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低Pr数流体非稳态自然对流流动的标度分析_刘滔.pdf 6页
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低Pr数流体非稳态自然对流流动的标度分析_刘滔
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上海闵行区部分流动人口产前检查现状的调查分析
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可吸入颗粒物在管内湍流流动时的动力学特性及热泳沉积
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PSM 转基因从作物到作物亲属的流动
ReviewReceived:12May2014Revised:22June2014Acceptedarticlepublished:30June2014PublishedonlineinWileyOnlineLibrary:15August2014()DOI10.1002/ps.3850Dealingwithtransgene?owofcropprotectiontraitsfromcropstotheirrelativesJonathanGressel*AbstractGenesregularlymovewithinspecies,to/fromcrops,aswellastotheircon-speci?cprogenitors,feralandweedyforms(‘vertical’gene?ow).Genesoccasionallymoveto/fromcropsandtheirdistantlyrelated,hardlysexuallyinterbreedingrelatives,withinagenusoramongcloselyrelatedgenera(diagonalgene?ow).Regulatorshavesingledouttransgene?owasanissue,yetnon-transgenicherbicideresistancetraitsposeequalproblems,whichcannotbemitigated.Therisksarequitedi?erentfromgenes?owingtonatural(wild)ecosystemsversusruderalandagroecosystems.Transgenicherbicideresistanceposesamajorriskifintrogressdiseaseandinsectresistancelessso.Technologieshavebeenproposedtocontaingeneswithincrops(chloroplasttransformation,malesterility)thatimperfectlypreventgene?owbypollentothewild.Containmentdoesnotpreventrelatedweedsfrompollinatingcrops.Repeatedbackcrossingwithweedsaspollenparentsresultsingeneestablishmentintheweeds.Transgenicmitigationreliesoncouplingcropprotectiontraitsinatandemconstructwithtraitsthatlowerthe?tnessoftherelatedweeds.Mitigationtraitscanbemorphological(dwar?ng,noseedshatter)orchemical(sensitivitytoachemicalusedlaterinarotation).Tandemmitigationtraitsaregeneticallylinkedandwillmovetogether.Mitigationtraitscanalsobespreadbyinsertingtheminmulticopytransposonswhichdispersefasterthanthecropprotectiongenesinrelatedweeds.Thus,therearegene?owrisksmainlytoweedsfromsomerisksthatcanandshouldbedealtwith.?2014SocietyofChemicalIndustryKeywords:gene?transgene?ow1INTRODUCTIONTherehasbeenmuchpolemicaldiscourseontherisksoftransgene?owfromcrops,usuallytothe‘wild’,howitwilla?ect‘geneticpurity’andthatthis‘genecontamination’willbeirreversible.Thisreviewendeavourstoputsuchargumentsinbiologicalandagronomicperspective,withoutusingsuchloadedtermswiththeirracistundertones,andthentodiscusswaystodealwithtransgene?owwherethereisarisk.Thisreviewwillnotdealwithtransgenemovementduetoseedspread,e.g.transgenicseedsthatfallfromvehiclesalongrightsofway,1a?ectingruderalecosystems,andthatcouldspreadtoadjacent?elds,andlegalexportofcropsforprocessing,deliveringtransgenestoplaceswheretheyareconcomitantlynotallowedtobecultivated.2Thereviewalsodoesnotdealwithpotentialrisksofallengineeredtraitsbeingintroducedtocrops,butratherislimitedtocropprotectiontraits.Forbroaderrecentreviews,seeGressel3andOliverandLi.42GENEFLOWCTHEBASISOFEVOLUTION(withoutknowingtheterm).