Chalcone synthase: Difference between revisions
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CHS exists as a homodimeric protein with each monomer approximately 42-45 kDa in size.<ref name="pmid12636085">{{cite journal | author = Austin MB, Noel JP | title = The chalcone synthase superfamily of type III polyketide synthases | journal = Nat Prod Rep | volume = 20 | issue = 1 | pages = 79–110 | year = 2003 | month = February | pmid = 12636085 | doi = 10.1039/b100917f }}</ref> Each monomer possesses a [[keto-synthase|β-keto synthase]] (KS) activity that catalyzes the sequential head to tail incorporation of two-carbon [[acetate]] units into a growing polyketide chain. CHS contains a five layer αβαβα core, a location of the [[active site]] and [[dimerization]] interface that is highly similar to [[thiolase]]-fold containing enzymes. The dimerization interface contains both hydrophobic and hydrophilic residues and is generally flat except for a pair of [[N-terminal]] helices that lay entwined across the top. Although the helices are not involved in reaction, they may contain intracellular localization signals as in yeast thiolase. They may also undergo a conformational change to participate in the formation of transient multi-protein complexes with other enzymes in the various pathways diverging from the general [[phenylpropanoid]] biosynthetic pathway. |
CHS exists as a homodimeric protein with each monomer approximately 42-45 kDa in size.<ref name="pmid12636085">{{cite journal | author = Austin MB, Noel JP | title = The chalcone synthase superfamily of type III polyketide synthases | journal = Nat Prod Rep | volume = 20 | issue = 1 | pages = 79–110 | year = 2003 | month = February | pmid = 12636085 | doi = 10.1039/b100917f }}</ref> Each monomer possesses a [[keto-synthase|β-keto synthase]] (KS) activity that catalyzes the sequential head to tail incorporation of two-carbon [[acetate]] units into a growing polyketide chain. CHS contains a five layer αβαβα core, a location of the [[active site]] and [[dimerization]] interface that is highly similar to [[thiolase]]-fold containing enzymes. The dimerization interface contains both hydrophobic and hydrophilic residues and is generally flat except for a pair of [[N-terminal]] helices that lay entwined across the top. Although the helices are not involved in reaction, they may contain intracellular localization signals as in yeast thiolase. They may also undergo a conformational change to participate in the formation of transient multi-protein complexes with other enzymes in the various pathways diverging from the general [[phenylpropanoid]] biosynthetic pathway. |
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===Localization=== |
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The enzyme is localized in the [[cytosol]]. Specifically, it is associated with the [[endoplasmic reticulum]] membrane. <ref> {{cite journal | author = Hzardina G, Jensen RA | title = Spatial organization of enzymes in plant metabolic pathways| journal = Annu Rev Plant Physiol Plant Mol Biol | volume = 43 | pages = 241 – 67| year = 1992 }} </ref> In another study, it was shown that CHS and CHI co-localize at the nucleus as well. <ref> {{cite journal | author = Saslowsky D, Winkel-Shirley B| title = Localization of flavonoid enzymes in Arabidopsis roots | journal = The Plant Journal : for cell and molecular biology | volume = 27 | issue = 1| pages = 37-48 | year = 2001 | pmid = 11489181}}</ref> |
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=== Active Site === |
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| ⚫ | There are two distinct bi-lobed active site cavities located at the bottom edge of each monomer’s αβαβα core. Identical six-residue loops, which meet at the dimer interface, separate the two active sites from each other. The loops being with Thr132 in the active site and ends with a cis-peptide bond to Pro138. A Met137 residue plugs a hole in the other monomer’s active site. Therefore, the active site is buried except for a 16 Å CoA-binding tunnel that connects the catalytic surface to the outer surrounding [[milieu]]. The width of the tunnel is too narrow for the aromatic substrates and products that must pass through it, implying that there must be some dynamic mobility within and around the tunnel when placed in solution. |
