AtMYB12

ThePlantJournal(2008)56,316–326doi:

10.1111/j.1365-313X.2008.03597.x

AtMYB12regulatescaffeoylquinicacidand?avonolsynthesisintomato:expressioninfruitresultsinveryhighlevelsofbothtypesofpolyphenol

JieLuo1,2,EugenioButelli1,LionelHill1,AdrianParr3,RicardaNiggeweg1,?,PaulBailey1,BerndWeisshaar4andCathieMartin1,*1

JohnInnesCentre,NorwichResearchPark,Colney,Norwich,NR47UH,UK,2

China-UKHUST-RResGeneticEngineeringandGenomicsJointLaboratory,CollegeofLifeScienceandTechnology,HuazhongUniversityofScienceandTechnology,Wuhan430073,China,3

InstituteofFoodResearch,NorwichResearchPark,Cotney,Norwich,NR47UA,UK,and4

DepartmentofBiology,BielefeldUniversity,ChairofGenomeResearch(Lehrstuhlfu¨rGenomforschung),D-33594Bielefeld,Germany

Received26May2008;accepted3June2008;publishedonline29July2008.*

Forcorrespondence(fax+441603450045;e-mailcathie.martin@bbsrc.ac.uk).?

Presentaddress:BASFAktiengesellschaft,67117Limburgerhof,Germany.

TheEMBLdatabaseaccessionnumberfortheSlMYB12cDNAsequenceisEU419748.

Summary

Plantpolyphenolicsexhibitabroadspectrumofhealth-promotingeffectswhenconsumedaspartofthediet,andthereisconsiderableinterestinenhancingthelevelsofthesebioactivemoleculesinplantsusedasfoods.AtMYB12wasoriginallyidenti?edasa?avonol-speci?ctranscriptionalactivatorinArabidopsisthaliana,andthishasbeencon?rmedbyectopicexpressionintobacco.AtMYB12isabletoinducetheexpressionofadditionaltargetgenesintobacco,leadingtotheaccumulationofveryhighlevelsof?avonols.Whenexpressedinatissue-speci?cmannerintomato,AtMYB12activatesthecaffeoylquinicacidbiosyntheticpathway,inadditiontothe?avonolbiosyntheticpathway,anactivitywhichprobablymirrorsthatoftheorthologousMYB12-likeproteinintomato.Asaresultofitsbroadspeci?cityfortranscriptionalactivationintomato,AtMYB12canbeusedtoproducefruitwithextremelyhighlevelsofmultiplepolyphenolicanti-oxidants.Ourdataindicatethattranscriptionfactorsmayhavedifferentspeci?citiesfortargetgenesindifferentplants,whichisofsigni?cancewhendesigningstrategiestoimprovemetaboliteaccumulationandtheanti-oxidantcapacityoffoods.

Keywords:transcriptionfactor,?avonoids,caffeoylquinicacids,secondarymetabolism,metabolicengineer-ing,polyphenols.

Introduction

Onesubclassofplantpolyphenols,?avonoids,exhibitsabroadspectrumofhealth-promotingeffects(Houetal.,2004;Josephetal.,1999;Minketal.,2007;RenaudanddeLorgeril,1992;Seerametal.,2004)whenconsumedinfoodsofplantorigin.Dietary?avonoidsinhibitlow-densitylipidoxidationandthusreducetheprimaryriskfactorforarth-erosclerosisandrelateddiseases(Brouillardetal.,1997;Hannum,2004).Longer-termdietaryadministrationof?avonoidsofferscardioprotectioninratsandimprovesthelevelsofriskfactorsinmousemodelsofcardiovasculardisease,althoughitislikelythattheyprotectindirectlybyinducingendogenousscavengingmechanismsforreactive

