Root gravitropism and root hair development constitute coupled developmental responses regulated by auxin homeostasis in the Arabidopsis root apex

Authors

  • Stamatis Rigas,

    1. Department of Agricultural Biotechnology, Agricultural University of Athens, Athens, Greece
    Search for more papers by this author
    • These authors contributed equally to this work.
  • Franck Anicet Ditengou,

    1. Institute of Biology II, Faculty of Biology, Albert-Ludwigs-University of Freiburg, Freiburg, Germany
    Search for more papers by this author
    • These authors contributed equally to this work.
  • Karin Ljung,

    1. Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, Swedish University of Agricultural Sciences, Umeå, Sweden
    Search for more papers by this author
  • Gerasimos Daras,

    1. Department of Agricultural Biotechnology, Agricultural University of Athens, Athens, Greece
    Search for more papers by this author
  • Olaf Tietz,

    1. Institute of Biology II, Faculty of Biology, Albert-Ludwigs-University of Freiburg, Freiburg, Germany
    Search for more papers by this author
  • Klaus Palme,

    1. Institute of Biology II, Faculty of Biology, Albert-Ludwigs-University of Freiburg, Freiburg, Germany
    2. Centre of Biological Systems Analysis, Albert-Ludwigs-University of Freiburg, Freiburg, Germany
    3. Freiburg Institute of Advanced Sciences (FRIAS), Albert-Ludwigs-University of Freiburg, Freiburg, Germany
    4. Centre for Biological Signalling Studies (bioss), Albert-Ludwigs-University of Freiburg, Freiburg, Germany
    Search for more papers by this author
  • Polydefkis Hatzopoulos

    Corresponding author
    1. Department of Agricultural Biotechnology, Agricultural University of Athens, Athens, Greece
    • Author for correspondence:

      Polydefkis Hatzopoulos

      Tel: +30 210 5294321

      Email: phat@aua.gr

    Search for more papers by this author

Summary

  • Active polar transport establishes directional auxin flow and the generation of local auxin gradients implicated in plant responses and development. Auxin modulates gravitropism at the root tip and root hair morphogenesis at the differentiation zone.
  • Genetic and biochemical analyses provide evidence for defective basipetal auxin transport in trh1 roots.
  • The trh1, pin2, axr2 and aux1 mutants, and transgenic plants overexpressing PIN1, all showing impaired gravity response and root hair development, revealed ectopic PIN1 localization. The auxin antagonist hypaphorine blocked root hair elongation and caused moderate agravitropic root growth, also leading to PIN1 mislocalization. These results suggest that auxin imbalance leads to proximal and distal developmental defects in Arabidopsis root apex, associated with agravitropic root growth and root hair phenotype, respectively, providing evidence that these two auxin-regulated processes are coupled. Cell-specific subcellular localization of TRH1-YFP in stele and epidermis supports TRH1 engagement in auxin transport, and hence impaired function in trh1 causes dual defects of auxin imbalance.
  • The interplay between intrinsic cues determining root epidermal cell fate through the TTG/GL2 pathway and environmental cues including abiotic stresses modulates root hair morphogenesis. As a consequence of auxin imbalance in Arabidopsis root apex, ectopic PIN1 mislocalization could be a risk aversion mechanism to trigger root developmental responses ensuring root growth plasticity.

Ancillary