第三节 春化作用新

第三节春化作用 几个概念 植物生长的温度三基点cardinaltemperature温周期现象thermoperiodicity 春化作用vernalization 春化作用的概念春化作用的性质春化作用的机制 Lysenko 1898 1976 Inordertoobtainacertainresult youmustwanttoobtainpreciselythatresult ifyouwanttoobtainacertainresult youwillobtainit IneedonlysuchpeopleaswillobtaintheresultsIneed 小麦对低温反应的类型冬性半冬性春性 Summerannualandvernalization requiringwinter annualtypesofhenbane B andArabidopsis C Inbothexamples asingle dominantgeneisresponsibleforthevernalization requiringhabit Allplantsweregrowninlongdays inductivephotoperiods withoutvernalization Therapid floweringsummerannuals whichhaveinitiatedflowering areatleftandthewinter annualtypesatright Acabbageplantthathadbeengrowninthegreenhousefor5years Cabbageisabiennialandrequiresexposuretoprolongedwintercoldinordertoflowerthesecondspringafterplanting Thelargecabbagehasneverbeenexposedtowinterandthereforecannotflower 春化作用的性质 有效低温与春化时间去春化作用 再春化作用 Novernalization Vernalization Exposedasaseedlingto4 Cfor40days 有效低温与春化时间 脱春化作用 春化作用的机理 春化作用的感受时期和感受部位春化素 vernalin 春化作用的分子机理 矮牵牛 天仙子 春化素 vernalin SD LD GA SD 赤霉素是春化素吗 Featuresofvernalization OccursatshootmeristemRequiresseveralweeksofexposuretolowtemperatures Effectsofvernalizationmaintainedthroughmanymitoticdivisions Effectsofvernalizationresetatmeiosis 春化作用的分子机理 NaturalecotypesofArabidopsisbehaveaswinterannuals Commonly used early floweringgenotypesofArabidopsis Landsbergerecta Columbia RLD Theseflowerinacold indpendentmannerafterproducing 5 15rosetteleaves SanteFeandColumbiaAnalysis Indicates3 1segregationwithlatefloweringdominient GeneticAnalysisofCrossingbetweenColumbiaandSantaFe GeneMappingoflatefloweringgene FRIGIDA FRIencodesa609aminoacidproteinofunknownfunctioncontainingtwocoil coildomainsimplicatedinproteinproteinnteraction Arabidopsisfloweringtimemutants TwoArabidopsisplants sownatthesametime Theplantontheleftisalreadyflowering whereastheplantontherightisdelayedbecauseitcarriesactiveFRI FRIplantverylateflowering Mutagenisewithradiation Screenforearlyfloweringplants 3lossoffunctionAllelesofFRI 4lossoffunctionAllelesofFLC FLC基因 FloweringLocusC AtranslationalfusioncomposedoftheglucuronidasecodingsequencesclonedintotheNheIrestrictionsite withinFLCexon6 ofacomplementingFLCgenomicclonewasintroducedintofca 1seedlings FLC GUSexpressionisseenthroughoutthenon vernalizedseedlingbutrestrictedtothevasculature strongestincotyledonandhypocotylbutalsodetectableinolderleaves invernalizedseedlings VernalizationblockstheexpressionofFLCincold requiringwinterannualArabidopsisecotypes Winterannualwithoutcold FLCmRNA Winterannualafter40dayscold Winterannualwithoutcold butwithflcmutation FLCencodesaMADS box containingprotein EncodesMADSboxtranscriptionfactor delayingfloraltransitionRepressestranscriptionofAP1 SOC1 encodingMADSboxtranscriptionfactoracceleratingfloweringHighlyexpressedinnon vernalizedSAMAftervernaliztion geneisepigeneticallyswitchedoffforremainderofplant slifecycle permittingfloweringinresponsetolongdaystooccur Membersoftheautonomouspathwayareindicatedintheyellowbox Somemembersofthispathway