Dinoflagellate chloroplasts - where have all the genes gone?

The chloroplast genome has a similar organization across a wide range of plants and algae. It comprises a circular molecule of greater than or equal to 120 kb with greater than or equal to 120 genes. However, the organization of chloroplast genes seems to be unique in dinoflagellate algae. In this ecologically important group of organisms, most of the chloroplast genes appear to have been lost, presumably to the nucleus. The remaining genes, encoding polypeptides that are important for the light reactions of photosynthesis, are located on plasmid-like minicircles of 2-4 kb. This pattern raises important questions about why organelle genomes are retained and which particular genes they should include.