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The active site contains a conserved catalytic triad of Cys164, His303 and Asn336. These residues aid in multiple decarboxlyation and condensation reactions, with Cys164 acting as the active site [[nucleophile]]. Phe215 and Phe265 are two other important [[amino acids]] that act as “gatekeepers” to block the lower protein of the opening between the CoA-binding tunnel and the active site cavity. This limits the access of water to the active site while accommodating substrates and intermediates of varying shapes and sizes. Phe215 also orients the substrates at the active site during elongation of the polyketide intermediate. |
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| ⚫ | There are two distinct bi-lobed active site cavities located at the bottom edge of each monomer’s αβαβα core. Identical six-residue loops, which meet at the |
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== Mechanism == |
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The active site contains a conserved [[catalytic triad]] of Cys164, His303 and Asn336. These aid in multiple decarboxlyation and condensation reactions. |
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The first step involves a transfer of a coumaroyl moiety from a 4-coumaroyl-CoA starter molecule to Cys164. <ref> {{cite pmid|21909286}}</ref> Next, a series of condensation reactions of three acetate units from malonyl-CoA occurs, each proceeding through an [[acetyl-CoA]] [[carbanion]] derived from malonyl-CoA [[decarboxylation]]. This extends the polyketide intermediate. After the generation of a thioester-linked tetraketide, a regiospecific C1,C6 [[Claisen condensation]] occurs, forming a new ring system to generate naringenin chalcone. |
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== Regulation== |
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=== Metabolic Control=== |
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CHS is noncompetitively inhibited by flavanoid pathway products such as [[naringenin]] and [[chalcone naringenin]]. <ref> {{cite journal | author = Hinderer W, Seitz HU| title = Chalcone synthase from cell suspension cultures of Daucus carota| journal = L. Arch Biochem Biophys| volume = 240| pages = 265-72 | year = 1985 | pmid = 4015104}}</ref> Despite lack of direct evidence in vivo, flavonoids are believed to accumulate in the cytosol to a level that blocks CHS activity to avoid toxic levels in plants. <ref> {{cite journal | author = Whitehead JM, Dixon RA| title = Chalcone synthase from cell suspension cultures of Phaseolus vulgaris | journal = Biochem Biophys Acta| volume = 747| pages = 1777-86 | year = 1983}} </ref> |
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=== Gene Control === |
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CHS is constituively expressed in plants but can also be subject to induced expression through light/ UV light and well as in response to pathogens, elicitors and wounding. The CHS promoter contains a G-box motif with a sequence of CACGTG. This has been shown to play a role in response to light. <ref> {{cite journal | author = Schulze LP, Becker AM, Schulr W, Hahlbrock K, Dangl JL| title = Functional architecture of the light-responsive chalcone synthase promoter from parsley | journal = Plant Cell| volume = 1 | issue = 7| pages = 707-14| year = 1989 | pmid = 2535519}} </ref> Other light sensitive domains include Box I, Box II, Box III, Box IV or three copies of H-box (CCTACC). <ref> {{cite journal | author = Dao TTH, Linthorst HJM, Verpoorte R| title = Chalcone synthase and its functions in plant resistance| journal = Phytochemistry Reviews: proceedings of the Phytochemical Society of Europe| volume = 10| issue = 3| pages = 397-412| year = 2011| pmid = 21909286| doi = 10.1007/s11101-011-9211-7}}</ref> |
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| ⚫ | Although higher plant chalcone synthases have been extensively studied, little information is available on the enzymes from bryophytes (primitive plants). Cloning of CHS from the moss ''[[Physcomitrella patens]]'' revealed an important transition from the chalcone synthases present in microorganisms to those present in higher plants.<ref name=clark>{{cite journal |author=Jiang C, Schommer C, Kim S-Y, Suh D-Y |title=Cloning and Characterization of Chalcone Synthase from the moss Physcomitrella patens |journal = [[Phytochemistry (journal)|Phytochemistry]] |volume=67 |issue=23 |pages=2531–2540 |year=2006 |pmid=17083952 |doi=10.1016/j.phytochem.2006.09.030}}</ref> |
