A small acidic protein 1 (SMAP1) mediates responses of the Arabidopsis root to the synthetic auxin 2,4-dichlorophenoxyacetic acid

Authors

  • Abidur Rahman,

    1. Research Group for Plant Resource Application, Japan Atomic Energy Research Institute, Takasaki 370-1292, Japan,
    2. Biology Department, University of Massachusetts, Amherst, MA 01003, USA,
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  • Akari Nakasone,

    1. Research Group for Plant Resource Application, Japan Atomic Energy Research Institute, Takasaki 370-1292, Japan,
    2. Institute of Molecular and Cellular Biosciences, The University of Tokyo, Tokyo 113-0032, Japan
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    • Present address: Radiation-Applied Biology Division, Japan Atomic Energy Agency, Takasaki, 370-1292, Japan.

  • Tory Chhun,

    1. Center for Supports to Research and Education Activities Isotope Division, Kobe University, Kobe 657-8501, Japan, and
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  • Chiharu Ooura,

    1. Advanced Science Research Center, Japan Atomic Energy Research Institute, Takasaki 370-1292, Japan,
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    • Present address: Methodology Research Group, Research Development Division, Fujirebio Inc., Hachioji, Tokyo 192-0031, Japan.

  • Kamal Kanti Biswas,

    1. Research Group for Plant Resource Application, Japan Atomic Energy Research Institute, Takasaki 370-1292, Japan,
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    • Present address: Department of Environmental Life Sciences, Tohoku University, Sendai 980-8577, Japan.

  • Hirofumi Uchimiya,

    1. Advanced Science Research Center, Japan Atomic Energy Research Institute, Takasaki 370-1292, Japan,
    2. Institute of Molecular and Cellular Biosciences, The University of Tokyo, Tokyo 113-0032, Japan
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  • Seiji Tsurumi,

    1. Center for Supports to Research and Education Activities Isotope Division, Kobe University, Kobe 657-8501, Japan, and
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  • Tobias I. Baskin,

    1. Biology Department, University of Massachusetts, Amherst, MA 01003, USA,
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  • Atsushi Tanaka,

    1. Research Group for Plant Resource Application, Japan Atomic Energy Research Institute, Takasaki 370-1292, Japan,
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    • Present address: Radiation-Applied Biology Division, Japan Atomic Energy Agency, Takasaki, 370-1292, Japan.

  • Yutaka Oono

    Corresponding author
    1. Research Group for Plant Resource Application, Japan Atomic Energy Research Institute, Takasaki 370-1292, Japan,
    2. Advanced Science Research Center, Japan Atomic Energy Research Institute, Takasaki 370-1292, Japan,
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    • Present address: Radiation-Applied Biology Division, Japan Atomic Energy Agency, Takasaki, 370-1292, Japan.


Summary

2,4-dichlorophenoxyacetic acid (2,4-D), a chemical analogue of indole-3-acetic acid (IAA), is widely used as a growth regulator and exogenous source of auxin. Because 2,4-D evokes physiological and molecular responses similar to those evoked by IAA, it is believed that they share a common response pathway. Here, we show that a mutant, antiauxin resistant1 (aar1), identified in a screen for resistance to the anti-auxin p-chlorophenoxy-isobutyric acid (PCIB), is resistant to 2,4-D, yet nevertheless responds like the wild-type to IAA and 1-napthaleneacetic acid in root elongation and lateral root induction assays. That the aar1 mutation alters 2,4-D responsiveness specifically was confirmed by analysis of GUS expression in the DR5:GUS and HS:AXR3NT-GUS backgrounds, as well as by real-time PCR quantification of IAA11 expression. The two characterized aar1 alleles both harbor multi-gene deletions; however, 2,4-D responsiveness was restored by transformation with one of the genes missing in both alleles, and the 2,4-D-resistant phenotype was reproduced by decreasing the expression of the same gene in the wild-type using an RNAi construct. The gene encodes a small, acidic protein (SMAP1) with unknown function and present in plants, animals and invertebrates but not in fungi or prokaryotes. Taken together, these results suggest that SMAP1 is a regulatory component that mediates responses to 2,4-D, and that responses to 2,4-D and IAA are partially distinct.

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