Peculiar features of the plastids of the colourless alga Euglena longa and photosynthetic euglenophytes unveiled by transcriptome analyses

Kristina Zahonova, Zoltan Fussy, Erik Bircak, Anna M. G. Novak Vanclova, Vladimir Klimes, Matej Vesteg, Juraj Krajcovic, Miroslav Obornik, Marek Elias

Preprint posted on 29 June 2018

Article now published in Scientific Reports at

It’s not easy being green – how a remodelled chloroplast is maintained in a non-photosynthetic algae by looking at the transcriptome of Euglena longa to reveal how it assembles and maintains its non-photosynthetic, but still vital, plastid.

Selected by Ellis O'Neill


Euglena are a group of  algae that show characteristics of both plants and animals, while in evolutionary terms are related to the human pathogens Trypanosoma and LeishmaniaEuglena longa is a non-photosynthetic species, which cannot lose its plastid, unlike the photosynthetic species E. gracilis. Not much is known about the cell biology of E. longa or why it maintains a non-photosynthetic plastid.


This preprint presents the transcriptome of E. longa in comparison with those already available from three other photosynthetic Euglena to investigate the mechanisms of plastid maintenance and the targeting of proteins into this organelle. The authors show some very interesting features of the plastid, such as differences in import of proteins, with very different requirements when large amounts of photosynthetic machinery are needed. For instance, the photosynthetic membranes are not required in E. longa and the machinery for inserting proteins into this membrane are lacking.

This paper discusses fascinating details of the plastid biology and in particular picks apart protein import and the housekeeping proteins in these different species. There has not previously been much work looking at the specifics of the plastid maintenance and housekeeping in this group of alga and, by combining the new transcriptome data with that already known, the authors have had the opportunity to really look at how this group of organisms have similarities and differences with other plastid-baring organisms. There are many hypothesis developed that would need testing, but the proposals in this paper are a great starting point.

Future Outlook

There are a few transcriptomes available from this group of algae, and we can expect more to come out for species of particular interest. However, there are no genomes available, and this remains a goal of this field. Once we understand a bit more about how genes are regulated there will be great opportunities to study the cell biology and biochemistry and to leverage this group of algae for biotechnology.

Further Reading

Euglena gracilis transcriptome


Euglena for biotechnology



Posted on: 11 July 2018 , updated on: 17 July 2018

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Author's response

Kristina Záhonová shared

Euglenophytes are an interesting group of algae with various trophic strategies. Euglena longa represents an organism that secondarily lost its photosynthetic abilities. We present a comparative analysis of deeply covered euglenophyte transcriptomes and reveal their specificities with respect to plastid maintenance. Euglenophytes appear to possess a simplified plastid import machinery with most known chloroplast translocon (TOC/TIC) components absent. Some of the nucleus-encoded plastid-targeted proteins are translocated as translational fusions and split in the plastid stroma upon import. We also document how several cases of functional horizontal gene transfers from prokaryotes shape the euglenophyte biology. In summary, our analyses point out several possible directions of future molecular biology research in euglenophytes.

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