LETTERdoi:10.1038/nature14346PrimarytranscriptsofmicroRNAsencoderegulatorypeptidesDominiqueLauressergues1,2,Jean-MaloCouzigou1,2,He´le`neSanClemente1,2,YvesMartinez3,ChristopheDunand1,2,GuillaumeBe´card1,2&Jean-PhilippeCombier1,2MicroRNAs(miRNAs)aresmallregulatoryRNAmoleculesthatinhibittheexpressionofspecifictargetgenesbybindingtoandcleavingtheirmessengerRNAsorotherwiseinhibitingtheirtrans-lationintoproteins1.miRNAsaretranscribedasmuchlargerprim-arytranscripts(pri-miRNAs),thefunctionofwhichisnotfullyunderstood.Hereweshowthatplantpri-miRNAscontainshortopenreadingframesequencesthatencoderegulatorypeptides.Thepri-miR171bofMedicagotruncatulaandthepri-miR165aofArabid-opsisthalianaproducepeptides,whichwetermmiPEP171bandmiPEP165a,respectively,thatenhancetheaccumulationoftheircorrespondingmaturemiRNAs,resultingindownregulationoftar-getgenesinvolvedinrootdevelopment.ThemechanismofmiRNA-encodedpeptide(miPEP)actioninvolvesincreasingtranscriptionofthepri-miRNA.Fiveotherpri-miRNAsofA.thalianaandM.truncatulaencodeactivemiPEPs,suggestingthatmiPEPsarewide-spreadthroughouttheplantkingdom.SyntheticmiPEP171bandmiPEP165apeptidesappliedtoplantsspecificallytriggertheaccu-mulationofmiR171bandmiR165a,leadingtoreductionoflateralrootdevelopmentandstimulationofmainrootgrowth,respectively,suggestingthatmiPEPsmighthaveagronomicalapplications.ThebiogenesisofmiRNAsinvolvestwomaturationsteps:proces-singoflargepri-miRNAstoshorterpre-miRNAs,andtheirsubsequentmaturationtoproduceactive,maturemiRNAs1.Whetherthepri-miRNAsthemselveshavearegulatoryfunctionisnotknown.Likeprotein-encodingmRNAs,pri-miRNAsaresynthesizedbyRNApoly-meraseII1;therefore,wehypothesizedthattheymightalsoencodepro-teinsorpeptides.Totestthishypothesis,westudiedthemiR171familyinthemodelplantMedicagotruncatula,becausewehavepreviouslydocumentedtheroleofoneofitsmembers(miR171h)inmycorrhiza-tion2.HereweselectedmiR171bforfurtheranalysisbecauseitregulatestheformationoflateralroots,amoreeasilymonitoreddevelopmentalstep.Wefirstidentifiedth...
