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Degradome and Secretome of Pollination Drops of Ephedra

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Abstract

Although secreted proteins (a secretome) are known to occur in gymnosperm pollination drops, this study shows evidence for the presence of a protein degradome for the first time. A protein degradome is composed of protein and peptide fragments, a product of protein breakdown, whereas a secretome is composed of whole, secreted, and often biologically active extracellular proteins. Harvested Ephedra pollination drops from seven species were pooled either by collection date or, in the case of less abundant sample volumes, by species. Samples were processed by one of two methods: 1. gel electophoresis or by 2. liquid-liquid extraction, followed by chromatographic separation. Processed samples were trypsin-digested and analyzed with a Thermo Scientific LTQ Orbitrap Velos. On average, two-thirds of the detected and characterized proteins found in Ephedra spp. pollination drops were intracellular proteins, such as ubiquitin. The remaining third represent proteins known to be secreted, often involved in apoplastic processes such as defense and carbohydrate-modification, typical of known conifer pollination drop proteins. Characterized proteins detected in our comparative study of Ephedra spp drops ranged from 6 in E. monosperma to 20 in E. foeminea. We propose that the intracellular proteins detected are present as the result of nucellar tissue degeneration during pollination drop formation; previous proteomic investigations of pollination drops were in taxa that lack nucellar degeneration during drop formation Discovery of a degradome in pollination drops is novel and significant in that its presence has biological implications for pollination biology. We predict that degradomes in pollination drops are not restricted to Ephedra, but should also occur in species with nucellar tissue breakdown that coincides with pollination drop formation, such as in cycads and Ginkgo and some Pinaceae. Analysis of several collection dates of E. monosperma shows a large number of proteins that change over the course of the pollination drop secretion period, which suggests that variation in pollination drop contents over time may be important in the pollination biology of Ephdera.

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Acknowledgments

The authors would like to thank University of Victoria (UVic), UVic-Genome BC Proteomics Centre (UVic-GBCP), Genome Canada, and Genome BC for their support, as well as the Natural Sciences and Engineering Research Council of Canada (NSERC) for a Discovery Research Grant Program (PvA), and a Post-graduate Scholarship Program Grant (NAP). We acknowledge the expert assistance of B. Gowen (UVic), D. Smith (UVic) and Carol Parker (UVic-GBCP), as well as the invaluable assistance in sample collections from S. Ickert-Bond, C. Rydin, K. Bolinder, A. Rydberg, J. Jernstedt and I. Loera-Carrizales.

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  1. Centre for Forest Biology, Department of Biology, University of Victoria, Victoria, BC, V8W 3N2, Canada

    Patrick von Aderkas, Natalie Prior, Susannah Gagnon, Stefan Little & Alexandra Lunny

  2. Department of Plant Sciences, Mail Stop 1, University of California, Davis, One Shields Avenue, Davis, CA, 95616, USA

    Stefan Little

  3. UVic – Genome BC Proteomics Centre, University of Victoria, Victoria, BC, V8W 3N2, Canada

    Tyra Cross, Darryl Hardie & Christoph Borchers

  4. Department of Biochemistry, Biophysics & Molecular Biology, Iowa State University, Ames, IA, 50011, USA

    Robert Thornburg

  5. Department of Ecology, Environment and Plant Science, Stockholm University, SE-106 91, Stockholm, Sweden

    Chen Hou

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  1. Patrick von Aderkas
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von Aderkas, P., Prior, N., Gagnon, S. et al. Degradome and Secretome of Pollination Drops of Ephedra . Bot. Rev. 81, 1–27 (2015). https://doi.org/10.1007/s12229-014-9147-x

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