title: Localized iron supply triggers lateral root elongation in Arabidopsis by altering the AUX1-mediated auxin distribution.
abstract: Root system architecture depends on nutrient availability, which shapes primary and lateral root development in a nutrient-specific manner. To better understand how nutrient signals are integrated into root developmental programs, we investigated the morphological response of Arabidopsis thaliana roots to iron (Fe). Relative to a homogeneous supply, localized Fe supply in horizontally separated agar plates doubled lateral root length without having a differential effect on lateral root number. In the Fe uptake-defective mutant iron-regulated transporter1 (irt1), lateral root development was severely repressed, but a requirement for IRT1 could be circumvented by Fe application to shoots, indicating that symplastic Fe triggered the local elongation of lateral roots. The Fe-stimulated emergence of lateral root primordia and root cell elongation depended on the rootward auxin stream and was accompanied by a higher activity of the auxin reporter DR5-β-glucuronidase in lateral root apices. A crucial role of the auxin transporter AUXIN RESISTANT1 (AUX1) in Fe-triggered lateral root elongation was indicated by Fe-responsive AUX1 promoter activities in lateral root apices and by the failure of the aux1-T mutant to elongate lateral roots into Fe-enriched agar patches. We conclude that a local symplastic Fe gradient in lateral roots upregulates AUX1 to accumulate auxin in lateral root apices as a prerequisite for lateral root elongation.
authors.affiliation: Molecular Plant Nutrition, University of Hohenheim, D-70593 Stuttgart, Germany.
authors.forename: Ricardo F H
authors.initials: RF
authors.lastname: Giehl
authors.forename: Joni E
authors.initials: JE
authors.lastname: Lima
authors.forename: Nicolaus
authors.initials: N
authors.lastname: von Wirén
mesh_terms: D017360:Arabidopsis / Q000254:growth & development* / Q000378:metabolism*; D007210:Indoleacetic Acids / Q000378:metabolism*; D007501:Iron / Q000378:metabolism*; D018517:Plant Roots / Q000254:growth & development* / Q000378:metabolism*
chemical_list: D007210:Indoleacetic Acids; D007501:Iron