects in the future. As part of studies to determine the role of photosynthetic components in insect resistance, leaves from mutant lines of corn were compared with normal lines for insect resistance in the presence and absence of light. In studies designed to discover novel chemicals that defend against insects, extracts from range plants, and extracts and pure compounds from novel fungi were found to be active against agriculturally important pest caterpillars. Progress achieved during the life of the bridging project has the potential to benefit researchers in allied fields from academia, government, and industry; and will facilitate the development of corn lines with reduced levels of insect damage and fungal toxins in kernels.

4. Accomplishments
1. Environmental influences on pest resistance gene expression in popcorn kernels determined. Insect damage causes hundreds of millions of dollars of losses in the U.S. alone, and is often associated with ear mold toxins in corn. Plant resistance is an economical means to manage insects, but there continues to be a need for determining what genes are involved in producing resistance. Maize gene microarrays were used to compare gene expression in popcorn kernels from commercial fields in three different growing seasons at two sites. Differentially expressed genes coded for directly toxic proteins or those that interfere with nutrition, proteins involved in forming physical barriers, and regulatory proteins. Based on differing levels of expression, changes in expression of some resistance genes were associated with varying levels of ear mold toxins. This knowledge can be used to guide breeding for insect resistance in crop plants, thereby enhancing yield and quality.

2. Regulatory site for gene involved in producing an important insect resistance chemical in corn identified. Insect damage causes hundreds of millions of dollars of losses in the U.S. alone, and is often associated with ear mold toxins in corn. Plant resistance is an economical means to manage insects, but there continues to be a need for determining what genes are involved in producing resistance. To obtain more information about how the production of an insect-defensive chemical is regulated at the genetic level, chromosomal segments of a critical gene involved in production of the protective chemical were isolated from four different wild relatives of corn that are more insect resistant. Nearly identical segments among all the isolated chromosomal regions, were identified for the first time, which, based on location relative to the gene, are likely to be binding sites for the regulatory protein. This information suggests the chromosome segments are involved in regulating the production of the protective chemical. These segments could be used in future experiments to identify/isolate the gene coding for the regulatory protein, ultimately leading to enhanced corn yields and quality.

Review Publications
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. 38(1):1247-1263.

Dowd, P.F., Sarath, G., Mitchell, R., Saathoff, A.J., Vogel, K.P. 2013. Insect resistance of a full sib family of tetraploid switchgrass Panicum virgatum L. with varying lignin levels. Genetic Resources and Crop Evolution. 60(1):975-984.

Dowd, P.F., Johnson, E.T., Price, N.P. 2012. Enhanced pest resistance of maize leaves expressing monocot crop plant derived ribosome inactivating protein and agglutinin. Journal of Agricultural and Food Chemistry. 60(1):10768-10775.

Last Modified: 06/26/2017
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