includingFRIandthethreeproteinswithwhichitinteractsFRIGIDA LIKE1 FRL1 FRIGIDAESSENTIAL FES andSUPPRESSOROFFRIGIDA4 SUF4 upregulateFLCexpression Incontrast thewild typefunctionofothermembersofthispathwayistodownregulateFLC TheactivationofFLCexpressionbytheFRIcomplexandbyautonomouspathwaymutantsisdependentontheactivityofproteinsofthePaf1complex VERNALIZATIONINDEPENDENT3 VIP3 toVIP6 alsoknownasEARLYFLOWERING8 ELF8 andELF7 theSWR1complexanATP dependentchromatinremodellingcomplex SUPRESSOROFFRIGIDA3 SUF3 SWR1COMPLEXPROTEIN6 SWC6 ACTINRELATEDPROTEIN4 ARP4 PHOTOPERIODINDEPENDENTEARLYFLOWERING1 PIE1 whichdepositsthehistonevariantH2A ZintochromatinandlysinemethyltransferasesARABIDOPSISTRITHORAX1 ATX1 ATX2andEARLYFLOWERINGSHORTDAYS EFS alsoknownasSETDOMAINGROUP8 SDG8 Mono ubiquitinationofhistoneH2BisimportantforFLCactivity thisiscatalysedbyUBIQUTINCONJUGATINGENZYME1 UBC1 UBC2 HUB1 HISTONEMONOUBIQUTINATION andHUB2 OtherproteinsimportantforFLCactivityareEARLYinSHORTDAYS4 ESD4 ELF5andHUA2 TheactivityofargininemethyltransferasesPROTEINARGININEMETHYLTRANSFERASE PRMT repressesFLCexpressioninnonvernalizedplantsandmayalsoplayaroleinthevernalizationpathway reviewedinHe 2009 Themajorcomponentsofthevernalizationpathwayareshowninthebluebox VERNALIZATION5 VRN5 alsoknownasVERNALIZATIONINSENSITIVE LIKE1 VIL1 isaplanthomeodomain PHD proteinrelatedtoVIN3 VRN1 aB3domainDNA bindingprotein isalsorequiredforstablerepressionofFLC Thedaylength photoperiod pathwayisrepresentedherebyCONSTANS CO whichisupregulatedinlongdays COactivatestheexpressionofthefloralintegrators SUPPRESSOROFCONSTANS1 SOC1 andFT whichintegratethesignalsfromtheautonomouspathwayandthephotoperiodpathway ThefloweringpathwaysinArabidopsis Summary FLCisoneofthekeygenesthatplaysadominantroleinvernalization Vernalizationpathwaygene namedVIN3 VRN1andVRN2downregulatetheactivityofFLCbyepigeneticregulation AutonomouspathwaynormallyfunctionstopreventFLCmRNAaccumulation VIN3andVRN5 twocloselyrelatedPHDfingerproteins haveactivityofdeacetylase ThegenesrequiredfortherepressionofFLCbyvernalization VRN2 componentofPolycombrepressorcomplexthatmediatesH3K27methylationVRN1 aplantspecificDNAbindingprotein H3K9methylation Modificationofhistonescanaltergeneexpression H3K4methylationgeneactivation H3K9 H3K27methylationgeneinactivation Lane1 0daysV seedlingswerenotexposedtocold Lane2 0daysV T0 seedlingswereexposedtocoldfor10daysandharvestedforRNAisolationwithoutexposuretowarmtemperature Lanes3and4 sameasLane2exceptthatseedlingswereexposedtocoldfor20and40days Lane5 40daysV T10 after40daysofcoldtreatmentvernalizedseedlingsweregrownfor10daysat22 Cbeforeharvesting Although10daysaftervernalizationisshowninthelastlane wehavefoundthatVIN3mRNAbecomesundetectablewithin3daysofgrowthat22 C VIN3andFLCmRNAlevelsduringcold PcGandtrxGproteinsepigeneticallycontrolfloweringandflowerdevelopment a Histonemodifications mark nucleosomesatspecificgenes ThenucleosomeisanoctamercontainingtwomoleculeseachofhistoneH2A H2B H3 andH4 Forsimplicity onlyoneofeachofthetwoH2AandH3tailsareshowninthefigure