(Last modification: 11. Mar. 2009)

   Equisetum is a genus of vascular plants that reproduce by spores rather than seeds. The genus includes 15 species commonly known as horsetails and scouring rushes. It is the only living genus in class Equisetopsida, formerly of the division Equisetophyta (Arthrophyta in older works), though recent molecular analyses place the genus within the ferns (Pteridophyta). More information is in Wikipedia: Horsetail, Schachtelhalme.

    Equisetum arvense (Field Horsetail,  Acker-Schachtelhalm) appears to be the species that is most promising in looking for unusual type III PKS. Interestingly, the plant does not only contain flavonoids (Veit et al., 1990; Veit et al., 1995a), but also styrylpyrones, and these are present specifically only in gametophytes and rhizomes, not in sporophytes (Veit et al., 1993; Veit et al., 1995b). Such styrylpyrones like bisnoryangonin and hispidin had been known for a long time from fungi, and precursor feeding studies clearly suggested that they were biosynthesized from phenylpropanoids (4-coumarate -> bisnoryangonin; caffeate -> hispidin) and two malonates (see e.g. Towers et al., 1974; Wat and Towers, 1979). To the best of my knowledge, the enzymes in fungi were not investigated.

    The discovery in the fern Equisetum arvense and the information that styrylpyrones (e.g. bisnoryangenin) are often byproducts of CHS and STS reactions of course raised the question whether a CHS-related protein was responsible for the biosynthesis of the styrylpyrones in the plant. An enzyme assay with extracts from gametophytes was developed (Herderich et al., 1997), and the enzyme was characterized (Beckert et al., 1997). All properties were as expected from a type III plant PKS, except possibly for the size: 'Molecular weight determination by FPLC indicated that this protein has a native molecular weight of ca 56-77 kDa'. This is a bit low for a dimeric protein with subunits of about 40-44 kDa, as is typical for type III PKS. However, similar sizes were initially often reported for CHS and other enzymes later proven to be type III PKS. Taken together, the available data clearly suggest that the styrylpyrone synthase (SPS) should be a CHS-related protein, but unfortunately that has not been proven by cloning the cDNA or the gene. It is noteworthy, however, that the DNA databases contain an entry for a type III PKS from this plant (AB030004), and that was labelled as CHS, presumably based on its strong similarity to other CHS.

    The figure below shows the reaction of SPS (two condensations, ring-folding to a pyrone), and a comparison with type III PKS which also use phenylpropanoid starters, but carry out only one (BAS) or three condensation reactions (CHS, STS, STCS, CTAS). Of particular interest are the latter three, because the expected SPS products (e.g. bisnoryangonin) are often byproducts of those enzyme reactions in vitro: more...

Reaktion von Styrylpyronsynthase (SPS), grün umrandet, mit 4-Coumaroyl-CoA als typischem Substrat: Zwei Kondensationen zu einem Triketid, dann Faltung zum Styrylpyron (Bisnoryangonin).
Zum Vergleich gezeigte Reaktionen: BAS (Benzalacetonsynthase), CHS (Chalconsynthase), STS (Stilbensynthase), STCS (Stilbencarboxylatsynthase), und CTAS (4-Coumaroyltriacetatsynthase). Die Farben kennzeichnen die Kondensationsreaktionen.

