strigolactones VS Auxin.docx

strigolactones VS Auxin.docx

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strigolactonesVSAuxin

Agusti,J.,etal.（2011）."Strigolactonesignalingisrequiredforauxin-dependentstimulationofsecondarygrowthinplants."ProcNatlAcadSciUSA108（50）:

20242-20247.

Longdistancecell-to-cellcommunicationiscriticalforthedevelopmentofmulticellularorganisms.Inthisrespect,plantsareespeciallydemandingastheyconstantlyintegrateenvironmentalinputstoadjustgrowthprocessestodifferentconditions.Oneexampleisthickeningofshootsandroots,alsodesignatedassecondarygrowth.Secondarygrowthismediatedbythevascularcambium,astemcell-liketissuewhosecell-proliferatingactivityisregulatedoveralongdistancebytheplanthormoneauxin.Howauxinsignalingisintegratedatthelevelofcambiumcellsandhowcambiumactivityiscoordinatedwithothergrowthprocessesarelargelyunknown.Here,weprovidephysiological,genetic,andpharmacologicalevidencethatstrigolactones（SLs）,agroupofplanthormonesrecentlydescribedtobeinvolvedintherepressionofshootbranching,positivelyregulatecambialactivityandthatthisfunctionisconservedamongspecies.WeshowthatSLsignalinginthevascularcambiumitselfissufficientforcambiumstimulationandthatitinteractsstronglywiththeauxinsignalingpathway.Ourresultsprovideamodelofhowauxin-basedlong-distancesignalingistranslatedintocambiumactivityandsuggestthatSLsactasgeneralmodulatorsofplantgrowthformslinkingthecontrolofshootbranchingwiththethickeningofstemsandroots.

Beveridge,C.A.,etal.（2009）."Peahasitstendrilsinbranchingdiscoveriesspanningacenturyfromauxintostrigolactones."PlantPhysiol151（3）:

985-990.

Beveridge,C.A.andJ.Kyozuka（2010）."Newgenesinthestrigolactone-relatedshootbranchingpathway."CurrOpinPlantBiol13

（1）:

34-39.

Shootbranchingiscontrolledbytheformationandsubsequentoutgrowthofaxillarybudsintheaxilsofleaves.Axillarybudsareindeterminatestructuresthatcanbearrestedandawaitendogenousorenvironmentalcuesforoutgrowth.Amajorbreakthroughinthisareaofplantdevelopmenthasbeenthediscoverythataspecificgroupofterpenoidlactones,namedstrigolactones,candirectlyorindirectly,inhibitaxillarybudoutgrowth.Sincethatdiscovery,newbranchingmutantshavebeenidentifiedwithreducedstrigolactonelevelsorwhicharedefectiveinstrigolactoneregulationorresponse.DWARF27andDWARF14probablyactonstrigolactonebiosynthesisandstrigolactonemetabolismorsignaltransduction,respectively.Auxinsignalingmutantshavealsobeenusefulindemonstratingthatstrigolactonelevelsaremediatedbyaclassicalauxinsignaltransductionpathway.Thediscoveryandcharacterizationofthesemutantsisanimportantfirststeptowardunderstandingthemechanismsofstrigolactonebiosynthesisandsignalingandtheirimportanceinregulatingshootbranching.

Brewer,P.B.,etal.（2009）."StrigolactoneactsdownstreamofauxintoregulatebudoutgrowthinpeaandArabidopsis."PlantPhysiol150

（1）:

482-493.

Duringthelastcentury,twokeyhypotheseshavebeenproposedtoexplainapicaldominanceinplants:

auxinpromotestheproductionofasecondmessengerthatmovesupintobudstorepresstheiroutgrowth,andauxinsaturationinthesteminhibitsauxintransportfrombuds,therebyinhibitingbudoutgrowth.Therecentdiscoveryofstrigolactoneasthenovelshoot-branchinginhibitorallowedustotestitsmodeofactioninrelationtothesehypotheses.Wefoundthatexogenouslyappliedstrigolactoneinhibitedbudoutgrowthinpea（Pisumsativum）evenwhenauxinwasdepletedafterdecapitation.WealsofoundthatstrigolactoneapplicationreducedbranchinginArabidopsis（Arabidopsisthaliana）auxinresponsemutants,suggestingthatauxinmayactthroughstrigolactonestofacilitateapicaldominance.Moreover,strigolactoneapplicationtotinybudsofmutantordecapitatedpeaplantsrapidlystoppedoutgrowth,incontrasttoapplyingN-1-naphthylphthalamicacid（NPA）,anauxintransportinhibitor,whichsignificantlyslowedgrowthonlyafterseveraldays.WhereasstrigolactoneorNPAappliedtogrowingbudsreducedbudlength,onlyNPAblockedauxintransportinthebud.Wild-typeandstrigolactonebiosynthesismutantpeaandArabidopsisshootswerecapableofinstantlytransportingadditionalamountsofauxininexcessofendogenouslevels,contrarytopredictionsofauxintransportmodels.Thesedatasuggestthatstrigolactonedoesnotactprimarilybyaffectingauxintransportfrombuds.Rather,theprimaryrepressorofbudoutgrowthappearstobetheauxin-dependentproductionofstrigolactones.

Cazzonelli,C.I.,etal.（2009）."RegulationofcarotenoidcompositionandshootbranchinginArabidopsisbyachromatinmodifyinghistonemethyltransferase,SDG8."PlantCell21

（1）:

39-53.

