Research ArticleCELL BIOLOGY

Microbial arms race: Ballistic “nematocysts” in dinoflagellates represent a new extreme in organelle complexity

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Science Advances  31 Mar 2017:
Vol. 3, no. 3, e1602552
DOI: 10.1126/sciadv.1602552

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Abstract

We examine the origin of harpoon-like secretory organelles (nematocysts) in dinoflagellate protists. These ballistic organelles have been hypothesized to be homologous to similarly complex structures in animals (cnidarians); but we show, using structural, functional, and phylogenomic data, that nematocysts evolved independently in both lineages. We also recorded the first high-resolution videos of nematocyst discharge in dinoflagellates. Unexpectedly, our data suggest that different types of dinoflagellate nematocysts use two fundamentally different types of ballistic mechanisms: one type relies on a single pressurized capsule for propulsion, whereas the other type launches 11 to 15 projectiles from an arrangement similar to a Gatling gun. Despite their radical structural differences, these nematocysts share a single origin within dinoflagellates and both potentially use a contraction-based mechanism to generate ballistic force. The diversity of traits in dinoflagellate nematocysts demonstrates a stepwise route by which simple secretory structures diversified to yield elaborate subcellular weaponry.

Keywords
  • Convergent evolution
  • cnidocyst
  • extrusome
  • secretory
  • secretion
  • minicollagen
  • mucocyst
  • trichocyst
  • red queen

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