Links zu Enzymen mit zwei Kondensationsreaktionen

Zitate

• Beckert, C., Horn, C., Schnitzler, J.-P., Lehning, A., Heller, W., Veit, M., 1997. Styrylpyrone biosynthesis in Equisetum arvense L. Phytochemistry 44, 275-283.
     Styrylpyrone synthase was detected in cell free extracts from gametophytes of Equisetum arvense. This new enzyme catalyses the formation of styrylpyrones from malonyl-CoA and hydroxycinnamoyl- CoA precursors. A standard enzyme assay was established. The enzyme activity was characterized in partially purified protein extracts. p-Coumaroyl-CoA was accepted as substrate at pH 6.0-8.5 in various buffer systems with the formation of bisnoryangonin, and optimum enzyme activity was observed in potassium phosphate buffer at pH 7.5. Caffeoyl-CoA was accepted as substrate only in potassium phosphate buffer at pH 6.0-7.5 with formation of hispidin; optimum enzyme activity was observed at pH 7.0. The apparent K-m values were 220 µM for caffeoyl-CoA and 230 µM for p-coumaroyl-CoA. The temperature optimum of the enzyme activity was 37 degree for bisnoryangonin and 30 degree for hispidin formation. Molecular weight determination by FPLC indicated that this protein has a native molecular weight of ca 56-77 kDa. Styrylpyrones accumulate in rhizomes of sporophytes and gametophytes of E. arvense as major constitutive metabolites. In these organs no flavonoids could be detected. In green sprouts, styrylpyrone accumulation is only detected as a local response to mechanical wounding or microbial attack, and flavonoids are accumulated as major polyketide metabolites. Thus, chalcone synthase is active in the sporophytes and might have developed in the course of evolution from styrylpyrone synthase present in the more primitive gametophytes.
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• Herderich, M., Beckert, C., Veit, M., 1997. Establishing styrylpyrone synthase activity in cell free extracts obtained from gametophytes of Equisetum arvense L. by high performance liquid chromatography-tandem mass spectrometry. Phytochemical Analysis 8, 194-197.
     Styrylpyrone synthase is a polyketide synthase, catalyzing the formation of styrylpyrones from hydroxycinnamoyl-CoA precursors and malonyl-CoA. After Incubation of cell free extracts obtained from Equisetum arvense L. gametophytes with p-coumaroyl-CoA or caffeoyl-CoA, high performance liquid chromatography atmospheric pressure chemical ionization-tandem mass spectrometry (HPLC-APCI- MS) led to the identification of bisnoryangonin and hispidin, respectively, as metabolites. These findings enabled the development of an assay for styrylpyrone synthase activity based on HPLC analysis of the reaction products. The technique could also be useful for product identification in related polyketide synthase reactions.
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• Towers, G. H. N., Vance, C. P., Nambudiri, A. M. D., 1974. Photoregulation of phenylpropanoid and styrylpyrone biosynthesis in Polyporus hispidus. Recent Advances in Phytochemistry 8, 81-94.
  Review, no Abstract.
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• Veit, M., Beckert, C., Höhne, C., Bauer, K., Geiger, H., Hoehne, C., 1995a. Interspecific and intraspecific variation of phenolics in the genus Equisetum subgenus Equisetum. Phytochemistry 38, 881-891.
     The patterns of phenolics in methanolic extracts from the overground sporophytes of all species of the subgenus Equisetum are given. From the interspecific variation in the accumulated flavonoid glycosides and other phenolics, all taxa of the subgenus can be distinguished. The retention characteristics in a standard HPLC method and maxima of the on-line UV spectra of all compounds detected are given. The HPLC method allows the quantification of phenolics in herbal remedies containing Equisetum, as well as in the crude drug material and therefore could be useful for both quality control and chemotaxonomic studies. All species show quantitative and qualitative variations during plant development. As an example, we present chromatograms of different developmental stages of E. arvense and accumulation dynamics of some phenols in that species. Phenolics accumulating in different organs of the plant are distinct. Apart from the spores, only diploid tissues are able to accumulate flavonoids. The haploid vegetative gametophytes accumulate caffeic acid esters and styrylpyrones in high contents. The rhizomes are also free of flavonoids, but contain various styrylpyrones, besides hydroxycinnamoyl esters. Styrylpyrones seem to replace flavonoids in gametophytes and sporophytic rhizomes of Equisetum species.
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• Veit, M., Geiger, H., Czygan, F. C., Markham, K. R., 1990. Malonylated flavone 5-O-glucosides in the barren sprouts of Equisetum arvense. Phytochemistry 29, 2555-2560.
     Equisetum arvense exists as two chemotypes one occurring in Asia and North America and the other in Europe. Barren sprouts from Asia and North America contain flavone 5-glucosides and their malonyl esters, whereas European material is free from these compounds. Both types contain quercetin 3-O-ß-d-glucopyranoside, and its malonyl ester. Quercetin 3-O-sophoroside, genkwanin 4'-O-ß-d-glucopyranoside and protogenkwanin 4'-O-ß-d-glucopyranoside are only found in European material. The structures of all new compounds are proven.
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• Veit, M., Geiger, H., Kast, B., Beckert, C., Horn, C., Markham, K. R., Wong, H., Czygan, F.-C., 1995b. Styrylpyrone glucosides from Equisetum. Phytochemistry 39, 915-917.
     Two styrylpyrone glucosides, 3'-deoxyequisetumpyrone (3,4- hydroxy-6-(4'-hydroxy-E-styryl)-2-pyrone-3O-b-D- glucopyranoside) and 4'-O-methylequisetumpyrone (3,4-hydroxy-6- (3'-hydroxy-4'-methoxy-E-styryl)-2-pyrone-3-O-b-D-glucopyranoside) have been isolated from the rhizomes of Equisetum arvense. The structures of the new derivatives were elucidated spectroscopically. These compounds are accumulated as the main phenolics in rhizomes and gametophytes of all Equisetum species. In these organs, they represent a sink for compounds derived from hydroxycinnamoyl CoA esters and malonyl units, whereas sporophytic shoots contain no styrylpyrones but a considerable variety of flavonoid glycosides.
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• Veit, M., Geiger, H., Wray, V., Abou-Mandour, A., Rozdzinski, W., Witte, L., Strack, D., Czygan, F.-C., 1993. Equisetumpyrone, a styrylpyrone glucoside in gametophytes from Equisetum arvense. Phytochemistry 32, 1029-1032.
     A new styrylpyrone was isolated from vegetative gametophytes of Equisetum arvense. Its structure was determined spectroscopically to be 3,4-dihydroxy-6-(3',4'-dihydroxy-E-styryl)-2-pyrone 3-O-ß-D-glucopyranoside or a tautomer thereof. In methanolic extracts of the reproductive organs of Equisetum arvense, E. palustre and E. fluviatile, equisetum pyrone is the main phenolic compound. In sterile sporophytes of these species, the compound was present only in spring at low concentrations. This is the first report of a styrylpyrone glycoside from plants.
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• Wat, C.-K., Towers, G. H. N., 1979. Metabolism of the aromatic amino acids by fungi. Recent Advances in Phytochemistry 13, 371-432.
  Review, no Abstract available
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DEFINITION  Equisetum arvense CHS mRNA for chalcone synthase, complete cds.

