Gwenael Piganeau

French National Centre for Scientific Research | CNRS

Diatoms, a prominent group of phytoplankton, have a significant impact on both the oceanic food chain and carbon sequestration, thereby playing a crucial role in regulating the climate. These highly diverse organisms exhibit a wide geographic distribution across various latitudes. In addition to their ecological significance, diatoms represent a vi...

While duplications have long been recognized as a fundamental process driving major evolutionary innovations, direct estimates of spontaneous chromosome duplication rates, leading to aneuploid karyotypes, are scarce. Here, from mutation accumulation (MA) experiments, we provide the first estimates of spontaneous chromosome duplication rates in six...

Phytoplankton–bacteria interactions rule over carbon fixation in the sunlit ocean, yet only a handful of phytoplanktonic–bacteria interactions have been experimentally characterized. In this study, we investigated the effect of three bacterial strains isolated from a long-term microcosm experiment with one Ostreococcus strain (Chlorophyta, Mamiello...

Phytoplankton plays a fundamental role in the ecology of ocean systems and is the key player in the global carbon cycle. At a time of global warming, understanding the mechanisms of its adaptation to temperature is therefore of paramount importance. Cosmopolitan planktonic species abundant in different marine environments provide both a unique oppo...

The genomic revolution has bridged a gap in our knowledge about the diversity, biology and evolution of unicellular photosynthetic eukaryotes, which bear very few discriminating morphological features among species from the same genus. The high-quality genome resources available in the class Mamiellophyceae (Chlorophyta) have been paramount to esti...

While duplications have long been recognized as a fundamental process driving major evolutionary innovations, direct estimations of spontaneous chromosome duplication rates are scarce. Here, we provide the first estimations of spontaneous whole chromosome duplication rates in four green algae and in one diatom species from mutation accumulation (MA...

While sex is now accepted as a ubiquitous and ancestral feature of eukaryotes, direct observation of sex is still lacking in most unicellular eukaryotic lineages. Evidence of sex is frequently indirect and inferred from the identification of genes involved in meiosis from whole genome data and/or the detection of recombination signatures from genet...

Although interactions between microalgae and bacteria are observed in both natural environment and the laboratory, the modalities of coexistence of bacteria inside microalgae phyco-spheres in laboratory cultures are mostly unknown. Here, we focused on well-controlled cultures of the model green picoalga Ostreococcus tauri and the most abundant memb...

The importance of marine phytoplankton in food webs and biogeochemical cycles makes the study of prokaryotic and eukaryotic phytoplankton species essential to understand changes in the global ecosystem. As plankton is transported by ocean currents, its community composition varies. Some species are abundant in contrasting environments, which raises...

Ostreococcus tauri is a simple unicellular green alga representing an ecologically important group of phytoplankton in oceans worldwide. Modern molecular techniques must be developed in order to understand the mechanisms that permit adaptation of microalgae to their environment. We present for the first time in O. tauri a detailed characterization...

Benthic diatoms are the main primary producers in shallow freshwater and coastal environments, fulfilling important ecological functions such as nutrient cycling and sediment stabilization. However, little is known about their evolutionary adaptations to these highly structured but heterogeneous environments. Here, we report a reference genome for...

The genome sequence of the algal species Prasinoderma coloniale reveals a novel phylum of green plants.

Virus-microbe interactions in the ocean are commonly described by “boom and bust” dynamics, whereby a numerically dominant microorganism is lysed and replaced by a virus-resistant one. Here, we isolated a microalga strain and its infective dsDNA virus whose dynamics are characterized instead by parallel growth of both the microalga and the virus. E...

Benthic diatoms are the main primary producers in shallow freshwater and coastal environments, fulfilling important ecological functions such as nutrient cycling and sediment stabilization. However, little is known about their evolutionary adaptations to these highly structured but heterogeneous environments. Here, we report a reference genome for...

The democratization of sequencing technologies fostered a leap in our knowledge of the diversity of marine phytoplanktonic microalgae, revealing many previously unknown species and lineages. The evolutionary history of the diversification of microalgae can be inferred from the analysis of their genome sequences. However, the link between the DNA se...

Among marine phytoplankton, Mamiellales encompass several species from the genera Micromonas, Ostreococcus and Bathycoccus, which are important contributors to primary production. Previous studies based on single gene markers described their wide geographical distribution but led to discussion because of the uneven taxonomic resolution of the metho...

