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.
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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.).
The authors declare no competing financial interests.
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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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