2022/12/22TheGeneticsofMitochondriaandChliroplasts1Chapter9

TheGeneticsofMitochondriaandChloroplasts2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts2ChapterOutlineTheClassicalGeneticsofOrganellesTheMolecularGeneticsofMitochondriaMitochondrialDNAandHumanDiseaseTheMolecularGeneticsofChloroplastsTheOriginandEvolutionofMitochondriaandChloroplasts2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts3Mitochondria,Chloroplasts,andtheBiologicalEnergyWheel2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts4ThebiologicalenergywheelCarlCorrensOneofthethreebotanistswhorediscoveredMendel’sPrinciples.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts5Section1

TheClassicalGeneticsofOrganellesThegeneticmaterialoforganelleshasbeenstudiedbytracingtheinheritanceofleafpigmentationinplants,antibioticresistanceinalgae,andmetaboliccompetenceinyeast.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts6Mostoftheearlystudieswereperformedwithplants,whichpossessbothmitochondrialandchloroplasts.Consequently,itwasnotalwayspossibletodeterminewhichofthetwotypesoforganelleswasresponsiblefornuclearheredity.Laterstudiesusedyeast,forwhichtheinvolvementofchloroplastscouldbeexcluded.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts7ThecommonpreceptsharedbyallofthemisthatorganellehereditydoesnotfollowsimpleMendelianrules.Instead,itischaracterizedbyunequalcontributionsofthetwoparentsandbyanirregularsegregationofalleles;thatis,itviolatesMendel’sPrincipleofSegregation.Organelleheredityisthereforenon-Mendelianheredity.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts81.LeafVariegationinPlantsTheleavesinplantssometimesexhibitastrikingpatternofcolorvariegation.Somesectorsaregreen,otherspurewhite.Intermediateshadesofpaleoryellowgreenmayalsoexist.漂亮是大家想研究葉片花斑的一個(gè)原因LeafVariegationcausedbythesegregationofdifferenttypesofchloroplasts.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts9Chloroplastsortingduringmitosis.Theirregulardistributionofchloroplastsduringcelldivisionmayproduceacellthatlackchloroplastscapableofmakingchlorophyll.Throughfurtherdivisions,suchacellwillproduceawhitesectoroftissueinanotherwisegreenleaf.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts10Correns’experimentsontheinheritanceofleafvariegationinMirabilis(紫茉莉).GreenfemaleXwhitemale(onavariegatingplant).GreenmaleXwhitefemale(onavariegatingplant).2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts11Inmirabilis(紫茉莉),thechloroplastsaretransmittedtotheoffspringthroughthefemalereproductivecellsbutarelargely,ifnotentirely,excludedfromthemalereproductivecells.Whenaplantinheritsamixtureofpigmentedandunpigmentedchloroplastsfromthefemaleparent,itstissuesmayvariegatebecausethetwotypesofchloroplastssortthemselvesoutduringdevelopment.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts12(天竺葵)2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts13Thisnon-Mendelian,bipararentalinheritanceindicatesthatthecolorofPelargonium(天竺葵)leavesisdeterminedbyamixtureofmaternalandpaternalfactorslocatedoutsidethenucleus,presumablyinthechloroplasts.Itthereforeseemsthatinthechloroplastsaretransmittedthroughthepollenaswellasthroughtheovule.Pelargonium2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts14TheexperimentsofCorrensandBaurdemonstratedthatleafvariegationisinheritedasanon-Mendeliantrait,oneisthatisalmostcertainlycontrolledbyfactorslocatedinthechloroplasts.ThediscoverythatchloroplastscontainDNAhasmadethishypothesisveryattractive.Yet,inspiteoftheworkofmanyscientists,themolecularbasisofleafvariegationisstillunknown.