A hemizygous supergene controls homomorphic and heteromorphic self-incompatibility systems in Oleaceae.

Self-incompatibility (SI) has evolved independently multiple times and prevents self-fertilization in hermaphrodite angiosperms. Several groups of Oleaceae such as jasmines exhibit distylous flowers, with two compatibility groups each associated with a specific floral morph.1 Other Oleaceae species in the olive tribe have two compatibility groups without associated morphological variation.2,3,4,5 The genetic basis of both homomorphic and dimorphic SI systems in Oleaceae is unknown. By comparing genomic sequences of three olive subspecies (Olea europaea) belonging to the two compatibility groups, we first locate the genetic determinants of SI within a 700-kb hemizygous region present only in one compatibility group. We then demonstrate that the homologous hemizygous region also controls distyly in jasmine. Phylogenetic analyses support a common origin of both systems, following a segmental genomic duplication in a common ancestor. Examination of the gene content of the hemizygous region in different jasmine and olive species suggests that the mechanisms determining compatibility groups and floral phenotypes (whether homomorphic or dimorphic) in Oleaceae rely on the presence/absence of two genes involved in gibberellin and brassinosteroid regulation.

Divergent selection for feed efficiency in pigs altered the duodenum transcriptomic response to feed intake and its DNA methylation profiles.

Feed efficiency is a trait of interest in pigs as it contributes to lowering the ecological and economical costs of pig production. A divergent genetic selection experiment from a Large White pig population was performed for 10 generations, leading to pig lines with relatively low- (LRFI) and high- (HRFI) residual feed intake (RFI). Feeding behavior and metabolic differences have been previously reported between the two lines. We hypothesized that part of these differences could be related to differential sensing and absorption of nutrients in the proximal intestine. We investigated the duodenum transcriptome and DNA methylation profiles comparing overnight fasting with ad libitum feeding in LRFI and HRFI pigs (n = 24). We identified 1,106 differentially expressed genes between the two lines, notably affecting pathways of the transmembrane transport activity and related to mitosis or chromosome separation. The LRFI line showed a greater transcriptomic response to feed intake than the HRFI line. Feed intake affected genes from both anabolic and catabolic pathways in the pig duodenum, such as rRNA production and autophagy. Several nutrient transporter and tight junction genes were differentially expressed between lines and/or by short-term feed intake. We also identified 409 differentially methylated regions in the duodenum mucosa between the two lines, while this epigenetic mark was less affected by feeding. Our findings highlighted that the genetic selection for feed efficiency in pigs changed the transcriptome profiles of the duodenum, and notably its response to feed intake, suggesting key roles for this proximal gut segment in mechanisms underlying feed efficiency.NEW & NOTEWORTHY The duodenum is a key organ for the hunger/satiety loop and nutrient sensing. We investigated how the duodenum transcriptome and DNA methylation profiles are affected by feed intakes in pigs. We observed thousands of changes in gene expression levels between overnight-fasted and fed pigs in high-feed efficiency pig lines, but almost none in the related low-feed efficiency pig line.

Characterization of the RNA Mycovirome Associated with Grapevine Fungal Pathogens: Analysis of Mycovirus Distribution and Their Genetic Variability within a Collection of Botryosphaeriaceae Isolates.

Botryosphaeriaceae are fungi involved in the decay of various woody species, including the grapevine, leading to significant production losses. This fungal family is largely ubiquitous, and seven species of Botryosphaeriaceae have been identified in French vineyards, with variable levels of aggressiveness, both in vitro and in planta. Mycoviruses can impact the life traits of their fungal hosts, including aggressiveness, and are one of the factors influencing fungal pathogenicity. In this study, the RNA mycovirome of fifteen Botryosphaeriaceae isolates was characterized through the high-throughput sequencing of double-stranded RNA preparations from the respective samples. Eight mycoviruses were detected, including three potential novel species in the Narnaviridae family, as well as in the proposed Mycobunyaviridae and Fusagraviridae families. A large collection of Botryosphaeriaceae isolates was screened using RT-PCR assays specific for 20 Botryosphaeriaceae-infecting mycoviruses. Among the mycoviruses detected, some appeared to be specialists within a single host species, while others infected isolates belonging to multiple Botryosphaeriaceae species. This screening allowed us to conclude that one-third of the Botryosphaeriaceae isolates were infected by at least one mycovirus, and a significant proportion of isolates (43.5%) were found to be coinfected by several viruses, with very complex RNA mycoviromes for some N. parvum isolates.

A Selective Bottleneck During Host Entry Drives the Evolution of New Legume Symbionts.

During the emergence of new host-microbe symbioses, microbial fitness results from the ability to complete the different steps of symbiotic life cycles, where each step imposes specific selective pressures. However, the relative contribution of these different selective pressures to the adaptive trajectories of microbial symbionts is still poorly known. Here, we characterized the dynamics of phenotypic adaptation to a simplified symbiotic life cycle during the experimental evolution of a plant pathogenic bacterium into a legume symbiont. We observed that fast adaptation was predominantly explained by improved competitiveness for host entry, which outweighed adaptation to within-host proliferation. Whole-population sequencing of bacteria at regular time intervals along this evolution experiment revealed the continuous accumulation of new mutations (fuelled by a transient hypermutagenesis phase occurring at each cycle before host entry, a phenomenon described in previous work) and sequential sweeps of cohorts of mutations with similar temporal trajectories. The identification of adaptive mutations within the fixed mutational cohorts showed that several adaptive mutations can co-occur in the same cohort. Moreover, all adaptive mutations improved competitiveness for host entry, while only a subset of those also improved within-host proliferation. Computer simulations predict that this effect emerges from the presence of a strong selective bottleneck at host entry occurring before within-host proliferation and just after the hypermutagenesis phase in the rhizosphere. Together, these results show how selective bottlenecks can alter the relative influence of selective pressures acting during bacterial adaptation to multistep infection processes.

