How is sterol synthesis regulated in higher plants?

Goad, L. John

doi:10.1042/bst0110548

Cited by 46 publications

(28 citation statements)

References 24 publications

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“…1). Previously, it was pointed out that cycloartenol synthase might catalyze the formation of both cycloartenol and triterpenes depending on the different physiological conditions such as pH or electrolyte concentration of the cells [21]. However, it is now clear, at least for β-amyrin and lupeol, that distinct enzymes, triterpene synthases, are responsible for the formation of each triterpene.…”

Section: ′-And 5′-racementioning

confidence: 99%

“…From the observation that sterol and triterpene biosynthesis differed in time during plant development [20], it is argued that cycloartenol synthase might change its function from cycloartenol synthesis to triterpene synthesis depending on the physiological conditions such as pH or electrolyte concentration of the cells [21]. Although detection of activities and purification of several triterpene synthases appeared in the literature, there is no definite evidence that distinct triterpene synthases, other than cycloartenol synthase, actually catalyze the formation of each skeletal type of triterpene in plants [4].…”

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β‐Amyrin synthase

Kushiro

Shibuya

Ebizuka

1998

European Journal of Biochemistry

290

268

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β-amyrin, a typical pentacyclic triterpene having an oleanane skeleton, is one of the most commonly occuring triterpenes in nature and is biosynthesized from (3S)-2,3-oxidosqualene. The enzyme, β-amyrin synthase, catalyzing the cyclization of oxidosqualene into β-amyrin, generates five rings and eight asymmetric centers in a single transformation. A homology-based PCR method was attempted to obtain the cDNA of this enzyme from the hairy root of Panax ginseng which produces oleanane saponins together with dammarane-type saponins. Two sets of degenerate oligonucleotide primers were designed at the regions which are highly conserved among known oxidosqualene cyclases (OSCs). Nested PCRs using these primers successfully amplified the core fragment which revealed the presence of two OSC clones PNX and PNY. Specific amplification of each clone by 3′-RACE and 5′-RACE was carried out to obtain the whole sequences. The two clones exhibited 60% amino acid identity to each other. A full-length clone of PNY was ligated into the yeast expression vector pYES2 under the GAL1 promoter to give pOSC PNY . β-amyrin production was observed with the mutant yeast lacking lanosterol synthase, transformed by this plasmid. The sequence of pOSC PNY contains an open reading frame of 2289 nucleotides which codes for 763 amino acids with a predicted molecular mass of 88 kDa. Sequence comparison with other OSCs showed a high level of similarity with lanosterol, cycloartenol and lupeol synthases. The other clone, pOSC PNX , was shown to be cycloartenol synthase by similar expression in yeast. The present studies have revealed that distinct OSC exists for triterpene formation in higher plants, and the high level of similarity with cycloartenol synthase indicates close evolutional relationship between sterol and triterpene biosynthesis.

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Section: ′-And 5′-racementioning

confidence: 99%

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confidence: 99%

β‐Amyrin synthase

Kushiro

Shibuya

Ebizuka

1998

European Journal of Biochemistry

290

268

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“…Even though TRW has been vigorously proven to produce lupeol in the transformed yeast, it might alter its specificity to produce other triterpenes but lupeol depending upon different physiological conditions in the intact plant, possibly by post translational modifications or by simple conformational changes. The latter possibility has been discussed by Goad [25], as in vitro activities of all the known OSCs are very susceptible to the change of pH, detergents and electrolyte concentrations [26]. To resolve this interesting issue, cDNA cloning of triterpene synthases of different product specificities is now in progress from triterpene rich plants including T. officinale.…”

Section: Molecular Evolution Of Plant Oxidosqualene Cyclasesmentioning

confidence: 99%

Two branches of the lupeol synthase gene in the molecular evolution of plant oxidosqualene cyclases

