Unusual organisation of the plastid genome of the dinoflagellate Amphidinium operculatum

Abstract

We have previously reported an anomalous organization of several plastid genes in the dinoflagellate Amphidinium operculatum. These genes are located on individual minicircles of around 2.4 kbp, with a single gene on each minicircle. Each minicircle also has a `core¿ region, which is similar but not identical between minicircles. This gene organization contrasts markedly with that in other plastid genomes, which typically have 100 or so genes located on one molecule. Using dinoflagellate DNA and PCR with primers based on conserved regions of several genes, we have identified additional genes for plastid proteins on minicircles. We have identified one minicircle containing two genes. PCR using primers based on the core region has allowed us to identify a number of `empty¿ minicircles that do not appear to contain any genes (although one empty minicircle has short regions of similarity to other genes). These empty minicircles have a recognisable core region, however. We have carried out transcript analysis of a number of minicircles, including the one carrying two genes. We have also tested the hypothesis that dinoflagellate plastid transcripts undergo editing.