The Syntaxins SYP31 and SYP81 Control ER–Golgi Trafficking in the Plant Secretory Pathway

Authors

  • Julia Bubeck,

    1. Department of Cell Biology, Heidelberg Institute for Plant Sciences, University of Heidelberg, Im Neuenheimer Feld 230, 69120 Heidelberg, Germany
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    • These authors contributed equally to this work.

  • David Scheuring,

    1. Department of Cell Biology, Heidelberg Institute for Plant Sciences, University of Heidelberg, Im Neuenheimer Feld 230, 69120 Heidelberg, Germany
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    • These authors contributed equally to this work.

  • Eric Hummel,

    1. Department of Cell Biology, Heidelberg Institute for Plant Sciences, University of Heidelberg, Im Neuenheimer Feld 230, 69120 Heidelberg, Germany
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  • Markus Langhans,

    1. Department of Cell Biology, Heidelberg Institute for Plant Sciences, University of Heidelberg, Im Neuenheimer Feld 230, 69120 Heidelberg, Germany
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  • Corrado Viotti,

    1. Department of Cell Biology, Heidelberg Institute for Plant Sciences, University of Heidelberg, Im Neuenheimer Feld 230, 69120 Heidelberg, Germany
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  • Ombretta Foresti,

    1. Center for Plant Sciences, School of Biology, University of Leeds, LS2 9JT, UK
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  • Jürgen Denecke,

    1. Center for Plant Sciences, School of Biology, University of Leeds, LS2 9JT, UK
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  • David K. Banfield,

    1. Department of Biology, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
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  • David G. Robinson

    Corresponding author
    1. Department of Cell Biology, Heidelberg Institute for Plant Sciences, University of Heidelberg, Im Neuenheimer Feld 230, 69120 Heidelberg, Germany
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*David G. Robinson, david.robinson@urz.uni-heidelberg.de

Abstract

Overexpression of the Golgi and endoplasmic reticulum (ER) syntaxins SYP31 and SYP81 strongly inhibits constitutive secretion. By comparing the secreted reporter α-amylase with the ER-retained reporter α-amylase-HDEL, it was concluded that SYP81 overexpression inhibits both retrograde and anterograde transport, while SYP31 overexpression mainly affected anterograde transport. Of the other interacting SNAREs investigated, only the overexpression of MEMB11 led to an inhibition of protein secretion. Although the position of a fluorescent tag does not influence the correct localization of the fusion protein, only N-terminal-tagged SYP31 retained the ability of the untagged SNARE to inhibit transport. C-terminal-tagged SYP31 failed to exhibit this effect. Overexpression of both wild-type and N-terminal-tagged syntaxins caused standard Golgi marker proteins to redistribute into the ER. Nevertheless, green fluorescent protein (GFP)–SYP31 was still visible as fluorescent punctae, which, unlike SYP31–GFP, were resistant to brefeldin A treatment. Immunogold electron microscopy showed that endogenous SYP81 is not only present at the ER but also in the cis Golgi, indicating that this syntaxin cycles between these two organelles. However, when expressed at non-inhibitory levels, YFP–SYP81 was seen to locate principally to subdomains of the ER. These punctate structures were physically separated from the Golgi, suggesting that they might possibly reflect the position of ER import sites.

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