title: Auxin influx carriers stabilize phyllotactic patterning.
abstract: One of the most striking features of plant architecture is the regular arrangement of leaves and flowers around the stem, known as phyllotaxis. Peaks in concentration of the plant hormone auxin, generated by the polar localization of the PIN1 auxin efflux carrier, provide the instructive signal for primordium initiation. This mechanism generates the spacing between neighboring primordia, which results in regular phyllotaxis. Studies of the role of auxin transport in phyllotactic patterning have focused on PIN1-mediated efflux. Recent computer simulations indicate an additional role for transporter-mediated auxin uptake. Mutations in the AUX1 auxin influx carrier have not, however, been reported to cause an aerial phenotype. Here, we study the role of AUX1 and its paralogs LAX1, LAX2, and LAX3. Analysis of the quadruple mutant reveals irregular divergence angles between successive primordia. A highly unusual aspect of the phenotype is the occurrence of clusters of primordia, in violation of classical theory. At the molecular level, the sharp peaks in auxin levels and coordinated PIN polarization are reduced or lost. In addition, the increased penetrance of the phenotype under short-day conditions suggests that the AUX LAX transporters act to buffer the PIN-mediated patterning mechanism against environmental or developmental influences.
authors.affiliation: Institute of Plant Sciences, University of Bern, Altenbergrain 21, 3013 Bern, Switzerland.
authors.forename: Katherine
authors.initials: K
authors.lastname: Bainbridge
authors.forename: Soazig
authors.initials: S
authors.lastname: Guyomarc'h
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Bayer
authors.forename: Ranjan
authors.initials: R
authors.lastname: Swarup
authors.forename: Malcolm
authors.initials: M
authors.lastname: Bennett
authors.forename: Therese
authors.initials: T
authors.lastname: Mandel
authors.forename: Cris
authors.initials: C
authors.lastname: Kuhlemeier
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D019521:Body Patterning; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D017931:DNA Primers; D018506:Gene Expression Regulation, Plant; D007210:Indoleacetic Acids / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism; D018547:Plant Stems / Q000033:anatomy & histology* / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: C100794:AUX1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D017931:DNA Primers; D007210:Indoleacetic Acids; D026901:Membrane Transport Proteins; C116363:PIN1 protein, Arabidopsis; D012333:RNA, Messenger