H2AK120residesonanexposedsurfaceofthenucleosomecore b c d LikelycomponentsandfunctionsofArabidopsisPcGandtrxGproteincomplexesequivalenttoanimalPRC2 PRC1 andTRXcomplexesareshown b DuringvernalizationinArabidopsis thePHD PRC2complexcatalyzesH3K27me3methylationthroughtheSWNhistonemethyltransferasesubunit VIN3 VEL1 andVRN5areplant specific whereastheotherfourmembersarehomologsoftheanimalPRC2corecomponents BecausethreeofthefourcorecomponentsofanimalPRC2havebeenduplicatedinArabidopsis itislikelythatseveralrelatedcomplexesexistthatdifferincomponentsandtargetgenespecificities 2 Forexample insomecomplexes CLFmayreplaceSWNasthehistonemethyltransferaseunit c LHP1 acomponentofArabidopsisPRC1 bindsH3K27me3 PRC1maycatalyzeH2AK120UbubiquitinationviaitsE3ligasecomponentsAtRING1a AtRING1b AtBMI1A andAtBMI1B EMF1islikelyanother plant specific componentwhoseprecisefunctionisunclear d ULT1andATX1maybecomponentsofanArabidopsistrxGcomplexthatcatalysesH3K4me3 ATX1 ARABIDOPSISHOMOLOGOFTRITHORAX1 CLF CURLYLEAF EMF1 EMBRYONICFLOWER1 FIE FERTILIZATIONINDEPENDENTENDOSPERM LHP1 LIKEHETEROCHROMATINPROTEIN1 MSI1 MULTICOPYSUPPRESSOROFIRA1 PcG Polycombgroup PHD PRC2 PLANTHOMEODOMAIN POLYCOMBREPRESSIVECOMPLEX2 PRC1 POLYCOMBREPRESSIVECOMPLEX1 SWN SWINGER trxG trithoraxgroup ULT1 ULTRAPETALA1 VEL1 VERNALIZATION5 VIN3 LIKE1 VIN3 VERNALIZATIONINSENSITIVE3 VRN2 VERNALIZATION2 VRN5 VERNALIZATION5 FLCexpressionismodulatedbychromatinstructure a Innonvernalizedplants FLCchromatinbearsthemarksofanactivegene highlevelsofacetylationoflysineresiduesintheN terminaltailsofhistonesH3andH4andhighlevelsofH3K4me3aroundthestartoftranscriptionandH3K36me3inthetranscribedregionofthegene theblueovalsrepresentthenucleosomeswiththeN terminaltailsindicatedasredlines b VIN3isinducedbylowtemperaturesandisrequiredforthechangesinhistonemodificationsthatareassociatedwithrepressionofFLC inplantsgrownatlowtemperatures VIN3isincorporatedintoapolycombrepressioncomplex2 PRC2 duringvernalization ThiscomplexdepositstherepressivemarkH3K27me3onchromatinaroundthestartoftranscriptionduringgrowthatlowtemperatures Neitherthehistonedeacetylase s HDAC northehistonedemethylasesthatremovetheactivemarkshavebeenidentified c Invernalizedplantsthathavebeenreturnedtowarmertemperatures therepressivemarkH3K27me3spreadsbidirectionallyacrosstheFLClocus ThePRC2 lackingVIN3 isassociatedwiththechromatincoveringtheFLClocus indicatedbythecolouredballs BindingofLHP1isessentialformaintenanceofFLCrepression Threephasesofvernalizationareenvisaged aninsensitivephase aphasewheresilencingoccurs andhistonemodificationsaccumulate andaphasewhereFLCisfullysilenced ThedashedandsolidlinesrepresenttheaccumulationofepigeneticmarksinEdi 0andLov 1 respectively Duetoahighinitiallevelandhigheraccumulationrate fullsilencingwouldbereachedafter4wkofcoldinEdi 0and10 12wkofcoldinLov 1 Genes Dev 2006 20 3079 3083 a Priortocoldexposure FLCisactivelyexpressed ThecomplexesthatmaintainthisactivechromatinconformationincludethePAFcomplex whichmethylateshistone3tailsatlysine4and36 H3K4triMeandH3K36triMe aSWR1 