title: AUXIN UP-REGULATED F-BOX PROTEIN1 regulates the cross talk between auxin transport and cytokinin signaling during plant root growth.
abstract: Plant root development is mediated by the concerted action of the auxin and cytokinin phytohormones, with cytokinin serving as an antagonist of auxin transport. Here, we identify the AUXIN UP-REGULATED F-BOX PROTEIN1 (AUF1) and its potential paralog AUF2 as important positive modifiers of root elongation that tether auxin movements to cytokinin signaling in Arabidopsis (Arabidopsis thaliana). The AUF1 mRNA level in roots is strongly up-regulated by auxin but not by other phytohormones. Whereas the auf1 single and auf1 auf2 double mutant roots grow normally without exogenous auxin and respond similarly to the wild type upon auxin application, their growth is hypersensitive to auxin transport inhibitors, with the mutant roots also having reduced basipetal and acropetal auxin transport. The effects of auf1 on auxin movements may be mediated in part by the misexpression of several PIN-FORMED (PIN) auxin efflux proteins, which for PIN2 reduces its abundance on the plasma membrane of root cells. auf1 roots are also hypersensitive to cytokinin and have increased expression of several components of cytokinin signaling. Kinematic analyses of root growth and localization of the cyclin B mitotic marker showed that AUF1 does not affect root cell division but promotes cytokinin-mediated cell expansion in the elongation/differentiation zone. Epistasis analyses implicate the cytokinin regulator ARR1 or its effector(s) as the target of the SKP1-Cullin1-F Box (SCF) ubiquitin ligases assembled with AUF1/2. Given the wide distribution of AUF1/2-type proteins among land plants, we propose that SCF(AUF1/2) provides additional cross talk between auxin and cytokinin, which modifies auxin distribution and ultimately root elongation.
authors.affiliation: Department of Genetics, University of Wisconsin, Madison, Wisconsin 53706-1574, USA.
authors.forename: Xiaohua
authors.initials: X
authors.lastname: Zheng
authors.forename: Nathan D
authors.initials: ND
authors.lastname: Miller
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Lewis
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Christians
authors.forename: Kwang-Hee
authors.initials: KH
authors.lastname: Lee
authors.forename: Gloria K
authors.initials: GK
authors.lastname: Muday
authors.forename: Edgar P
authors.initials: EP
authors.lastname: Spalding
authors.forename: Richard D
authors.initials: RD
authors.lastname: Vierstra
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000166:cytology / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D003583:Cytokinins / Q000378:metabolism* / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism; D004843:Epistasis, Genetic / Q000187:drug effects; D044783:F-Box Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant / Q000235:genetics; D023281:Genomics; D007210:Indoleacetic Acids / Q000378:metabolism* / Q000494:pharmacology; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D018517:Plant Roots / Q000166:cytology / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D059386:Reverse Genetics; D015398:Signal Transduction / Q000187:drug effects; D014157:Transcription Factors / Q000378:metabolism
chemical_list: C117138:ARR1 protein, Arabidopsis; C568261:AUF1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D003583:Cytokinins; D004268:DNA-Binding Proteins; D044783:F-Box Proteins; D007210:Indoleacetic Acids; D026901:Membrane Transport Proteins; C116363:PIN1 protein, Arabidopsis; D014157:Transcription Factors