ACCESSION   AB030004

VERSION     AB030004.1  GI:6714619

KEYWORDS    CHS; chalcone synthase.

SOURCE      Equisetum arvense (field horsetail)

  ORGANISM  Equisetum arvense

            Eukaryota; Viridiplantae; Streptophyta; Embryophyta; Tracheophyta;

            Moniliformopses; Equisetophyta; Equisetopsida; Equisetales;

            Equisetaceae; Equisetum.

REFERENCE   1

  AUTHORS   Yamazaki,Y. and Sankawa,U.

  TITLE     Equisetum arvense CHS

  JOURNAL   Published Only in Database (2000)

REFERENCE   2  (bases 1 to 1472)

  AUTHORS   Yamazaki,Y. and Sankawa,U.

  TITLE     Direct Submission

  JOURNAL   Submitted (13-JUL-1999) Ushio Sankawa, Toyama International Health

            Complex, Toyama Wellness Foundation International, Traditional

            Medicine Research Center; 151 Tomosugi, Toyama, Toyama 939-8224,

            Japan (E-mail:sankawa@toyama-pref-ihc.or.jp, Tel:81-76-428-0829,

            Fax:81-76-428-0834)

FEATURES             Location/Qualifiers

     source          1..1472

                     /organism="Equisetum arvense"

                     /mol_type="mRNA"

                     /db_xref="taxon:3258"

     gene            1..1472

                     /gene="CHS"

     CDS             142..1359

                     /gene="CHS"

