Evolution of TPS20-related terpene synthases influences chemical diversity in the glandular trichomes of the wild tomato relative Solanum habrochaites

A systematic screen of volatile terpene production in the glandular trichomes of 79 accessions of Solanum habrochaites was conducted and revealed the presence of 21 mono- and sesquiterpenes that exhibit a range of qualitative and quantitative variation. Hierarchical clustering identified distinct terpene phenotypic modules with shared patterns of terpene accumulation across accessions. Several terpene modules could be assigned to previously identified terpene synthase (TPS) activities that included members of the TPS-e/f subfamily that utilize the unusual cis-prenyl diphosphate substrates neryl diphosphate and 2z,6z-farnesyl diphosphate. DNA sequencing and in vitro enzyme activity analysis of TPS-e/f members from S. habrochaites identified three previously unassigned enzyme activities that utilize these cisoid substrates. These produce either the monoterpenes α-pinene and limonene, or the sesquiterpene 7-epizingiberene, with the in vitro analyses that recapitulated the trichome chemistry found in planta. Comparison of the distribution of S. habrochaites accessions with terpene content revealed a strong preference for the presence of particular TPS20 alleles at distinct geographic locations. This study reveals that the unusually high intra-specific variation of volatile terpene synthesis in glandular trichomes of S. habrochaites is due at least in part to evolution at the TPS20 locus.