Inter-regulation of the unfolded protein response and auxin signaling

Authors

  • Yani Chen,

    1. Department of Energy Plant Research Laboratory, Department of Plant Biology, Michigan State University, East Lansing, MI, USA
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  • Kyaw Aung,

    1. Department of Energy Plant Research Laboratory, Department of Plant Biology, Michigan State University, East Lansing, MI, USA
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  • Jakub Rolčík,

    1. Laboratory of Growth Regulators, Faculty of Science, Palacký University and Institute of Experimental Botany AS CR, Olomouc, Czech Republic
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  • Kathryn Walicki,

    1. Department of Energy Plant Research Laboratory, Department of Plant Biology, Michigan State University, East Lansing, MI, USA
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  • Jiří Friml,

    1. Department of Functional Genomics and Proteomics, Central European Institute of Technology (CEITEC), Masaryk University, 62500, Brno, Czech Republic
    2. Institute of Science and Technology Austria (IST Austria), Klosterneuburg, Austria
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  • Federica Brandizzi

    Corresponding author
    1. Department of Energy Plant Research Laboratory, Department of Plant Biology, Michigan State University, East Lansing, MI, USA
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Summary

The unfolded protein response (UPR) is a signaling network triggered by overload of protein-folding demand in the endoplasmic reticulum (ER), a condition termed ER stress. The UPR is critical for growth and development; nonetheless, connections between the UPR and other cellular regulatory processes remain largely unknown. Here, we identify a link between the UPR and the phytohormone auxin, a master regulator of plant physiology. We show that ER stress triggers down-regulation of auxin receptors and transporters in Arabidopsis thaliana. We also demonstrate that an Arabidopsis mutant of a conserved ER stress sensor IRE1 exhibits defects in the auxin response and levels. These data not only support that the plant IRE1 is required for auxin homeostasis, they also reveal a species-specific feature of IRE1 in multicellular eukaryotes. Furthermore, by establishing that UPR activation is reduced in mutants of ER-localized auxin transporters, including PIN5, we define a long-neglected biological significance of ER-based auxin regulation. We further examine the functional relationship of IRE1 and PIN5 by showing that an ire1 pin5 triple mutant enhances defects of UPR activation and auxin homeostasis in ire1 or pin5. Our results imply that the plant UPR has evolved a hormone-dependent strategy for coordinating ER function with physiological processes.

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