316

oxygenspecies(Vinaetal.,2007).Inaddition,?avonolsaffordprotectionbymechanismsbeyondtheiractivitiesasanti-oxidantsorasinducersofscavengingpathwaysforreactiveoxygenspecies,forexamplebyinhibitingplateletaggregationandhencefactorscontributingtostrokeandthrombosis(Nijveldtetal.,2001).Thesedatafromcell-basedassaysandfeedingtrialswithanimalsaresupportedbyhumanepidemiologicalstudiesthathaveshowninversecorrelationsbetweenconsumptionof?avonol-richdietsandtheoccurrenceofcardiovasculardisease,certaincancersandage-relateddegenerativediseases(Hertogetal.,1993;Houetal.,2004;Josephetal.,1999;RenaudanddeLorgeril,

ª2008TheAuthors

Journalcompilationª2008BlackwellPublishingLtd

AtMYB12regulationofpolyphenolmetabolism317

1992;Seerametal.,2004).Basedonsuchstudies,ithasbeensuggestedthatasystemicincreaseinthedailyintakeofcertain?avonoidscouldleadtobetween7and31%reduc-tionintheincidenceofallcancersandbetween30and40%reductionindeathsfromcoronaryheartdisease(Hertogetal.,1993;Soobratteeetal.,2006).

Anotherimportantgroupofplant-basedbioactivepoly-phenolsarethecaffeoylquinicacids(CQAs,Figure1),ofwhichchlorogenicacid(CGA)isthemajorsolublephenolicinSolanaceousspeciessuchaspotato,tomatoandeggplant(aubergine),andincoffee(Clifford,1999;JohnsonandSchaal,1952;Lepelleyetal.,2007;Mooresetal.,1948;Niggewegetal.,2004).Consequently,CGAisoneofthemostabundantpolyphenolsinthehumandiet,andisthemajoranti-oxidantintheaverageUSdiet.CQAshavesigni?cantanti-oxidantactivityandcanlimitlow-densitylipidoxidation.OtherCQAs,suchasdicaffeoylquinicacid(diCQA)andtricaffeoylquinicacid(triCQA),offerevengreaterprotectionthanmonocaffeoylquinicacid(CGA)(Islam,2006).DietaryCQAsarealsobene?cialinspeci?cways:consumptionoftriCQAreducesthebloodglucosecontentofdiabeticrats(Islam,2006),CQAsareneuropro-tectiveagainstretinaldamage(Nakajimaetal.,2007),3,4,5-triCQAinhibitsHIV/AIDSprogression(Tamuraetal.,2006),anddiCQAhasanti-hepatotoxicactivity(Choietal.,2005),suggestingthatCQAsofferprotectionbyarangeofmechanisms.

Plantpolyphenolicshavesynergisticeffectsonhealth;theanti-bacterialactivitiesof?avonoidsareenhancedwhentheyareadministeredincombination(Arimaetal.,2002),andquercetinandkaempferolinhibitcancercellprolifera-tionsynergistically(Acklandetal.,2005).Thuscombinationsof?avonoids,whicharepresentnaturallyinfruitandvegetables,aremoreeffectiveinpreventingdiseasethanindividual?avonoids.

Variousstrategieshavebeenusedtoincreasethepro-ductionofpolyphenoliccompoundssuchasCQAsand?avonolsinfoodplants.Overexpressionofgenesencodingindividualbiosyntheticenzymescanleadtomodestincreasesinthelevelsof?avonols(Muiretal.,2001;Niggewegetal.,2004).Theproblemwiththistypeofstrategyisthatitdoesnotinducetheentirebiosyntheticpathway,andtheoverallincreaseinendproductsisusuallynothighenoughforpracticalapplicationpurposes.Analternativestrategyinvolvesexpressionofregulatorygenesthatdirectlyinducethesepathways.Forexample,increasesin?avonolsupto20-foldwereobtainedbysimultaneousexpressionofthemaizetranscriptionfactorsLcandC1(whichinduceanthocyaninbiosynthesisinmaize)intomatofruit(Bovyetal.,2002).Althoughthistypeofstrategygenerallyprovidesamoreeffectivemeansofengineeringmetabolismandachievessigni?cantenhancementsinthelevelsofendproducts,careisneededwhenchoosingthetranscriptionfactor(s)touse,toensuretheyhavetheappropriatespeci?cityinthetargetcropspecies.Forexam-ple,becauseLcandC1transcriptionfactorswereunableinducethewhole?avonolbiosyntheticpathwayintomato,theoveralllevelsof?avonolderivatives(20timesmorethaninthecontrol)werestillnotgreatenoughforapplicationpurposes.Inaddition,thisstrategyisproblematicforpathwayssuchasCQAbiosynthesis,whereregulatoryproteinshavenotyetbeenidenti?ed.

