Biosynthesis of C20 and C22 Fatty Acids by Developing Seeds of Limnanthes alba

Pollard, Mike; Stumpf, P.K.

doi:10.1104/pp.66.4.649

Cited by 84 publications

(51 citation statements)

References 11 publications

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“…In most plant cells, exogenous acetate is not usually incorporated into C18 and shorter fatty acids because acetate does not readily cross the plastidic membranes, and plastids have their own endogenous pool of acetate used for fatty acid synthesis (32)(33)(34). Even when endogenous acetate has been reported to be incorporated in short fatty acids, glucose has been demonstrated to be a far better substrate, because it can either be imported in nongreen plastids directly as glucose 6-phosphate and used as the source for the plastidic pool of acetate (35,36) or be broken down to triose phosphates in the cytosol and taken up in plastids via triose phosphate translocators (37).…”

Section: Resultsmentioning

confidence: 99%

Elucidation of the Biosynthetic Pathway of the Allelochemical Sorgoleone Using Retrobiosynthetic NMR Analysis

Dayan

Kagan

Rimando

2003

Journal of Biological Chemistry

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NMR analyses of the labeling pattern obtained using various 13 C-labeled precursors indicated that both the lipid tail and the quinone head of sorgoleone, the main allelopathic component of the oily root exudate of Sorghum bicolor, were derived from acetate units, but that the two moieties were synthesized in different subcellular compartments. The 16:3 fatty acid precursor of the tail is synthesized by the combined action of fatty-acid synthase and desaturases most likely in the plastids. It is then exported out of the plastids and converted to 5-pentadecatriene resorcinol by a polyketide synthase. This resorcinol intermediate was identified in root hair extracts. The lipid resorcinol intermediate is then methylated by a S-adenosylmethionine-dependent O-methyltransferase and subsequently dihydroxylated by a P450 monooxygenase to yield the reduced form of sorgoleone.Sorgoleone (2-hydroxy-5-methoxy-3-[(Z,Z)-8Ј,11Ј,14Ј-pentadecatriene]-p-benzoquinone) (1) is the main allelopathic component of the oily root exudate of sorghum (Sorghum bicolor (L.) Moench) ( Fig. 1) (1-3). The term sorgoleone is also used to describe a group of lipophilic p-benzoquinones structurally related to 1 that are also produced by sorghum roots having a hydroxy and a methoxy substitution at positions 2 and 5, respectively, and either a 15-or 17-carbon aliphatic tail with various degrees of unsaturation at position 3 (3).The primary mechanism of phytotoxic action of 1 is associated with inhibition of photosynthesis in higher plant systems by competing for the binding site of plastoquinone on photosystem II (4 -6). This lipophilic p-benzoquinone is also known to hinder electron transfer reactions involved in mitochondrial respiration and to inhibit the enzyme p-hydroxyphenylpyruvate dioxygenase (7,8).The herbicidal and allelopathic properties of 1 make isolation of the genes responsible for its biosynthesis desirable, as manipulation of those genes in sorghum or their introduction in other plant species could provide a better understanding of the role of 1 in plant-plant interaction and natural weed control. To identify the genes and characterize the enzymes they encode, it is necessary to determine the steps involved in the biosynthesis of 1. Little has been reported on this subject.Sorgoleone is found exclusively as a hydrophobic droplet exuding from the tips of root hairs (2), and a recent investigation of sorghum roots suggested that the production of 1 is compartmentalized in the highly physiologically active root hairs (9). The biosynthesis of secondary metabolites occurring in root hairs has not been studied in detail, although other specialized cells at the interface between a plant surface and its environment (i.e. trichomes) are known to produce unique secondary metabolites (10 -12).It has been postulated that the biosynthesis of 1 and related resorcinolic lipids is the result of the convergence of two pathways, namely the fatty acid biosynthetic pathway for the synthesis of the aliphatic tail and the activity of polyketide synthase-...

