Divergent evolution of flavonoid 2-oxoglutarate-dependent dioxygenases in parsley
Flavone synthases (FNSs) catalyze the oxidation of flavanones to flavones, i.e. the formation of apigenin from (2 S)-naringenin. While many plants express a microsomal-type FNS II, the soluble FNS I appears to be confined to a few species of the Apiaceae and was cloned recently from parsley plants....
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Veröffentlicht in: | FEBS letters 2003-06, Vol.544 (1), p.93-98 |
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Sprache: | eng |
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Zusammenfassung: | Flavone synthases (FNSs) catalyze the oxidation of flavanones to flavones, i.e. the formation of apigenin from (2
S)-naringenin. While many plants express a microsomal-type FNS II, the soluble FNS I appears to be confined to a few species of the Apiaceae and was cloned recently from parsley plants. FNS I belongs to the Fe
II/2-oxoglutarate-dependent dioxygenases characterized by short conserved sequence elements for cofactor binding, and its evolutionary context and mode of action are under investigation. Using a homology-based reverse transcription polymerase chain reaction approach, two additional flavonoid-specific dioxygenases were cloned from immature parsley leaflets, which were identified as flavanone 3β-hydroxylase (FHT) and flavonol synthase (FLS) after expression in yeast cells. Sequence alignments revealed marginal differences among the parsley FNS I and FHT polypeptides of only 6%, while much less identity (about 29%) was observed with the parsley FLS. Analogous to FNS I, FLS oxidizes the flavonoid γ-pyrone by introducing a C2, C3 double bond, and (2
R,3
S)-dihydrokaempferol (
cis-dihydrokaempferol) was proposed recently as the most likely intermediate in both FNS I and FLS catalysis. Incubation of either FNS I or FLS with
cis-dihydrokaempferol exclusively produced kaempferol and confirmed the assumption that flavonol formation occurs via hydroxylation at C3 followed by dehydratation. However, the lack of apigenin in these incubations ruled out
cis-dihydrokaempferol as a free intermediate in FNS I catalysis. Furthermore, neither (+)-
trans-dihydrokaempferol nor unnatural (−)-
trans-dihydrokaempferol and 2-hydroxynaringenin served as a substrate for FNS I. Overall, the data suggest that FNS I has evolved uniquely in some Apiaceae as a paraphyletic gene from FHT, irrespective of the fact that FNS I and FLS catalyze equivalent desaturation reactions. |
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ISSN: | 0014-5793 1873-3468 |
DOI: | 10.1016/S0014-5793(03)00479-4 |