Wehavefoundthatitispossibletoaccumulateveryhighlevelsofpolyphenoliccompoundsbytissue-speci?c

expres-

ª2008TheAuthors

Journalcompilationª2008BlackwellPublishingLtd,ThePlantJournal,(2008),56,316–326

318JieLuoetal.

sionofasinglegenefromArabidopsisthalianaencodingthetranscriptionfactorAtMYB12(Mehrtensetal.,2005).Impor-tantly,eventhoughitwasidenti?edasa?avonol-speci?ctranscriptionalactivatorinArabidopsis,aresultthathasbeencon?rmedbyitsexpressionintobacco,AtMYB12canactivatetheCQAbiosyntheticpathwaywhenexpressedinatissue-speci?cmannerintomato,afunctionthatprobablymirrorsthefunctionoftheorthologousMYB12-likeproteinintomato.Consequently,AtMYB12canbeusedtoproducefruitwithextremelyhighlevelsofmultiple,health-promot-ing,hydrophilic,polyphenolicanti-oxidants.Results

EffectsofconstitutiveexpressionofAtMYB12onphenylpropanoidmetabolismintobacco

AtMYB12hasbeenidenti?edasatranscriptionfactorthatspeci?callyactivates?avonolaccumulationinArabidopsis(Mehrtensetal.,2005).TodeterminewhetherAtMYB12couldworkinthesamewayinotherspecies,weintroducedtheAtMYB12cDNAintotobacco(Nicotianatabacum)underthecontrolofthestrongconstitutiveCaMV35Spromoter.Ofmorethan15independenttransformants,threelines(lines10,13and15)withvariouslevelsoftransgeneexpressionwereinvestigatedfurther.Thetransgeniclinesgrewslightly

moreslowlythancontrols.Theonlyothervisibledifferencewasthatthe?owersofthetransgenicplantsweremorepalelycolouredthantheirwild-typecounterparts(Figure2a),andthisphenotypewascorrelatedwiththeexpressionleveloftheAtMYB12transgene.Thelevelsofphenolicsinleavesand?owersoftransgenicplantswerecomparedtothoseinwild-typeplants(Figure2bandTableS1).Individualphenolicswereidenti?edbyexamina-tionoftheirfragmentationpatterns,andcomparison,wherepossible,tofragmentationpatternsreportedinthelitera-ture.IntheabsenceofNMRdata,theseidentitiesshouldbeconsideredasprobableratherthanproven.CQAswerebyfarthemostabundantphenolicsinwild-typeleaves(15.1Æ1.7mgg)1DW),althoughlowlevels(0.4Æ0.1mgg)1DW)ofquercetinglycosides(mainlyrutin)wereidenti?ed,butkaempferolglycosideswerebarelydetect-able.ExpressionofAtMYB12resultedin46-foldand83-foldincreasesofrutin(22.1Æ2.5mgg)1DW)andkaempferolrutinoside(19.2Æ2.1mgg)1DW)inleaves,respectively.Inaddition,atwofoldincreaseinCGAlevels(to36.2Æ4.3mgg)1DW)wasdetectedinleavesofthetransgeniclines,and,intotal,levelsofpolyphenolsinexcessof77.5mgg)1DWaccumulatedintobaccoleaves.Theincreasesin?avo-nollevelsintobaccowereconsiderablygreaterthanthosereportedforoverexpressionofAtMYB12inArabidopsis(three-tofourfold;Mehrtensetal.,2005).

