Rate variation as a function of gene origin in plastid-derived genes of peridinin-containing dinoflagellates

BACHVAROFF, T.R., M.V. SÁNCHEZ PUERTA & C.F. DELWICHE.

JOURNAL OF MOLECULAR EVOLUTION

SPRINGER

Año: 2006 vol. 62 p. 42 - 52

0022-2844

Peridinin-pigmented dinoflagellates contain secondary plastids that seem to have undergone more nearly complete plastid genome reduction than other eukaryotes.  Many typically plastid-encoded genes appear to have been transferred to the nucleus, with a few remaining genes found on minicircles. To understand better the evolution of the dinoflagellate plastid, four categories of plastid-associated genes in dinoflagellates were defined based on their history of transfer and evaluated for rate of sequence evolution, including: minicircle genes (presumably plastid-encoded), genes probably transferred from the plastid to the nucleus (plastid-transferred), and genes that were likely acquired directly from the nucleus of the previous plastid host (nuclear-transferred). The fourth category, lateral-transferred genes, are plastid-associated genes that do not appear to have a cyanobacterial origin. The evolutionary rates of these gene categories were compared using relative rate tests and likelihood ratio tests.  For comparison with other secondary plastid-containing organisms, rates were calculated for the homologous sequences from the haptophyte Emiliania huxleyi.  The evolutionary rate of minicircle and plastid-transferred genes in the dinoflagellate was strikingly higher than nuclear-transferred and lateral-transferred genes, and also substantially higher than all plastid-associated genes in the haptophyte.  Plastid-transferred genes in the dinoflagellate had an accelerated rate of evolution that was variable, but in most cases not as extreme as the minicircle genes. Furthermore, the nuclear-transferred and lateral-transferred genes showed rates of evolution that are similar to other taxa. Thus, nucleus to nucleus transferred genes have a more typical rate of sequence evolution while those whose history was wholly or partially within the dinoflagellate plastid genome have a markedly accelerated rate of evolution.