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Section: Resultsmentioning

confidence: 99%

Elucidation of the Biosynthetic Pathway of the Allelochemical Sorgoleone Using Retrobiosynthetic NMR Analysis

Dayan

Kagan

Rimando

2003

Journal of Biological Chemistry

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“…the curled cotyledon stage) slightly preceding the maximal rate of oil accumulation in the embryo (Bowman, 1994). Arabidopsis seed oil contains gadoleic acid (C20) and erucic acid (C22; James and Dooner, 1991), which are synthesized by the elongation of plastid-exported oleic acid (C18) using cytosol-derived malonyl-CoA (Pollard and Stumpf, 1980;Bao et al, 1998). Hence, we surmise that this peak in ACL mRNA accumulation (which also coincides with peak cytosolic ACCase expression) is for expanding the supply of cytosolic acetyl-CoA to support the biosynthesis of gadoleic and erucic acids.…”

Section: Discussionmentioning

confidence: 99%

“…1). These biomolecules include oils containing very long chain fatty acids, waxes (Pollard and Stumpf, 1980;Bao et al, 1998), flavonoids and stilbenoids (Hrazdina et al, 1978;Preisig-Muller et al, 1997), malonic acid (Stumpf and Burris, 1981), isoprenoids such as essential oils, sterols, sesquiterpenes, and polyprenols (Demetzos et al, 1994;Menhard and Zenk, 1999;Eisenreich et al, 2001), some of the cellular Cys (Rotte and Leustek, 2000;Dominguez-Solis et al, 2001), a subset of the glucosinolates (Graser et al, 2000), malonyl derivatives including D-amino acids, 1-aminocyclopropane carboxylic acid (the precursor of ethylene), and xenobiotics such as pesticides (Hohl and Barz, 1995), and, in transgenic plants, bioplastics based on derivatives of polyhydroxybutyrate (Poirier, 2001).…”

Section: Discussionmentioning

confidence: 99%

Molecular Characterization of a Heteromeric ATP-Citrate Lyase That Generates Cytosolic Acetyl-Coenzyme A in Arabidopsis,

Fatland¹,

Ke²,

Anderson³

et al. 2002

Plant Physiology

196

194

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Acetyl-coenzyme A (CoA) is used in the cytosol of plant cells for the synthesis of a diverse set of phytochemicals including waxes, isoprenoids, stilbenes, and flavonoids. The source of cytosolic acetyl-CoA is unclear. We identified two Arabidopsis cDNAs that encode proteins similar to the amino and carboxy portions of human ATP-citrate lyase (ACL). Coexpression of these cDNAs in yeast (Saccharomyces cerevisiae) confers ACL activity, indicating that both the Arabidopsis genes are required for ACL activity. Arabidopsis ACL is a heteromeric enzyme composed of two distinct subunits, ACLA (45 kD) and ACLB (65 kD). The holoprotein has a molecular mass of 500 kD, which corresponds to a heterooctomer with an A 4 B 4 configuration. ACL activity and the ACLA and ACLB polypeptides are located in the cytosol, consistent with the lack of targeting peptides in the ACLA and ACLB sequences. In the Arabidopsis genome, three genes encode for the ACLA subunit (ACLA-1, At1g10670; ACLA-2, At1g60810; and ACLA-3, At1g09430), and two genes encode the ACLB subunit (ACLB-1, At3g06650 and ACLB-2, At5g49460). The ACLA and ACLB mRNAs accumulate in coordinated spatial and temporal patterns during plant development. This complex accumulation pattern is consistent with the predicted physiological needs for cytosolic acetyl-CoA, and is closely coordinated with the accumulation pattern of cytosolic acetyl-CoA carboxylase, an enzyme using cytosolic acetyl-CoA as a substrate. Taken together, these results indicate that ACL, encoded by the ACLA and ACLB genes of Arabidopsis, generates cytosolic acetyl-CoA. The heteromeric organization of this enzyme is common to green plants (including Chlorophyceae, Marchantimorpha, Bryopsida, Pinaceae, monocotyledons, and eudicots), species of fungi, Glaucophytes, Chlamydomonas, and prokaryotes. In contrast, all known animal ACL enzymes have a homomeric structure, indicating that a evolutionary fusion of the ACLA and ACLB genes probably occurred early in the evolutionary history of this kingdom.Acetyl-coenzyme A (CoA) is an intermediate metabolite that is juxtaposed between catabolic and anabolic processes. As the entry point for the tricarboxylic acid (TCA) cycle, acetyl-CoA can be considered the gateway in the oxidation of carbon derived from the catabolism of fatty acids, certain amino acids (e.g. Leu, Ile, Lys, and Trp), and carbohydrates. Furthermore, acetyl-CoA is the intermediate precursor for the biosynthesis of a wide variety of phytochemicals. Because membranes are impermeable to CoA derivatives, it can be inferred that acetyl-CoA is generated in at least four distinct metabolic pools representing the four subcellular compartments where acetyl-CoA metabolism occurs: plastids, mitochondria, peroxisomes, and the cytosol (Fig. 1). Therefore, plants should have distinct acetyl-CoA-generating systems in mitochondria (for the TCA cycle), in plastids (for de novo fatty acid biosynthesis), in peroxisomes (the product of ␤-oxidation of fatty acids), and in the cytosol (for the biosynthesis of isoprenoids, flavo...