ª2008TheAuthors

Journalcompilationª2008BlackwellPublishingLtd,ThePlantJournal,(2008),56,316–326

AtMYB12regulationofpolyphenolmetabolism319

FlowersoftobaccoexpressingAtMYB12alsohadincreasedrutin,kaempferolrutinoside,CGAandkaempferolmalonylglucosidecontentscomparedtowild-type?owers,andlowerlevelsofanthocyanins(Figure2c),whereasthelevelsofpolyamineconjugatesremainedunchanged.Theinversecorrelationbetweenanthocyaninand?avonollevelsin?owersre?ectscompetitionbetweenthesetwobranchesof?avonoidmetabolism;competitionthatisbelievedtooccurthroughtherelativeactivitiesofdihydro?avonol4-reductaseand?avonolsynthaseondihydro?avonolprecursors(Daviesetal.,2003).

EffectsofAtMYB12ongeneexpressionintobaccoExpressionofthegenesencodingenzymesinvolvedin?avonolandCGAbiosynthesiswascomparedbetweencontrolplantsandlinesexpressingAtMYB12byRNAgelblots(Figure2d).Amongthegenesthatweretested,thoseencodingphenylalanineammonialyase(PAL),chalconesynthase(CHS),chalconeisomerase(CHI)and?avonolsynthase(FLS)wereinducedbyAtMYB12expressionintobacco.ThegeneencodinghydroxycinnamoylCoAqui-natetransferase(HQT),whichisinvolvedinCGAbiosyn-thesis(Niggewegetal.,2004),wasnotinduced,andexpressionofthegeneencodingdihydro?avonol4-reduc-tase(DFR),whichisrequiredspeci?callyforanthocyaninbiosynthesis,wasnotdetectedineitherthecontrolortheAtMYB12-expressingplants.Theseresultscon?rmthegenesoriginallyidenti?edastargetsofAtMYB12(Mehr-tensetal.,2005;Strackeetal.,2007),exceptthatthegenesencodingPALwerenotidenti?edastargetsofAtMYB12inArabidopsis.

Effectsoffruit-speci?cexpressionofAtMYB12intomatoOurresultsshowthatAtMYB12canactasaveryeffective,positiveregulatorofthe?avonolbiosyntheticpathwayintobacco.ToexploitthepotentialofAtMYB12formetabolicengineering,thegenewasthenintroducedintotomato,drivenbythefruit-speci?cE8promoter,whichismostactiveindevelopingfruitafterthebreakerstage(Deikmanetal.,1992).Twovarietiesoftomato(Solanumlycopersicumcv.MicroTomandcv.MoneyMaker)weretransformedwithpSLJ-E8-MYB12,andmorethan30independentkanamycin-resistantplants(T0)wereobtainedforeachvariety.

AtMYB12primarytransformantsdevelopednormallyduringvegetativegrowthandwereindistinguishablefromcontrols.Transgenicfruitalsodevelopednormallyandwereindistinguishablefromfruitofcontrolplantsuntiltheturningstage.Atmaturity,insteadofturningthepink-redcolourofcontrolfruit,thetransgenicMicroTomfruitwereorange(Figure3a).ThisphenotypecorrelatedwiththeexpressionlevelofAtMYB12andthecontentof?avonolderivativesinthetransgenicfruit.Thesameorangefruit

phenotypewasobservedinthefruitofthetransformantsintheMoneyMakerbackground(Figure3b).

MatureT0fruitsofeachvarietywerescreenedfortheirrutinandkaempferolrutinosidecontents(Figures3candFigureS1forMicroTomandMoneyMaker,respectively).Becauseoftheshortergenerationtimeandrelativeeaseofcultivationofdwarfvarieties,transgenicplantsintheMicroTombackgroundwithvariouslevelsof?avonolderivativeswereselectedforfurthergenotyping,andthetranscriptlevelsofAtMYB12inthefruitoftheseplantswereanalysedbyquantitativeRT-PCR(Figure3d).ControlfruitshowednoAtMYB12transcript,whilealltransgenicplantstestedshowedAtMYB12transcriptsinfruitandallthetransgeniclinesexpressingAtMYB12producedorangefruitasopposedtothenormalredwild-typefruit.Furthermore,therewasagoodcorrelationbetweenthetranscriptlevelsofAtMYB12andthekaempferolrutinosidecontentsofthefruit.Threeofthetransgenicplants(lines9,12and22)wereusedforfurtheranalyses.Forallthreelines,thetransgenewasinheritedina3:1ratiobytheT1progeny,asexpectedforsingle-copytransgeneinsertions.

