Evolutionary divergence of β–expansin structure and function in grasses parallels emergence of distinctive primary cell wall traits

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1、ThePlantJournal(2015)81,108–120doi:10.1111/tpj.12715Evolutionarydivergenceofb–expansinstructureandfunctioningrassesparallelsemergenceofdistinctiveprimarycellwalltraits,†‡§JavierSampedro*,MaraGuttman,Lian-ChaoLiandDanielJ.Cosgrove*1DepartmentofBiology,PennsylvaniaStateUniv

2、ersity,UniversityPark,PA16802USAReceived4September2014;revised19October2014;accepted21October2014;publishedonline29October2014.*Forcorrespondence(e-mailsjavier.sampedro@usc.es;dcosgrove@psu.edu).†Presentaddress:DepartamentodeFisiologıaVegetal,UniversidaddeSantiago,Santia

3、godeCompostela15782,Spain.‡Presentaddress:USDA-ARS800BuchananSt,Albany,CA94710,USA.§Presentaddress:PharmaceuticalDevelopment&ManufacturingSciencesJanssenR&D,LLC,Malvern,PA19355,USA.SUMMARYExpansinsarewall-looseningproteinsthatpromotetheextensionofprimarycellwallswithoutth

4、ehydroly-sisofmajorstructuralcomponents.Previously,proteinsfromtheEXPA(a–expansin)familywerefoundtolooseneudicotcellwallsbuttobelesseffectiveongrasscellwalls,whereasthereversepatternwasfoundforEXPB(b–expansin)proteinsobtainedfromgrasspollen.Tounderstandtheevolutionaryands

5、tructuralbasesfortheselectivityofEXPBaction,weassessedtheextension(creep)responseofcellwallsfromdiversemonocotfamiliestoEXPAandEXPBtreatments.CellwallsfromCyperaceaeandJuncaceae(fami-liescloselyrelatedtograsses)displayedatypicalgrassresponse(‘b–response’).Wallsfrommoredis

6、tantmonocots,includingsomespeciesthatsharewithgrasseshighlevelsofarabinoxylan,respondedpreferen-tiallytoa–expansins(‘a–response’),behavinginthisregardlikeeudicots.AnexpansinwithselectiveactivityforgrasscellwallswasdetectedinCyperaceaepollen,coincidingwiththeexpressionofge

7、nesfromthedivergentEXPB–Ibranchthatincludesgrasspollenb–expansins.TheevolutionaryoriginofthisbranchwaslocatedwithinPoalesonthebasisofphylogeneticanalysesanditsassociationwiththe‘sigma’whole-gen-omeduplication.Acceleratedevolutioninthisbranchhasremodeledtheproteinsurfacein

8、contactwiththesubstrate,potentiallyforbindinghighlysubstitutedarabinoxylan.Weproposethattheevolu