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Chloroplasts

Ever decreasing circles

Nature volume 400, pages 119–120 (1999)Cite this article

Chloroplasts constitute the photosynthetic machinery of eukaryotes. They derive from endosymbiotic cyanobacteria and bear hallmarks of that prokaryotic ancestry2. The chloroplast genome is smaller than that of a cyanobacterium, but is still circular with a single replication origin and genes assembled into operons (expression units incorporating numerous, often related, genes). Until now, all known chloroplast genomes adhered to this uniform architecture, but dinoflagellates buck the trend.

Zhang et al.1 show that, despite a common origin with other chloroplasts, dinoflagellate chloroplasts have adopted a unique genome architecture in which each gene has its own minicircle. In other words, dinoflagellate chloroplasts contain a small family of plasmid-like molecules, each carrying a gene for a protein or ribosomal RNA. The authors1 find that all minicircles in a given dinoflagellate species have a repeat region that appears to participate in inter-circle gene conversion, thereby maintaining identity between circles, and they propose that this region contains a replication origin and an anchor point for circle segregation during chloroplast division. This repeat region could be a key to development of a genetic transformation system for dinoflagellate chloroplasts — it should be easy to introduce a plasmid-type construct, incorporating the repeat and a selectable marker, into them.

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Figure 1: The dinoflagellate Diplopelta bomba.

GERT HANSEN

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  1. the Plant Cell Biology Research Centre, School of Botany, University of Melbourne, Parkville, 3052, Australia

    Geoff McFadden

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  1. Geoff McFadden
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McFadden, G. Ever decreasing circles. Nature 400, 119–120 (1999). https://doi.org/10.1038/22011

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