EffectsofAtMYB12onphenylpropanoidmetabolismintomato

Ripefruitfrombothtransgenicandcontrollineswerehar-vested,andthepeeland?eshwereanalysedseparatelyfortheirpolyphenolcontentsbyHPLCandLC/MS/MS(Figure3eandTableS2).Themain?avonoidincontrolpeelextractwasnaringininchalcone,withsmallamountsofrutin,kaempferolrutinoside,CGA,diCQAandtriCQA(Figure3e,TableS2andFigureS2),con?rmingresultsreportedrecentlybyMocoetal.(2006).The?eshofcontrolplantscontainedonlysmallamountsofCQAsandotherphenolics.Inboththepeelandthe?eshoftransgenicfruit,massivelevelsof?avonolderivatives(mainlyrutinandkaempferolrutinoside)weredetected.Surprisingly,highlevelsofCQAs(CGA,diCQAandtriCQA)werealsodetectedinthefruitofthelinesexpressingAtMYB12(Figure3e).Themajorphenolicsinwholefruitwerequanti?edusingpuri?edstandardsasshowninTable1.Onawhole-fruitbasis,morethan15mgg)1DWofCQAsand72mgg)1DWof?avonolsweredetectedinthetransgenicfruitintheMicroTomback-ground,whichisequivalentto22-and65-foldhigherlevels,respectively,comparedtocontrolfruit.IntheMoneyMakerbackground,AtMYB12alsoincreasedthelevelsofbothCQAsand?avonols(tomorethan3and48mgg)1DW,respectively).InuntransformedMoneyMaker,thetotallev-elsofthesepolyphenolswerelowerthaninMicroTom,afeaturethatiscommontolarger-fruitedvarietiescomparedtocherrytomatoes(Raffoetal.,2002).

Thehigh-polyphenolphenotypewasmaintainedinmaturefruitofhemizygousT1andhomozygousT2individ-ualsofthreesingle-copyAtMYB12lines(Table2),showing

ª2008TheAuthors

Journalcompilationª2008BlackwellPublishingLtd,ThePlantJournal,(2008),56,316–326

320JieLuoetal.

thatthehigh-?avonol/high-CQAphenotypewasinheritedstablyinsubsequentgenerationsandwasinfactsomewhatenhancedastheAtMYB12transgenewasbroughttohomozygosity.

EffectsofAtMYB12ongeneexpressionintomato

TheeffectofAtMYB12ontheexpressionofgenesinvolvedin?avonoidbiosynthesiswasexaminedbyquantitativeRT-PCRinfruitfromtheT1generationofplants.RNAwasextractedfromfruitattheturningstage.ExpressionlevelsofphenylpropanoidpathwaygenesencodingPAL,cinnamate4-hydroxylase(C4H),4-hydroxycinnamoylCoAligase(4CL),CHS,CHI,?avanone-3-hydroxylase(F3H),?avonoid-3¢-hydroxylase(F3¢H),?avonoid-3¢5¢-hydroxylase(F3¢5¢H),FLS,DFR,anthocyanidinsynthase(ANS),?avonol-3-glucosyltransferase(GT),?avonol-3-glucoside-rhamno-syltransferase(RT),p-coumaroylester3-hydroxylase(C3H),hydroxycinnamoylCoAshikimate/quinatetransferase(HCT)andHQTwerecomparedincontrolandtransgenicfruitexpressingAtMYB12.TranscriptsofPAL,F3H,F3¢H,FLS,GTandRTgeneswerereadilydetectableincontrolfruit(Fig-ure3f).IntransgenicAtMYB12fruit,weobservedmorethan100-foldinductionofthegenesencodingPAL,CHSandGT,between50-and100-foldinductionofthegenesencodingCHI,ANSandC3H,between10-and50-foldinductionof

the

ª2008TheAuthors

Journalcompilationª2008BlackwellPublishingLtd,ThePlantJournal,(2008),56,316–326