Carotenoidpigmentsarecriticalforplantsurvival,andcarotenoidcompositionistunedtothedevelopmentalstage,tissue,andtoenvironmentalstimuli.WereportthecloningoftheCAROTENOIDCHLOROPLASTREGULATORY1（CCR1）gene.Theccr1mutanthasincreasedshootbranchingandalteredcarotenoidcomposition,namely,reducedluteininleavesandaccumulationofcis-carotenesindark-grownseedlings.TheCCR1genewaspreviouslyisolatedasEARLYFLOWERINGINSHORTDAYSandencodesahistonemethyltransferase（SETDOMAINGROUP8）thatmethylateshistoneH3onLys4and/or36（H3K4andH3K36）.ccr1plantsshowreducedtrimethyl-H3K4andincreaseddimethyl-H3K4surroundingtheCAROTENOIDISOMERASE（CRTISO）translationstartsite,whichcorrelateswithlowlevelsofCRTISOmRNA.Microarraysofccr1revealedthedownregulationof85genes,includingCRTISOandgenesassociatedwithsignalinganddevelopment,andupregulationofjust28genes.ThereductioninCRTISOtranscriptabundanceexplainsthealteredcarotenoidprofile.Thechangesinshootbranchingareadditivewithmoreaxillarybranchingmutants,butthealteredcarotenoidprofilemaypartiallyaffectshootbranching,potentiallybyperturbedbiosynthesisofthecarotenoidsubstratesofstrigolactones.TheseresultsareconsistentwithSDG8regulatingshootmeristemactivityandcarotenoidbiosynthesisbymodifyingthechromatinsurroundingkeygenes,includingCRTISO.Thus,theleveloflutein,themostabundantcarotenoidinhigherplantsthatiscriticalforphotosynthesisandphotoprotection,appearstoberegulatedbyachromatinmodifyingenzymeinArabidopsisthaliana.

Cheng,X.,etal.（2013）."Theinteractionbetweenstrigolactonesandotherplanthormonesintheregulationofplantdevelopment."FrontPlantSci4:

199.

Planthormonesaresmallmoleculesderivedfromvariousmetabolicpathwaysandareimportantregulatorsofplantdevelopment.Themostrecentlydiscoveredphytohormoneclasscomprisesthecarotenoid-derivedstrigolactones（SLs）.Foralongtimethesecompoundswereonlyknowntobesecretedintotherhizospherewheretheyactassignalingcompounds,butnowweknowtheyarealsoactiveasendogenousplanthormonesandtheyhavebeeninthespotlighteversince.TheinitialdiscoverythatSLsareinvolvedintheinhibitionofaxillarybudoutgrowth,initiatedamultitudeofotherstudiesshowingthatSLsalsoplayaroleindefiningrootarchitecture,secondarygrowth,hypocotylelongation,andseedgermination,mostlyininteractionwithotherhormones.Theircoordinatedactionenablestheplanttorespondinanappropriatemannertoenvironmentalfactorssuchastemperature,shading,daylength,andnutrientavailability.Here,wewillreviewthecurrentknowledgeonthecrosstalkbetweenSLsandotherplanthormones-suchasauxin,cytokinin,abscisicacid（ABA）,ethylene（ET）,andgibberellins（GA）-duringdifferentphysiologicalprocesses.Wewillfurthermoretakeabird'seyeviewofhowthishormonalcrosstalkenablesplantstorespondtotheireverchangingenvironments.

Crawford,S.,etal.（2010）."Strigolactonesenhancecompetitionbetweenshootbranchesbydampeningauxintransport."Development137（17）:

2905-2913.

Strigolactones（SLs）,ortheirderivatives,wererecentlydemonstratedtoactasendogenousshootbranchinginhibitors,buttheirbiosynthesisandmechanismofactionarepoorlyunderstood.HereweshowthatthebranchingphenotypeofmutantsintheArabidopsisP450familymember,MAX1,canbefullyrescuedbystrigolactoneaddition,suggestingthatMAX1actsinSLsynthesis.WedemonstratethatSLsmodulatepolarauxintransporttocontrolbranchingandthatboththesyntheticSLGR24andendogenousSLsynthesissignificantlyreducethebasipetaltransportofasecondbranch-regulatinghormone,auxin.Importantly,GR24inhibitsbranchingonlyinthepresenceofauxininthemainstem,andenhancescompetitionbetweentwobranchesonacommonstem.Together,theseresultssupporttwocurrenthypotheses:

thatauxinmovingdownthemainsteminhibitsbranchactivitybypreventingtheestablishmentofauxintransportoutofaxillarybranches;andthatSLsactbydampeningauxintransport,thusenhancingcompetitionbetweenbranches.

daCosta,C.T.,etal.（2013）."Whenstressanddevelopmentgohandinhand:

mainhormonalcontrolsofadventitiousrootingincuttings."FrontPlantSci4:

133.

Adventitiousrooting（AR）isamultifactorialresponseleadingtonewrootsatthebaseofstemcuttings,andtheestablishmentofacompleteandautonomousplant.ARhastwomainphases:

（a）induction,witharequirementforhigherauxinconcentration;（b）formation,inhibitedbyhighauxinandinwhichanatomicalchangestakeplace.Thefirststagesofthisprocessinseveredorgansnecessarilyincludewoundingandwaterstressresponseswhichmaytriggerhormonalchangesthatcontributetoreprogramtargetcellsthatarecompetenttorespondtorootingstimuli.A