Activation of ethylene-related genes in response to aphid feeding on resistant and susceptible melon and tomato plants

The simple gaseous compound ethylene (ET) has long been recognized as a common component of plant responses to insect feeding and pathogen attack. However, it is presently uncertain whether it plays a role in host-plant resistance to piercing-sucking insects such as aphids. In these experiments, we investigated the expression of key ET-associated genes in resistant and susceptible interactions in two model systems: the tomato-Mi-Macrosiphum euphorbiae (Thomas) (Hemiptera: Aphididae: Macrosiphini) system and the melon-virus aphid transmission gene (Vat)-Aphis gossypii Glover (Hemiptera: Aphididiae: Aphidini) system. We examined expression patterns of genes associated with ET synthesis, perception, signal transduction, and downstream response. When compared with control plants, plants infested with aphids showed marked differences in gene expression. In particular, ET signaling pathway genes and downstream response genes were highly upregulated in the resistant interaction between A. gossypii and Vat+, indicating ET may play a role in Vat-mediated host-plant resistance. A key integrator between the ET and jasmonic acid pathways (Cm-ERF1) showed the strongest response.