PARENT SESSION

Symposium S7B Evolution of photosynthesis
Thursday September 2nd, 2004 2:40 PM-4:40 PM Room 511D
Chair: Beverley Green
Co-Chair: Bob Blankenship

Anomalous chloroplast genome organisation in dinoflagellates. Adrian Barbrook^*,1, Ellen Nisbet¹, Lila Koumandou¹, Christopher Howe¹, ¹ Dept of Biochemistry, University of Cambridge, Cambridge, UK

ABSTRACT- The chloroplast genome of most plants and algae is a circular molecule of 120-200 kbp, encoding approximately 120 genes. These genes primarily code for proteins involved in photosynthesis, and components of the chloroplast transcription and translation machinery. However, recent studies of the dinoflagellate chloroplast genome indicate a very different organisation. A small set of chloroplast genes have been found to reside on separate 2-3 kb minicircles. These minicircles share a highly conserved non-coding "core" region and contain 1 to 3 genes, which are always found in the same orientation with respect to the core region. A number of "empty" minicircles have also been reported, which are 0.3-2.5 kb in size, carry a normal core region, but contain no apparent functional ORF. Other interesting aspects of the dinoflagellate plastid genes include unusual predicted start codons (e.g. GTA), an accelerated rate of evolution, unusual codon usage, and deletions in typically highly conserved genes, like psaA. Whilst about 13 chloroplast genes have been retained in peridinin-containing dinoflagellate chloroplasts it appears from EST and hybridisation studies that many normally chloroplast located genes have been transferred to the nucleus. Many open questions still remain, such as whether this organisation is common among all photosynthetic dinoflagellates, why the dinoflagellate chloroplast genome has transferred all but a handful of genes to the nucleus, whether these minicircles indeed localise to the chloroplast, how the minicircle genes are transcribed and whether the predicted start codons are indeed functional. We discuss the peculiarities of the dinoflagellate chloroplast genome in Amphidinium operculatum, its likely origin, and further investigation of the minicircle system.

KEY WORDS: chloroplast, minicircles, dinoflagellate, genome