Abstract
The 2-oxoglutarate-dependent dioxygenase (2-OGD) superfamily is one of the largest protein families in plants. The main oxidation reactions they catalyze in plants are hydroxylation, desaturation, demethylation, epimerization, and halogenation. Four members of the 2-OGD superfamily, i.e., flavonone 3β-hydroxylase (F3H), flavones synthase I (FNS I), flavonol synthase (FLS), and anthocyanidin synthase (ANS)/leucoanthocyanidin dioxygenase (LDOX), are present in the flavonoid pathway, catalyzing hydroxylation and desaturation reactions. In this review, we summarize the recent research progress on these proteins, from the discovery of their enzymatic activity, to their functional verification, to the analysis of the response they mediate in plants towards adversity. Substrate diversity analysis indicated that F3H, FNS Ⅰ, ANS/LDOX, and FLS perform their respective dominant functions in the flavonoid pathway, despite the presence of functional redundancy among them. The phylogenetic tree classified two types of FNS Ⅰ, one mainly performing FNS activity, and the other, a new type of FNS present in angiosperms, mainly involved in C-5 hydroxylation of SA. Additionally, a new class of LDOXs is highlighted, which can catalyze the conversion of (+)-catechin to cyanidin, further influencing the starter and extension unit composition of proanthocyanidins (PAs). The systematical description of the functional diversity and evolutionary relationship among these enzymes can facilitate the understanding of their impacts on plant metabolism. On the other hand, it provides molecular genetic evidence of the chemical evolution of flavonoids from lower to higher plants, promoting plant adaptation to harsh environments.
Highlights
Flavonoid compounds are a class of important secondary metabolites, widely distributed in the plant kingdom
Abscisic acid (ABA) is a vital stress response-associated phytohormone induced by diverse stresses, and flavonone 3β-hydroxylase (F3H) in several species are induced by ABA [39]
With the popularity of high-throughput sequencing technologies, including transcriptomics and genomics, an increasing number of 2-oxoglutarate-dependent dioxygenase (2-OGD) genes have been identified in various species
Summary
Flavonoid compounds are a class of important secondary metabolites, widely distributed in the plant kingdom. Flavonoids have a structure consisting of 2-phenyl chromene as the main framework and exhibit the basic skeleton C6–C3–C6. Flavonoids have a structure consisting of 2-phenyl chromene as the main framew oofr1k3 and exhibit the basic skeleton C6–C3–C6. The carbon framework is always modified via acylation, methoxylation, hydroxylation, or O-glycosylation of hydroxyl groups as well as C-glycosylation directly on the carbon atoms of the skeleton, catalyzed by serine carbwoexlyl paespCti-dgalysec-oliskyela(tSioCnPdLi)r,eOct-lmy eotnhythlteracnasrfbeoranseato(OmMs To)f, t2h-eoxskoeglleuttoanra, tcea-tdaelpyzeneddebnyt sdeir-oinxeygceanrbaosexy(p2-eOptGidDa)s,ea-lnikdeg(lSyCcPosLy),ltOra-nmsefethraysletra(GnsTf)erfaasme i(lOieMs, Tre),s2p-eocxtoivgelluyta[r8a–t1e0-d].eIpnenaddedni-t tdioionx, ytgheencaysteo(c2h-rOoGmDe )P, a4n50d ghlyydcroosxyyltlraasnesafenrdasteh(eGsTh)ofratm-chilaieins, rdeeshpyedctriovgeelyna[s8e–/1r0e]d.uIcntaasde(dSiDtiRon) ,ftahme iclyietsocphlraoymae Pg4r5e0athyrodlreoxdyularisneganthdethme oshdoifritc-acthioanin adnedhydderroigveantiazsaet/iornedoufcttahsee C(S6D–CR3) –faCm6 ilbiaessipc laskyealegtorenat[1ro1l,1e2d].urTihnegrtehfoerme,oddiivfiecrastiifoiendanmdoddeifriicvaattiioznatihoans oefntrhicehCe6d–Cth3e– tCyp6ebsaosifcflsakveolentooinds[1(1in,1c2lu].dTinhgeriesfoofrlaev, odnivees,rsfilfiavedonmeso,dfliafivcoantioolns,hfalasveannroiclsh,eadndthaenttyhpoecsyao-f nfliadvinosn)oiindps l(ainnctsluadnidngpriosomfloatveodntehse, afldaavpotnaetiso, nflaovf opnlaonlsts, fltoavhaanrsohlst,earnredstarniatlheoncvyiarnoindminesn)tisn. FFiigguurree11..SScchheemmaatitcicddiaigargarmamofotfhtehecactatlyaltyictimc emcehcahnaisnmismof o2f-O2-GODGsD.Tsh.Tehuepupeprpcearscea“sSe”“iSn”diincadtiecsates ddiivveerrsseessuubbssttrraatteess;;SS--OOiinnddiiccaatteess tthhee pprroodducts after oxidation; 2-OG, 2-oxoglutarate. ANSs oxidize leucoanthocyanidin to yield anthocyanin monomers (pelargonidin, cyanidin, and delphinidin), which can be further used. ANSs oxidize leucoanthocyanidin to yield anthocyanin monomers (pelargonidin, cyantoidpirno,dauncdedcealtpehchininidsiann),dwahnitchhoccaynanbienfgulrytchoesriduesesdbytoapnrtohdoucycaenciantercehdiuncstaasneds a(AntNhoRcsy)aannidn gUlGycToss,irdeesspebcytiavnetlhyo[c2y6a,2n7i]n. With the development of molecular biology, more techniques and means are being usedWtoiitdhetnhteifydtehveefloupnmctieonntooffgmenoelse.cuGliavrenbitohleogimy,pmorotarencteecohfn2i-qOuGeDs sanindpmlaenatnmseatraebobleisinmg, uthseidr ctoonidtiennuteifdy ftuhnecftuionnctailosntuodf ygeinetsh.eGflivaevnonthoeidimmpeotartbaonlcisemofp2a-tOhGwDays isnipnldainstpmenestabloe-. lSiosm,e tnheewir iscsounetsinhuaevde fbuenenctimonenaltiostnueddy, siunchthaes eflvaovlountiooindarmyertealbatoiloinsmshippast,hnwewayfuisncitniodniss-, panendsfaubnlec.tiSoonmalerendeuwndisasnuceys ahmavoengbe2e-On GmDesn.tiIonnethdi,ssruecvhiewas, weveosluytsitoenmaaryticraelllaytidoensschriipbse, ntheewlafutenscttifounnsc,tiaonndalfurnescetiaornchal prerodgurnedssanrceygaarmdionnggt2h-eOrGoDles.oIfnththeisforuevr i2e-wO,GwDe msyesmtembeartsiFc3aHlly, FdNeSs,crAibNeS/thLeDlOatXes, tanfudnFcLtiSoninalthreesfleaavrcohnopidropgartehsws areyg, asrdwinegll athsethreoirleevoofluthtieonfoaruyr 2cl-aOsGsifiDcamtieomn banerdsfFu3nHct,ioFnNalSp, rAedNiSct/iLoDn,OaXn,dadnidscuFsLsSreincetnhtedfislacvoovneroiieds ipnartehlwataioyn, taos2w-OeGllDass tahnedirpelvanotlumtieotnaabroylicslmas.sification and functional prediction, and discuss recent discoveries in relation to2-OGDs and plant metabolism
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