Seeonlineversionforlegendandreferences.1172Cell136,March20,2009©2009ElsevierInc.DOI10.1016/j.cell.2009.03.009SnapShot:AuxinSignalingandTransportDolfWeijers1andJirˇíFriml21WageningenUniversity,6703HA,Wageningen,TheNetherlands;2VIBandGhentUniversity,9052Ghent,Belgium1172.e1Cell136,March20,2009©2009ElsevierInc.DOI10.1016/j.cell.2009.03.009SnapShot:AuxinSignalingandTransportDolfWeijers1andJirˇíFriml21WageningenUniversity,6703HA,Wageningen,TheNetherlands;2VIBandGhentUniversity,9052Gent,BelgiumAuxincontrolsnumerousprocessesinplantsbydeterminingtherateofcelldivisionandexpansion,oracell’sdevelopmentalfate.Thedifferentialdistributionofauxinwithinplanttissuesdeterminesthespatio-temporalaspectofauxinsignalingatthetissuelevel.Auxinactionispredominantlymediatedbyanuclearsignalingpathwaythatcontrolstheexpressionofauxin-responsivegenes.Themajorformofauxinisindole-3-aceticacid(IAA).(1)IntracellularIAAissynthesizedfromindolethroughtryptophanorthroughotherintermediates.TheYUCMonooxygenasescatalyzethesynthesisoftheIAAprecursorindoleacetamide.TheTAA1aminotransferaseconvertsTrpintotheIAAprecursorIPA.ExpressionofYUCandTAA1genesisinfluencedbyinternalandenvironmentalsignals.ThepooloffreeIAAisactivelycontrolledbycatabolichomeostasisthroughconjugationofIAAtosugars(byUGT84B1),methyl(byIAMT1),oraminoacids(byenzymesoftheGH3family).Althoughsomeoftheseconjugatesareinactive,othersmayhaveauxinicactivity.(2)Themajornaturallyoccurringauxin(IAA)canfreelydiffuseacrosstheplasmamembraneinitsprotonated(IAAH)formthatoccursintherelativelyacidiccellwall(pH5.5).AuxinentryintothecellisadditionallyfacilitatedbytheAUX1/LAXpermeases.Inthecellinterior(pHis7.0)IAAbecomesnegativelycharged(IAA−)andcon-sequentlybecomestrappedinthecell.(3)IAA−canleavethecellthroughPGP1/19ABCtransporters,whichtypicallyhavenonpolarlocalization,andbyPINproteins,whicharetypicallypolar.ThesubcellularlocalizationofPINproteinsdeterminesthedirectionofintercellularauxintransport.Thismechanismallowseachtransportingcelltoinfluencehowm...