Shibuya

Zhang

Endo

et al. 1999

European Journal of Biochemistry

107

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Two new triterpene synthase cDNAs, named as OEW and TRW, were cloned from olive leaves (Olea europaea) and from dandelion roots (Taraxacum officinale), respectively, by the PCR method with primers designed from the conserved sequences found in the known oxidosqualene cyclases. Their ORFs consisted of 2274 bp nucleotides and coded for 758 amino acid long polypeptides. They shared high sequence identity (78%) to each other, while they showed only about 60% identities to the known triterpene synthases LUPI (lupeol synthase clone from Arabidopsis thaliana) and PNY (b-amyrin synthase clone from Panax ginseng) at amino acid level. To determine the enzyme functions of the translates, they were expressed in an ERG7 deficient yeast mutant. Accumulation of lupeol in the cells of yeast transformants proved both of these clones code for lupeol synthase proteins. An EST (expression sequence tag) clone isolated from Medicago truncatula roots as a homologue of cycloartenol synthase gene, exhibits high sequence identity (75±77%) to these two lupeol synthase cDNAs, suggesting it to be another lupeol synthase clone. Comparatively low identity (< 57%) of LUP1 from Arabidopsis thaliana to either one of these clones leaves LUP1 as a distinct clone among lupeol synthases. From these sequence comparisons, now we propose that two branches of lupeol synthase gene have been generated in higher plants during the course of evolution.Keywords: lupeol synthase; Olea europaea; Taraxacum officinale; triterpene synthase; molecular evolution.In mammals, plants, fungi and yeasts, sterols serve as essential membrane constituents, growth regulating substances and precursors of various hormones [1,2]. In the plant kingdom, besides sterols, a large number of nonsteroidal triterpene derivatives exist that are recognized as secondary metabolites due to their apparent lack of physiological functions in the producing plants [3]. They are produced species specifically, and thus could be considered as a chemical expression of plant species. It is reasonable to assume the ability of sterol biosynthesis to be inherent to all plants and highly conserved from the progenitors, while the ability to produce characteristic triterpenoids by individual plant species to be acquired in the process of plant evolution.Biosynthetic pathways leading to sterols and triterpenes are completely identical to each other up to the formation of 2,3-oxidosqualene and branch at its cyclization step [4]. As structural diversity of triterpene is primarily generated at this cyclization step catalyzed by triterpene synthases, it can be said that diversity of these synthases reflects diversity of plant species (Fig. 1). Up to now, cDNA cloning of four cycloartenol synthases (from Arabidopsis thaliana (CAS1) [5], Pisum sativum [6], Panax ginseng [7] and Allium macrostemon [8]), three triterpene synthases two b-amyrin synthases (PNY and PNY2) from P. ginseng [7,9], and a lupeol synthase (LUP1) from A. thaliana [10] and another oxidosqualene cyclase (OSC) of unknown function from P. ginsen...

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“…For triterpenoid saponin synthesis, 2,3-oxidosqualene is cyclized to one of a number of different potential products, the most common being ␤-amyrin (1). Until recently, a key question in understanding triterpenoid biosynthesis has centered around whether the generation of different cyclization products from 2,3-oxidosqualene involves distinct oxidosqualene cyclase enzymes or whether these reactions may be mediated by a single enzyme (5)(6)(7). This question has now been resolved by the cloning and characterization of triterpene synthases that cyclize 2,3-oxidosqualene to ␤-amyrin (␤-amyrin synthases) or to other triterpenoid products (lupeol synthases and multifunctional triterpene synthases) from a diverse collection of dicots, which includes ginseng (Panax ginseng; refs.…”

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A new class of oxidosqualene cyclases directs synthesis of antimicrobial phytoprotectants in monocots

Haralampidis

Bryan²,

Qi³

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

171

204

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Here we show the novel oxidosqualene cyclase AsbAS1 catalyzes the first committed step in the synthesis of antifungal triterpenoid saponins that accumulate in oat roots. We also demonstrate that two sodium azide-generated saponin-deficient mutants of oat, which define the Sad1 genetic complementation group, are defective in the gene encoding this enzyme and provide molecular genetic evidence indicating a direct link between AsbAS1, triterpenoid saponin biosynthesis, and disease resistance. Orthologs of AsbAS1 are absent from modern cereals and may have been lost during selection, raising the possibility that this gene could be exploited to enhance disease resistance in crop plants.

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How is sterol synthesis regulated in higher plants?

Cited by 46 publications

References 24 publications

β‐Amyrin synthase

β‐Amyrin synthase

Two branches of the lupeol synthase gene in the molecular evolution of plant oxidosqualene cyclases

A new class of oxidosqualene cyclases directs synthesis of antimicrobial phytoprotectants in monocots

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