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts152.AntibioticResistanceinChlamydomonas(衣藻)Photosyntheticgreenalgaeareanimportantpartofthebiosphere.Theyareabundantintheoceans,wheretheyformthefoundationofthefoodchain,buttheyarealsofoundontheland.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts16Oneterrestrialspecies,Chlamydomonasreinharditti,hasbeenusedextensivelyingeneticresearch.Thisunicellular,haploidorganismexistsintwodifferentmatingtypes,denotedplusandminus.Cellsofoppositematingtypecanfuseforproduceadiploidzygote.Thezygotethenundergoesmeiosistoproducefourhaploidoffspring,whichdividemitoticallytoproduceclonesofvegetativecells.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts17Analysisoftheseclonesindicatesthatmatingtypeiscontrolledbyanucleargenewithtwoalleles,mt+(specifyingtheplusmatingtype)andmt-(specifyingtheminusmatingtype).TwoofthefouroffspringfromaChlamydomonaszygotearethethereforetwomt+andtwomt-.ManyothernucleargeneswithaMendelianpatternofsegregationhavebeenidentifiedinChlamydomonas.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts18EachhaploidChlamydomonascellcontainsasinglelargechloroplastandseveralmitochondrial.Whenmt+andmt-cellsfuse,theirorganellesarecombinedinthesamediploidcell.Itisnotaltogetherclearwhathappenstotheseorganellesinsidethezygote,butwhenthefourhaploidoffspringareproduced,eachhasonechloroplastandseveralmitochondria.Thebasicnumberoforganellesisthereforepreserved.2022/12/18TheGeneticsofMitoIn1954RuthSager,anAmericangeneticist,discoveredthatantibioticresistanceinChlamydomonasisinheritedasanonMendeliantrait.In1954RuthSager,anAmerica2022/12/22TheGeneticsofMitochondriaandChliroplasts20Thisinvolvedirradiatingthemt+cellswithUVlightjustpriortomating.WhenSagermatedirradiatedmt+cellstounirradiatedmt-

cells,shefoundthatsomeoftheoffspringinheritedthecytoplasmictraitofthemt-parentinsteadofthatofthemt+parent.ThesephenomenawerefinallyexplainedwhenDNAwasdiscoveredintheChlamydomonaschloroplast.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts21Bothmt+andmt-cellspossessthisDNA,butwhenmatingoccurs,theDNAcontributedbythemt-

cellisdegraded,probablybyanucleasethatspecificallyrecognizesit.TheoffspringfromacrossthereforeretainonlytheDNAinheritedfromthemt+chloroplast.Asaresult,thetraitencodedbythisDNA—andstreptomycinresistanceisoneofthem—arealwaysinheritedthroughthemt+parent.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts22When

mt+cellsareirradiatedpriortomating,thesystemthatdestroysthemt-chloroplastDNAispartiallyincapacitated.Consequently,someofthemt+chloroplastDNAsurvivesandistransmittedtotheoffspring.ThisDNAmayactuallyrecombinewiththemt+chloroplastDNA,generatingoffspringthatinheritedchloroplastgenesfrombothparents.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts23這是第一張非核DNA的基因結(jié)構(gòu)圖AgeneticmapofchloroplastDNAinChlamydomonas,basedontheworkofSagerandRamains.Symbols:ac1,ac2,acetaterequirement;sm4,streptomycindependence;nea,neamineresistance;sm3,low-levelstreptomycinresistance;sm2,high-levelstreptomycinresistance;ery,erythromycinresistance;spc,spectinomycinresistance;tm,temperaturesensitivity.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts243.MetabolicDefectsinYeastSomemutantstrainsofyeastformtinycolonieswhengrownonarich,glucose-containingmedium.Thesestrainsarecalledpetitemutants.Wild-typeyeaststrainsformlarge,orgrandecoloniesonglucosemedium.Additionaltestswithdifferentfoodsourcessuggestthatpetitemutantssufferfromadefectinglucosemetabolism.