## 2 Results and Discussion
### Phylogenetic Tree and Homology-Based Model of LLA66  
We also performed phylogenetic tree analysis and found that LLA66 was more homologous to long-chain _cis_-prenyltransferases (Figure 5), unlike the C40/C45 products identified in LLA66-expressing yeast. To explain this discrepancy, we generated the homology-based model of LLA66 (Figure 6) based on the structure of _S. aureus_ UPPS. When the LLA66 model is superimposed and compared with the structure of _E. coli_ UPPS, we found that the large amino acids, such as N117 and/or L121 in the LLA66 structure, could limit the final chain lengths. The corresponding residues in _E. coli_ UPPS structure are smaller Ala92 and Glu96, respectively, in the middle of the active site, while L137 at the bottom was shown to determine the C55 product [17]. Therefore, LLA66 could be evolved from a long-chain _cis_-prenyltransferase in this plant through the putative mutation(s). In eukaryotes, dolichols of C70-120 play indispensable roles as glycosyl carrier lipids for the biosynthesis of glycoproteins in the endoplasmic reticulum. For this function, one human _cis_-prenyltransferase (DHDDS) and two yeast _cis_-prenyltransferases (Rer2 and Srt1), which can synthesize long-chain products, are known. Rer2 was found to be the major player for glycoprotein biosynthesis in yeast. We demonstrate here that LLA66 produced C40 and C45 products in _S. cerevisiae_, but could not rescue the growth defect of the _rer2\(\Delta\)_ mutant because it failed to make a long enough lipid for protein glycosylation in yeast. Because the genome of _L. longiflorum_ is not sequenced, LLA66 is the only identified _cis_-prenyltransferase so far. Judging from long-chain glycosyl carrier lipids and several _cis_-prenyltransferases in other plants, there are likely other _cis_-prenyltransferases, but not LLA66, responsible for biosynthesis of glycoproteins in _L. longiflorum_. In addition to dolichols, seed plants produce other types of \(Z\),_E_-mixed polyisoprenoids, such as ficaprenol (tri-_trans_, poly-_cis_-polyprenol, C45-75) and betulaprenol (di-_trans_, poly-_cis_-polyprenol, C30-45 and \(\geq\)C70) in abundance [15]. For the nine _cis_-prenyltransferases identified from the genome of _A. thaliana_, one expressed in _E. coli_ produced a C130 long-chain product [18]. Others yield shorter products, including a C80 by LEW1 expressed in _E. coli_[19], a C35 _cis_, _trans_-mixed heptaprenyl diphosphate by the synthase expressed in _E. coli_[20], and a mixture of polyprenols with a dominating 7-isoprene preenol (C35) by _At_CPT6 expressed in _S. cerevisiae_[21]. Figure 5: Phylogenetic tree analysis. Data showing phylogenetic distances of LLA66 from other _cis_-prenyltransferases in human, _A. thaliana_, _Solanum Lyopersicum_, _S. cerevisiae_, and _E. coli_. Similarly, various products were ascribed to the seven tomato _SIC_PTs [a single preonl in a range Pren-2 (C10) to Pren-4 (C20) for _SIC_PT1, _SIC_PT2, and _SIC_PT6, a single Pren-13 (C65) for _SIC_PT3, and medium-chain-length products, Pren-5 (C25) to Pren-13 (C65) with no clear distribution profile for _SIC_PT4, _SIC_PT5, and _SIC_PT7] [14]. Interestingly, since only one of the tomato CPTs, _SIC_PT3, was shown to complement the growth defect of the _rer2\(\Delta\)_ mutant, only this enzyme has been postulated to be involved in dolichol biosynthesis. RNAi-mediated suppression of _SIC_PT3 resulted in a \(\sim\)60% decrease in dolichol content. However, the involvement of _SIC_PT3 in dolichol biosynthesis requires the participation of a distantly related partner protein, designated as a CPT-binding protein (_SIC_PTBP), which is a close homolog of the human Nogo-B receptor for supporting DHDDS activity [22]. A very short-chain C10 nervyl diphosphate, produced from condensation of IPP with DMAPP catalyzed by a _cis_-penyltransferase, has been identified in tomatoes, serving as a precursor to monoterpenes [23]. LLA66 is regulated by gibberellin during the development of lily anthers [24], but the real function is still unknown.