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“…Such studies usirig whole plant tissues and green algae have been previously conducted to demonstrate the in vivo activity of desa-turases that use fatty acids bound to glycerolipids or COA as substrates (e.g. Gurr et al, 1969;Pollard and Stumpf, 1980;Stymne and Stobart, 1986).…”

Section: E Tabolism Of Exogenous 14c-fatty Acids By Coriander Endosmentioning

confidence: 99%

“…Acyl-COA esters may also serve as substrates for fatty acid desaturases. Although such reactions have yet to be conclusively demonstrated in higher plants, the desaturation of eicosanoyl-COA is the proposed biosynthetic route of A5-eicosenoic acid in seeds of meadowfoam (Limanthes alba) (Pollard and Stumpf, 1980;Moreau et al, 1981). Finally, Shibahara et al (1990) have proposed a mechanism in pulp of kaki (Diospyros kaki) in which the double bonds of oleic acid and cis-vaccenic acid can be enzymically shifted between the A' and Al1 positions.…”

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confidence: 99%

Metabolic Evidence for the Involvement of a [delta]4-Palmitoyl-Acyl Carrier Protein Desaturase in Petroselinic Acid Synthesis in Coriander Endosperm and Transgenic Tobacco Cells

Cahoon

Ohlrogge

1994

Plant Physiol.

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We have previously demonstrated that the double bond of petroselinic acid ( 18:1Akis) in coriander (Coriandrum safivum L.) seed results from the activity of a 36-kD desaturase that is structurally related to the Ag-stearoyl-acyl carrier protein (ACP) desaturase (E.B. Cahoon, J. Shanklin, J.B. Ohlrogge [1992] Proc Natl Acad Sci USA 89: 11 184-1 1188). To further characterize the biosynthetic pathway of this unusual fatty acid, 14C-labeling experiments were conducted using developing endosperm of coriander. Studies were also performed using suspension cultures of transgenic tobacco (Nicotiana tabacum L.) that express the coriander 36-kD desaturase, and as a result produce petroselinic acid and A4-hexadecenoic acid. When supplied exogenously to coriander endosperm slices, [I -14C]palmitic acid and stearic acid were incorporated into glycerolipids but were not converted to petroselinic acid. This suggested that petroselinic acid is not formed by the desaturation of a fatty acid bound to a glycerolipid or by reactions involving acyl-coenzyme As (COA). Instead, evidence was most consistent with an acyl-ACP route of petroselinic acid synthesis. For example, the exogenous feeding of [l-'4C]lauric acid and myristic acid to coriander endosperm slices resulted in the incorporation of the radiolabels into long-chain fatty acids, including primarily petroselinic acid, presumably through acyl-ACP-associated reactions. In addition, using an in vitro fatty acid biosynthetic system, homogenates of coriander endosperm incorporated [2-'4C]malonyl-CoA into petroselinic acid, of which a portion was detected in a putative acyl-ACP fraction. Furthermore, analysis of transgenic tobacco suspension cultures expressing the coriander 36-kD desaturase revealed significant amounts of petroselinic acid and A4-hexadecenoic acid in the acyl-ACP pool of these cells. Also presented is evidence derived from [U-'4C]nonanoic acid labeling of coriander endosperm, which demonstrates that the coriander 36-kD desaturase positions double bonds relative to the carboxyl end of acyl-ACP substrates. l h e data obtained in these studies are rationalized in terms of a biosynthetic pathway of petroselinic acid involving the A4 desaturation of palmitoyl-ACP by the 36-kD desaturase followed by two-carbon elongation of the resulting A4-hexadecenoyl-ACP.

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Biosynthesis of C₂₀ and C₂₂ Fatty Acids by Developing Seeds of Limnanthes alba

Cited by 84 publications

References 11 publications

Elucidation of the Biosynthetic Pathway of the Allelochemical Sorgoleone Using Retrobiosynthetic NMR Analysis

Elucidation of the Biosynthetic Pathway of the Allelochemical Sorgoleone Using Retrobiosynthetic NMR Analysis

Molecular Characterization of a Heteromeric ATP-Citrate Lyase That Generates Cytosolic Acetyl-Coenzyme A in Arabidopsis,

Metabolic Evidence for the Involvement of a [delta]4-Palmitoyl-Acyl Carrier Protein Desaturase in Petroselinic Acid Synthesis in Coriander Endosperm and Transgenic Tobacco Cells

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