Abstract
Anthocyanins and proanthocyanidins, the major flavonoids in black and red rice grains, respectively, are mainly derived from 3′,4′-dihydroxylated leucocyanidin. 3′-Hydroxylation of flavonoids in rice is catalyzed by flavonoid 3′-hydroxylase (F3′H: EC 1.14.13.21). We isolated cDNA clones of the two rice F3′H genes (CYP75B3 and CYP75B4) from Korean varieties of white, black, and red rice. Sequence analysis revealed allelic variants of each gene containing one or two amino acid substitutions. Heterologous expression in yeast demonstrated that CYP75B3 preferred kaempferol to other substrates, and had a low preference for dihydrokaempferol. CYP75B4 exhibited a higher preference for apigenin than for other substrates. CYP75B3 from black rice showed an approximately two-fold increase in catalytic efficiencies for naringenin and dihydrokaempferol compared to CYP75B3s from white and red rice. The F3′H activity of CYP75B3 was much higher than that of CYP75B4. Gene expression analysis showed that CYP75B3, CYP75B4, and most other flavonoid pathway genes were predominantly expressed in the developing seeds of black rice, but not in those of white and red rice, which is consistent with the pigmentation patterns of the seeds. The expression levels of CYP75B4 were relatively higher than those of CYP75B3 in the developing seeds, leaves, and roots of white rice.
Highlights
Rice is a staple food in many Asian countries
Sequence Analysis of CYP75B3s and CYP75B4s cDNA clones of CYP75B3 and CYP75B4 were isolated from the white rice, Iimi (IM), black rice, Heugnam (HN) and Heugjinju (HJJ), and red rice, Jeogjinju (JJJ) and Hongjinju (HoJJ)
CYP75B4-IM was identical to the registered sequence in the public database, but an amino acid substitution at position 351 was shared by CYP75B4-HN and CYP75B4-HJJ from black rice and another substitution at positions seven was shared by CYP75B4-JJJ and CYP75B4-HoJJ from red rice
Summary
Rice is a staple food in many Asian countries. white rice is most commonly consumed, pigmented rice is used in Asian diets. Pigmented rice grains contain large amounts of flavonoids. The major flavonoids in black rice grains are anthocyanins, which are mainly composed of cyanidin-3-O-glucoside, and peonidin-3-O-glucoside, and in red rice grains are proanthocyanidins and flavan-3-ols oligomers, which have catechin as the main extension unit [11,12,13,14,15]. Small quantities of aglycones and glycosides of flavanones, flavones, dihydroflavonols, and flavonols are present in black and red rice grains [13,15,16,17]. Flavonoids are barely detected in white rice grains, except for small quantities of tricin (3 ,5 -dimethoxylated flavone) [18,19]. Apnrtohaoncythanoicnyaanndidpinroabniothsoycnytahneidsiisn both inclubdieossytenpthsetshisatbaorteh caintaclluydzeedsbteypsflatvhaant oanree 3c-ahtyaldyrzoexdylbayse f(lFav3aHn)oanned3d-hihydyrdorxoyfllaasveon(Fo3lH4)-readnudctase (DFRd).ihAyndtrhooflcayvaonniodli4n-riesdsuycntatshee(sDizFeRd).bAynathnothcyoacnyiadninidisinsysnytnhethsiazseed(bAyNanSt)h, owcyhaenreidaisnpsyronathnatsheo(cAyNanS)id, in is synthwoefhstiehzreeedapsbaptyrhowlaeanuytch.ooFac3ny’aHthn,iodwciynhaiicsnhisdycinanttahrleeysdzizeuecBdt-abrisynegle(LuhcAyodRarno)txdhyoulcarytiinaongnidloainftefrlesadtveuopcntsoaoisdefs(t,LhaAedRdp)sadtdhuiwrvienargysi.ltayFt3etosHtet,hpwes hich catalycozme Bpo-rsiintiognhoyfdflraovxoynloaitdios ninorficfleagvroainnos.idTsri,caindidsssydnivtheerssiizteydttohrtohuegchoamdpifofesriteinotnpoatfhflwaavyoinnowidhsicihn rice grainasp. Apnrtohaoncythanoicnyaanndidpinroabniothsoycnytahneidsiisn both inclubdieossytenpthsetshisatbaorteh caintaclluydzeedsbteypsflatvhaant oanree 3c-ahtyaldyrzoexdylbayse f(lFav3aHn)oanned3d-hihydyrdorxoyfllaasveon(Fo3lH4)-readnudctase (DFRd).ihAyndtrhooflcayvaonniodli4n-riesdsuycntatshee(sDizFeRd).bAynathnothcyoacnyiadninidisinsysnytnhethsiazseed(bAyNanSt)h, owcyhaenreidaisnpsyronathnatsheo(cAyNanS)id, in is synthwoefhstiehzreeedapsbaptyrhowlaeanuytch.ooFac3ny’aHthn,iodwciynhaiicsnhisdycinanttahrleeysdzizeuecBdt-abrisynegle(LuhcAyodRarno)txdhyoulcarytiinaongnidloainftefrlesadtveuopcntsoaoisdefs(t,LhaAedRdp)sadtdhuiwrvienargysi.ltayFt3etosHtet,hpwes hich catalycozme Bpo-rsiintiognhoyfdflraovxoynloaitdios ninorficfleagvroainnos.idTsri,caindidsssydnivtheerssiizteydttohrtohuegchoamdpifofesriteinotnpoatfhflwaavyoinnowidhsicihn rice grainasp. igTernicininfoisrmsyedntbhyestihzeedacttihornouofgfhlaavodnieffseyrnenthtapseatIhI w(FaNySIiIn) iws hutiiclhizeadp.iFgleanviannofonerm2-ehdydbryoxtyhleasaection of fla(vFo2Hne) csoynnvtehratssenaIIri(nFgNenSinII)tois2u-htyildizroexdy.flaFvlaavnoanneonine t2h-ehyCd-grloyxcoyslyalsfelav(Fo2nHe b) icoosynnvtehretssisnpaartihnwgeaynin to
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