Geranyllinalool synthases in Solanaceae and other angiosperms constitute an ancient branch of diterpene synthases that are involved in the synthesis of defensive compounds.

Many angiosperm plants, including basal dicots, eudicots, and monocots, emit (E,E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT), which is derived from geranyllinalool, in response to biotic challenge. An Arabidopsis geranyllinalool synthase (GLS) belonging to the e/f clade of the terpene synthase (TPS) family and two Fabaceae GLSs that belong to the TPS-g clade have been reported, making it unclear which is the main route to geranyllinalool in plants. We identified a tomato (Solanum lycopersicum) TPS-e/f gene TPS46 encoding geranyllinalool synthase (SlGLS), and a homolog (NaGLS) from Nicotiana attenuata. The Km value of SlGLS for GGPP was 18.7 μM, with a Kcat value of 6.85 s-1. In leaves and flowers of N. attenuata, which constitutively synthesize 17-hydroxygeranyllinalool glycosides, NaGLS is expressed constitutively but the gene can be induced in leaves with methyljasmonate (MeJA). In tomato, SlGLS is not expressed in any tissue under normal growth but is induced in leaves by alamethicin and MeJA treatments. SlGLS, NaGLS, AtGLSs and several other GLSs characterized only in vitro come from four different eudicot families and constitute a separate branch of the TPS-e/f clade that diverged from kaurene synthases (KSs), also in the TPS-e/f clade, before the gymnosperm/angiosperm split. The early divergence of this branch and the GLS activity of genes in this branch in diverse eudicot families suggest that GLS activity encoded by these genes predates the angiosperm-gymnosperm split. However, while a TPS sequence belonging to this GLS lineage was recently reported from a basal dicot, no representative sequencess have yet been found in monocot or non-angiospermous plants.