The dinoflagellates contain diverse plastids of uncertain origin. To
determine the origin of the peridinin- and fucoxanthin-containing
dinoflagellate plastid, we sequenced the plastid-encoded psaA, psbA,
and rbcL genes from various red and dinoflagellate algae. The psbA
gene phylogeny, which was made from a data set of 15 dinoflagellates,
22 rhodophytes, 5 cryptophytes, 7 haptophytes, 7 stramenopiles, 2
chlorophytes, and a glaucophyte as the outgroup, supports monophyly of
the peridinin-, and fucoxanthin-containing dinoflagellates, as a
sister group to the haptophytes. The monophyletic relationship with
the haptophytes is recovered in the psbA + psaA phylogeny, with
stronger support. The rubisco tree utilized the "Form I" red algal
type of rbcL and included fucoxanthin-containing dinoflagellates. The
dinoflagellate + haptophyte sister relationship is also recovered in
this analysis. Peridinium foliaceum is shown to group with the diatoms
in all the phylogenies. Based on our analyses of plastid sequences, we
postulate that 1) the plastid of peridinin-, and
fucoxanthin-containing dinoflagellates originated from a common
ancestor, 2) the ancestral dinoflagellate acquired its plastid from a
haptophyte though a tertiary plastid replacement, 3) "Form II"
rubisco replaced the ancestral rbcL after the divergence of the
peridinin-, and fucoxanthin-containing dinoflagellates, and 4) we
confirm that the plastid of Peridinium foliaceum originated from a
Stramenopiles endosymbiont.
Key words: Dinoflagellates, evolution, plastid, psaA, psbA, rbcL