Of well explored model organisms belong to PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/28192408 the plant (Archaeplastida) and the animal (Opisthokonta) groups, which both evolved from primary endosymbiotic events that generated chloroplasts and mitochondria. The heterokonts, on the other hand, probably evolved from serial secondary* Correspondence: [email protected] Contributed equally 1 Institut de Biologie de l’Ecole Normale Sup ieure, CNRS UMR 8197 INSERM U1024, Ecole Normale Sup ieure, 46 rue d’Ulm, 75005 Paris, France Full list of author information is available at the end of the articleendosymbiosis events in which a heterotrophic eukaryote engulfed both autotrophic red and green eukaryotic algae [2-4]. As a consequence, these organisms derive from the combination of three distinct nuclear genomes. The group includes highly diverse, ecologically important photosynthetic groups, such as diatoms, as well as non-photosynthetic members, such as oomycetes (for example, Phytophthora infestans, the causative agent of potato late blight). Diatoms typically constitute a major component of phytoplankton in freshwater and marine environments. They are involved in various biogeochemical cycles,?2010 Maheswari et al; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Maheswari et al. Genome Biology 2010, 11:R85 http://genomebiology.com/2010/11/8/RPage 2 ofmost notably those involving carbon, nitrogen and silicon, and contribute 30 to 40 of marine primary productivity [5,6]. Consequently, they are responsible for approximately one-fifth of the oxygen that is generated through photosynthesis on our planet. Morphologically, they exhibit different shapes and symmetries, the centric diatoms being radially symmetric and the pennates displaying bilateral symmetry. In spite of their tremendous ecological importance, the molecular mechanisms that enable them to succeed in a range of diverse environments remain largely unexplored. Results from the first diatom genome projects from Thalassiosira pseudonana and Phaeodactylum tricornutum showed the presence of various genes needed for efficient management of carbon and nitrogen – for example, QVD-OPHMedChemExpress Q-VD-OPh encoding urea cycle components [7,8]. However, these studies could only predict the functions of around 55 of diatom genes. The comparative study of the two diatom genomes [8] revealed that only 57 of genes are shared between the two diatoms, and that horizontal gene transfer from prokaryotes is pervasive in diatoms. Thus, the necessity for functional genomics and reverse genetics approaches to further explore diatom gene repertories is clear. P. tricornutum is a pennate diatom that has been extensively studied physiologically and phylogenetically. In addition, it does not have an obligate requirement for silicic acid like other diatoms, and can undergo morphological transitions between three possible morphotypes [9]. The organism harbors a small genome (27.4 Mb) [8], it can be routinely transformed with efficiencies superior to those reported for other diatoms [10-13], and gene silencing is now possible using RNA interference [14]. For these reasons P. tricornutum is emerging as a model species for dissecting diatom molecular and cellular biology [15-20]. In a pilot study of the P. tricornutum genome using 1,000.
