—Enzymes with terpene synthase activities and their relationships with TPSs. (A) Reported enzymes with terpene synthase activities. Three enzymes were listed with terpene synthase activities including prenyltransferase, TPS, and IDS. No sequence similarity was detected between prenyltransferase and TPS. However, PPD motif was detected to share homology between TPS and IDS. (B) Amino acid sequence alignment of PPD motif among sequences from both IDSs (locus names were labeled with black fonts) and TPSs (red fonts). Amino acid residues were indicated by capital letters in the right column. Letters highlighted by red, green, and blue colors shared 100% homology among sequences from both TPSs and IDSs. Amino acid residues highlighted by yellow color share high homology among IDSs but low homology among TPSs. (C) Phylogenetic analysis of amino acid sequences from PPD motifs. Sequences from IDSs were indicated by right braces and the remaining sequences were from TPSs. The subfamilies TPS-a, -b, -e/f, and -g were highlighted by purple, benzo, yellow, and orange colors. (D) The Ka/Ks analysis of 33 PPD amino acid residues from 34 IDS and 17 TPSs by the SLR program as described in Materials and Methods.