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JournalofExperimentalBotany,,–160,2021
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Towardsthereplacementofwheat‘GreenRevolution’ genes
Stephen Pearce*
DepartmentofSoilandCropSciences,ColoradoStateUniversity,307UniversityAve,FortCollins,CO80523,USADownloadedfrom
*Correspondence:stephen.******@
Thisarticlecommentson:levelsofbioactiveGA,which,amongotheractions,promotes
TangT,BotwrightAcuñaT,-dwarfricevarietiescarryarecessive
-sensitiveRht18andgibberellin-loss-of-functionmutationinGA20ox2thatencodesacritical
insensitiveRht-D1bdwarfinggenesonvegetativeandre-GAbiosynthesisenzyme(Spielmeyeret al.,2002).Becausethis
,the
Botany72,445–,andthusitsimpactsoncell
elongation,aremostevidentinthesetissues.
FirstintroducedintowheatbreedingprogramsintheIncontrast,themostcommondwarfingallelesinwheatareRht-
1930s,theRht-B1bandRht-D1b‘GreenRevolution’al-B1bandRht-D1bthatencodeN-terminallytruncatedDELLA
lelesremainthemostwidelyuseddwarfinggenesinproteinsthatimpedeGAsignaling(Penget al.,1999).Thesevari-
today’‘Norin10’,releasedin
developinggrains,althoughtheseallelesalsoreducethe1950sandsubsequentlytransferredtoNormanBorlaugat
coleoptilelength,limitingtheirutilityindryenvironmentsCIMMYT,wheretheywereintegratedinto‘GreenRevolution’
,Tangvarietiesthatweredistributedworldwide(Hedden,2003).Itis
et al.(2021)showinaseriesofcomprehensivefieldtrialsremarkable,andatestamenttotheirvalueforwheatgrowers,
thatanalternativedwarfingallele,Rht18,confersare-that>80 yearsaftertheirfirstuseinformalbreedingprograms
ductioninheightnearlyidenticaltoRht-D1b,buthasnotheseallelesremainsuchanintegralcomponentofwheatvariety
%ofcultivarsinaworldwide
promiseofreplacingdwarfingallelesasastrategytoop-winterwheatpanelthatwerereleasedinthe21stcenturycarry
‘GreenRevolution’alleles(Würschumet al.,2017),
whileamongvarietiesbredfortheEasternandCentralUSA,the
Thevalueofbeingshortproportionis>90%(Guediraet al.,2010).
Despitetheirwidespreaddeployment,wheatvarieties
Inagriculture,semi-dwarfplantshaveseveralimportantad-carryingtheseallelesperformlesswellinwarm,dryen-
vantagesovertheirtaller,,shortervironmentssuchasinpartsofAustraliaandMediterranean
stemsposelesscompetitionforlimitedresources,meaningclimates,wherelimitedsoilmoisturerequiresthatseedsbe
thatagreaterproportionoftheplant’sphotosynthateispar--B1bandRht-D1bareexpressedin
titionedintospikeandgraindevelopment,improvingharvestthecoleoptile,thistissueisshorterinplantscarryingthese
indexandyieldinmostenvironments(Youssefianet al.,1992).alleles,reducingtherateofseedlingemergenceandnega-
Furthermore,geneticvariantsthatrestricttherateofcelltivelyimpactingcropestablishmentintheseenvironments
elongationinthestem,resultinginashorterplant,meanthat(Rebetzkeet al.,2014).Thesedrawbackshaveincentivized
growerscanfullyexploitthebenefitsoffertilizationandirriga-thesearchforalternativedwarfingallelesthatmightcom-
tionwithoutriskingtheircroplodgingduetoexcessive 
Althoughmanygenescontributetoplantheight,mostsemi-,re-
dwarfcropvarietiesgrowntodaycarryoneofasmallnumbersearchershaveidentifiedanumberofsuchallelesandhave
ofvariantsthatmodifythelevelsoractivityoftheplanthor-recentlymadeprogressincharacterizingtheirmodeofac-
monegibberellin(GA).Activelygrowingtissuescontainhightion(Gasperiniet al.,2012;Fordet al.,2018;Busset al.,
©TheAuthor(s).
ThisisanOpenAccessarticledistributedunderthetermsoftheCreativeCommonsAttributionLicense(/),
whichpermitsunrestrictedreuse,distribution,andreproductioninanymedium,providedtheoriginalworkisproperlycited.
