Reverse-Genetic Characterization of Solasonine-Based Chemical Defense in Eggplant

Abstract

Plants and insects interact with each other in the environment, and among these interactions, plant insect herbivore interactions are of considerable ecological and agricultural consequences. Plants have a rich repertoire of secondary metabolites which are species/family specific, which serve the purpose of combating various biotic and abiotic stressed, which includes herbivory. Steroidal alkaloids found in Solanaceae family is an example of class of such secondary metabolites. Umesh et al. 2021 using various insect assays in 5 eggplant varieties containing varying amounts of steroidal alkaloid contents demonstrated that steroidal alkaloid solasonine found in eggplant (Solanum melongena) negatively affects the preference and performance of generalist folivore tobacco cutworm (Spodoptera litura) thus indicating that solasonine might be involved in protection of eggplant from insect herbivores. Lucier et al. 2024 decoded the steroidal alkaloid biosynthesis pathway from cholesterol in eggplant and determined the genes involved, with UGT93N3 being the terminal gene in solasonine biosynthesis. Using this information, we hypothesized that high solasonine content is indeed responsible for lower preference and performance of high solasonine containing variety JK Purple Long. To test this hypothesis, we performed reverse genetic characterization of terminal solasonine biosynthesis gene UGT93N3 using virus-induced gene silencing (VIGS) and virusmediated overexpression (VOX) to silence and overexpress UGT93N3 gene respectively for reducing and increasing solasonine content in eggplant variety JK Purple Long and performed insect preference (dual-choice assays) and performance (neonate mortality assays) assays to analyze the effect of solasonine content on preference and performance of tobacco cutworm.