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A symbiotic SNARE protein generated by alternative termination of transcription

Nature Plants volume 2, Article number: 15197 (2016) Cite this article

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Abstract

Many microbes interact with their hosts across a membrane interface, which is often distinct from existing membranes. Understanding how this interface acquires its identity has significant implications. In the symbiosis between legumes and rhizobia, the symbiosome encases the intracellular bacteria and receives host secretory proteins important for bacterial development. We show that the Medicago truncatula SYNTAXIN 132 (SYP132) gene undergoes alternative cleavage and polyadenylation during transcription, giving rise to two target-membrane soluble NSF attachment protein receptor (t-SNARE) isoforms. One of these isoforms, SYP132A, is induced during the symbiosis, is able to localize to the peribacteroid membrane, and is required for the maturation of symbiosomes into functional forms. The second isoform, SYP132C, has important functions unrelated to symbiosis. The SYP132A sequence is broadly found in flowering plants that form arbuscular mycorrhizal symbiosis, an ancestral mutualism between soil fungi and most land plants. SYP132A silencing severely inhibited arbuscule colonization, indicating that SYP132A is an ancient factor specifying plant–microbe interfaces.

In biotic interactions, how organisms communicate across species boundaries is a central question. In intimate host–microbe interactions, the interface is often defined by a specialized membrane. Since this interfacial membrane frequently originates from a pre-existing membranous compartment (such as the plasma membrane) of the host cell, one major challenge to understanding host–microbe communication is to elucidate how a new, specialized membrane is distinguished from its progenitor. In the legume–rhizobia symbiosis, intracellular bacteroids are individually surrounded by a peribacteroid membrane, which is derived from the host plasma membrane and functions as a destination for protein secretion from the host1,2. Thus, the host cell must clearly define the peribacteroid membrane to ensure the proper targeting of secretory vesicles. In plants, syntaxin proteins target membrane-localized receptors (also known as t-SNARE) for secretory vesicles3. Previously, we have found that a transcript annotated as SYNTAXIN 132 (or SYP132) is co-expressed with DNF1, which encodes a component of the nodule-specific signal peptidase2. In Medicago truncatula nodules, SYP132 protein has been shown to localize to both the plasma and the peribacteroid membranes4–6. How secretory vesicles distinguish these two membranes is currently unknown.

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Figure 1: The nodule-specific SYP132A is produced through alternative cleavage and polyadenylation.
Figure 2: Differential subcellular localization of SYP132 protein isoforms.
Figure 3: SYP132A is required for the maturation of symbiosomes.
Figure 4: SYP132A is necessary for arbuscular mycorrhizal symbiosis.
Figure 5: Biogenesis of SYP13 proteins in higher plants.

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Acknowledgements

We are grateful to D. Hebert, S. Hazen and T. Baskin (University of Massachusetts, Amherst) for access to instruments and C. Haney (University of British Columbia, Vancouver) for modifying the pHellsGate8 vector with the mCherry reporter. We thank F. M. Ausubel (Massachusetts General Hospital, Boston), J. S. Griffitts (Brigham Young University, Provo), S. R. Long (Stanford University, Stanford) and A. Caicedo (University of Massachusetts, Amherst) for insightful discussions of the manuscript. This work was supported by the University of Massachusetts Amherst and USDA Hatch Grant (to D.W.).

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  1. Huairong Pan and Onur Oztas: These authors contributed equally to this work.

Authors and Affiliations

  1. Department of Biochemistry and Molecular Biology, University of Massachusetts Amherst, 01003, Massachusetts, USA

    Huairong Pan, Onur Oztas, Christina Stonoha & Dong Wang

  2. Molecular and Cellular Biology Graduate Program, University of Massachusetts Amherst, 01003, Massachusetts, USA

    Onur Oztas

  3. National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, 200032, China

    Xiaowei Zhang & Ertao Wang

  4. Laboratory of Plant Genetics and Molecular Evolution, School of Life Sciences, Nanjing University, Nanjing, 210093, China

    Xiaoyi Wu & Bin Wang

  5. Plant Biology Graduate Program, University of Massachusetts Amherst, 01003, Massachusetts, USA

    Christina Stonoha

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  1. Huairong Pan
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Contributions

D.W., H.P., O.O., E.W. and B.W. designed the research; H.P., O.O., X.W. and X.Z. performed the experiments; D.W., C.S., B.W., X.W. performed alignments and evolutionary analysis; D.W., H.P., O.O. and C.S. wrote the manuscript.

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Correspondence to Dong Wang.

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Pan, H., Oztas, O., Zhang, X. et al. A symbiotic SNARE protein generated by alternative termination of transcription. Nature Plants 2, 15197 (2016). https://doi.org/10.1038/nplants.2015.197

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