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J Exp Bot. 2015 Aug;66(16):5055-65. doi: 10.1093/jxb/erv177. Epub 2015 Apr 28.

Auxin-binding pocket of ABP1 is crucial for its gain-of-function cellular and developmental roles.

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Institute of Science and Technology (IST) Austria, 3400 Klosterneuburg, Austria Department of Plant Systems Biology, Flanders Institute for Biotechnology (VIB) and Department of Plant Biotechnology and Bioinformatics, Ghent University, BE-9052 Gent, Belgium.
Institute of Science and Technology (IST) Austria, 3400 Klosterneuburg, Austria.
VIB Department for Molecular Biomedical Research, VIB, 9052 Gent, Belgium.
Mendel Centre for Plant Genomics and Proteomics, Masaryk University, CEITEC MU, CZ-625 00 Brno, Czech Republic.
Institute of Experimental Botany of the Academy of Sciences of the Czech Republic, 165 02 Prague, Czech Republic.
Institute of Science and Technology (IST) Austria, 3400 Klosterneuburg, Austria


The plant hormone auxin is a key regulator of plant growth and development. Auxin levels are sensed and interpreted by distinct receptor systems that activate a broad range of cellular responses. The Auxin-Binding Protein1 (ABP1) that has been identified based on its ability to bind auxin with high affinity is a prime candidate for the extracellular receptor responsible for mediating a range of auxin effects, in particular, the fast non-transcriptional ones. Contradictory genetic studies suggested prominent or no importance of ABP1 in many developmental processes. However, how crucial the role of auxin binding to ABP1 is for its functions has not been addressed. Here, we show that the auxin-binding pocket of ABP1 is essential for its gain-of-function cellular and developmental roles. In total, 16 different abp1 mutants were prepared that possessed substitutions in the metal core or in the hydrophobic amino acids of the auxin-binding pocket as well as neutral mutations. Their analysis revealed that an intact auxin-binding pocket is a prerequisite for ABP1 to activate downstream components of the ABP1 signalling pathway, such as Rho of Plants (ROPs) and to mediate the clathrin association with membranes for endocytosis regulation. In planta analyses demonstrated the importance of the auxin binding pocket for all known ABP1-mediated postembryonic developmental processes, including morphology of leaf epidermal cells, root growth and root meristem activity, and vascular tissue differentiation. Taken together, these findings suggest that auxin binding to ABP1 is central to its function, supporting the role of ABP1 as auxin receptor.


ABP1; Auxin; Auxin binding; PIN proteins.; Site-directed mutagenesis

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