Gliding motility of the diatom Craspedostauros australis correlates with the intracellular movement of raphid-specific myosins

Raphid diatoms are one of the few eukaryotes capable of gliding motility, which is remarkably fast and allows for quasi-instantaneous directional reversals. Besides other mechanistic models, it has been suggested that an actomyosin system provides the force for diatom gliding. However, in vivo data on the dynamics of actin and myosin in diatoms are lacking. In this study we demonstrate that the raphe-associated actin bundles required for diatom movement do not exhibit a directional turnover of subunits and thus their dynamics do not contribute directly to force generation. By phylogenomic analysis we identified four raphid diatom-specific myosins in Craspedostauros australis (CaMyoA-D) and investigated their in vivo localization and dynamics through GFP-tagging. Only CaMyoB-D but not CaMyoA exhibited coordinated movement during gliding, consistent with a role in force generation. The characterization of raphid diatom-specific myosins lays the foundation for unraveling the molecular mechanisms that underlie the gliding motility of diatoms.