Figure 4.

Hypothetical evolutionary scheme for the 19′-hexanoyloxy-fucoxanthin-containing dinoflagellates. (I) Acquisition of a plastid by a secondary symbiogenesis in which a red algal cell was engulfed by a colorless ancestor. The red algal nuclear psbO gene was transferred to the dinoflagellate nucleus (dashed arrow) and the sequence subsequently diverged. (II) Loss of the peridinin-type plastid and the nuclear psbO gene for the plastid. (III) Acquisition of a new plastid by a tertiary symbiogenesis in which a haptophyte alga was engulfed by a dinoflagellate that may or may not have already lost its original peridinin-type plastid. psbO-R, psbO-P, and psbO-H indicate the psbO genes of the red algal secondary endosymbiont, the peridinin-containing dinoflagellate, and the haptophyte tertiary endosymbiont, respectively.