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| ⚫ | The chalcone synthase [[gene]] of ''[[Petunia]]'' plants is famous for being the first gene in which the phenomenon of [[RNA interference]] was observed; researchers intending to upregulate the production of pigments in light pink or violet flowers introduced a [[transgene]] for chalcone synthase, expecting that both the native gene and the transgene would express the enzyme and result in a more deeply colored flower [[phenotype]]. Instead the transgenic plants had mottled white flowers, indicating that the introduction of the transgene had downregulated or silenced chalcone synthase expression.<ref name=Napoli_1990>{{cite journal |author=Napoli C, Lemieux C, Jorgensen R |title=Introduction of a Chimeric Chalcone Synthase Gene into Petunia Results in Reversible Co-Suppression of Homologous Genes in trans |journal=Plant Cell |volume=2 |issue=4 |pages=279–289 |year=1990 |pmid=12354959 |doi=10.1105/tpc.2.4.279 |pmc=159885}}</ref> Further investigation of the phenomenon indicated that the downregulation was due to post-transcriptional inhibition of the chalcone synthase [[gene expression]] via an increased rate of [[messenger RNA]] degradation.<ref name=Van_Blokland_1994>{{cite journal | author = Van Blokland R, Van der Geest N, Mol JNM, Kooter JM | title = Transgene-mediated suppression of chalcone synthase expression in ''Petunia hybrida'' results from an increase in RNA turnover | journal = Plant J | year = 1994 | volume = 6 | pages = 861–77 | url=http://www.blackwell-synergy.com/links/doi/10.1046/j.1365-313X.1994.6060861.x/abs/ | doi = 10.1046/j.1365-313X.1994.6060861.x | issue = 6 }}</ref> |
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== Species distribution and evolution == |
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[[Naringenin-chalcone synthase]] uses [[malonyl-CoA]] and [[4-coumaroyl-CoA]] to produce [[Coenzyme A|CoA]], [[naringenin chalcone]], and CO<sub>2</sub>. |
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| ⚫ | Although higher plant chalcone synthases have been extensively studied, little information is available on the enzymes from bryophytes (primitive plants). Cloning of CHS from the moss ''[[Physcomitrella patens]]'' revealed an important transition from the chalcone synthases present in microorganisms to those present in higher plants.<ref name= |
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== RNA interference == |
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| ⚫ | The chalcone synthase [[gene]] of ''[[Petunia]]'' plants is famous for being the first gene in which the phenomenon of [[RNA interference]] was observed; researchers intending to upregulate the production of pigments in light pink or violet flowers introduced a [[transgene]] for chalcone synthase, expecting that both the native gene and the transgene would express the enzyme and result in a more deeply colored flower [[phenotype]]. Instead the transgenic plants had mottled white flowers, indicating that the introduction of the transgene had downregulated or silenced chalcone synthase expression.<ref name=Napoli_1990>{{cite journal |author=Napoli C, Lemieux C, Jorgensen R |title=Introduction of a Chimeric Chalcone Synthase Gene into Petunia Results in Reversible Co-Suppression of Homologous Genes in trans |journal=Plant Cell |volume=2 |issue=4 |pages=279–289 |year=1990 |pmid=12354959 |doi=10.1105/tpc.2.4.279 |pmc=159885}}</ref> Further investigation of the phenomenon indicated that the downregulation was due to post-transcriptional inhibition of the chalcone synthase [[gene expression]] via an increased rate of [[messenger RNA]] degradation.<ref name=Van_Blokland_1994>{{cite journal | author = Van Blokland R, Van der Geest N, Mol JNM, Kooter JM | title = Transgene-mediated suppression of chalcone synthase expression in ''Petunia hybrida'' results from an increase in RNA turnover | journal = Plant J | year = 1994 | volume = 6 | pages = 861–77 | url=http://www.blackwell-synergy.com/links/doi/10.1046/j.1365-313X.1994.6060861.x/abs/ | doi = 10.1046/j.1365-313X.1994.6060861.x | issue = 6 }}</ref> |
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==References== |
==References== |
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{{Reflist |
{{Reflist}} |