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts25Inmanycasesthisdefectistraceabletothemitochondriaofthepetitecells,whichareill-formedandlackmanyofthemacromoleculesfoundinwild-typemitochondria.Thesemitochondrialdefectspreventpetitecellsfromcarryingoutaerobicmetabolism.BorisEphrussi2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts26Theneutralpetite(中性小菌落)mutantsarecharacterizedbyaninabilitytotransmitthepetitephenotypetotheoffspringofcrosseswithwild-typestrains.Whensuchcrossesareperformed,allfourhaploidoffspringfromapairofmatedcellsgrowintograndecolonies——suggestingthatpetitemutationhasbeenlost.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts27Bycontrast,suppressivepetite(抑制性小菌落)mutantsare,underappropriateconditions,abletotransmitthepetitephenotypetoalltheirprogeny—suggestingthatthewild-typeconditionhasbeenlost.Withbothtypesofmutants,reciprocalcrossesbetweenthemutantsandwild-typestrainsgiveidenticalresults;thus,theyeastmatingtypesarenotinvolvedintheinheritanceofthepetitetrait.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts28Non-mendeliansegregationof(a)neutraland(b)suppressivepetitemutationinyeast.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts29InheritanceofmtDNAincrossesbetweenpetiteandwild-typestrainsofyeast.孢子形成2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts30WhatisthenatureofthemtDNAinsuppressivepetitemutants?PhysicalandchemicalanalysishasshownthatitisasmallerDNAmoleculethanwild-typemtDNAandthatisalsoveryA:T-rich.ThesetwofeaturesmayendowthesuppressivepetitemtDNAwithaexplicativeadvantageoverwild-type.However,afullunderstandingofwhythesuppressivepetiteDNAiseffectivelytransmittedthroughcrosseswillrequiremoreresearch.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts31KeyPointsOrganelleheredityischaracterizedbyunequalparentalcontributionsandbyirregularphenotypicsegregations.Thenon-Mendelianfeaturesoforganelleheredityaredue,inpart,thepreferentialtransmissionofchloroplastsandmitochondriathroughthegametesofonesex,whichinhighereukaryotesisusuallythefemale.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts32Section2

TheMolecularGeneticsofMitochondriaMitochondriacontainDNAmoleculeswithanassortmentofgenes.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts33MitochondrialgeneticsystemsconsistofDNAandthemolecularmachineryneededtoreplicateandexpressthegenescontainedinthisDNA.Thismachineryincludesthemacromoleculesneededfortranscriptionandtranslation.Mitochondriaevenpossestheirownribosomes.Manyofthesemacromoleculesareencodedbymitochondrialgenes,butsomeareencodedbynucleargenesandarethereforeimportedfromcytosol.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts341.MitochondrialDNAMitochondrialDNA(mtDNA)moleculesvaryenormouslyinsize,fromabout6kbinmalaria-causingparasitePlasmodiumto2500kbinsomeofthefloweringplants.EachmitochondrionappearstocontainseveralcopiesoftheDNA,andbecauseeachcellusuallyhasmanymitochondria,thenumberofmtDNAmoleculespercellcanbeverylarge.Inavertebrateoocyte:over108copiesInasomaticcells:about1000copies.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts35MostmtDMAmoleculesarecircular,butinsomespecies,suchasthealgaChlamydomonasreinharditiiandtheciliateParameciumaurelia(雙小核草履蟲(chóng)),theyarelinear.ThecircularmtDNAmoleculaesappeartobeorganizedinmanydifferentways.MtDNA(yellow)intheunicellularorganismEuglenagracilis.ThenuclearDNA(red)isalsovisible.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts36Inthevertebrates37distinctgenesarepackedintoa16-to17-kbcircleleavinglittleornospacebetweengenes.InsomeoftheflowingplantsanunknownnumberofgenesaredispersedoveralargecircularDNAmoleculehundredsorthousandsofkilobasesinsize.Intheseplantsthemitochondrialgenesmaybecomeseparatedontodifferentcircularmoleculesbyaprocessofintramolecularrecombination.