“Therefore,amaizelandraceshouldnotbeconsideredasaseparateentity,butratherasanopengeneticsystem”.5“Iftransgenicvarietiesareintroducedcommer-ciallyintothesesystems,itislikelythattheywillbemanagedlikethelocalmaizepopulationsandthatcreolisationwilltakeplace.Geneswillbeexchangedbetweentransgenicvarietiesandlocallandracesthroughpollen?owbetweenplantsaswellasbymixingseedsatseveralstepsinthecroppingprocess”.6Similarly,sorghumlandracesarepreserved,butwithcontinualgeneexchangewithwildandweedysorghums,atthecentreoforiginanddiversity.7Thiscross-pollinationcanbebene?cial,e.g.inprovidingnoveltraitstolandraces,preventingfarmersfromabandoningthem.Othercasescanbe(near)neutral,andinsomecasesdeleterious,resultinginthefarmerdiscardingthem.Geneticmaterialfromcropsisoftenfoundinrelatedwildandweedyspeciesfromnat-uralcross-pollination(Table1).Thereisnoregulatoryscrutinyofsuchgenemovementineitherdirectionfornon-transgenictraits,andinthecaseofnon-transgenicherbicideresistance,whenthereareweedsrelatedtothecrop,thereisgoodreasonforhavingreg-ulatoryinterference.2.1Howdogenes?ow?Genemovementbetweensexuallycompatibleindividuals,‘verti-calgene?ow’,canoccuramongvarietiesandstrains,andamongDarwinconsideredmutationstobethebasisofspeciesevolu-tion,butthemutationsneednothavebeeninthegenesofthespeciesinquestion.Instead,mutationscanalsocomefromarelatedspecies,orevenfurthera?eld.Thegenomeofanyspeciesorevencultivarisconstantlychanging,andthustheterm‘geneticpurity’ofvarietiesisinappropriate,asvarietiescontinuallychangethroughselection,breedingorgeneticengineering.Forexample,Mexicanfarmerspreservethetaste,colourandtextureofland-racesbyselection,butactivelymixseedfromdi?erentlocalestoenhancelandracevigourandpreventinbreedingdepressionPestManagSciC667?Correspondenceto:JonathanGressel,PlantSciences,WeizmannInstituteofScience,Rehovot,Israel.E-mail:Jonathan.gressel@weizmnn.ac.ilPlantSciences,WeizmannInstituteofScience,Rehovot,Israel658www.soci.org?2014SocietyofChemicalIndustryTransgene?owofcropprotectiontraitsfromcropstotheirrelativeswww.soci.orgTable1.Recentexamplesofnaturalgene?owfromcroptoweedsCaconstantoccurrenceaGeneTraitTypeof?owFromToRef.VernalisationDiagonalTriticumaestivumAegilopscylindrica72663bpofWPG118Non-codingDiagonalTriticumaestivumAegilopsperegrina73BoltingVerticalBetavulgarisB.maritima74MorphologicalandenzymeMarkersVerticalRaphanussativaR.raphanistrum75,76ChloroplastMarkersDiagonalBrassicanapusB.oleraceaandB.rapa77AFLPMarkersVerticalCarrotDaucuscarotaQueenAnne’sLaceD.carota78MicrosatelliteMarkersDiagonalLactucasativaL.serriola79MolecularMarkersHelianthusannuusH.petiolaris80RAPDMarkersVerticalHelianthusannuusWeedysun?ower81MicrosatelliteMarkersVerticalcv.AgrostisstoloniferaFeralA.stolonifera25SSRMarkersVerticalcv.OryzasativaFeralO.sativa82AFLPandSSAPMarkersVerticalCichoriumintybuschicoryWeedyC.intybus83RFLPMarkersDiagonalSorghumbicolorS.halepense84aForanentryintothevastolderliteratureonthesubject,seeEllstrand85andAnderssonanddeVicente.86somereadilyinterbreedingspecies.Often,cultivatedandweedyitoccurs,itisanexceptionratherthantherule.Hybridforma-forms,aswellaswildprogenitors,aregivendi?erentLatinbino-tionbetweentworelatedspeciescanbecommonorrare,butmials,ashashappenedwithrice,sun?owers,radishes,etc.,eventhehybridindividualsaretypicallysterile.Still,thosefewhybridthoughtheprogenitorsarebotanicallythesamespecies.o?springthatthensuccessfullyself-pollinateorbackcrosstoa‘Horizontal’gene?owisnotsexuallytransmittedandcanoccurparentallinearetypicallymorefertileandviableineachsubse-amongkingdomsordistantlyrelatedspecies.Itisfarmorecom-quentgeneration,andthetraitcanbecome?xed.Theangleofmoninprokaryoticorganisms,e.g.phagesmoveplasmidswiththediagonalcanbevariable,fromafewhybridstoveryveryantibioticresistanceamongbacteria.Horizontalgene?owisveryfewhybridsbeingfertile.Inmanycases,noviableo?springcanuncommonbetweenplantsandbacteria.Forexample,virtuallyallbeobtainedinF2orBC1generations.9Thus,hybridformationsoilshavebacteriathatdegradeatrazine.Millionsofhectareshavebetweentwospeciesisnotasignthatthegenewillintrogressbybeensprayedwithatrazinefordecades,andmanyweedshavebackcrossingintotheweedyrelative,assomeassumewhentheyevolvedresistance.Noreportedcaseofresistancehasresultedobserveahybrid.Sometimes,diagonalgene?owoccursthroughfromasoilbacteriumgene,inspiteofweedrootsbeingbathedinanintermediate‘bridge’speciesthatismorecompatiblewiththeDNAofsuchbacteria.Still,overevolutionarytimetherehasbeencropthantheultimaterecipient.10Somecropprotectiontraits,horizontalgene?owamongnon-interbreedingorganisms,butthebothtransgenicandnon-transgenic,haveverticallyanddiago-riskofitsnaturaloccurrenceto,oramong,plantsisconsideredtonallyintrogressedintoweedyspecies(Table2),andmanyofthesebeinconsequentiallylow,andisnotconsideredbyanymajorreg-casesarecauseforconcern.ulatoryagency.EngineeringanoveltransgeneintoacropisaformDiagonalgene?owdoesnotusuallyoccurwithinbotanicalgen-ofhuman-expeditedhorizontalgene?ow.era,butitisharderto?ndpublisheddataoninterspeci?cnegativeAthirdtypeofgeneintrogression,coined‘diagonal’,8occurshybridisation,asthebreedersdonottypicallypublishnegativebetweenrelatedbutincompletelyincompatiblespecies.Wheredata.Someexampleswheretherearepublicationsseemobvious.Table2.Recentexamplesofgene?owofcropprotectiontraitstorelativesviapollenaGene/transgeneTraitbTypeof?owFromToRef.alsImidazolinoneRVerticalRiceOryzasativaWeedyriceO.sativa19,29,87CpTIandBt/CpTInsectRVerticalRiceWeedyrice88alsImidazolinoneRDiagonalTriticumaestivumAegilopscylindrica69,89,90SinglemajorgenesChlorotoluronanddifenzoquatRDiagonalTriticumaestivumAegilopsbiuncialis91DiseaseRDiagonalTriticumaestivumAegilopscylindrica92barGlufosinateRVerticalSugarbeetWeedybeet93BtCry1AcInsectRDiagonalBrassicanapusB.juncea94,95epspsGlyphosateRDiagonalBrassicanapusB.juncea,B.carinata96,97alsImidazolinoneRVerticalHelianthusannuus‘Wild’H.annuus98epspsGlyphosateRVerticalAgrostisstoloniferaFeralA.stolonifera26epspsGlyphosateRDiagonalAgrostisstoloniferaPolypogonmonspeliensis99aPublishedcasesofwithin-cropgene?owarenot100considered,asobviouslycanoccur,ashasbeenmostevidentwithoilseedrapewheregene?owhascausedstackingofgenes,e.g.Knispeletal.,andwheatwhereadventitiousimidazolinoneresistancewasfoundincerti?edseedthatwasnotsupposedtocontainthegene.101bR=resistance.PestManagSci2015;71:/journal/ps659www.soci.orgNew-worldevolvedpotatoes(Solanumtuberosum)andtomato(S.lycopersicum)donotcrosswithold-worldS.nigrum11andS.hirsu-tum.12Breedershadlongtriedtomakesuchinterspeci?ccrossestobringindiseaseandinsectresistancestocrops,buttheirexper-iments‘had’toberepeatedinthetransgenicera(fornovalidsci-enti?creasons).2.2Isgene?owtowildspeciesnecessarilydeleterious?Someecologistsandenvironmentalistsdisinformthepublicandusetheterm‘wild’whentheirdataareactuallyaboutweedyspeciesgrowinginruderaloragroecosytems,andnotaboutwildspeciesinnaturalecosystems.Themajorecologicaldi?erencesbetweenweedyandwildhavebeeneruditelydescribedbyWar-wickandStewart.13Itisabasicassumptionofmanytechnologydetractorsthattransgene?owtowildspeciesisdeleterious,andthattransgeneswill‘swamp’localgenesand‘contaminate’naturalpopulations,causealossof‘geneticpurity’andleadtoalossofbiodiversity.14Itistellingthatnoexamplesarepresentedinsuchhysteria-mongeringmanuscriptsandtheirconcomitantuniversitypressreleases.Swampingisusuallydoubtful,aspollenmustgetfromthecroptothedistantwildecosystem.Pollenlosesvitalitywithtime,andtherewillbeadistancebetweenthetwoecosys-tems,anddistanceequalstime.Then,croppollenmustcompetewithmuchlargerquantitiesoflocallyproducedwildpollen,pollenthatismorevitalbecauseitisfresher,andusuallyhaslessgeneticcompatibilityproblems.Thefewresultingo?springfromcrop×wildcrossesarelesslocallyadaptedthanwildtypeinthenaturalecosystem,andmosto?springwillbecompetedtooblivion.Whetherthetransgenebecomesestablishedinanecosystemthendependsonthenatureofthetransgene.Forexample,atransgeneencodingherbicideresistancecanhavenoconceivable?tnessadvantage,asherbicidesarenotusedinwildecosystems.Ascropscancrosswithrelatives,itisprettyobviousthatresearchershaverecon?rmedwhatisknownusingmutantgenes,andwithtransgenesconferringcropprotectiontraits(Table2).Somelaboratoryexamplesshowthatdiseaseandinsectresis-tancesprovidea?tnessadvantagewhenchallengedwithlargeinoculaofpathogensorpopulationsofinsects.Thisadvantageislessofafactorinthe?eld,wherediseaseandinsectpressuresarelower,aswellassporadicintime.15Caseswheregene?owmaypreservebiodiversityofwildrel-ativesofcropscanbeenvisaged.Forexample,thenewwheatrustUG99isspreadingaroundtheworld.ManywildTriticumandcloselyrelatedAegilopsspeciesfromthecentreoforiginandbiodi-versitywerescreenedforpossibleresistanceasahopefulsolutiontotherust,andalmostallstrainswerehighlysusceptible(MilletE,privatecommunication).IfUG99rustgetsintonearbywheat?elds,thesenearbywildstrainswillbedevastated.Ifwheatisren-deredUG99resistant,theresistancewillspreadtothewildspeciesandpossiblysavethem.IfthewheatisrenderedUG99resistantbybreeding,therearenohurdlestoimmediatedeployment.Ifdonetransgenically,thewildrelativeswouldprobablybedevastatedbyUG99bythetimeregulatoryapprovalisachieved.2.3Istransgene?owtolandracesnecessarilydeleterious?Whereassomeargueformaintaining(thenon-existent)‘geneticpurity’oflandraces,otherscounterarguethattransgene?owofcropprotectiontraitsintolandraceswillfacilitatetheircontinuedcultivation.Farmersarelesslikelytoabandonthelandracesforhigher-yieldingcultivarsorhybridsifthelandracesareresistanttoinsectsandpathogens,orifweedscanbecost-e?ectivelyJGresselcontrolledwithouthandlabour.Thus,iftheintentionreallyistopreservethecultivationoflandraces,andnotjusthavetheirpresenceingenebanks,thensuchgene?owisobligatory.Thisisespeciallytruefordiseaseandinsectresistancesforcropsofresource-poorfarmerswhotypicallycultivatelandraces.Suchtraitsrequirenofurtherinput,unlikeherbicideresistance,whichrequiresthepurchaseofherbicides,yetherbicideresistanceobviateshandlabourandisdesirablewherelabourishardorexpensive.2.4Istransgene?owtoweedsnecessarilydeleterious?Cropprotectiontraitshavealreadyintrogressedfromcropstorelatedweeds(Table2).Here,theanswerforcropprotectiontraitsisusuallya?rmativeforherbicideresistance,butnotsomuchforothertraitssuchasdiseaseorinsectresistance,16,17wheredataaremoreambiguousowingtothesporadicnatureofdiseaseandinsectincidencesa?ectingweeds.Suchgeneswouldclearlyincreaseweed?tnesseswhenmicrobialorinsectbiocontrolmeasuresareusedagainsttheweed.Manytransgenicherbicideresistancesareconsideredtobenec-essaryjustbecausetheynowallowcontrolofweedsrelatedtotheweedstypicallyhavethesamenaturalherbicide-resistance-conferringpathwaysasthecrop.Thus,onemajoradvantageoftheherbicideislostifthereisgene?owtorelatedweeds.Thishasbeenthecasewithnon-transgenic,mutantimidazolinone-resistantrice,whichhadbeenexcellentincontrol-lingweedyrice.18C21Diseaseandinsectresistancetransgeneswouldprovidea?tnessadvantagetoaweed,butnotenoughtosavetheweedfromeventualchemicalormanualweedcontrol,loweringthee?ectiveriskfromsuchtransgenesinthe?eld.Ifdis-easeresistanceintrogressesintoruderalweedpopulations,thiswouldbeanagronomicproblemininstanceswheretheweedisanalternatehostforthepathogens.Thereisalwaysaneedtoevaluatetheriskindepthpriortodecid-ingwhethertoputacropprotectiontraitintoaspecies.Thetypicalreactiontoarequesttoinsertadisease-resistance-conferringgeneintocarrothasbeenthatthiswouldbecontraindicated.Basedonthe‘precautionaryprinciple’,itwouldbeassumedthatsuchagenemightconferenhancedcompetitive?tnessonweedycarrot(akaQueenAnne’sLace),whichisconspeci?cwithcarrot.Amorein-depthstudyoftheliteraturebroughtabouttherealisationthatweedycarrotisalreadyresistanttothedisease.22Thisnaturalresis-tanceisprobablyduetothebad-tastingortoxiccompoundsbredoutoftheprogenitorduringdomestication.The‘precautionary’conclusionshouldbethatitiscontraindicatedtobringtheresis-tancegenetothecropfromtheweedbybreedingorcisgenics,andthattransgenicdiseaseresistancecouldbetoxicologicallyfarsaferthanthenaturalresistanceinthespecies.3DEALINGWITHDELETERIOUSFLOWOFCROP-PROTECTINGTRANSGENESFromtheprevioussectionitisclearthatitisnotreallynecessarytodealwiththerisksemanatingfromtransgene?owtoallecosys-tems,buttofocusonagro-andruderalecosystems,mainlyonherbicide-resistance-conferringtransgenes,astheywouldclearlybemoredeleteriousifspreadthanothercropprotectiontraits.Therearebasicallytwo(notmutuallyexclusive)waystodealwithgene?ow:containment(preventingthegenefromspreadingfromthecrop)andmitigation(preventingthegenefromestablishingtoasigni?cantproportionofthepopulation).BothstrategiesarePestManagSciC667</journal/ps?2014SocietyofChemicalIndustryTransgene?owofcropprotectiontraitsfromcropstotheirrelativeswww.soci.orgTable3.ConceptsofbiologicalcontainmentofgenesConceptAssayedinEvaluationRef.CleistogamyRice×weedyrice2C6%outcrossing29ChloroplastProposedInadequateassumption31C33ChloroplastNicotianaspp.0.01C0.4%pollenoutcrossingfreepollinationto34,35cropChloroplastSetariaspp.0.4%pollenoutcrossingfreepollinationtocrop36ChloroplastArabidopsis0.004%pollenoutcrossing102GURTaNeedsevaluation51TransgenicmalesterilitybTobaccoTotalmalesterility(butcanbepollinatedbyweed)103Chysanthemum104CytoplasmicmalesterilitySun?owerVariableallowingoutcrossing105Sorghum106MicroRNAmalesterilityEggplantRestorationbyethanol,maybeproblemin?eld107environmentsTotal(bisexual)sterilityTobaccocMustbevegetativelypropagated108Generald40Arabidopsise109No?oweringPanicumvirgatumHigherbiomassyield110TransgeneexcisionfrompollenfTobaccoWeedcanbepollenparentandrecurrentpollen111parentFloweringtimeBrassicanapus×B.rapaOverlapsevenindi?erentgeographies112TransgeneinrootstockGraftedcherriesWorksunlesssuckersfromrootstockarenot113removedTransgeneinvirusNicotianabenthamianaSinglegenerationSinglegenerationSingle114CucurbitsGrainsgeneration4443Transgenein:viralrepliconsviralfragmentTomatoSinglegenerationSinglegeneration115116abGeneticuserestrictiontechnologies,alsonicknamed‘terminator”.52cUtilisesoverexpressedmutatedmelonethylenereceptorgenesCm-ETR1/H69AorCm-ERS1/H70A.Utilisesbarnase(ribonuclease)undergamete-speci?cAtDMC1promoter,andbarstarinhibitorofbarnaseunderthecontrolofconstitutiveACT2promoter,dwhichisinactiveingametes.eUtilisesRNAisilencing.fUtilisesRNAisilencingofAtRAD51CandSWITCH1(SWI).UtilisesaserineresolvaseCinHrecombinase(CinH)anditsrecognitionsitesRS2asatransgeneexcisionvector.discussedinarecentbook,4whichobviouslydealswiththisatcrop,andnorealgene?owCjustgenepresenceintracesofdeadgreaterlengthanddepththancanbecoveredinthefollowingmaterial.Itcouldhavebeenpreventedbymitigation.discussion.Transgene?owcanoccurtonon-transgenicvarieties,whichmaybeundesirable,mainlyforeconomicreasons.Physicalseparation3.1Containmentbydistance,ashasalwaysbeenpractisedbybreeders,neednotTwotypesofstrategyhavebeentriedtokeepgenesfrommov-beattheverylongdistancessometechnologydetractorsproposeingoutoftransgeniccrops:physicalcontainmentandbiotechno-(basicallyasaploytomakeitimpossibletocultivatetransgenics).logicalcontainment.VariousproposedcontainmentstrategiesarePhysicalseparationcanbeintherangeofdistances(10C20m)summarisedinTable3.alreadypractisedbybreeders,becausemostjurisdictionshaveanallowablethresholdof0.9%inadvertenttransgenicmaterial.24Itisnighimpossibleforthetransgenetoestablishinnon-transgenic3.1.1Physicalcontainmentvarietiesiffoundationandcerti?edseedsarekeptatthelongerPhysicalcontainmentutilisesbarrierstopreventgene?ow.distancesmandatedfortheirproduction.Thesebarriersinclude?ltersinthelabs,meshongreen-Similarly,isolationdistanceswerethought(withoutdata)tohouses/screenhousesandisolationdistancesinthe?eld.Therebesu?cienttocontainpollenoftransgenicherbicide-resistantseemtobenoreportswherephysicalcontainmentofplanttrans-bentgrass(Agrostisstolonifera).Thetransgene(andphenotype)genesfailedinthelaboratoryorgreenhouse,butthathasnotwerefoundinferalbeenthecaseinthe?eld.ProdiGenecultivatedtransgenicmaize,Cpopulations,aswellasinahybridwitharelatedspecies.2527Biologicalcontainmentormitigationmightproducingapharmaceuticalproduct,anddependedonisolationhavepreventedthisdebacle,asdiscussedbelow.distancesandhumanclean-uptopreventproblems.Tracesoftheirtransgenewerefoundonminutequantitiesofmaizeleaf3.1.2Biologicalcontainmenttrashadheringtothefollowingcrop.23ThecompanynolongerTherehavebeenavarietyofsuggestionsonhowtokeeptrans-existsinlargepartbecauseofthisdebacle,eventhoughtheregenescontainedwithincrops,butsometimesdependingonbiol-wasnogeneexpressioninthedeadmaterialadheringtothenextogytocontaingenesnaturallyisnaive.SuggestionshavebeenPestManagSciC667?