Comparative chloroplast genomics between Euglena viridis and Euglena gracilis (Euglenophyta)

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Bennett M.S., Wiegert K.E. and Triemer R.E. 2012. Comparative chloroplast genomics between Euglena viridis and Euglena gracilis (Euglenophyta). Phycologia 51: 711–718. DOI: 10.2216/12-017.1The chloroplast genomes of Euglena gracilis, Eutreptia viridis, Eutreptiella gymnastica, Colacium vesiculosum, Strombomonas acuminata and the colourless Euglena (Astasia) longa, which had secondarily lost the ability to photosynthesize, were previously reported. These studies had shown that there was a great diversity in the size of euglenoid chloroplast genomes and in the arrangement of gene clusters. However, while these genomes provided important insights into the evolution of the chloroplast genome across genera, they did not address genomic variability within a genus. In an effort to continue with these investigations, we sequenced the chloroplast genome of Euglena viridis and compared this to the E. gracilis chloroplast genome in order to explore intrageneric chloroplast evolution. The chloroplast genome of E. viridis was also compared to those of the other previously published euglenoid chloroplast genomes. Our results showed that while the chloroplast genome of E. viridis most closely resembled that of E. gracilis, the chloroplast genomes did show significant differences. The chloroplast genome of E. viridis was far more compact, had a gene cluster that was reversed in both gene order and strand orientation, had a region that was comprised almost entirely of open reading frames and had substantially fewer introns. However, despite these differences, it was clear from the chloroplast genome sequence that E. viridis and E. gracilis were very closely related and that the majority of euglenoid chloroplast evolution probably occurred before the divergence of the genus Euglena.