動(dòng)物mtDNA小，植物mtDNA大2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts37IntramolecularrecombinationinthemtDNAoftheChinesecabbage,Brassicacampestris.RecombinationbetweentherepeatedelementsinthelargecircularDNAmoleculepartitionsthismoleculeintotwosmallerones.Alternatively,therepeatedelementsinthetwosmallmoleculesmayrecombinewitheachothertoproduceasinglelargemolecule.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts38ThisrecombinationismediatedbyrepetitivesequenceslocatedinthemtDNA.Anexchangebetweentwooftherepetitivesequencescanpartitionthe“master”mtDNAcircleintotwosmallercircles,aprocessthatsuperficiallyresemblestheexcisionofalambdaprophagefromE.colichromosome.Insomespecies,severalDNAcirclesofdifferentsizesareformedbyrecombinationbetweenpairsofrepetitivesequenceslocatedatdifferentpositionsaroundthemasterDNAcircle.機(jī)制很難研究2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts39AnimalmtDNAissmallandcompact.Inhumanbeings,themtDNAis16659bplongandcontains37genes,incl.2:rRNAs,22:tRNA,and13:oxidativephosphorylation,theprocessthatmitochondriausetorecruitenergy.Inmice,cattle,andfrogs,themtDNAissimilartothathumanbeings—anindicationofabasicconservationofstructurewithinthevertebratesubphylum(脊椎動(dòng)物亞門).2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts40MapofhumanmtDNAshowingthepatternoftranscription.GenesontheinnercirclearetranscribedfromtheLstrandoftheDNA,whereasgenesontheoutercirclearetranscribedfromtheHstrand.Thearrowsshowthedirectionoftranscription.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts41InvertebratemtDNAisaboutthesamesizeasvertebratemtDNA,butithasasomewhatdifferentgeneticorganization.ThesedifferencesseemtohavebeencausedbystructuralrearrangementsofthegeneswithinthecircularmtDNAmolecules.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts42Infungi,themtDNAisconsiderablylargerthanitisinanimals.YeastpossessescircularmtDNAmolecules78kblong.Thesemoleculescontainatleast33genes,incl.2:rRNAs,23to25:tRNA,1:oxidativephosphorylation.TheyeastmtDNAislargerthananimalmtDNAbecauseseveralofitsgenescontainintronsandtherearelongnoncodingsequencesbetweensomeofthegenes.AnimalmtDNAdoesnotcontainintrons.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts43PlantmtDNAismuchlargerthanthemtDNAofotherorganisms.Itisalsomorevariableinstructure.OneofthefirstplantmtDNAtobesequencedisfromliverwort,Marchantiapolymorpha(地錢).ThemtDNAfromthisprimitive,non-vascularplant(非維管植物)isa186-kbcircularmoleculewith94substantialopenreadingframe(ORFs,開(kāi)放閱讀框),somecorrespondingtoknowngenesandothershavingstillunassignedgeneticfunctions.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts44ThelatterORFsarethereforecalledURFs,forunassignedreadingframes.Invascularplants,themtDNAislargerthanitisinMarchantiamtDNA.Maize:570-kb,watermelon:300-kb.HigherplantmtDNAmoleculescontainmanynoncodingsequences,includingsomethatareduplicated.TheactualnumberofgenespermtDNAmoleculeisunknown.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts45PhysicalmappingofsomeofthesegeneshasshownthattheyarelocatedindifferentpositionsonthemtDNAcirclesofdifferentspecies,evenwhenthespeciesarefairlycloselyrelated.ThisimpliesthatthemtDNAofhigherplantshasundergonemanygeneticrearrangementsduringitsevolution.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts462.ExpressionofMitochondrialGenesCodonMeansinmammalianMeansinmtDNAAGAArginineTerminationcodonAGGArginineTerminationcodonUGATerminationcodonTryptophanAUAIsoleucineInitiationcodon線粒體密碼子的例外有三種特殊的表達(dá)方式2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts47RNAediting:someofthenucleotidesarechangedafterthetranscripthasbeensynthesized.CtoU;occasionallyUtoC.RNAeditingaltersthecompositionofcodonsinplantmitochondrialtranscripts,includingsomethatwouldotherwisesignaltheendofpolypeptidesynthesis.EditingalterstheinformationthatisactuallyencodedinthatmtDNAandallowsfunctionalpolypeptidestobesynthesized.