Abstract
Latex of a succulent shrub Euphorbia tirucalli includes flamable metabolites sterols and triterpenoids, and so can be processed into biofuel. We have isolated a gene for squalene synthase (EtSS), which produces the first lipophilic intermediate in the sterol-biosynthesis pathway. The 411 residues of EtSS amino-acid sequence exhibits high homology with those from other dicot plants, in contrast to low amino-acid identity to those from monocot plants. In situ hybridization analysis indicated that EtSS expression is dominant in cambia within bundle sheathes. N-terminal 380-residues of EtSS was overexpressed as a fusion protein in E. coli and this protein was subjected to in vitro enzyme reaction and GC-MS analysis to detect a product squalene. Overexpression of entire region of EtSS in E. tirucalli callus resulted in upregulation of phytosterol accumulation. This work was partly performed as one of the technology development projects of the "Green Biotechnology Program" in NEDO.
