Tomato defense mechanisms against herbivorous insects

Abstract

The tomato plant is a vegetable crop of significant economical importance for the consumption of its edible berries and is considered a model plant within the Solanaceae. Cultivated tomato plants suffer from severe yield losses due to a variety of herbivorous pests. Insect herbivory has resulted in the evolution of a wide array of morphological and biochemical plant defense mechanisms. Plants respond to insect herbivory or wounding by expressing systemic signals that initiate different phytohormone signaling pathways. Systemin, an 18 amino acid peptide released from its 200 amino acid precursor prosystemin, coordinates the systemin-mediated signaling pathways in tomato which involves the activation of jasmonic acid and the release of volatile organic compounds. Tomato and its relatives also possess a wide range of glandular and non-glandular trichomes types. Glandular trichomes are specialized hairs which originate from the plants surface, capable of producing and releasing varying secondary metabolites. Many of the wild tomato species are more resistant to insect pests than cultivated tomatoes due to an enhanced production of resistance-related metabolites, such as acyl sugars, terpenes, and methyl ketones. Dissecting the systemin-mediated hormonal signaling pathways and trichome mediated defense responses in tomato will provide valuable information to improve future breeding strategies for new tomato varieties and to engineer tomato plants with enhanced insect resistance. Here, we review recent advances in molecular research on the role of systemic signaling and phytohormone pathways in the tomato defense response against insect herbivores, with a focus on systemin mediated signaling. Next, we highlight the role of different trichomes in tomato and its relatives and summarize the role of several important trichome-produced compounds in tomato.