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Insights into Nonhost Disease Resistance Can They Assist Disease Control in Agriculture.pdf

Insights into Nonhost Disease R…

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简介:本文档为《Insights into Nonhost Disease Resistance Can They Assist Disease Control in Agriculturepdf》,可适用于工程科技领域,主题内容包含CURRENTPERSPECTIVEESSAYInsightsintoNonhostDiseaseResistance:CanTheyAssistD符等。

CURRENTPERSPECTIVEESSAYInsightsintoNonhostDiseaseResistance:CanTheyAssistDiseaseControlinAgricultureTheoftenstatedtruismthatmostplantspeciesareresistanttomostplantpathogensreflectsthemanyobservationsthatapathogenisolatedfromoneplantspeciesinmostcasescannotinfect,reproduce,andcausediseaseonotherdistantlyrelatedspeciesWhatdeterminespathogenhostrangeisanimportantandintriguingquestioninfundamentalhost–pathogenbiologyManystudieshaveinvestigatedthisareawithbiochemical,pharmacological,andmicroscopystudies,andnowseveralrecentpublications(Collinsetal,Lipkaetal,),includingoneinthisissueofThePlantCell(Steinetal,),havefocusedthepowerofmoleculargeneticsontheproblemwithstudiesofinfection(orratherlackofinfection)ofArabidopsisthalianabyfungalpathogensofcropplants,particularlypowderymildewspeciesThenewknowledgecouldhaveimplicationsfornovelstrategiesfordiseasecontrolinagriculturePOWDERYMILDEWINFECTIONPowderymildews,alargegroupofAscomycetefungalspecies,areobligatebiotrophs,meaningthattheyrelycompletelyonlivinghostplanttissueforsurvival,andinmanycases,eachspeciesisspecializedtoinfectaverynarrowrangeofplantspeciesForexample,thepowderymildewfungusBlumeriagraminisfsphordei(Bgh),whichcausesaseriousdiseaseofbarley(Hordeumvulgare),infectsonlybarleyanditscloserelativesInfectioninitiateswiththegerminationofconidiosporesontheplantleafsurface,followedbytheformationofstructurescalledappressoria(asortoffungalbatteringram),fromwhichdevelopinfectionhyphaecalledpenetrationpegsThesehyphaebreachhostepidermalcellwallsandtheinfectioninduceddomeshapedextensionsoftheinnersurfaceofthewall,calledpapillae,probablybyphysicalpressureandenzymaticdegradationThetipsoftheinfectionhyphaethenexpandtoformmultifingeredfeedingstructurescalledhaustoriathatinvaginatebutdon’tpenetratethehostplasmamembraneThismeansallnutrientsforfungalgrowthfromthehost,andpotentialsignalmoleculesfromthepathogen,mustcrossadoublemembraneinterface(Huckelhoven,Zhangetal,)Thefungalcoloniesthatarisefrominfectionproducethesporesforthenextcycleofinfection,anditistheappearanceofthesepowderysporesontheleafsurfacethatisthehallmarkofsuccessfulinfectionintheexperimentalsystemsdescribedbelowGENEFORGENERESISTANCEANDADAPTEDPATHOGENSPopulationsofhostspeciesofabiotrophicfungusarefrequentlyhighlypolymorphicforresistanceandsusceptibilitytoisolatesoftheadaptedpathogenspeciesResistanceisusuallyassociatedwiththehypersensitivereaction(HR),alocalizedhostcelldeathresponseattheinfectionsitethatoccursafterthefungushasbreachedthehostcellwallandattemptedtoinitiateahaustoriumThistypeofresistanceismediatedbythewellstudiedgeneforgeneinteractionsbetweenhostresistance(R)genesandpathogenavirulence(Avr)genesForexample,incultivatedbarley,differentRgenesmaptotheMlalocus,whichcontainsgenesencodingnucleotidebindingsite–leucinerichrepeat(NBSLRR)proteinsthatcontrolspecificrecognitionofmildewstrainsdependentonthecorrespondingAvrgenotype(Zhouetal,)NONHOSTRESISTANCETOBARLEYMILDEWINARABIDOPSISIncontrastwithbarley,allindividualsofArabidopsisareresistanttoallisolatesofBgh,andthisformofresistance,callednonhostresistance,isgeneticallyilldefined(Heath,ThordalChristensen,)However,arecentseriesofarticleshighlightedherehavemadesignificantadvancesinourunderstandingofnonhostresistancetomildewsTheArabidopsis–BghinteractionisparticularlywellsuitedforthesestudiesbecausemildewinfectionoccursattheleafsurfaceandisrestrictedtoepidermalcellsThus,infectionattemptsareeasilyvisualizedbymicroscopy,andmutantplantswithalteredresponsestoinfectionandreducedresistancetothebarleypathogencanbeidentifiedMoreover,atleasttwospeciesofpowderymildewthatcausediseaseonArabidopsisareknown,andtheseinfectionsprovidecomparisonsbetweenthestepsininfectionbymildewspeciesadaptedtoArabidopsisandinfectionbythenonadaptedbarleymildewNonhostresistancehastwophasesDuringtheprehaustorialphase,BghsporesgerminateandformappressoriaontheleafsurfaceofArabidopsis,cellwallpenetrationoccurs,hyphalgrowthceaseswithintheinfectioninducedpapillaeatoftheinfectionsites,andhaustoriafailtodevelop(Collinsetal,Assaadetal,)Duringtheposthaustorialphase,haustoriathatformattheremaininginfectionsitesbecomeencasedincalloseandthehostcellundergoestheHRAmajordifferencebetweengeneforgeneresistanceandnonhostresistancetomildewsisthattheformeroccursmainlyafterhaustoriumformation,whereasthelatteroccursmainlybeforehaustoriumformationandmostlyisnotassociatedwiththeHRHowever,theHRisafeatureincommonwiththelowfrequencyofnonhostpenetrationswhereinitiationofhaustoriaoccurs,leadingtothequestion:HowdoesBghcausediseaseonbarleybutnotonArabidopsisThePlantCell,Vol,–,March,wwwplantcellorgªAmericanSocietyofPlantBiologistsMUTATIONFORTHEDISSECTIONOFNONHOSTRESISTANCE:PENETRATIONMUTANTSMicroscopicexaminationofmutatedArabidopsisplantsinoculatedwithBghsporeshasbeenusedtoidentifymutantswithalteredresponsestoinfectionMorespecifically,stainsforcallosedepositionaroundhaustoriaortheappearanceofincreasedautofluorescenceatinfectionsiteswereusedtodetectmutantplantswithincreasedfrequencyofhaustorialinitiationperinfectionsiteinrosetteleavesThreegenes,PENETRATION(PEN),PEN,andPEN,havebeenidentifiedandcloned(Collinsetal,Lipkaetal,Steinetal,)Singlemutantsofthesethreegeneshaveincreasedfrequencyofhaustorialformation,butnoincreaseinoverallsusceptibilitytoBghasindicatedbycoloniesproducingviablesporesPEN(Collinsetal,)encodesamembraneassociatedsyntaxincontainingaSNARE(forsolubleNethylmaleimide–sensitivefactorattachmentproteinreceptor)domainandisamemberofalargefamilyofproteinsinvolvedinmembranefusionandsecretioneventsInpenmutants,thereisreducedinhibitionofhyphaldevelopmentfollowingcellwallpenetration,resultinginasevenfoldincreaseinhaustorialinitiationHowever,theHRoccurs,andconsequentlynofungalcolonyformationresults,whichindicatesthatPENisonlyonecomponentofamorecomplexnonhostresistancemechanismthatpreventsBghgrowthonArabidopsisPENfunctionsinresistancethroughanundefinedmechanisminvolvingsecretoryvesiclesItsexpressionisinducedduringBghinfection,andafunctionalgreenfluorescentprotein(GFP)–PENfusionissecretedandaccumulatesatpapillae(Assaadetal,Bhatetal,)thatformatthesiteofinfectionpegformationIfPENisinvolvedinsecretionofbuildingblocksofpapillae,itsroleispartiallyredundantbecauseelectronmicroscopyanalysisofthecompletelossoffunctionmutantpendidnotfindanymajordetectablealterationinpapillaeHowever,therateofpapillaformationisreducedinBghinfectedpenmutants,andthishasbeenproposedasapotentialcauseforthebreakdownofthisearlycomponentofnonhostresistance(Assaadetal,)PEN(Lipkaetal,)isoneofgenesencodingpredictedglycosylhydrolasesintheArabidopsisgenomeHowever,thesubstratesandproductsofPENactivityarepresentlyunknownpenmutantsshowanincreaseofBghhaustoria,similartopenmutants,andadditiveeffectsareobservedinpenpendoublemutantsNeithermutanthasanyeffectoninfectionofsusceptiblegenotypesofArabidopsisbyvirulentstrainsoftheadaptedmildewspeciesGolovinomycesorontiiHowever,penbutnotpenallowsincreasedhaustoriumformationandsubsequentHRinductioninArabidopsisbythepotatopathogenPhytophthorainfestanspenalsolimitsgrowthofPlectosphaerellacucumerina,anecrotrophicpathogenofArabidopsisThisindicatesthattheeffectofpenisbroaderthanthatofpen(whichaffectsonlyBghinfection)together,theseresultsindicatethepossibilitythatPENandPENactindifferentpathwaysInaddition,PENGFPfunctionalfusionproteinislocalizedtoperoxisomesthatmovetoandaccumulateatBghpenetrationsites,consistentwiththepredictedroleofthisorganelleindeliveringanantifungalproducttowhereitisneededtoinhibithaustoriumdevelopmentPEN(Steinetal,)encodesanATPbindingcassette(ABC)transporterproteinthatwaspreviouslyannotatedaspleiotropicdrugresistanceliketransporter(PDRvandenBruleandSmart,)PriortoBghinfection,functionalPENGFPislocalizedtotheplasmamembraneandthenaccumulatesatthepenetrationsiteduringBghinfectionItalsoaccumulatesattheinfectionsitesofthecompatiblemildewfungusErysiphecichoracearumThefrequencyofBghhaustoriumformationandsubsequentHRalsoincreasesinpenmutants,andinthisrespect,theyaresimilartobothpenandpenmutants(Collinsetal,Steinetal,)Alsosimilartopenmutants,penmutantsallowincreasedhaustoriumformationbyPinfestansandaremoresusceptibletoPcucumerinaHowever,whiletheArabidopsismildewpathogenEcichoracearuminfectspenandpenmutants,itinducesextensivesalicylicacid–dependentleafchlorosisandfailstosporulateonpenmutants,possiblyduetotheintracellularaccumulationofthecargoofthePDRtransporterTHEMOLECULARBASISOFNONHOSTRESISTANCEWhatdoalloftheseresultstellusaboutnonhostresistancetomildewinArabidopsisFirst,itisadynamicprocessinvolvingorganellemovement,secretionprocesses,membranechanges,andaccumulationofthreePENproteinsattheinfectionsite(Assaadetal,Bhatetal,Lipkaetal,Steinetal,)Theseprocessesarepotentiallyactivatedbyinfectionpegpressure,chemicalsignalsfromthepathogen(pathogenassociatedmolecularpatternsPAMPsforexample,chitin,aspecificconstituentoffungalcellwalls),orsignalsresultingfromenzymaticdegradationofthehostcellRecentstudieshavehighlightedtheimportanceofhostreceptorsforPAMPsinbasalresistance(ZipfelandFelix,)Second,nonhostresistancehasacomplexgeneticbasiswiththreegenes,PEN,PEN,andPEN,identifiedsofarthatareinvolvedinbiosyntheticandsecretionprocessesthatcontrolprehaustorialresistancePENandPENprobablyactinthesamepathwaybecausepenisepistatictopeninatleastoneassay(Steinetal,)AplausiblemodelforPENisthatitisinvolvedinavesiclebasedsecretorypathway,probablyspecificfornonhostresistancetomildews(Shimadaetal,)ThecargoofPENanditsactivityinpapillaeareasyetundefinedPENislikelyinvolvedinperoxisomebasedbiosynthesisanddeliveryofoneormoreunidentifiedantifungalmetabolitestotheinfectionsiteAlthoughPENandPENoccurindifferentlocations