158 |
2020).Tohelpevaluatethepotentialoftheseallelesforcomprehensiveanalysisofthegrowthdynamicsfromseed-
wheatbreeding,carefullydesignedfieldexperimentswilllingemergencetomaturity,Tanget 
,Tanget -D1bconferanear-identicalreductioninheightinboth
forthe‘GreenRevolution’,spikelength,stemdensity,
tillernumber,andahostofothertraitsthatarecoretargetsfor
,whiletheRht-
CharacterizingalternativedwarfingallelesD1ballelereducedcoleoptilelength,therewasnoshortening
TheRht18semi-dwarfallelehasadifferentmodeofaction
findingsarehighlyencouraging,andsuggestthatreplacing
fromRht-D1b,andisassociatedwithincreasedexpressionof
‘GreenRevolution’semi-dwarfingalleleswithRht18couldbe
GA2ox-A9,whichencodesaGA-inactivatingenzymethat
apromisingstrategytoimprovewheatproductivity,especially
reducesbioactiveGAlevels(Fordet al.,2018).ThroughaDownloadedfrom
Box 1. Mechanismstoreducewheatheight
geneswillimproveourunderstandingofthepathwayscontributingtoheight,facilitatesearchesforadditional
geneticdiversity,
genesthathavebeencharacterizedtodateplayimportantrolesinhormonebiosynthesisandsignaling
pathways,andconferreducedheightthroughdifferentmechanisms.
-B1bandRht-D1b‘GreenRevolution’allelesencodetruncatedDELLA
proteinsthatareinsensitivetoGA,
attheselociconferdifferentdegreesofheightreduction,includingtheseveredwarfingalleleRht-B1c.
,Rht18,Rht14,and
Rht24areprobablyallelic,andallthreeareassociatedwithincreasedexpressionofGA2ox-
removesGAprecursors,reducingbioactiveGAlevels,andthuscellelongation,
locus,Rht12,appearstoactinasimilarmanner,andisassociatedwithincreasedexpressionofGA2ox-A13.
,recessive,loss-of-functionallelesofGA20ox2,whichencodesaGA
biosynthesisenzyme,reducebioactiveGAlevels,andthuscellelongation,,
theseallelesareunlikelytobeselectedduetofunctionalredundancy,butcouldbeinducedwithreverse
geneticstoolssuchasTILLINGorCRISPR/Cas9.
,butplantscarryingthisalleleexhibitreducedsensitivity
tobrassinosteroids.
| 159
indryenvironmentswhereseedlingemergenceandcropes-semi-dwarfingallelesinricethat,becauseoffunctionalredun-
,areunlikelyotherwisetobeselected.
ofRht18amongglobalwheatvarietiesisincreasing,sug-Tohelpaddressoururgentneedtoincreasefoodproduc-
gestingthatthisalleleissubjecttoactiveselectioninbreedingtion,itisimperativethatbreederscanaccessbroadgenetic
programs(Würschumet al.,2017).diversitytofine-tunecriticaltraits(EshedandLippman,2019).
Togainabettersenseofthispotential,itwillbeimportantBysubjectinganexpandedsetofalternativedwarfingalleles
totesttheimpactsofRht18inlarge,replicatedyieldtrialstocomprehensivefieldphenotypingfollowingtheexampleof
usingindependentgeneticbackgroundsandamorediverseTanget al.,breederswillhavemoreoptionstodevelopoptimal
setofenvironments,
Thesetrialsmightincludeananalysisofbelow-groundtraitsapplicabletomosttraits,thisapproachislikelytobepar-
byleveraginghigh-throughputrootimagingorremotesensingticularlyvaluableforplantheightconsideringitshistorically
technologies(Atkinsonet al.,2019;Yanget al.,2020).
Downloadedfrom
GAalsopromotesrootcellelongation(Baiet al.,2013),itwillgenomicsanalysesandtraditionalfield-basedphenotypingand
beinterestingtocomparetheimpactofdifferentdwarfingal-selection,wemaysoonseetheemergenceofmoresemi-dwarf
lelesonrootlengthandarchitecture,particularlyasthefre-wheatvarietiescarryingagreaterdiversityofreducedheight
quencyandseverityofdroughteventsarelikelytoincreaseingenes,eitherincombinationwith—orasreplacementsfor—
‘GreenRevolution’alleles.
CustomizingwheatheightfordiverseAcknowledgements
environmentsIamgratefultoDrScottHaleyforhelpfulcommentsandinputonan
Perhapsmostimportantly,thisstudyprovidesfurthersup-earlierdraftofthismanuscript.
portforthehypothesisthatthereisnothingintrinsically
uniqueaboutthe‘GreenRevolution’semi-dwarfingallelesKeywords:Dwarfing,gibberellin,GreenRevolution,Rht,wheat.
height,regardlessofmechanism,willincreasephotosynthate
excellentcandidateallelesamongthosealreadydescribedReferences
thatmightsimilarlybesubjectedtoexpandedfieldtestingtoAtkinson JA,Pound MP,Bennett MJ,Wells 
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(Box1).TheseincludeindependentGA-sensitiveallelessuch
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asRht12(Sunet al.,2019;Busset al.,2020)andRht25(Mowithseedlingroottraitsandtheircorrelationwithplantheightinwheat.
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Inadditiontocharacterizingknowndwarfingloci,wheatre-Buss W,Ford BA,Foo E,Schnippenkoetter W,Borrill P,Brooks B,
Ashton AR,Chandler PM,Spielmeyer 
searchersnowhaveaccesstotoolssuchasCRISPR/Cas9[clus-determinethecausalroleofGA2oxidaseA13inRht12dwarfismofwheat.
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2019;Busset al.,2020).Therefore,itmaybepossibletode-isduetoincreasedGA2-oxidaseA9expressionandreducedGAcontent.
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