Plant glandular secreting trichomes are epidermal protuberances that produce structurally diverse specialized metabolites, including medically important compounds. Trichomes of many plants in the nightshade family (Solanaceae) produce O-acylsugars, and in cultivated and wild tomatoes these are mixtures of aliphatic esters of sucrose and glucose of varying structures and quantities documented to contribute to insect defense. We characterized the first two enzymes of acylsucrose biosynthesis in the cultivated tomato Solanum lycopersicum. These are type I/IV trichome-expressed BAHD acyltransferases encoded by Solyc12g006330─or S. lycopersicum acylsucrose acyltransferase 1 (Sl-ASAT1)─and Solyc04g012020 (Sl-ASAT2). These enzymes were used-in concert with two previously identified BAHD acyltransferases-to reconstruct the entire cultivated tomato acylsucrose biosynthetic pathway in vitro using sucrose and acyl-CoA substrates.Comparative genomics and biochemical analysis of ASAT enzymes were combined with in vitro mutagenesis to identify amino acids that influence CoA ester substrate specificity and contribute to differences in types of acylsucroses that accumulate in cultivated and wild tomato species. This work demonstrates the feasibility of the metabolic engineering of these insecticidal metabolites in plants and microbes.Solanum | glandular trichomes | acylsugar | specialized metabolism | genotype to phenotype P lants are masters of metabolism, producing hundreds of thousands of small molecules known as specialized metabolites, which vary widely in structure, abundance, and physical and biological properties. These metabolites tend to be produced by enzymes that evolve faster than those that produce "central" metabolites such as amino acids, nucleotides, sugars, and cofactors (1-3), and the pathways and metabolic intermediates involved in biosynthesis of many specialized metabolites remain mysterious. Despite the growing availability of genomic DNA sequences, understanding the genetic and biochemical mechanisms that contribute to this phenotypic diversity and plasticity presents enduring and major challenges in plant biochemistry. It is of great interest to understand and manipulate the biosynthesis of these biologically active molecules.Specialized metabolites typically are produced in a cell-or tissue-specific manner and are generally limited in their taxonomic distribution. Glandular secreting trichomes provide an example of such a differentiated structure; these epidermal "hairs" produce a variety of metabolites of importance to humans, including aromatic flavor components (e.g., in hops for beer and Mediterranean herbs for cooking), psychoactive cannabinoids in Cannabis, and the antimalarial drug artemisinin in Artemisia annua (4, 5).Some trichome-produced metabolites have documented direct and indirect antiherbivore activities (4, 6-8). For example, acylsugars are a group of structurally related specialized metabolites produced in plants of the nightshade family-the Solanaceae (9, 10). Characterized examples ...