Microbial arms race: Ballistic "nematocysts" in dinoflagellates represent a new extreme in organelle complexity
Authors: Gavelis GS, Wakeman KC, Tillmann U, Ripken C, Mitarai S, Herranz M, Özbek S, Holstein T, Keeling PJ, Leander BS
CellNetworks People: Holstein Thomas
Journal: Sci Adv. 2017 Mar 31;3(3):e1602552. doi: 10.1126/sciadv.1602552.

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.