2006 The Arabidopsis Group 1 LEA Protein ATEM6 Is Required for Normal Seed__ Development

TheArabidopsisGroup1LATEEMBRYOGENESISABUNDANTProteinATEM6IsRequiredforNormalSeedDevelopment1[W]

AliciaJ.Manfre,LeaM.Lanni,andWilliamR.MarcotteJr.*

DepartmentofGeneticsandBiochemistry(A.J.M.,L.M.L.,W.R.M.)andDepartmentofBiologicalSciences(W.R.M.),ClemsonUniversity,Clemson,SouthCarolina29634–0324

Aspartoftheembryomaturationprocess,orthodoxseedsundergoadevelopmentallyregulateddehydrationperiod.TheLATEEMBRYOGENESISABUNDANT(LEA)genesencodealargeanddiversefamilyofproteinsexpressedduringthistime.ManyhypothesizethatLEAproteinsactbymitigatingwaterlossandmaintainingcellularstabilitywithinthedesiccatedseed,althoughthemechanismsoftheiractionsremainlargelyunknown.ThemodelplantArabidopsis(Arabidopsisthaliana)containstwogenesbelongingtothegroup1LEAfamily,ATEM1andATEM6,andknockoutmutationsinthesegenesarebeingsoughtasameanstobetterunderstandgroup1LEAproteinfunctionduringembryomaturation.Wehaveidenti edaT-DNAinsertionalleleoftheATEM6geneinwhichtheT-DNAispresentjustdownstreamoftheproteincodingregion.Whilethisgeneistranscriptionallyactiveandencodesawild-typeprotein,thereisnodetectableATEM6proteininmatureseeds.Mutantseedsdisplayprematureseeddehydrationandmaturationatthedistalendofsiliques,demonstratingthatthisproteinisrequiredfornormalseeddevelopment.Weproposethatonefunctionforgroup1LEAproteinsinseeddevelopmentistobufferthewaterlossthatoccursduringembryomaturationandthatlossofATEM6expressionresultsinthemutantphenotype.

Seedsareremarkablestructuresthatserveastheconnectionbetweensuccessivegenerationsofplants.Aspartofthenormaldevelopmentalprogramofortho-doxseeds,mostcellularwaterislostduringthelatterstagesofembryomaturationandmanyseedsdehy-dratetoaslowas5%oftheiroriginalwatercontent.Despitethelowlevelofretainedwater,seedembryosremainviableandmature,anddryseedsreadilygerminateunderappropriateenvironmentalconditions.Therefore,plantsmusthaveevolvedamechanismthatallowscellstotoleratethelowwaterpotentialfoundindryseeds.

TheLATEEMBRYOGENESISABUNDANT(LEA)genesareexpressed,asthenameimplies,lateinembryomaturationandduringthedevelopmentallyregulatedperiodofdehydrationattheendofseed

ThisworkwassupportedbytheNationalResearchInitiativeoftheU.S.DepartmentofAgriculture(USDA)CooperativeStateResearch,EducationandExtensionService(CSREES;grantno.2002–35318–12627toW.R.M.);theCSREES/USDA(projectno.SC–1700200toW.R.M.);theHowardHughesMedicalInstituteSC-LIFEUndergraduateResearchProgram;andtheClemsonUniversityCalhounHonorsCollege,TechnicalContributionNumber5061oftheClemsonUniversityExperimentStation.

*Correspondingauthor;e-mailmarcotw@clemson.edu;fax864–656–0119.

Theauthorresponsiblefordistributionofmaterialsintegraltothe ndingspresentedinthisarticleinaccordancewiththepolicydescribedintheInstructionsforAuthors(doc.xuehai.net)is:WilliamR.MarcotteJr.(marcotw@clemson.edu).[W]

TheonlineversionofthisarticlecontainsWeb-onlydata.Article,publicationdate,andcitationinformationcanbefoundatdoc.xuehai.net

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development.LEAproteinsarethoughttoplayanimportantroleinthematurationprocess,andstudiesinbarley(Hordeumvulgare)havedemonstratedthataccumulationofLEAproteinsinembryosiscorrelatedwiththeacquisitionofdesiccationtolerance(Bartelsetal.,1988).Thiscorrelationsuggeststhatthesepro-teinsareanintegralpartofoneormoretolerancemechanisms.ManyLEAgenescanalsobeinducedbytheapplicationofabscisicacidandbyvariouskindsofwaterstressinbothreproductiveandvegetativetis-sues(Bergeetal.,1989;BostockandQuatrano,1992;WilhelmandThomashow,1993;Biesetal.,1998).Inaddition,thereisatleastoneexampleofaconstitu-tivelyexpressedLEAgene(Welinetal.,1994).

LEAgenesarefoundthroughouthigherplants,in-cludingmonocots,dicots,andgymnosperms,anddif-ferencesintemporalexpressionpatternandsequencesimilarityamongtheencodedproteinshaveallowedthemtobesubdividedintogroups(Dureetal.,1989;Cuming,1999;Wise,2003).Basedlargelyonpredic-tionsofregionsofsecondarystructure,thedifferentgroupshavebeenproposedtocontributeinonewayoranothertothemaintenanceofviability.Forexam-ple,thegroup1andgroup4LEAproteinsarepre-dictedtoexistlargelyasrandomcoils(McCubbinetal.,1985;Soulagesetal.,2002).Withahighdegreeof exibility,theseproteinscouldinteractwithavarietyofcellularcomponents,includingotherproteins,andcontributetostabilityeitherbysharingtheirhydrationshellofwaterorbyusingtheirownhydroxylatedaminoacidstoserveasareplacementforwaterasitislostfromthecell(waterreplacementhypothesis).Group2andgroup3LEAproteinshavealsobeen

PlantPhysiology,January2006,Vol.140,pp.140–149,doc.xuehai.net

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