                     /codon_start=1

                     /product="chalcone synthase"

                     /protein_id="BAA89501.1"

                     /db_xref="GI:6714620"

                     /translation="MTVLEESADASSRRLAQRANGPATVLAIGTANPANVFEQSSYPD

                     FYFDITNSQHMTELKLKFSRMCQKSGIKKRYMHLNSEILKANPSLCAYWEKSLDVRQD

                     IAVVEVPKLGKEASLKAIKEWGQPKSKITHLVFCTTSGVDMPGADWALTKLLGLRPSV

                     KRLMMYQQGCFAGGTVLRVAKDVAENNKGARVLVVCSEITCVTFRGPSETHLDSLVGQ

                     ALFGDGAAAVILGSDPLPEENPCFELHWSGSNILPDSDGAIDGHLREVGLTFHLMKDV

                     PGIISKNIGKVLNDAFRSAFDESGNAEDRPASVNDIFWIAHPGGPAILDQVEEKMKLA

                     PEKMRATRDVLSEYGNMSSACVLFIMDHMRRMSAQNKLQTTGEGLDWGVLLGFGPGLT

                     VETVLLKSIRLAC"

ORIGIN     

        1 attggagcgt ccttagttca ctccatagat taatcttaga ttaagctgag cctagccttt

       61 gcttaatctc tgctagatct tgtcttaagt tgaggttatc cttggcttaa acttggctcg

      121 atcagtaacc tagccttgac catgactgtc cttgaagagt ctgccgatgc ctcgtccaga

      181 aggttggcgc agcgagccaa tgggcctgcc accgttctcg ccatcggaac tgctaaccct

      241 gctaatgtct ttgagcagag ctcctatcct gatttctact tcgacatcac caatagtcag

      301 catatgactg aactcaagct caaattctcc cgcatgtgtc agaagtccgg gattaagaag

      361 cggtacatgc acttgaacag tgaaattctg aaggctaatc ccagcctctg cgcgtactgg

      421 gagaagtccc tggatgtgag gcaagacata gcagtggtgg aggtccctaa gctggggaag

      481 gaggcctccc tcaaggctat taaggagtgg ggtcagccca agtccaaaat aacacacctc

      541 gtcttctgca ccacaagcgg ggttgacatg cctggggctg actgggcgct aaccaagctc

      601 ctcggcctcc gcccgagtgt caagcggctc atgatgtacc agcaagggtg ctttgcaggc

      661 ggaacggtgc ttcgtgtggc gaaggatgtg gcggagaata acaagggagc tcgggtcttg

      721 gttgtttgca gtgagattac ttgtgtcacc ttccgggggc cgagtgagac ccatttggac

      781 agtttggttg ggcaggcctt gtttggtgac ggtgcggcag cggtcatcct gggttctgac

      841 ccgctcccag aagagaatcc ttgcttcgag cttcattgga gcggatcaaa cattctacca

      901 gatagtgacg gtgccattga cggccacttg cgcgaggtcg ggctcacctt ccacctcatg

      961 aaggacgtgc cggggatcat ctccaagaac attgggaaag tcctgaacga cgccttccgc

     1021 agtgcgtttg atgagtcagg gaatgctgaa gaccgtcctg ctagtgttaa cgatatcttc

     1081 tggatcgcac acccaggagg gccagcgatc cttgaccaag ttgaggagaa gatgaagctg

     1141 gcgcccgaga agatgcgggc gacgcgggac gtgctatcgg agtatgggaa catgtcaagc

     1201 gcatgtgtac tcttcatcat ggaccacatg cggcggatgt cggcacaaaa caagctgcag

     1261 acaactgggg aaggcctgga ttggggtgtg ctcctgggct ttggacctgg attaacagtt

     1321 gagactgtgc tgcttaaaag catacgatta gcttgttgat cattagccct ttgtaattat

     1381 taccatttcc cctattatgt gttgtaatat cgtattatgt gtatcactac ttcctaatta

     1441 atgaatttag tgctttgcat tgtctaaaaa aa

//

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