The co-regulation of caterpillar and plant defense genes

The relationship between plants and insects is incredibly intricate, involving complicated cascades of biochemical pathways. Nicotine is an alkaloid synthesized in the roots of tobacco plants and transferred systematically in the plant in response to insect damage. Nicotine functions as an inducible chemical defense compound upon herbivory. While at the same time the fate of the caterpillar is dependent on its digestive performance and the ability to overcome toxic components of its diet. This is especially true for natural plant allelochemicals. Insects use detoxification genes such as cytochrome P450s, and glutathione S-transferases that are known to be inducible by xenobiotics, and are involved in host plant adaptation. In this experiment tobacco plants were grown from seeds in an environmentally controlled growth chamber for 8 weeks. Sixth instar Helicoverpa zea caterpillars were caged onto individual tobacco leaves, one caterpillar per plant, and allowed to feed for 24 hours, periodically repositioning the cage to ensure optimal herbivory. The leaves and the caterpillars were harvested and RNA was purified from each sample (plant and caterpillar) and labeled with cyanine 3 or cyanine 5 dyes, which then was hybridized onto tobacco oligo microarrays. Analysis of the arrays produced hundreds of significantly altered genes in both the tobacco plant and caterpillar in comparison to their controls. The results in this study show how tobacco plants respond to caterpillar herbivory and with the advent of caterpillar microarrays we can show for the first time how caterpillars respond on a genomic scale to these challenges.