Red grain colour gene (R) of wheat is a Myb-type transcription factor

Euphytica(2005)143:239–242DOI:10.1007/s10681-005-7854-4

C

Springer2005

Redgraincolourgene(R)ofwheatisaMyb-typetranscriptionfactor

EikoHimi&KazuhikoNoda

ResearchInstituteforBioresources,OkayamaUniversity,Chuo2-20-1,Kurashiki,Okayama,Japan

( authorforcorrespondence:e-mail:knoda@rib.okayama-u.ac.jp)

Keywords:dormancy, avonoid,MYB,pigment,transcriptionfactor

Summary

Redpigmentofwheatgrainwasreportedtobepolyphenolcompounds,phlobapheneorproanthocyanidin,whichweresynthesizedthroughthe avonoidbiosynthesispathway.Weexaminedtheexpressionoffourgenesinthe avonoidpathwayindevelopingwheatgrains:chalconesynthase(CHS),chalconeisomerase(CHI), avanone3-hydroxylase(F3H),anddihydro avonol4-reductase(DFR).Theexpressionofthesegenesinthewhite-grainedwheatlineswasreduced,comparedwiththatinthered-grainedwheats.TheseresultssuggestthattheRgenesforgraincolour,locatedonthelongarmsofchromosomes3A,3Band3D,aretranscriptionalactivatorsofthe avonoidsynthesisgenes.Weidenti edthreeMyb-typetranscriptionfactors(Tamyb10-A1on3A,Tamyb10-B1on3BandTamyb10-D1on3D),whichwerealsolocatedinthesameregionastheRloci,andwereexpressedpredominantlyindevelopinggrains.Inwheatlineswiththerecessivealleler3(3B)Tamyb10-B1hadadeletionwhichcausedaframe-shiftinitsopenreadingframe.Tamyb10-A1,and-D1werenotexpressedinwheatswithr2(3A)andr1(3D).

Introduction

Redgraincolourofwheathasbeenassociatedwiththedevelopmentofgraindormancyandaffectsbrightnessofwheat ourduetocontaminationofredpigmentinmillingprocess(Flintham,2000;Warneretal.,2000;Himietal.,2002).Redpigmentingraincoattissuearederivativesofcatechin-tannin,probably,phlobapheneorproanthocyanidin(Miyamoto&Everson,1958).Thesepolyphenolcompoundsandanthocyanin,typicalplantpigments,aresynthesizedthroughthe avonoidbiosynthesispathway(Winkel-Shirley,2001).Weiso-latedtheearlygenesofthe avonoidbiosynthesispathway(CHS,CHI,F3HandDFR)andfoundthattheexpressionofthesegeneswasalmostcompletelysuppressedinthedevelopinggrainsofwhite-grainedwheats,comparedwiththatinred-grainedwheats(Himietal.,2005).

WheatgraincolourwascontrolledbytheRgenesontheendregionofthelongarmsofwheatchromosomes3A,3Band3D(McIntoshetal.,1998).EachRgene(R1on3D,R2on3A,orR3on3B)wasdominantandinheritedmonogenicly(McIntoshetal.,1998).AsingleRgenewasabletoupregu-latethefourgenesinthe avonoidbiosynthesispath-way,suggestingthattheRgeneisatranscriptionfactor.

Severaltranscriptionfactorsinthe avonoidsyn-thesispathwayhavebeenreportedinmaize,Arabidop-sisandsnapdragon(VomEndtetal.,2002).TwotypesoftranscriptionfactorsgroupedastheR/Bfamily(basichelix–loop–helix(bHLH)-type)andtheC1/Plfamily(Myb-type)wereabletoupregulateallthestructuralgenesrequiredfortheproductionofanthocyanin.Inadditiontothesefactors,transcriptionfactors(P,TT2,TT8andDel)thatregulateonlyapartofthe avonoidbiosynthesisgenesinaspeci ctissuehavebeenalsoreported(Martinetal.,1991;Nesietal.,2001;VomEndtetal.,2002).

Inthispaper,wereportthreemyb-typetranscrip-tionfactors(Tamyb10s)isolatedfromwheat,whichcanactivatethe avonoidbiosynthesisgenesandwhichdifferinexpressionandstructureinparallelwithal-lelicdifferencesattheRloci.