Plant terpenoid synthases: molecular biology and phylogenetic analysis

Abstract

This review focuses on the monoterpene, sesquiterpene, and diterpene synthases of plant origin that use the corresponding C10, C15, and C20 prenyl diphosphates as substrates to generate the enormous diversity of carbon skeletons characteristic of the terpenoid family of natural products. A description of the enzymology and mechanism of terpenoid cyclization is followed by a discussion of molecular cloning and heterologous expression of terpenoid synthases. Sequence relatedness and phylogenetic reconstruction, based on 33 members of the Tps gene family, are delineated, and comparison of important structural features of these enzymes is provided. The review concludes with an overview of the organization and regulation of terpenoid metabolism, and of the biotechnological applications of terpenoid synthase genes.

Figure 1

Organization of terpene biosynthesis in plants. DMADP, dimethylallyl diphosphate. IDP, isopentenyl diphosphate.

Figure 2

Biosynthesis of representative monoterpenes from GDP.

Figure 3

Biosynthesis of representative sesquiterpenes from FDP.

Figure 4

Biosynthesis of representative diterpenes involving ionization and cyclization of GGDP directly, and preliminary cyclization to CDP by protonation of the terminal double bond.

Figure 5

Phylogenetic tree of plant terpenoid synthases reconstructed by using Dayhoff’s (63) distances between proteins and the neighbor-joining method (64). Scale bar indicates 1% sequence divergence. Numbers are the actual bootstrap values of branches. Tpsa through Tpsf designate Tps gene subfamilies defined by a minimum of 40% identity between members at the amino acid level.

Figure 6

Alignment of representative deduced amino acid sequences of monoterpene, sesquiterpene, and diterpene synthases of grand fir. ag1, (E)-α-bisabolene synthase; ag2, myrcene synthase; ag4, δ-selinene synthase; and ag22, abietadiene synthase (20, 31, 50). Conserved tandem arginines are shaded yellow with the minimum mature protein indicated by a vertical bar. A conserved insert sequence is shaded green. Aspartate-rich motifs are shaded blue. Dots mark absolutely conserved residues (red), highly conserved histidines (green), a highly conserved serine (orange), conserved acidic residues (blue), conserved aromatic residues (purple), and a highly conserved cysteine (yellow). The glycosyl hydrolysase-like domain is underlined in red. The active-site domain is underlined in blue.