likecomplex whichdepositsahistone2AvariantinthenucleosomesofFLCchromatin andH2BubiquitinaseslikeHUB1andHUB2thatubiquitinatehistone2Btails H2Bub1 AlthoughFLCisinanactivestate therearerepressivecomplexespresentsuchasPolycombRepressionComplex2andsomedegreeoflysine27methylationofhistone3 H3K27triMe arepressivemodification b Duringcoldexposure FLCrepressionisinitiated VIN3isinduced VIN3andVIL1 VRN5associatewiththePolycombcomplex thedensityofrepressivechromatinmodificationssuchaslysine27methylationofhistone3increases andrepressorssuchasLIKEHETEROCHROMATINPROTEIN1 LHP1 assembleonFLCchromatin c Asvernalizationproceeds thedensityofrepressivemodifications particularlyH3K27triMeandlysine9methylationofhistone3 H3K9triMe mediatedbyanunknownH3K9methyltransferase HMTase increases d Eventually amitoticallystablestateofrepressionthatnolongerrequiresVIN3isachieved Thismitoticallystablestateislikelytoinvolvepositivefeedbackloopsinwhichtherepressivechromatinmodificationsservetorecruitthechromatin modifyingcomplexesincludingVRN1tomaintainarepressivestate AstheFLClocuspassestothenextgeneration theactivechromatinstaterepresentedin a isre established Vernalization mediatedchangesinFLCchromatin Mutantsoftheautonomouspathway fca fy fpa ld fld andfve arelate floweringinlongdaysandshortdays aphenotypethatcanbeovercomebyvernalization theseinducedmutations therefore conferavernalizationrequirement orgrowthinfar redenrichedlight ThelevelofFLCmRNAisincreasedinthesemutants indicatingthattheautonomouspathwaynormallyfunctionstopreventFLCmRNAaccumulation Autonomouspromotionpathway FCAGene MutantscarryingrecessiveallelesofFCAarelatefloweringand again thisisreversedtoearlyfloweringbyvernalization FCA FY FLK FPA LD FLDandFVE NoneofthesefactorsregulateoneanotheratthemRNAlevel butinsteadappeartoregulateFLCthroughdifferentmechanisms FCAisanRNA bindingproteinthatinteractswiththe3 endRNA processingfactorFYtocontrolFLC FPAandFLKarealsoRNA bindingproteins butFPAatleastregulatesFLCindependentlyofFCA ThisindicatesthattheseproteinsregulateFLCthroughRNAprocessing buthowdirectthisregulationmightbeisunknown FLDandFVEarecloselyrelatedtohumanproteinsfoundinhistonedeacetylaseco repressorcomplexesand consistentwiththis theydeacetylatehistonesattheFLClocus TheymaythereforeactwithinthesamecomplextoregulateFLC NootheridentifiedautonomouspathwaycomponentsaffecttheacetylationofhistonesattheFLClocus LDencodesahomeodomainprotein buthowitregulatesFLCisunknown ThelevelofFLCmRNAisdownregulatedbytheautonomouspathwaycomponents FCAencodesanRNAbindingproteinwithaWWproteininteractiondomain Macknightetal 1997 ItinteractswithFY aconservedRNAprocessingfactor AmodelfortheregulationofexpressionofFLCandcold regulatedgenesHAT histoneacetyltransferase HDAC histonedeacetylase a FLCistranscriptionallyactiveinseedsandseedlings preventingtheplantfromfloweringandprolongingvegetativedevelopment b Exposuretoalongperiodofcold thatis vernalization resultsintheexpressionofVIN3 red whichinitiatesrepressionofFLCtranscription andthebindingofthePcGproteinVRN2 aswellasVRN1andLHP1 