Beet Armyworm Secretions Trigger Expression of Defense Genes in Tomato

Plant-induced defense against herbivores is typically done by rerouting photosynthates to the synthesis of defense compounds rather than growth and reproduction. Hence, it is important that plants are able to sense and differentiate mechanical injury from injury caused by herbivores. Oral secretions from caterpillars were found to contain elicitors of plant-induced responses such as production of volatile organic compounds (VOCs). However, there are limited studies that show whether these elicitors are from salivary glands or from other organs related to feeding, such as the ventral eversible gland (VEG).

In this study, secretions from the VEG of beet armyworm (Spodoptora exigua) caterpillars were examined for the presence of elicitors that could induce plant defenses. To test this, the activity of defense-related enzymes, transcript levels of defense-related genes and volatile organic compounds (VOC) emission in tomato plants damaged by S. exigua caterpillars with the intact VEG (VEGI) and compared it with tomato plants damaged by caterpillars without the VEG (VEGA).

Tomato plants damaged by the VEGI caterpillars expressed significantly higher amounts of defense-related enzymes than plants damaged by VEGA caterpillars. There was also an up-regulation in genes encoding for jasmonic acid as well as those genes involved in the production of terpene VOCs in plants damaged by VEGI caterpillars. This led to increased emissions of VOCs detected in the headspace of plants damaged by VEGI caterpillars. Furthermore, the oral secretions of the VEGA caterpillars were less effective in inducing expression of the defense genes. This verifies that VEG secretions of beet armyworm caterpillars contain elicitors of plant defense response in tomato.

 Learn more on this experiment by visiting http://www.biomedcentral.com/1471-2229/14/140.