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==External links== |
==External links== |
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Revision as of 01:20, 4 March 2013
| Chalcone Synthase (Naringenin Chalcone Synthase) | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| EC no. | 2.3.1.74 | ||||||||
| CAS no. | 56803-04-4 | ||||||||
| Databases | |||||||||
| IntEnz | IntEnz view | ||||||||
| BRENDA | BRENDA entry | ||||||||
| ExPASy | NiceZyme view | ||||||||
| KEGG | KEGG entry | ||||||||
| MetaCyc | metabolic pathway | ||||||||
| PRIAM | profile | ||||||||
| PDB structures | RCSB PDB PDBe PDBsum | ||||||||
| Gene Ontology | AmiGO / QuickGO | ||||||||
| |||||||||
| Chalcone and stilbene synthases, C-terminal domain | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| Symbol | Chal_sti_synt_C | ||||||||
| Pfam | PF02797 | ||||||||
| Pfam clan | CL0046 | ||||||||
| InterPro | IPR012328 | ||||||||
| |||||||||
Chalcone synthase or ‘’’naringenin-chalcone synthase’’’ (CHS) is an enzyme ubiquitous to higher plants and belongs to a family of polyketide synthase enzymes (PKS) known as type III PKS, which are associated with the production of chalcones, a class of organic compounds found mainly in plants as natural defense mechanisms and as synthetic intermediates. It was the first type III PKS to be discovered.[1] It is the first committed enzyme in flavonoid biosynthesis. [2] The enzyme catalyzes the conversion of 4-coumaroyl-CoA and malonyl-CoA to naringenin chalcone.
Function
CHS catalysis serves as the initial step for flavonoid biosynthesis. Flavonoids are important plant secondary metabolites that serve various functions in higher plants. These include pigmentation, UV protection, fertility, antifungal defense and the recruitment of nitrogen-fixing bacteria.[3] CHS is believe to act as a central hub for the enzymes involved in the flavonoid pathway.[4] Studies have shown that these enzymes interact via protein-protein interactions.[5] Through FLIM FRET, it was shown that CHS interacts with chalcone isomerase (CHI), a consecutive step enzyme, as well as other non-consecutive step enzymes flavonone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR), and flavonol synthase I.[4]
Naringenin-chalcone synthase uses malonyl-CoA and 4-coumaroyl-CoA to produce CoA, naringenin chalcone, and CO2.
Reaction
4-coumaroyl-CoA and three units of malonyl-CoA are converted into four molecules of carbon dioxide, three molecules of coenzyme A and one unit of naringenin chalcone.
Structure
Subunits
CHS exists as a homodimeric protein with each monomer approximately 42-45 kDa in size.[6] Each monomer possesses a β-keto synthase (KS) activity that catalyzes the sequential head to tail incorporation of two-carbon acetate units into a growing polyketide chain. CHS contains a five layer αβαβα core, a location of the active site and dimerization interface that is highly similar to thiolase-fold containing enzymes. The dimerization interface contains both hydrophobic and hydrophilic residues and is generally flat except for a pair of N-terminal helices that lay entwined across the top. Although the helices are not involved in reaction, they may contain intracellular localization signals as in yeast thiolase. They may also undergo a conformational change to participate in the formation of transient multi-protein complexes with other enzymes in the various pathways diverging from the general phenylpropanoid biosynthetic pathway.
Localization
The enzyme is localized in the cytosol. Specifically, it is associated with the endoplasmic reticulum membrane. [7] In another study, it was shown that CHS and CHI co-localize at the nucleus as well. [8]
Active Site
There are two distinct bi-lobed active site cavities located at the bottom edge of each monomer’s αβαβα core. Identical six-residue loops, which meet at the dimer interface, separate the two active sites from each other. The loops being with Thr132 in the active site and ends with a cis-peptide bond to Pro138. A Met137 residue plugs a hole in the other monomer’s active site. Therefore, the active site is buried except for a 16 Å CoA-binding tunnel that connects the catalytic surface to the outer surrounding milieu. The width of the tunnel is too narrow for the aromatic substrates and products that must pass through it, implying that there must be some dynamic mobility within and around the tunnel when placed in solution.