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts48Curiously,mtRNAeditingisnotfoundinthenonvascularplants(mosses苔蘚andalgae藻),eventhoughallgroupsofhigherplants(ferns蕨類,gymnosperms裸子植物,andangiosperms被子植物)seemstohaveit.Thus,theeditingmechanismprobablyevolvedsometimeafterplatshadbecomeestablishedontheland.RNAeditingalsooccursinthemitochondriaofprotozoan.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts49Inprotozoan,smallRNAmoleculesthatarepartiallycomplementarytothemtRNAtranscriptsserveasguidesfortheeditingprocess.TheyarethereforecalledguideRNAs(gRNAs,引導(dǎo)RNA)Asimilarguidingmechanismmayoperateinplants,butthedetailsarecurrentlyunknown.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts502022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts51YetathirdpeculiarityofplantmitochondrialgeneexpressionisthatsomemitochondrialmRNAsareformedbytheprocessoftrans-splicing(反式剪切).Trans-splicingoccurswhensegmentsofagenearescatteredoverthemtDNAmolecule.Eachgenesegmentistranscribedindependently,andtheexonsofthedifferenttranscriptsaresplicedtogetherbyinteractionsbetweentheintronsthatflankthem.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts52Trans-splicinginwheatmitochondria.FourdifferentRNAscontributetothefinalmRNAencodingapolypeptideoftheenzymeNADHreductase.Thisprocessrequiresasinglecis-splicingreactionandthreetrans-splicingreactions.來(lái)自同一條mRNA的剪接稱為cis-splicing不同mRNA之間的剪接稱為trans-splicing2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts533.InterplaybetweenMitochondrialandNuclearGeneProductsMost—perhapsall—mitochondrialgeneproductsfunctionsolelywithinthemitochondrion.However,theydonotfunctionalone.Manynucleargeneproductsareimportedtoaugmentorfacilitatetheirfunction.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts54MitochondrialribosomesareconstructedwithrRNAtranscribedfrommitochondrialgenesandwithribosomalproteinsencodedbynucleargenes.Theribosomalproteinsaresynthesizedinthecytosolandimportedintothemitochondriaforassemblyintoribosomes.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts55Manyofthepolypeptidesneededforaerobicmetabolismarealsosynthesizedinthecytosol.Thesesincludesubunitsofseveralproteinsinvolvedinoxidativephosphorylation;forexample,theATPasethatisresponsibleforbindingtheenergyofaerobicmetabolismintoATP.However,becausesomeofthesubunitsofthisproteinaresynthesizedinthemitochondria,thecompleteproteinisactuallyamixtureofnuclearandmitochondrialgeneproducts.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts56Thisdualcompositionsuggeststhatnuclearandmitochondrialgeneticsystemsarecoordinatedinsomewaysothatequivalentamountsoftheirproductsaremade;possiblemolecularmechanismsforthiscoordinationarecurrentlyunderinvestigation.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts57KeyPointsmtDNAmoleculesrangefrom6kbto2500kbinsize,andmostofthemappeartobecircular.mtDNAmoleculescontaingenesforsomeoftherRNAs,tRNAs,andpolypeptidesusedwithinthemitochondrion.Thestructure,organization,andexpressionofmitochondrialgenesvaryamongspecies.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts58KeyPointsInsomeorganisms,thetranscriptsofmitochondrialgenesareeditedaftertheyaresynthesized.Bothmitochondrialandnucleargeneproductsareneededfornormalmitochondrialfunction.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts59Section3.

