AtMYB41 activates ectopic suberin synthesis and assembly in multiple plant species and cell types

ThePlantJournal(2014)80,216–229doi:

10.1111/tpj.12624

AtMYB41activatesectopicsuberinsynthesisandassemblyinmultipleplantspeciesandcelltypes

DylanK.Kosma1,*,JhadeswarMurmu2,FakhriaM.Razeq2,PatriciaSantos3,RichardBourgault4,IsabelMolina4andOwenRowland2,*1

DepartmentofPlantBiology,MichiganStateUniversity,EastLansing,MI48824USA,2

DepartmentofBiologyandInstituteofBiochemistry,CarletonUniversity,Ottawa,ONK1S5B6,Canada,3

DepartmentofPlant,SoilandMicrobialSciences,MichiganStateUniversity,EastLansing,MI48824,USA,and4

DepartmentofBiology,AlgomaUniversity,SaultSteMarie,ONP6A2G4,Canada

Received19November2013;revised17July2014;accepted21July2014;publishedonline25July2014.*Forcorrespondence(e-mailsdkosma@msu.edu;owen.rowland@carleton.ca).

SUMMARY

Suberinisalipidandphenoliccellwallheteropolymerfoundintherootsandotherorgansofallvascularplants.Suberinplaysacriticalroleinplantwaterrelationsandinprotectingplantsfrombioticandabioticstresses.Herewedescribeatranscriptionfactor,AtMYB41(At4g28110),thatcanactivatethestepsneces-saryforaliphaticsuberinsynthesisanddepositionofcellwall-associatedsuberin-likelamellaeinbothAra-bidopsisthalianaandNicotianabenthamiana.OverexpressionofAtMYB41increasedtheabundanceofsuberinbiosyntheticgenetranscriptsbyordersofmagnitudeandresultedintheaccumulationofupto22timesmoresuberin-typethancutin-typealiphaticmonomersinleaves.OverexpressionofAtMYB41alsoresultedinelevatedamountsofmonolignolsinleavesandanincreaseintheaccumulationofphenylpropa-noidandligninbiosyntheticgenetranscripts.Surprisingly,ultrastructuraldataindicatedthatoverexpres-sionledtotheformationofsuberin-likelamellaeinbothepidermalandmesophyllcellsofleaves.WefurtherimplicateAtMYB41intheproductionofaliphaticsuberinunderabioticstressconditions.Theseresultsprovideinsightintothemolecular-geneticmechanismsofthebiosynthesisanddepositionofaubiquitouscellwall-associatedplantstructureandwillserveasabasisfordiscoveringthetranscriptionalnetworkbehindoneofthemostabundantlipid-basedpolymersinnature.

Keywords:suberin,R2-R3MYB,transcriptionfactor,lignin,abioticstress,Arabidopsis,Nicotianabenthamiana.

INTRODUCTION

Thecolonizationoflandbyplantsrequiredtheacquisitionofspecializedmodi cationstothecellwall.Structureslikeligni edvasculatureandsuberizedendodermalcellsallowedplantstodevelopahomoiohydriclifestyle(thecapacitytomaintainaconstantwaterstatus)requiredforterrestrialhabitats.Suberin,analiphaticandphenolichet-eropolymer,issynthesizedinmanytissuesofhigherplantsincludingseedcoats,treebark,peridermsofmaturerootsandtubers,endodermalcellsofyoungroots,andabscis-sionscars(Pollardetal.,2008;Schreiber,2010;Beissonetal.,2012;Frankeetal.,2012).Itisalsodepositedasaresponsetoenvironmentalstressessuchashighsalinityandwounding(Kolattukudy,2001;Schreiberetal.,2005a,b;Frankeetal.,2009).Assuch,suberinrepresentsastructurevitaltomanyphysiologicalprocessesrelatedtoplantwaterstatusandprotectionfrombioticandabioticstressors.

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Suberinisanacylglycerolpolymer,genericallytermedapolyester,depositedontheinnersurfaceofthecellwallofspeci ccelltypessuchasendodermalandperidermalcells.Suberinstructureshavebeenpartiallyinferredfromchemicalanalysesofmonomersoroligomersreleasedbyeithertotalorpartialdepolymerization,respectively(Hollo-way,1972;Frankeetal.,2005;GracßaandSantos,2006;SantosandGracßa,2006).Forexample,rootsuberinsaretypicallydominatedby18:1x-hydroxyfattyacids(x-OHFAs)and18:1dicarboxylicfattyacids(DCA).Non-poly-mericaliphaticwaxesassociatedwithsuberizedtissueshavealsobeendescribed(Espelieetal.,1980;Lietal.,2007a).Similartosuberin,plantcuticlescompriseanali-phaticacylglycerol-basedpolyestermatrix,cutin,withassociatedwaxes.Incontrasttosuberin,thecuticleisdepositedontheoutermostsurfaceoftheepidermalcell

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AtMYB41activatesdepositionofsuberin217

wallofaerialplantorgans.InArabidopsis,cutinandsub-erindifferchemicallyintermsofdegreeofunsaturation,carbonchainlength,andphenoliccontent.Arabidopsiscutinconsistsofapproximately50%18:2monomers.Con-versely,18:2monomersonlycompriseabout2%ofrootsuberin.Instead,Arabidopsisrootsuberinisdominatedby18:1monomers(>55%).Arabidopsiscutincomprisesalmostexclusively16-and18-carbonmonomerswhereassuberinconsistsofarangeof16-to24-carbonmonomers.Suberinhasamuchhigherphenoliccontentthancutin,primarilyintheformofthephenylpropanoidferulicacid.ThegeneticresourcesofArabidopsisandpotato(Sola-numtuberosum)haveprovidedforthediscoveryofanumberofsuberinbiosyntheticgenes(Beissonetal.,2012;Li-Beissonetal.,2013).Despitethisprogress,notranscrip-tionalregulatorsofsuberinsynthesishavebeende ni-tivelyidenti ed.However,severaltranscriptionfactorsrelatedtoplantcuticlebiosynthesishavebeenidenti edandcharacterized.TheseincludemembersoftheAP2/ERE-BP,theHD-ZIPIV,theWWdomain-containing,andtheR2-R3MYBtranscriptionfactororco-activatorfamilies(YeatsandRose,2013).RegulatorsofcuticlebiosynthesisrelatedtomRNAstability,RNA-mediatedgenesilencing,andpost-translationalmodi cationhavealsobeenidenti-