,thefactthatpenisepistatictopenindicatesthatthecargoofthemembranelocalizedABCtransporterproteinPDRencodedbyPENcouldbetheproductofPENThisproducthasageneralCURRENTPERSPECTIVEESSAYThePlantCellactivityandaffectsinfectionofseveralfungalspeciesItschemicalnatureisunknown,althoughitispresumablyantifungalandacargomoleculeofPDRGivenitsbroadertoxiceffects,asimplebioassayapproachtoitspurificationshouldassistitsidentificationItisunlikelytobetheoneknownantimicrobialsmallmolecule,camelexin,synthesizedbyArabidopsis,sincethepadmutantsthataredeficientincamelexinbiosynthesisdonothaveapenphenotype(Steinetal,)BghinfectionsthatescapeprehaustorialresistanceinwildtypeandpenmutantplantsandprogresstoformhaustoriaaremoppedupbytheHRPosthaustorialresistanceisdependentongenesincludingPAD,EDS,andSAG(Lipkaetal,Steinetal,),whichareinvolvedinthebasalresistancepathwaysthatrestrictrampantdiseasedevelopmentduringcompatiblehost–pathogeninteractionsandalsoinsomeRgenepathwaysleadingtotheHR(Parkeretal,Feysetal,)Singlemutantsofpad,eds,andsaghavelittleeffectonthefrequencyofBghhaustoriaformationinArabidopsisHowever,wherehaustoriadoformtheHRislessfrequent,secondaryhyphalgrowthoccurs,andmicrocoloniesformInpensagpadtriplemutants,microcoloniesofBghwithoccasionalconidiophoresandmaturesporesdevelopthus,nonhostresistanceisalmostcompletelywhittledaway(Lipkaetal,)Thiseffectisevenmoreevidentafterinoculationwiththepeapowderymildew(Erysiphepisi)Whereaswildtypeplantsarecompletelyresistanttothisspecies,thetriplemutantsustainssporulatinginfectionssimilartothoseresultingfrominfectionwiththeArabidopsismildewGorontii(Lipkaetal,)AbreakdowninnonhostresistancewasalsoobservedinthepenedsdoublemutantinfectedwithEpisi(Steinetal,)Thus,nonhostresistanceisthesumofpreandposthaustorialresistancecomponentsTheobservationsofPENassociationwithperoxisomesthatmovetowardtheinfectionsiteandtheinvolvementofEDSinnonhostresistanceareconsistentwithanotherreportthatedsmutantstreatedwithanactincytoskeletoninhibitoraremoresusceptibletothewheatmildewpathogenBlumeriagraminisfsptritici(Yunetal,)Acytoskeletonbasedmechanismthatinvolvesvesiclemovementandexocytosisandfocusesabatteryofdefenseactivitiesattheinfectionsite(andpossiblytoemerginghaustoria)appearstobethebasisofnonhostresistanceTheinvolvementoftheHRandEDSPADSAG,necessaryforbothbasalresistanceandresistancemediatedbyoneoftwoclassesNBSLRRRproteins(Parkeretal,Feysetal,),indicatespossibleRproteinactivityinBgh–ArabidopsisnonhostinteractionsHowever,datacountertothisviewareprovidedbySteinetal()ManyArabidopsisNBSLRRRgenesalsorequireSGTaandRARforactivity(tabulatedinDoddsandSchwechheimer,),andSteinetal()reportthatwhereaspenedsdoublemutantsshowincreasedepiphyticgrowthafterinfectionwithBghandEpisiandsporulationofEpisi,penrarsgtatriplemutantsdonotSothequestionofwhetherRgenesarealsoinvolvedintheposthaustorialphaseofnonhostresistancerequiresfurtherexaminationTheunderstandingofnonhostresistancetoBghinArabidopsisissummarizedinFigureWHATARETHEREQUIREMENTSFORMILDEWADAPTATIONThearticleshighlightedherehavefocusedonthenatureofArabidopsisresistancetononadaptedmildewsHowever,whileBghfailstoinfectArabidopsis,itisadaptedtobarleyJusttheoppositeisthecasefortheArabidopsismildewEcichoracearumFromthepathogenperspective,whatisthemolecularbasisofpathogenadaptationtoitshostEvolutionofresistancetospecifictoxinssynthesizedbythehost,forexample,theproductsofthePENPENpathway,isonepossibilityAnothercouldinvolvebluntinghostbasalresistanceinducedbyPAMPperceptionLikebacterialpathogens(AbramovitchandMartin,CURRENTPERSPECTIVEESSAYFigureSchematicRepresentationofArabidopsisNonhostResistancetoBghAftergerminationofspores(Sp),formationofappressoria(Ap),andbreachingofthehostcellwall(CW)bythefungalpenetrationpeg(Pp),ofpenetrationsarestoppedincellwallextensionscalledpapillae(Pa)Thisresistanceisdependentonunidentifiedcargomolecules(greencircles)deliveredbyaPENmediatedvesicle(Ves)–basedsecretionsystemandonpostulatedtoxin(s)(darkbluecircles)synthesizedinperoxisomes(Per)inaPENmediatedpathwayanddeliveredbyaPENencodedABCtransporterintheplasmamembrane(PM)totheapoplastandpathogeninvasionsiteTheseeventsarecomponentsofprehaustorialresistanceTheactivationofthedynamicprehaustorialresistance,dependentoncytoskeletonfunction,maybeinducedbymechanicalorchemicalsignalsresultingfromcellwallpenetrationandorPAMPs(yellowcircles)producedbythepathogenanddetectedbyhostPAMPreceptors(PAMPR)Approximatelyofinfections(increasedtotoinpen,pen,andpensingleanddoublemutants)formhaustoria(H)andarestopped(posthaustorialresistance)bybasalresistancepossiblycontributedtobyPENpathwayproducts(darkbluecircles)andhypersensitivehostcelldeath(HR)dependentonEDS,SAG,andPADBecausethesegenesandtheHRarealsoassociatedwithgeneforgeneRgenes,itispossiblethatRproteinscouldalsofunctiontoperceiveeffectormolecules(lightbluecircles)secretedbyBghhaustoriaMarch),mildewsprobablysecretevirulenceeffectormoleculestobluntbasalresistance,includingbothpreandposthaustorialresistanceItisplausiblethatpathogeneffectorsarehostspecific,andthosefromBghcouldbenonfunctionalinArabidopsisduetofailureintheiruptakeandorabilitytointeractwithnonhostvirulencetargetsAnanalogyisthatakeythatopensonelockrarelyopensanotherNoBgheffectorshavebeendescribed,butevidenceforthemisprovidedbysequentialinoculationexperimentsinbarley,firstwithavirulentstrainandseveralhourslaterwithanavirulentstrainVirulentBghstrainsinducesusceptibilitytohostcellpenetrationandhaustoriumformationbythenormallyavirulentstrain(Lyngkjaeretal,),consistentwiththeideathatthefirststraindeliverseffectormoleculesthatinduceasusceptiblestateStudiesofgenesexpressedinrusthaustoriaarebeginningtoprovideinsightsintoproteinsdeliveredfromthesepathogenstoinfectedhostcells(Kemenetal,Catanzaritietal,),andintensivegenomicsstudiesofBghnowinprogresscouldidentifymildeweffectors(Bothetal,Zhangetal,)CharacterizationoffungalpathogeneffectorsandtheirhosttargetsisnowaresearchpriorityIncoevolvedhost–pathogeninteractions,effectors(Avrgeneproducts)arerecognizedbyhostRproteinsPathogensurvivaldependsonpolymorphismsinpathogenAvrgenesandhostRgenes(geneforgeneinteractions)sothatthepathogenisabletoreproduceinatleastsomeinteractionsSinglegenedifferencesbetweenformaespecialesofBgraminis(individualsofthesamepathogenspeciestaxonomicallyseparatedbytheirstrictadaptationtodifferentbutcloselyrelatedhostspecies)indicatethatAvrandRgeneequivalentsalsodeterminenonhostresistanceatthistaxonomiclevel(Tosa,)Similarly,singlepathogengenesthatencodesmallsecretedproteins,suchasPWL,determinethehostrangeofstrainsoftheblastfungusMagnaporthegriseaondifferentgrassspecies(Kangetal,Sweigardetal,)ThesedataagainsuggestRgene–

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