The active site contains a conserved catalytic triad of Cys164, His303 and Asn336. These residues aid in multiple decarboxlyation and condensation reactions, with Cys164 acting as the active site nucleophile. Phe215 and Phe265 are two other important amino acids that act as “gatekeepers” to block the lower protein of the opening between the CoA-binding tunnel and the active site cavity. This limits the access of water to the active site while accommodating substrates and intermediates of varying shapes and sizes. Phe215 also orients the substrates at the active site during elongation of the polyketide intermediate.
Mechanism
The first step involves a transfer of a coumaroyl moiety from a 4-coumaroyl-CoA starter molecule to Cys164. [9] Next, a series of condensation reactions of three acetate units from malonyl-CoA occurs, each proceeding through an acetyl-CoA carbanion derived from malonyl-CoA decarboxylation. This extends the polyketide intermediate. After the generation of a thioester-linked tetraketide, a regiospecific C1,C6 Claisen condensation occurs, forming a new ring system to generate naringenin chalcone.
Regulation
Metabolic Control
CHS is noncompetitively inhibited by flavanoid pathway products such as naringenin and chalcone naringenin. [10] Despite lack of direct evidence in vivo, flavonoids are believed to accumulate in the cytosol to a level that blocks CHS activity to avoid toxic levels in plants. [11]
Gene Control
CHS is constituively expressed in plants but can also be subject to induced expression through light/ UV light and well as in response to pathogens, elicitors and wounding. The CHS promoter contains a G-box motif with a sequence of CACGTG. This has been shown to play a role in response to light. [12] Other light sensitive domains include Box I, Box II, Box III, Box IV or three copies of H-box (CCTACC). [13] Although higher plant chalcone synthases have been extensively studied, little information is available on the enzymes from bryophytes (primitive plants). Cloning of CHS from the moss Physcomitrella patens revealed an important transition from the chalcone synthases present in microorganisms to those present in higher plants.[14]
The chalcone synthase gene of Petunia plants is famous for being the first gene in which the phenomenon of RNA interference was observed; researchers intending to upregulate the production of pigments in light pink or violet flowers introduced a transgene for chalcone synthase, expecting that both the native gene and the transgene would express the enzyme and result in a more deeply colored flower phenotype. Instead the transgenic plants had mottled white flowers, indicating that the introduction of the transgene had downregulated or silenced chalcone synthase expression.[15] Further investigation of the phenomenon indicated that the downregulation was due to post-transcriptional inhibition of the chalcone synthase gene expression via an increased rate of messenger RNA degradation.[16]
Naringenin-chalcone synthase uses malonyl-CoA and 4-coumaroyl-CoA to produce CoA, naringenin chalcone, and CO2.
References
- ^ Kreuzaler F, Hahlbrock K (1972). "Enzymatic synthesis of aromatic compounds in higher plants: formation of naringenin (5,7,4'-trihydroxyflavanone) from p-coumaroyl coenzyme A and malonyl coenzyme A". FEBS Lett. 28 (1): 69–72. doi:10.1016/0014-5793(72)80679-3. PMID 4646877.
{{cite journal}}: Unknown parameter|month=ignored (help) - ^ Tohge T, Yonekura-Sakakibara K, Niida R, Wantanabe-Takahasi A, Saito K (2007). "Phytochemical genomics in Arabidopsis thaliana: A case study for functional identification of flavonoid biosynthesis genes". Pure and Applied Chemistry. 79 (4): 811–23. doi:10.1351/pac200779040811.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Cain CC, Saslowsky DE, Walker RA, Shirley BW (1997). "Expression of chalcone synthase and chalcone isomerase proteins in Arabidopsis seedlings". Plant Mol. Biol. 35 (3): 377–81. doi:10.1023/A:1005846620791. PMID 9349261.
