Plant specialized metabolites are compounds produced in specific lineages whose synthesis most likely arose as adaptations to specific ecological conditions. One group of these compounds are acylsugars, which are produced in the glandular trichomes of many species in the Solanaceae family. Research indicates that differences in acylsugar core and acyl chains alter the effects of these compounds on insect deterrence or mortality. We can use natural chemical diversity to study what effects different acylsugars have on insects using in vitro techniques, but in planta methods are preferred. Identification of biosynthetic genes allows us to genetic engineer these pathways into plants to more precisely study the impact of these compounds in planta. This study is comprised of two projects characterizing biosynthetic pathways present in Solanum pennellii and Solanum quitoense. We are interested in how acylglucoses are made in S. pennellii-the first project focused on identification of an acylsucrose fructofuranosidase in S. pennellii, a wild relative of cultivated tomato. This S. pennellii glycosyl hydrolase converts acylsucroses to acylglucoses, the predominant acylsugar in several accessions of this species. In vitro and in planta data show this enzyme accepts S. pennellii P-type acylsucroses as substrates, but not F-type acylsucroses from cultivated tomato. Whether the plant produces P- or F-type acylsucroses is determined by different enzymatic activities of acyltransferases that alter acylation pattern in cultivated tomato and S. pennellii-representing a three gene epistatic interaction between those genes and the acylsucrose fructofuranosidase. Acylinositols represent a novel type of acylsugar produced in the Solanum genus, however, the biosynthetic pathway has not been studied. My second project involved characterization of the biosynthesis of these myo-inositol containing acylsugars in Solanum quitoense. VIGS analysis suggested this BAHD acyltransferase acetylates triacylinositols and in vitro analysis confirmed that hypothesis. Further VIGS analysis and in vitro assays identified an inositol acyltransferase that possessed characteristics matching other acylsugar biosynthetic enzymes, but this BAHD acyltransferase acylated myo-inositol at an aberrant acylation position. Alternative hypotheses were offered to reconcile the in vitro and in vivo results. Together, these two projects represent first steps towards understanding how the array of acylsugars in Solanaceae species are produced.
Read
