Study of gene expression in Zea maize induced by Helicoverpa zea herbivory

Helicoverpa zea (corn earworm caterpillars) were fed on Zea maize (corn plants) in order to ascertain which plant genes were affected by herbivory. Three treatments were performed on the maize plants: non-wounded maize plants, maize plants fed on by mock caterpillars (surgically cut, but still in possession of their salivary glands), and maize plants fed on by ablated caterpillars (salivary glands surgically removed). Feeding occurred for 48 hours followed by immediate flash freezing of the leaves in liquid nitrogen. RNA was extracted from the harvested leaf tissue and was used to prepare labeled complementary DNA with Cy-3 and Cy-5 dyes through the action of reverse transcription. The labeled cDNA was hybridized to maize oligo microarray chips and scanned with a microarray scanner.Results from the scanned microarray chips revealed a large number of genes in the maize plant genome that were affected by H. zea herbivory. The genes that experienced altered expression included ethylene pathway receptors chemical detoxification enzymes proteins and enzymes involved in DNA structure, replication and protection numerous control enzymes and receptors numerous general defensive proteins (secondary metabolites) and several genes involved in direct defense against microorganisms such as fungi and bacteria. These results are significant because they illustrate that more genes undergo altered expression in response to general wounding than in response to actual herbivory. This supports the idea that salivary gland extracts contain chemicals capable of suppressing and altering gene expression.