/journal/ps661www.soci.orgmadethat,ifthecropandtherelative?oweratdi?erenttimes,therecanbenohybridisation.Itisrarethatthereisnotatleastaslightoverlapin?oweringtime,whichwillallowgene?ow.Therewasaclaimthatcleistogamy,wheretheantherspol-linatepistilsbefore?owersopen,wouldpreventgene?ow.28Cleistogamyhadbeenconsideredtobesu?cienttocontain(non-transgenicCmutant)imidazolinoneherbicideresistanceinriceandkeepitfromspreadingtoweedyrice.Alas,thereisasmallpercentageofnon-cleistogamouscross-pollinationinrice,allowinghybridisationwithweedyrice.29Theexampleandtheunworkablemanagementstrategiesproposedwereadeathknelltothetechnologyinmuchoftheworld18,19andareasontoassurethatthemistakeswouldnotberepeatedwithtransgen-ics.Anewcleistogamousgene(‘superwoman’)hasbeenincorpo-ratedinsomericelines,anditlowerstheoutcrossingratesuchthatitwillkeepadventitiousoutcrossingtoothervarietiesataverylowlevel,30butwouldbeinsu?cienttocontaintransgenesfromweedyricebecauseofthe?tnessadvantagetotheweed.Withthepresenttendencytogotohigher-yieldinghybridricevarietieswherenon-cleistogamousparentallinesarerequired,itishardtoenvisagemuchutilityinthisnewmutation.ThevariousbiologicalcontainmentstrategiesproposedaresummarisedinTable3anddiscussedbelow.Insertingthecropprotectiontraitintotheplastome.Plastome(chloroplastgenome)inheritedtraitsarenottransmittedbypollenofmanyspecies(butnotallspeciesCespeciallynotlegumes).Thus,itwashypothesisedthattransgenesinsertedintotheplas-tomewouldnotspreadbypollen,anditwouldbeworthwhilecon-sideringtheuseofthismuchmorecomplicatedtransformationtechnologytogeneratetransgeniccrops.31C33Thiswouldonlybeappropriatefortraitsthatmustbeexpressedintheplastids,asthereislittleevidenceforenzymesleavingtheplastid.Thistechnologyhastwodrawbacks.Firstly,inspecieswherematerialinheritanceofchloroplasts(nopollentransmission)wasthoughttobeabsolute,thereistypicallyabout0.4%transmission.34C36Indeed,interspeci?cchloroplastmovementhasspontaneouslyoccurredinBrassica.37Oncethegen(i)eisoutofthebottle,itcanestablishinrelatedplants,ifithasa?tnessbene?t.Secondly,thecropneednotbethepollenparelatedweedcanbethepollenparent,andthehybridswillbearthetransgene.Theweedcanbetherecurrentbackcrossparentaswell,establishingthetransgeneintheweedypopulation.Indeed,wind-pollinatedrelatedweedsareoftentallerthanthecrops,andtheresultanthybridstypicallyhavethetallerweedasthepollenparent.Conditionalmalesterility.Mostcrophybridsforcultivationonalargescaleareformedwhereoneparentismalesterilesothathumansarenotneededtoemasculatemale?owers.Thisisusuallyachievedbyusingcytoplasmicmalesterility,whichisconditional.Thereisa‘restorer’line,whereahormoneoranenvironmentalstimulusisusedthatallowspollenformationandself-pollinationofthe(conditionally)malesterileparent.Thus,itwasassumed,aswithplastomeinheritance,thatamalesterilelinebearingatransgenewouldnotbeabletopassthetraitonthroughpollen.Thisconcepthasthesamedrawbacksasplastometransformation.Conditionally,malesterilelinestypicallyproducesmallamountsofpollen,notenoughtoa?ecthybridproduction,butenoughtotransferatraitandallowittoestablishslowly.Also,therelatedweedyorwildspeciescanbethepollenparentincrosses.Allsterilitysystemsforcontainmenthavebeenrecentlyreviewed.38Totalsterility.Ifaplantisunabletotransfertraitsbypollentorelatives,andifrelativescannotpollinateit,thentheonlywayaJGresseltransgenecouldtransmitisbyhorizontal,non-sexualgene?ow.Totalsterilitycannotbeachievedbyusingtheconditionalsys-temsdescribedabove,butbyusingabsolutesystems.Thiswouldrequirephysicaldeletion(notsuppression,whichisreversible)ofportionsofkeygenesinvolvedeitherin?owerproductionorsep-aratelyinpollenandovuleproduction.Suchplantswouldhavetobevegetativelypropagatedbytubers(orbyanalogousnatu-ralpropagules),cuttings,tissuecultureorarti?cialseed.39Obvi-ously,suchtechnologieswouldnotbeappropriateforcropswheretheharvestedmaterialisseed.Totalsterilitywouldbeappropri-atefortuber-orbulb-propagatedcrops,leafyvegetablecropsandforestry.Totalsterilitymayhaveanotheradvantage:itmightalsoincreasetheyieldofvegetativetissues,assexualreproductionhasahighenergycost,attheexpenseofbiomassproduction.VarioussystemsforobtainingtotalsterilityusingRNAsilencinghavebeenrecentlyreviewed,40butsilencedgenescanbackmu-tatetoactivegenes,whichcannotbeeasilyprevented.Withmod-erngenomics,itisrelativelyeasytopinpointcandidategenesfordeletion,toovercometheproblemofreversion.Genomeeditingtechnologiessuchaszinc?ngernucleases(ZFNs),transcriptionactivator-likee?ectornucleases(TALENs)41andclusteredregu-larlyinterspersedpalindromicrepeats(CRISPRs)42facilitateeasyremovalofgenesequencesfromagene,renderingitirreversiblyinactive,sothattotalsterilityisareadilyachievablegoalwithtrans-geniccrops,incaseswhereapplicable.Totalsterilityhasotheradvantagesbesidespreventinggene?ow.Ifithadbeenusedtopreventgene?owincreepingbentgrass(whichiseasilypropagatedvegetatively),itwouldhaveabrogatedpollen-inducedallergies(hayfever)fromthisspecies,whichmanyconsumerswould?ndmoreattractivethantheherbicide-resistanttransgenictrait.8Single-generationtransformation.Therearemanyvirusesthatarespeci?ctocropsthatcanbeengineeredtocarrycropprotectiontraits.Thiscanbewithdisarmedvirusesthatarenotpathogenic,orjustwithonlyenoughoftheviralnucleicacidtoactasavector.Theadvantagesofsuchvirus-basedtechnologiesisthatmostvirusesdonotinfectreproductivetissue,andthustheencodedtraitsarenotseedtransmissible.Theinitialdescriptionsofsuchtechnolo-giesusedleafinfectionwithsystemicviruses.43,44Morerecently,ashortpieceofvirushasbeenusedtovectoramultigenepathwayfortheproductionofametabolitethatcontrolsbacteriaandfun-galpathogens.45TheDNAcanbedeliveredviacropseed,andthetraitsarenotcarriedtothenextgeneration.Insomejurisdictionsthesearenotconsideredtobe‘transgenic’cropsbecause,bydef-inition,atransgenemustbeintrogressedintochromosomalDNA,andviralvectoredgenesremainextra-chromosomal.Others.The‘recoverableblockoffunction(RBF)system’,46thetwo-componentsegregationsystemcontrollingseedgermination47andproteintrans-splicing,48areeitherunidi-rectionalorleaky,andareanalysedatlengthasinappropriateforpreventinggeneout?owtorelatedspecies.8Chemicallyinducedtransgeneexpression49wouldpreventtransgeneexpressionwherevertheinducerisnotused(e.g.inthewild),butgoodinducersystemsarelackingorthechemicalthatinducesiscostly.Similarly,developingseedlessfruitbyhybridisingdiploidandtetraploidparentsandcultivatingthesterileo?springpreventsgene?owbyseed,andthepollenishighlysterile.50Atech-nologyhasbeenproposed(initiallyforprotectingintellectualpropertyandwasthushighlyvili?edbythosepoliticallyagainstmultinationalcorporations)wherethetransgeneisturnedo?(suppressed)byachemicalsuppressorjustpriortoplanting.Thistechnology,termedgeneticuserestrictiontechnology(GURT),51PestManagSciC667</journal/ps?2014SocietyofChemicalIndustry
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