XVI International Botanical Congess

Complete sequences of chloroplast ribosomal RNA genes and seven chloroplast protein genes from the dinoflagellate Heterocapsa triquetra reveal that each is located alone on a separate minicircular chromosome. The genes are the most divergent known from chloroplast genomes. Each circle has an unusual tripartite non-coding, highly conserved among the nine circles, but very divergent between species. Several other species have minicircular chloroplast genes, suggesting that this type of genomic organization evolved in ancestral peridinean dinoflagellates. Phylogenetic analyses indicate that dinoflagellate chloroplasts are related to apicomplexan and chromistan plastids, and supports their origin by secondary symbiogenesis.