blue Inthisprocess chromatinatFLCisepigeneticallymodifiedbythetrimethylationofH3K27 c Afterwarmertemperaturesreturn FLCrepressionismaintained allowingfloweringtobeinducedbyothercues d Duringflowerdevelopment theanthersandovariesaresitesofmeioticdifferentiation givingrisetohaploidcellsknownasmicrosporesandmegaspores respectively e Thesemeioticproductsundergomitoticproliferationtoformthemulticellularembryosacandpollengametophytes f PcG protein mediatedrepressionatFLCisremovedduringanundefinedresettingprocess g Then thepollencontributesspermnucleitotheembryosac andthesefertilizethehaploideggcellanddiploidcentralcell notshown formingtheembryoandendosperm respectively inanewseed inwhichFLCisre expressed TheactivationstateofthePcGproteintargetFLCisillustratedthroughouttheplantlifecycle EpigeneticinheritanceinplantsIanR Henderson StevenE JacobsenNature447 418 424 24May2007 FLC GUSisresetinthesomaticandsporogenoustissuesinthemalereproductiveorgan theanther andthepaternallyderivedgeneisexpressedinthesingle celledzygotesfromvernalizedplants Incontrast thematernallyderivedFLC GUSgeneisnotresetduringgametogenesisandisfirstexpressedduringembryogenesis a AsectionthroughanantherfromavernalizedFLC GUSplantimagedunderdarkfield GUScrystalsarepink Thepollenmothercells arrow areenteringmeiosis Scalebarsinallfiguresare50m b Anovulefromawild typefemaleplantonedayafterpollinationwithpollenfromavernalizedFLC GUSplant imagedunderbrightfield GUSproductisblue Thearrowpointstothesingle celledzygote c Anovulefromawild typefemaleplantthreedaysafterpollinationwithpollenfromavernalizedFLC GUSplantimagedunderbrightfield GUSproductisblue Thearrowpointstotheearlyglobular stageembryo d Asectionthroughanovuleprimordiaaroundthetimeofmeiosis arrow fromavernalizedFLC GUSplantimagedunderdarkfield NoGUSstainingisevident e AnovulefromavernalizedFLC GUSfemaleplantonedayafterpollinationwithpollenfromawild typeplant imagedunderbrightfield Nostainingisevident f AnovulefromavernalizedFLC GUSfemaleplantthreedaysafterpollinationwithpollenfromawild typeplant imagedunderbrightfield GUSproductisblue Thearrowpointstotheearlyglobular stageembryo ThreeindependentmolecularvernalizationresponseshavebeenidentifiedinArabidopsis definingtheFLC AGL24 andAGL19 branches SimilartoFLC itshomologueMAF2mightacttorepressSOC1andFT butthisisnotfirmlyestablished DownstreamfactorsofAGL19andAGL24remainunidentified Itispossiblethat atleastinpart AGL24actsthroughSOC1 becausepositiveregulationbetweenAGL24andSOC1occurs Dashedlinesrepresenthypotheticalgeneticlinks ThreeindependentmolecularvernalizationresponseshavebeenidentifiedinArabidopsis J Exp Bot 2008 59 6 1127 1135 Vernalization regulatedgenesrespondtodifferentlengthsofexposuretocold ThefloweringactivatorsAGL24andAGL19requirelongcoldexposurestobeactivated andaremostlyfunctionalfromthelatestagesofvernalizationon ThefloweringrepressorsFLCandMAF2functionbeforeandduringearlystagesofvernalization MAF2hasbeenproposedtopreventinductionoffloweringbyshortperiodsofcold whichcouldrepressFLC Ratcliffeetal 2003 Theupp