title: Small acidic protein 1 and SCFTIR1ubiquitin proteasome pathway act in concert to induce 2,4-dichlorophenoxyacetic acid-mediated alteration of actin in Arabidopsis roots.
abstract: 2,4-Dichlorophenoxyacetic acid (2,4-D), a functional analogue of auxin, is used as an exogenous source of auxin as it evokes physiological responses like the endogenous auxin, indole-3-acetic acid (IAA). Previous molecular analyses of the auxin response pathway revealed that IAA and 2,4-D share a common mode of action to elicit downstream physiological responses. However, recent findings with 2,4-D-specific mutants suggested that 2,4-D and IAA might also use distinct pathways to modulate root growth in Arabidopsis. Using genetic and cellular approaches, we demonstrate that the distinct effects of 2,4-D and IAA on actin filament organization partly dictate the differential responses of roots to these two auxin analogues. 2,4-D but not IAA altered the actin structure in long-term and short-term assays. Analysis of the 2,4-D-specific mutant aar1-1 revealed that small acidic protein 1 (SMAP1) functions positively to facilitate the 2,4-D-induced depolymerization of actin. The ubiquitin proteasome mutants tir1-1 and axr1-12, which show enhanced resistance to 2,4-D compared with IAA for inhibition of root growth, were also found to have less disrupted actin filament networks after 2,4-D exposure. Consistently, a chemical inhibitor of the ubiquitin proteasome pathway mitigated the disrupting effects of 2,4-D on the organization of actin filaments. Roots of the double mutant aar1-1 tir1-1 also showed enhanced resistance to 2,4-D-induced inhibition of root growth and actin degradation compared with their respective parental lines. Collectively, these results suggest that the effects of 2,4-D on actin filament organization and root growth are mediated through synergistic interactions between SMAP1 and SCFTIR1ubiquitin proteasome components.
authors.affiliation: Cryobiofrontier Research Center, Faculty of Agriculture, Iwate University, Morioka, 020-8550, Japan.
authors.forename: Maho
authors.initials: M
authors.lastname: Takahashi
authors.affiliation: Cryobiofrontier Research Center, Faculty of Agriculture, Iwate University, Morioka, 020-8550, Japan.
authors.forename: Kana
authors.initials: K
authors.lastname: Umetsu
authors.affiliation: Department of Radiation-Applied Biology, Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology (QST), Takasaki, 370-1292, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Oono
authors.affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, 277-8562, Japan.
authors.forename: Takumi
authors.initials: T
authors.lastname: Higaki
authors.affiliation: Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, OK, 73401, USA.
authors.forename: Elison B
authors.initials: EB
authors.lastname: Blancaflor
authors.affiliation: Cryobiofrontier Research Center, Faculty of Agriculture, Iwate University, Morioka, 020-8550, Japan.|Department of Plant Bio Sciences, Faculty of Agriculture, Iwate University, Morioka, 020-8550, Japan.
authors.forename: Abidur
authors.initials: A
authors.lastname: Rahman
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D000199:Actins; D029681:Arabidopsis Proteins; C514677:SMAP1 protein, Arabidopsis; D025801:Ubiquitin; D015084:2,4-Dichlorophenoxyacetic Acid
keywords: 
  Arabidopsis thaliana
  ; Actin; Auxin; Root growth; SMAP1; auxin signaling; ubiquitin proteasome pathway