Algal genomes reveal evolutionary mosaicism and the fate of nucleomorphs.


Cryptophyte and chlorarachniophyte algae are transitional forms in the widespread secondary endosymbiotic acquisition of photosynthesis by engulfment of eukaryotic algae. Unlike most secondary plastid-bearing algae, miniaturized versions of the endosymbiont nuclei (nucleomorphs) persist in cryptophytes and chlorarachniophytes. To determine why, and to address other fundamental questions about eukaryote-eukaryote endosymbiosis, we sequenced the nuclear genomes of the cryptophyte Guillardia theta and the chlorarachniophyte Bigelowiella natans. Both genomes have >21,000 protein genes and are intron rich, and B. natans exhibits unprecedented alternative splicing for a single-celled organism. Phylogenomic analyses and subcellular targeting predictions reveal extensive genetic and biochemical mosaicism, with both host- and endosymbiont-derived genes servicing the mitochondrion, the host cell cytosol, the plastid and the remnant endosymbiont cytosol of both algae. Mitochondrion-to-nucleus gene transfer still occurs in both organisms but plastid-to-nucleus and nucleomorph-to-nucleus transfers do not, which explains why a small residue of essential genes remains locked in each nucleomorph.

DOI: 10.1038/nature11681

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@article{Curtis2012AlgalGR, title={Algal genomes reveal evolutionary mosaicism and the fate of nucleomorphs.}, author={Bruce A Curtis and Goro Tanifuji and Fabien Burki and Ansgar Gruber and Manuel Irimia and Shinichiro Maruyama and Maria C Arias and Steven G Ball and Gillian H Gile and Yoshihisa Hirakawa and Julia F Hopkins and Alan Kuo and Stefan A Rensing and Jeremy Schmutz and Aikaterini Symeonidi and Marek Elias and Robert J M Eveleigh and Emily K Herman and Mary J Klute and Takuro Nakayama and Miroslav Oborn{\'i}k and Adrian Reyes-Prieto and E Virginia Armbrust and Stephen J Aves and Robert G Beiko and Pedro Coutinho and Joel B Dacks and Dion G Durnford and Naomi M Fast and Beverley R Green and Cameron J Grisdale and Franziska Hempel and Bernard Henrissat and Marc P H{\"{o}ppner and Ken-Ichiro Ishida and Eunsoo Kim and Luděk Kořen{\'y} and Peter G Kroth and Yuan Liu and Shehre-Banoo Malik and Uwe G Maier and Darcy McRose and Thomas Mock and Jonathan A D Neilson and Naoko T Onodera and Anthony M Poole and Ellen J Pritham and Thomas A Richards and Gabrielle Rocap and Scott W Roy and Chihiro Sarai and Sarah Schaack and Shu Shirato and Claudio H Slamovits and David F Spencer and Shigekatsu Suzuki and Alexandra Z Worden and Stefan Zauner and Kerrie Barry and Callum Bell and Arvind K Bharti and John A Crow and Jane Grimwood and Robin Kramer and Erika Lindquist and Susan Lucas and Asaf Salamov and Geoffrey I McFadden and Christopher E Lane and Patrick J Keeling and Michael W Gray and Igor V Grigoriev and John M Archibald}, journal={Nature}, year={2012}, volume={492 7427}, pages={59-65} }