title: Disruptions in AUX1-dependent auxin influx alter hypocotyl phototropism in Arabidopsis.
abstract: Phototropism represents a differential growth response by which plant organs can respond adaptively to changes in the direction of incident light to optimize leaf/stem positioning for photosynthetic light capture and root growth orientation for water/nutrient acquisition. Studies over the past few years have identified a number of components in the signaling pathway(s) leading to development of phototropic curvatures in hypocotyls. These include the phototropin photoreceptors (phot1 and phot2) that perceive directional blue-light (BL) cues and then stimulate signaling, leading to relocalization of the plant hormone auxin, as well as the auxin response factor NPH4/ARF7 that responds to changes in local auxin concentrations to directly mediate expression of genes likely encoding proteins necessary for development of phototropic curvatures. While null mutations in NPH4/ARF7 condition an aphototropic response to unidirectional BL, seedlings carrying the same mutations recover BL-dependent phototropic responsiveness if co-irradiated with red light (RL) or pre-treated with either ethylene. In the present study, we identify second-site enhancer mutations in the nph4 background that abrogate these recovery responses. One of these mutations--map1 (modifier of arf7 phenotypes 1)--was found to represent a missense allele of AUX1--a gene encoding a high-affinity auxin influx carrier previously associated with a number of root responses. Pharmacological studies and analyses of additional aux1 mutants confirmed that AUX1 functions as a modulator of hypocotyl phototropism. Moreover, we have found that the strength of dependence of hypocotyl phototropism on AUX1-mediated auxin influx is directly related to the auxin responsiveness of the seedling in question.
authors.affiliation: Division of Biological Sciences, University of Missouri, Columbia, Missouri 65211, USA.
authors.forename: Bethany B
authors.initials: BB
authors.lastname: Stone
authors.forename: Emily L
authors.initials: EL
authors.lastname: Stowe-Evans
authors.forename: Reneé M
authors.initials: RM
authors.lastname: Harper
authors.forename: R Brandon
authors.initials: RB
authors.lastname: Celaya
authors.forename: Karin
authors.initials: K
authors.lastname: Ljung
authors.forename: Göran
authors.initials: G
authors.lastname: Sandberg
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Liscum
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D005030:Ethylenes / Q000494:pharmacology*; D018546:Hypocotyl / Q000502:physiology* / Q000528:radiation effects; D007210:Indoleacetic Acids / Q000378:metabolism* / Q000528:radiation effects; D008027:Light; D009154:Mutation; D020125:Mutation, Missense; D018524:Phototropism / Q000502:physiology* / Q000528:radiation effects; D036226:Seedlings / Q000502:physiology / Q000528:radiation effects; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology / Q000528:radiation effects
chemical_list: C503425:ARF7 protein, Arabidopsis; C100794:AUX1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D005030:Ethylenes; D007210:Indoleacetic Acids; D014157:Transcription Factors; C036216:ethylene