Effect of a Unique Maize Defense Proteinase on Caterpillar Midgut Structure

Mississippi State University, Mississippi State MS

Investigators

Abstract

When plants are attacked by herbivorous insects, they often respond by producing proteins that protect them from being eaten. We have shown that a unique enzyme, a protease, coded for by the gebe mir1, accumulates in certain insect-resistant corn lines when they are attacked by the fall armyworm caterpillar. We have transferred the gene, mir1, into other plant cells using genetic engineering technology. When caterpillars eat these transgenic plant cells, their growth is retarded by 60 to 80%. It appears that caterpillars feeding on resistant plants or transgenic plant cells cannot use the nutrients in the plant for growth. Our hypothesis is that the protease damages the insect gut and prevents normal nutrient utilization. The purpose of this research project is to determine if the unique corn protease damages specific structures in the insect gut. To test this we will make mutations in mir1 that will change the characteristics of the enzyme. One mutation will eliminate protease activity, the other will remove a unique region of the enzyme. The mutated forms of mir1 will be transferred to plant cells. Transgenic plant cells that express mutated proteases will be fed to caterpillars. Then growth and gut structure of caterpillars fed transgenic plant cells expressing normal and mutated proteases will be assessed. If the protease activity is required to retard caterpillar growth and damage gut structure, then we expect that the normal protease will harm the caterpillars and the mutated forms will not. In addition, we will make pure preparations of the normal and mutated proteases by expressing mir1 and its mutated forms in insect cells. The purified proteases will be directly fed to the caterpillars to determine if they attack the insect gut. If the unique protease does specifically attack the insect gut, it may be possible, in the future, to use mir1 to genetically engineer plants to resist insect feeding.