We think that the reason why this paper is highly cited comes from a convergence of interests among people in several fields. Our paper reports on the very first sequencing and genome analysis of a green alga, ahead of the model organism Chlamydomonas which was long expected to come first, and therefore it attracted the interest of geneticists and molecular biologists working on this model and downwards. Ostreococcus tauri, the species from which the genome was sequenced, occupies a very interesting position in evolution, diverging at the very basis of the green lineage, which is of real interest for evolutionary biologists as well as plant biologists.

“If our research was not aiming at bringing immediate applications, it is obvious that a better knowledge of the diversity of these planktonic populations is part of the general effort to better understand the mechanisms underlying global warming of the planet.”

Ostreococcus is a marine micro-organism of wide occurrence, occupying a specific niche and playing an important role at the base of the marine trophic food chain, which is particularly relevant for physiologists and ecologists, especially in the context of an increasing concern for global balance in the natural environment of the oceans, where biological data are limited by inadequate modeling. Ostreococcus has a very small 12.5 Mb genome, whereas coding for more than 8,000 genes is required to encode all the functions of a completely autonomous photosynthetic organism, such as a plant.

The Ostreococcus genome is quite compact, often performing a given cellular function using a single gene when its plant or Chlamydomonas relatives have several paralogs, which obviously makes it a very interesting model for function and gene network analysis. Ostreococcus cells are very small discs, less than half-a-micron thick with a diameter in the 1-1.5 micron range.

It is currently the smallest eukaryote known, which has several interesting outcomes: its very small size imposes strong constraints on occupancy, and is probably at the lower limit of what a eukaryote can bear in this respect. Looking at limits tells where there is room for plasticity and what is essential to be kept. It also allows the use of high resolution techniques in microscopy which were previously only able to look at viruses, organelles, or prokaryotes. So, cell biologists are interested as well.

Ostreococcus is an organism of very recent discovery (1994), and little is known of its biology. It was therefore a challenge to anticipate, from the analysis of the genome, which biological capabilities this species would or would not possess. Of particular interest was the finding of genome heterogeneity with two chromosomes differing from all the others, which probably has to do with the reproductive biology of this organism and its adaptation to the environment. These aspects drive the attention of a larger audience, from marine biologists to computational biologists, biochemists, and geneticists.

When the genome of many prokaryotic pikoplankton has been sequenced, only two eukaryotic algae have had their genome sequenced and published: the red alga Cyanydioschyzon—which is a fresh water organism, as is Chlamydomonas—and the diatom Thalassiosira which was the only other marine eukaryote. These sequence data are the basis for further "post-genomics" experimental and in silico analysis as well as comparative studies in the green lineage.

Ostreococcus, a microscopic photosynthetic eukaryotic organism (i.e., an evolved organism with a nucleated cell using sunlight to assimilate carbon and inorganic nitrogen to grow, like plants), had only been discovered 14 years ago and has been shown since to be present worldwide and also to play an important role in the oceanic food chain, next to better known bacterial organisms.

The paper reports the genome sequence of Ostreococcus, and, from this sequence, which genes this species likely possess. From this gene registry, and from the way genes are encoded and located on the genome, the paper then anticipates which capabilities this organism is likely to have in terms of nutrition and reproduction.

The sequencing of the Ostreococcus genome, its analysis, and further experiments that the accumulated data will allow to be done, are thus bringing along knowledge on the biology and role of this organism in the ocean, in a very timely way, where very little had been known before. This is an important step towards a better understanding of life and its balance in the ocean, as well as that of the carbon cycle on earth, allowing modeling to take into account Ostreococcus and its relatives within these processes.

It was Hervé who first became interested in sequencing the genome of Ostreococcus. Hervé, who is a molecular biologist, is leading a team in the Oceanological Observatory of Banyuls (France) where Ostreococcus was discovered. The interest in using Ostreococcus as a model for a cell cycle was shared by Hervé’s colleague François-Yves Bouget. François-Yves was doing a post-doc at the VIB Plant Systems Biology department in Ghent at the time, and he suggested that the VIB BioInformatics & Evolutionary Biology team be led by Yves as a partner. Yves accepted, having assumed that it would be a quick and easy job annotating such a small genome, after having been involved in the annotation of Arabidopsis and the poplar genome and before jumping into researching some other big genomes from plants and fungi.

As sadly discovered by Pierre, who led the annotation job, it turned out to be just the opposite: the Ostreococcus genome appeared to be heterogeneous in a way never seen before. At one point, he even thought that the Ostreococcus genome was contaminated, and it was a difficult task for Hervé to convince team members that it was not so! Finding and modelling genes with different styles within the same genome took quite a long time for those involved.

New strains of closely related species/ecotypes are under sequencing either at the JGI or at the Genoscope (France). These strains have been isolated in various marine environments corresponding either to surface (high-light environment) or deep in the euphotic zone (low-light) or in shallow coastal lagoons.

This data will open the possibility of studying gene content as a function of an ecological niche or of these ecotypes and the development of an environmental genomics approach. We are also looking at the genome of viruses which are pathogens of Ostreococcus in order to analyze the relationship between the virus and its host during the appearance and disappearance of blooms of Ostreococccus and related Prasinophyceae.

  Are there any social or political implications for your research?