Planktonic photosynthetic organisms of the class Mamiellophyceae include the smallest eukaryotes (less than 2 µm), are globally distributed and form the basis of coastal marine ecosystems. Eight complete fully annotated 13–22 Mb genomes from three genera, Ostreococcus , Bathycoccus and Micromonas , are available from previously isolated clonal cult...

Diatoms emerged in the Mesozoic period and presently constitute one of the main primary producers in the world’s ocean and are of a major economic importance. In the current study, using whole genome sequencing of ten accessions of the model diatom Phaeodactylum tricornutum, sampled at broad geospatial and temporal scales, we draw a comprehensive l...

Diatoms emerged in the Mesozoic period and presently constitute one of the main primary producers in the world’s ocean and are of a major economic importance. In the current study, using whole genome sequencing of ten accessions of the model diatom Phaeodactylum tricornutum , sampled at broad geospatial and temporal scales, we draw a comprehensive...

Mutations are the origin of genetic diversity, and the mutation rate is a fundamental parameter to understand all aspects of molecular evolution. The combination of mutation-accumulation experiments and high throughput sequencing enabled the estimation of mutation rates in most model organisms, but several major eukaryotic lineages remain unexplore...

Mutations are the main origin of the biodiversity and biological innovations across the tree of life. The number of mutations in a population depends of the mutation rate, noted μ, a key parameter for understanding the evolutionary and adaptive capacity of a species. New mutations are submitted to selection and drift and their probability of fixati...

While the molecular events involved in cell responses to heat stress have been extensively studied, our understanding of the genetic basis of basal thermotolerance, and particularly its evolution within the green lineage, remains limited. Here, we present the 13.3 Mb haploid genome and transcriptomes of a halotolerant and thermotolerant unicellular...

Domestication of microalgae A B S T R A C T Mutations are the main origin of the biodiversity and biological innovations across the tree of life. The number of mutations in a population depends of the mutation rate, noted µ, a key parameter for understanding the evolutionary and adaptive capacity of a species. New mutations are submitted to selecti...

Larval recruitment, the transition of pelagic larvae into reef-associated juveniles, is a critical step for the resilience of marine fish populations but its molecular control is unknown. Here, we investigate whether thyroid-hormones (TH) and their receptors (TR) coordinate the larval recruitment of the coral-reef-fish Acanthurus triostegus. We dem...

Acanthurus triostegus weight at different developmental stages.

Acanthurus triostegus intestine length at different developmental stages.

Acanthurus triostegus T4 levels in larvae and juveniles.

TR and Klf9 expression levels in Acanthurus triostegus at different developmental stages (qPCR).

Transactivation assay of Acanthurus triostegus TR for several thyroid hormone derivatives.

Acanthurus triostegus T3 levels in larvae and juveniles.

Transactivation assay of Acanthurus triostegus TR for the competition of T3 and NH3.

List of primers used in this study.

T4 levels in external slope relocated Acanthus triostegus.

List of TR used for phylogenetic reconstruction.

Tiny photosynthetic microorganisms that form the picoplankton (between 0.3 and 3 μm in diameter) are at the base of the food web in many marine ecosystems, and their adaptability to environmental change hinges on standing genetic variation. Although the genomic and phenotypic diversity of the bacterial component of the oceans has been intensively s...

Mutation is the ultimate source of genetic variation, and knowledge of mutation rates is fundamental for our understanding of all evolutionary processes. High throughput sequencing of mutation accumulation lines has provided genome wide spontaneous mutation rates in a dozen model species, but estimates from non-model organisms from much of the dive...

Micro-algae of the genus Ostreococcus and related species of the order Mamiellales are globally distributed in the photic zone of world's oceans where they contribute to fixation of atmospheric carbon and production of oxygen, besides providing a primary source of nutrition in the food web. Their tiny size, simple cells, ease of culture, compact ge...

Microalgal–bacterial interactions are commonly found in marine environments and are well known in diatom cultures maintained in laboratory. These interactions also exert strong effects on bacterial and algal diversity in the oceans. Small green eukaryote algae of the class Mamiellophyceae (Chlorophyta) are ubiquitous and some species, such as Ostre...

Estimates of the fitness effects of spontaneous mutations are important for understanding the adaptive potential of species. Here, we present the results of mutation accumulation experiments over 265 to 512 sequential generations in four species of marine unicellular green algae, Ostreococcus tauri RCC4221, Ostreococcus mediterraneus RCC2590, Micro...

We have investigated whether there is adaptive evolution in mitochondrial DNA, using an extensive dataset containing over 500 animal species from a wide range of taxonomic groups. We apply a variety of McDonald-Kreitman style methods to the data. We find that the evolution of mitochondrial DNA is dominated by slightly deleterious mutations, a findi...

In surveys of marine phytoplankton diversity, prasinophyte algae are commonly found and are often a major component, especially in coastal areas. They form a paraphyletic assemblage of at least nine clades, with the Mamiellophyceae (prasinophyte clade II) being a major group. In the order Mamiellales, the three genera Bathycoccus, Micromonas and Os...

Cost effective next generation sequencing technologies now enable the production of genomic datasets for many novel planktonic eukaryotes, representing an understudied reservoir of genetic diversity. O. tauri is the smallest free-living photosynthetic eukaryote known to date, a coccoid green alga that was first isolated in 1995 in a lagoon by the M...

Marine phytoplankton produce half of the oxygen we breathe and their astounding diversity is just starting to be unraveled. Many microbial phytoplankton are thought to be phototrophic, depending solely on inorganic sources of carbon and minerals for growth rather than preying on other planktonic cells. However, there is increasing evidence that sym...

Current sampling of genomic sequence data from eukaryotes is relatively poor, biased, and inadequate to address important questions about their biology, evolution, and ecology; this Community Page describes a resource of 700 transcriptomes from marine microbial eukaryotes to help understand their role in the world's oceans.

Along the green lineage (Chlorophyta and Streptophyta), mitochondria and chloroplast are mainly uniparentally transmitted and their evolution is thus clonal. The mode of organellar inheritance in their ancestor is less certain. The inability to make clear phylogenetic inference is partly due to a lack of information for deep branching organisms in...

With the advent of next generation genome sequencing, the number of sequenced algal genomes and transcriptomes is rapidly growing. Although a few genome portals exist to browse individual genome sequences, exploring complete genome information from multiple species for the analysis of user-defined sequences or gene lists remains a major challenge....

Prasinoviruses are among the largest viruses (>200 kbp) and encode several hundreds of protein coding genes, including most genes of the DNA replication machinery and several genes involved in transcription and translation, as well as tRNAs. They can infect and lyse small eukaryotic planktonic marine green algae, thereby affecting global algal popu...

Metagenomics is the study of the DNA content of a community of microorganisms. With the advent of next-generation sequencing technologies, more and more metagenomes from various environments are being produced. This DNA sequence profusion has revolutionized microbiology, where many cellular-based molecular approaches are hampered by cultivation dif...

Background Bathycoccus prasinos is an extremely small cosmopolitan marine green alga whose cells are covered with intricate spider's web patterned scales that develop within the Golgi cisternae before their transport to the cell surface. The objective of this work is to sequence and analyze its genome, and to present a comparative analysis with oth...

The 154 single-copy core gene families in the green plant lineage.

Alignment of 154 single-copy core gene families in the green plant lineage.

Supplementary materials and methods, figures and tables.

Statistics of the genome shotgun sequencing.

Details of maximum likelihood phylogenetic trees describing B. prasinos RCC1105 HGT genes.

Among small photosynthetic eukaryotes that play a key role in oceanic food webs, picoplanktonic Mamiellophyceae such as Bathycoccus, Micromonas, and Ostreococcus are particularly important in coastal regions. By using a combination of cell sorting by flow cytometry, whole genome amplification (WGA), and 454 pyrosequencing, we obtained metagenomic d...

Relationship between numbers of reads assigned to each B. prasinos RCC1105 chromosome based on BLASTX-based analysis of contigs (see Materials and Methods for details) or direct assembly with Geneious. (TIF)

Percent of false assignment of O. ‘lucimarinus ’ proteins based on Best BLAST hit (BBH, blue line) or after filtration with gene-specific thresholds for identity and alignment length (FA, red line) as a function of read length (see Materials and Methods for details). (TIF)

Similarity between specific genes from selected gene classes of B. prasinos RCC1105 genome and T142 and T149 Newbler contigs (see Materials and Methods for details). (PDF)

Assignment of Geneious contigs for samples T142 and T149 to specific chromosomes of B. prasinos RCC1105 based on a BLASTX-based algorithm (see Materials and Methods for details). An estimate of coverage was computed as the ratio between the total length of contigs assigned to one chromosome and the length of this chromosome. This value may exceed 1...

Estimation of the number of major haplotypes and of their frequency for selected regions of genes with a high read coverage in both samples. (PDF)