Present address: Alligator Biosciences, IDEON Delta 5, Scheele vägen 19 A, SE-223 70 LUND, Sweden.
Co-expression of N-terminal truncated 3-hydroxy-3-methylglutaryl CoA reductase and C24-sterol methyltransferase type 1 in transgenic tobacco enhances carbon flux towards end-product sterols
Article first published online: 28 AUG 2003
The Plant Journal
Volume 36, Issue 1, pages 12–20, October 2003
How to Cite
Holmberg, N., Harker, M., Wallace, A. D., Clayton, J. C., Gibbard, C. L. and Safford, R. (2003), Co-expression of N-terminal truncated 3-hydroxy-3-methylglutaryl CoA reductase and C24-sterol methyltransferase type 1 in transgenic tobacco enhances carbon flux towards end-product sterols. The Plant Journal, 36: 12–20. doi: 10.1046/j.1365-313X.2003.01851.x
- Issue published online: 28 AUG 2003
- Article first published online: 28 AUG 2003
- Received 29 April 2003; revised 17 June 2003; accepted 20 June 2003.
- carbon flux;
- 4-desmethyl sterols;
- 3-hydroxy-3-methylglutaryl CoA reductase;
- C24-sterol methyltransferase type 1;
- transgenic tobacco
The enzymes 3-hydroxy-3-methylglutaryl CoA reductase (HMGR) and C24-sterol methyltransferase type 1 (SMT1) have been proposed to be key steps regulating carbon flux through the sterol biosynthesis pathway. To further examine this hypothesis, we co-expressed the catalytic domain of Hevea brasiliensis HMGR (tHMGR) and Nicotiana tabacum SMT1 in tobacco, under control of both constitutive and seed-specific promoters, resulting in increased accumulation of total sterol in seed tissue by 2.5- and 2.1-fold, respectively. This enhancement is greater than when tHMGR and SMT1 were expressed singularly where, for example, seed-specific expression enhanced total sterols by 1.6-fold. Significantly, the relative level of 4-desmethyl sterols (end-product sterols) was higher in seed co-expressing tHMGR and SMT1 from seed-specific promoters (79% of total sterols) than when co-expressed from constitutive promoters (59% of total sterols) and similar to wild-type seed (80% of total sterols). These results demonstrate that HMGR and SMT1 work in concert to control carbon flux into end-product sterols and that the sterol composition can be controlled by the temporal activity of the promoters driving transgene expression. In addition, constitutive expression of the transgenes resulted in elevated accumulation of substrates for C4-demethylation reactions, which indicates that one or several enzymes catalysing such reactions limit carbon flow to end-product sterols, at least in a physiological situation when the carbon flow is upregulated.