title: Auxin controls gravitropic setpoint angle in higher plant lateral branches.
abstract: Lateral branches in higher plants are often maintained at specific angles with respect to gravity, a quantity known as the gravitropic setpoint angle (GSA) [1]. Despite the importance of GSA control as a fundamental determinant of plant form, the mechanisms underlying gravity-dependent angled growth are not known. Here we address the central questions of how stable isotropic growth of a branch at a nonvertical angle is maintained and of how the value of that angle is set. We show that nonvertical lateral root and shoot branches are distinguished from the primary axis by the existence of an auxin-dependent antigravitropic offset mechanism that operates in tension with gravitropic response to generate angled isotropic growth. Further, we show that the GSA of lateral roots and shoots is dependent upon the magnitude of the antigravitropic offset component. Finally, we show that auxin specifies GSA values dynamically throughout development by regulating the magnitude of the antigravitropic offset component via TIR1/AFB-Aux/IAA-ARF-dependent auxin signaling within the gravity-sensing cells of the root and shoot. The involvement of auxin in controlling GSA is yet another example of auxin's remarkable capacity to self-organize in development [2] and provides a conceptual framework for understanding the specification of GSA throughout nature.
authors.affiliation: Centre for Plant Sciences, University of Leeds, Leeds, LS2 9JT, UK.
authors.forename: Suruchi
authors.initials: S
authors.lastname: Roychoudhry
authors.forename: Marta
authors.initials: M
authors.lastname: Del Bianco
authors.forename: Martin
authors.initials: M
authors.lastname: Kieffer
authors.forename: Stefan
authors.initials: S
authors.lastname: Kepinski
mesh_terms: D017360:Arabidopsis / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D044783:F-Box Proteins / Q000378:metabolism; D018466:Gravity Sensing / Q000502:physiology*; D007210:Indoleacetic Acids / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D018517:Plant Roots / Q000254:growth & development; D018520:Plant Shoots / Q000254:growth & development; D030821:Plants, Genetically Modified; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology
chemical_list: C559638:AFB4 protein, Arabidopsis; C516178:AFB5 protein, Arabidopsis; D029681:Arabidopsis Proteins; D044783:F-Box Proteins; D007210:Indoleacetic Acids; D011956:Receptors, Cell Surface; C501405:TIR1 protein, Arabidopsis