The complete plastid genome sequence of the haptophyte Emiliania huxleyi: a comparison to other plastid genomes.

The complete nucleotide sequence of the plastid genome of the haptophyte Emiliania huxleyi has been determined. E. huxleyi is the most abundant coccolithophorid and has a key role in the carbon cycle. It is also implicated in the production of dimethylsulphide (DMS), which is involved in cloud nucleation and may affect the global climate. Here, we report the plastid genome sequence of this ecologically and economically important species and compare its gene content and arrangement to other known plastid genomes. The genome is circular and consists of 105,309 bp with an inverted repeat of 4,841 bp. In terms of both genome size and gene content E. huxleyi cpDNA is substantially smaller than any other from the red plastid lineage. The genetic information is densely packed, with 86.8% of the genome specifying 110 identified protein-coding genes, 9 open reading frames, 28 different tRNAs, and 3 rRNAs. A detailed comparison to other plastid genomes, based on gene content, gene function, and gene cluster analysis is discussed. These analyses suggest a close relationship of the E. huxleyi cpDNA to the chlorophyll c-containing plastids from heterokonts and cryptophytes, and they support the origin of the chromophyte plastids from the red algal lineage.