{{cite journal}}: Unknown parameter|month=ignored (help)CS1 maint: multiple names: authors list (link) - ^ a b Crosby KC, Pietraszewska-Bogiel A, Gadella TW, Winkel BS (2011). "Förster resonance energy transfer demonstrates a flavonoid metabolon in living plant cells that displays competitive interactions between enzymes". FEBS Lett. 585 (14): 2193–8. doi:10.1016/j.febslet.2011.05.066. PMID 21669202.
{{cite journal}}: Unknown parameter|month=ignored (help)CS1 maint: multiple names: authors list (link) - ^ Hrazdina G, Wagner GJ (1985). "Metabolic pathways as enzyme complexes: evidence for the synthesis of phenylpropanoids and flavonoids on membrane associated enzyme complexes". Arch. Biochem. Biophys. 237 (1): 88–100. doi:10.1016/0003-9861(85)90257-7. PMID 3970546.
{{cite journal}}: Unknown parameter|month=ignored (help) - ^ Austin MB, Noel JP (2003). "The chalcone synthase superfamily of type III polyketide synthases". Nat Prod Rep. 20 (1): 79–110. doi:10.1039/b100917f. PMID 12636085.
{{cite journal}}: Unknown parameter|month=ignored (help) - ^ Hzardina G, Jensen RA (1992). "Spatial organization of enzymes in plant metabolic pathways". Annu Rev Plant Physiol Plant Mol Biol. 43: 241–67.
- ^ Saslowsky D, Winkel-Shirley B (2001). "Localization of flavonoid enzymes in Arabidopsis roots". The Plant Journal : for cell and molecular biology. 27 (1): 37–48. PMID 11489181.
- ^ Attention: This template ({{cite pmid}}) is deprecated. To cite the publication identified by PMID 21909286, please use {{cite journal}} with
|pmid=21909286instead. - ^ Hinderer W, Seitz HU (1985). "Chalcone synthase from cell suspension cultures of Daucus carota". L. Arch Biochem Biophys. 240: 265–72. PMID 4015104.
- ^ Whitehead JM, Dixon RA (1983). "Chalcone synthase from cell suspension cultures of Phaseolus vulgaris". Biochem Biophys Acta. 747: 1777–86.
- ^ Schulze LP, Becker AM, Schulr W, Hahlbrock K, Dangl JL (1989). "Functional architecture of the light-responsive chalcone synthase promoter from parsley". Plant Cell. 1 (7): 707–14. PMID 2535519.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Dao TTH, Linthorst HJM, Verpoorte R (2011). "Chalcone synthase and its functions in plant resistance". Phytochemistry Reviews: proceedings of the Phytochemical Society of Europe. 10 (3): 397–412. doi:10.1007/s11101-011-9211-7. PMID 21909286.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Jiang C, Schommer C, Kim S-Y, Suh D-Y (2006). "Cloning and Characterization of Chalcone Synthase from the moss Physcomitrella patens". Phytochemistry. 67 (23): 2531–2540. doi:10.1016/j.phytochem.2006.09.030. PMID 17083952.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Napoli C, Lemieux C, Jorgensen R (1990). "Introduction of a Chimeric Chalcone Synthase Gene into Petunia Results in Reversible Co-Suppression of Homologous Genes in trans". Plant Cell. 2 (4): 279–289. doi:10.1105/tpc.2.4.279. PMC 159885. PMID 12354959.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Van Blokland R, Van der Geest N, Mol JNM, Kooter JM (1994). "Transgene-mediated suppression of chalcone synthase expression in Petunia hybrida results from an increase in RNA turnover". Plant J. 6 (6): 861–77. doi:10.1046/j.1365-313X.1994.6060861.x.
{{cite journal}}: CS1 maint: multiple names: authors list (link)