Studies in phytosterol biosynthesis

Sterols are indispensable compounds in all eukaryotes, because they are structural components of plasma membranes. In mammals, insects, and higher plants, sterols are also converted to steroidal hormones. Because of their chemical significance, the main pathway of sterol biosynthesis has been studied extensively, and is believed to be fully understood (). The differences in the biosynthesis of sterols between higher plants and yeast/mammals are generally accepted to begin at the cyclization step of 2,3-oxidosqualene, a common precursor. Ergosterol and cholesterol are biosynthesized via lanosterol, catalyzed by lanosterol synthase (LAS), in yeast and in mammals (, ), respectively. Phytosterols, such as campesterol and sitosterol, are biosynthesized via cycloartenol and catalyzed by cycloartenol synthase (CAS) in higher plants () (, ). Recently, however, three different laboratories have identified LAS genes from dicotyledonous plant species including Arabidopsis thaliana (, ), Panax ginseng (), and Lotus japonica () using a yeast expression system. The existence of LAS genes in the plant kingdom led us to address the question of whether the biosynthetic pathway of phytosterols via lanosterol as the first cyclic intermediate exists.

Phytosterol side chain biosynthesis | SpringerLink

Phytosterol Biosynthesis - SlideShare

Enhanced Triterpene and Phytosterol Biosynthesis in …

Applying 13C-{1H}{2H} nuclear magnetic resonance (NMR) techniques, the elucidation of deuterium on C-19 behavior of phytosterol provided evidence that small amounts of phytosterol were biosynthesized via lanosterol.

PHYTOSTEROL BIOSYNTHESIS IN RIPENING TOMATOES …

We designate the biosynthetic pathway to phytosterols via lanosterol “the lanosterol pathway.” LAS1 expression is reported to be induced by the application of jasmonate and is thought to have evolved from an ancestral cycloartenol synthase to a triterpenoid synthase, such as β-amyrin synthase and lupeol synthase.


Biosynthesis of the Phytosterol Side Chain

N2 - Different combinations of three rate-limiting enzymes in phytosterol biosynthesis, the Arabidopsis thaliana hydroxyl methylglutaryl CoA1 (HMGR1) catalytic subunit linked to either constitutive or seed-specific β-conglycinin promoter, and the Glycine max sterol methyltransferase1 (SMT1) and sterol methyltransferase2-2 (SMT2-2) genes, under the control of seed-specific Glycinin-1 and Beta-phaseolin promoters, respectively, were engineered in soybean plants. Mature seeds of transgenic plants displayed modest increases in total sterol content, which points towards a tight control of phytosterol biosynthesis. However, in contrast to wild-type seeds that accumulated about 35% of the total sterol in the form of intermediates, in the engineered seeds driven by a seed-specific promoter, metabolic flux was directed to Δ 5-24-alkyl sterol formation (99% of total sterol). The engineered effect of end-product sterol (sitosterol, campesterol, and stigmasterol) over-production in soybean seeds resulted in an approximately 30% increase in overall sitosterol synthesis, a desirable trait for oilseeds and human health. In contradistinction, increased accumulation of cycloartenol and 24(28)-methylencylartanol (55% of the total sterol) was detected in plants harbouring the constitutive t-HMGR1 gene, consistent with the previous studies. Our results support the possibility thatmetabolic flux of the phytosterol family pathway is differentially regulated in leaves and seeds.

Phytosterol Biosynthesis and Untilization ..

Recently, lanosterol synthase genes were identified from dicotyledonous plant species including Arabidopsis, suggesting that higher plants possess dual biosynthetic pathways to phytosterols via lanosterol, and through cycloartenol.

Biosynthesis of Phytosterols ..

Lanosterol has been identified from several plant extracts including the latex of many Euphorbia plants (–), but whether lanosterol is the first cyclic intermediate in phytosterol biosynthesis in these plants is controversial. Because labeled cycloartenol was converted to lanosterol in the latex, but not vice versa (), lanosterol was not believed to be the first cyclic intermediate. However, it has been also reported that no conversion of cycloartenol to lanosterol has been demonstrated using the latex of Euphorbia lathyris (). Thus, whether Euphorbia plants with lanosterol have the lanosterol pathway has not been established. This argument may be resolved by means of a tracer experiment using the [6-13C2H3]MVL. Although this study found the lanosterol pathway only in Arabidopsis, one may clarify whether the lanosterol pathway exists generally in the plant kingdom by performing the tracer experiment using identified LAS genera, Panax and Lotus. Additionally, other plant species, for example, those of Euphorbia, Ochromonas, Nicotina, Pinus, and Pea, in which the lanosterol pathway has not been identified () can also be examined.

Dual biosynthetic pathways to phytosterol via …

AB - Different combinations of three rate-limiting enzymes in phytosterol biosynthesis, the Arabidopsis thaliana hydroxyl methylglutaryl CoA1 (HMGR1) catalytic subunit linked to either constitutive or seed-specific β-conglycinin promoter, and the Glycine max sterol methyltransferase1 (SMT1) and sterol methyltransferase2-2 (SMT2-2) genes, under the control of seed-specific Glycinin-1 and Beta-phaseolin promoters, respectively, were engineered in soybean plants. Mature seeds of transgenic plants displayed modest increases in total sterol content, which points towards a tight control of phytosterol biosynthesis. However, in contrast to wild-type seeds that accumulated about 35% of the total sterol in the form of intermediates, in the engineered seeds driven by a seed-specific promoter, metabolic flux was directed to Δ 5-24-alkyl sterol formation (99% of total sterol). The engineered effect of end-product sterol (sitosterol, campesterol, and stigmasterol) over-production in soybean seeds resulted in an approximately 30% increase in overall sitosterol synthesis, a desirable trait for oilseeds and human health. In contradistinction, increased accumulation of cycloartenol and 24(28)-methylencylartanol (55% of the total sterol) was detected in plants harbouring the constitutive t-HMGR1 gene, consistent with the previous studies. Our results support the possibility thatmetabolic flux of the phytosterol family pathway is differentially regulated in leaves and seeds.