MitochondrialDNAandHumanDiseaseMutationsinmitochondrialDNAcancausehumandiseases2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts60Leber’shereditaryopticneuropathy(LHON).成人期的突然失明嚴(yán)格的母系遺傳Pearsonmarrow-pancreassyndrome.兒童期骨髓細(xì)胞丟失及死亡，但父母不患病原因可能是卵子形成過(guò)程中mtDNA的刪除2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts61Pedigreesofmitochondrialdiseases(A)Atypicalpedigreepattern,showingmitochondrially-determinedhearingloss.(B)TheatypicalpatternofLeber'shereditaryopticatrophy,whichaffectsmainlymales.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts62KeyPointLeber’shereditaryopticneuropathyandPearsonmarrow-pancreassyndromeareduetomutationsinmtDNA.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts63Section4

ThemolecularGeneticsofChloroplastsChloroplastscontainDNAmoleculeswithanassortmentofgenes.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts64Chloroplastsarespecializedformsofageneralclassofplantorganellescalledplastids(質(zhì)體).Botanistsdistinguishamongseveralkindsofplastids,includingchromoplasts(plastidscontainingpigment),amyloplastids(plastidscontainingstarch),andelaioplasts(plastidscontainingoilorlipid).Allthethreetypesseemtodevelopfromsmallmembrane-boundedorganellescalledproplastids,and,withinaparticularplantspecies,allseemtocontainthesameDNA.ThisDNAisgenerallyreferredtoaschloroplastDNA(cpDNA).2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts651.ChloroplastDNAInhigherplants,cpDNAstypicallyrangefrom120to160kbinsize,andinalgae,from85to292kb.InafewspeciesofgreenalgaeinthegenusAcetabularia(傘藻屬),thecpDNAismuchlarger,about2000kb.AmongthespeciesofplantswhosechloroplastDNAhasbeenatleastpartiallycharacterized,thecpDNAseemstobeorganizedasaclosedcircularmolecule.However,insomespecies,especiallythosewithlargecpDNAs,alineararrangementcannotberuledout.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts66ThenumberofcpDNAmolecularinacelldependsontwofactors:thenumberofchloroplastsandthenumberofcpDNAmoleculeswithineachchloroplast.Chlamydomonasreinharditii:onechloroplast,anditcontainabout100copiesofthecpDNA.Euglenagracilis:15chloroplastspercell,andeachcontainsabout40copiesofcpDNA.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts67AllcpDNAmoleculescarrybasicallythesamesetofgenes,butindifferentspeciesthesegenesarearrangedindifferentways.MostcpDNAshaveapairoflargeinvertedrepeatsthatcontainthegenesfortherRNAs.Theserepeatsrangeanywherefrom10to76kbinlengthandarevariouslylocatedindifferentcpDNAmolecules.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts682.ChloroplastBiogenesisAllplastidsdevelopfromproplastids.Inthecaseofchloroplasts,thisdevelopmentisstimulatedbylightandinvolvesthetranscriptionofmanygenes,includingsomelocatedinthenucleus.Illuminationtriggersaprofoundchangeineachproplastid.Theorganellemembranesexpandstobudoffvesiclesthateventuallyarrangethemselvesinstacksformingstructurecalledgrana(基粒).2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts69Alltheproteinsandchlorophyllpigmentsneededforphotosynthesisaremadeandtargetedtotheirappropriatelocationswithintheemergingchloroplast.Someofthesemoleculesthatmakeupthegrana,andothersarelocatedinthestroma(基質(zhì)),whichistheprotoplasmicspacesurroundingthegrana.2022/12/18TheGeneticsofMito2022/12/22TheGeneticsofMitochondriaandChliroplasts70Theformationoffunctionalchloroplastsisaprocessreferredtoasbiogenesis(生源論).Onlysomeofthedetailsareknown.However,itisclearthatlightplaysanimportantrole.Theformationofchloroplastsandthemaintenanceoftheirstructureandfunctionduringthelifeofaplantdependonthecoordinatedexpressi