Analysis of OneKP Transcriptomes Reveals Unequal Distribution of Terpene Synthase Genes Across Diverse Taxa in the Plant Kingdom

Terpenoids, the largest and most structurally diverse class of natural compounds on earth, are mostly synthesized by plants to be involved in various plant-environment interactions. Some terpenoids are classified as primary metabolites essential for plant growth and development. Terpene synthases (TPSs), the key enzymes for terpenoid biosynthesis, are the major determinant of the tremendous diversity of terpenoid carbon skeletons. Most of our current knowledge of terpene synthase genes is based on studies in model species of plants. Among the ~50 plants with sequenced genomes, the vast majority (94%) of them belong to angiosperms, while only one from each of the three clades: gymnosperm, bryophyte and lycophyta. Given the high diversity of terpenoids, taxonomically specialized TPS genes should exist in some plant species or families. For example, the recent discovery of microbial-type TPS genes in Selaginella moellendorffii has provided new insights into the evolution of this gene family. As more genome and transcriptome sequences from non-model species are available, it is possible to obtain more TPS genes and examine them within a broader range of taxa. The One Thousand Plant Transcriptomes Constorium (OneKP) provides such a good resource, which contains transcriptomes for over 1000 plant species that span almost all major plant clades (from green algae to flowering plants). We checked transcriptomes of 1175 representative species using hmmsearch for the presence of Terpene synthase. 9876 plant TPSs are found in 842 species, and they are present and abundant in all clades of land plants. While we hardly find any TPSs in algae, they expanded dramatically upon the transition of plant life to land.