A dual legume-rhizobium transcriptome of symbiotic nodule senescence reveals coordinated plant and bacterial responses.

Senescence determines plant organ lifespan depending on aging and environmental cues. During the endosymbiotic interaction with rhizobia, legume plants develop a specific organ, the root nodule, which houses nitrogen (N)-fixing bacteria. Unlike earlier processes of the legume-rhizobium interaction (nodule formation, N fixation), mechanisms controlling nodule senescence remain poorly understood. To identify nodule senescence-associated genes, we performed a dual plant-bacteria RNA sequencing approach on Medicago truncatula-Sinorhizobium meliloti nodules having initiated senescence either naturally (aging) or following an environmental trigger (nitrate treatment or salt stress). The resulting data allowed the identification of hundreds of plant and bacterial genes differentially regulated during nodule senescence, thus providing an unprecedented comprehensive resource of new candidate genes associated with this process. Remarkably, several plant and bacterial genes related to the cell cycle and stress responses were regulated in senescent nodules, including the rhizobial RpoE2-dependent general stress response. Analysis of selected core nodule senescence plant genes allowed showing that MtNAC969 and MtS40, both homologous to leaf senescence-associated genes, negatively regulate the transition between N fixation and senescence. In contrast, overexpression of a gene involved in the biosynthesis of cytokinins, well-known negative regulators of leaf senescence, may promote the transition from N fixation to senescence in nodules.

Rv0180c contributes to Mycobacterium tuberculosis cell shape and to infectivity in mice and macrophages.

Mycobacterium tuberculosis, the main causative agent of human tuberculosis, is transmitted from person to person via small droplets containing very few bacteria. Optimizing the chance to seed in the lungs is therefore a major adaptation to favor survival and dissemination in the human population. Here we used TnSeq to identify genes important for the early events leading to bacterial seeding in the lungs. Beside several genes encoding known virulence factors, we found three new candidates not previously described: rv0180c, rv1779c and rv1592c. We focused on the gene, rv0180c, of unknown function. First, we found that deletion of rv0180c in M. tuberculosis substantially reduced the initiation of infection in the lungs of mice. Next, we established that Rv0180c enhances entry into macrophages through the use of complement-receptor 3 (CR3), a major phagocytic receptor for M. tuberculosis. Silencing CR3 or blocking the CR3 lectin site abolished the difference in entry between the wild-type parental strain and the Δrv0180c::km mutant. However, we detected no difference in the production of both CR3-known carbohydrate ligands (glucan, arabinomannan, mannan), CR3-modulating lipids (phthiocerol dimycocerosate), or proteins in the capsule of the Δrv0180c::km mutant in comparison to the wild-type or complemented strains. By contrast, we established that Rv0180c contributes to the functionality of the bacterial cell envelope regarding resistance to toxic molecule attack and cell shape. This alteration of bacterial shape could impair the engagement of membrane receptors that M. tuberculosis uses to invade host cells, and open a new perspective on the modulation of bacterial infectivity.

Widely rhythmic transcriptome in Calanus finmarchicus during the high Arctic summer solstice period.

Solar light/dark cycles and seasonal photoperiods underpin daily and annual rhythms of life on Earth. Yet, the Arctic is characterized by several months of permanent illumination ("midnight sun"). To determine the persistence of 24h rhythms during the midnight sun, we investigated transcriptomic dynamics in the copepod Calanus finmarchicus during the summer solstice period in the Arctic, with the lowest diel oscillation and the highest altitude of the sun's position. Here we reveal that in these extreme photic conditions, a widely rhythmic daily transcriptome exists, showing that very weak solar cues are sufficient to entrain organisms. Furthermore, at extremely high latitudes and under sea-ice, gene oscillations become re-organized to include <24h rhythms. Environmental synchronization may therefore be modulated to include non-photic signals (i.e. tidal cycles). The ability of zooplankton to be synchronized by extremely weak diel and potentially tidal cycles, may confer an adaptive temporal reorganization of biological processes at high latitudes.

Daily transcriptomes of the copepod Calanus finmarchicus during the summer solstice at high Arctic latitudes.

The zooplankter Calanus finmarchicus is a member of the so-called "Calanus Complex", a group of copepods that constitutes a key element of the Arctic polar marine ecosystem, providing a crucial link between primary production and higher trophic levels. Climate change induces the shift of C. finmarchicus to higher latitudes with currently unknown impacts on its endogenous timing. Here we generated a daily transcriptome of C. finmarchicus at two high Arctic stations, during the more extreme time of Midnight Sun, the summer solstice. While the southern station (74.5 °N) was sea ice-free, the northern one (82.5 °N) was sea ice-covered. The mRNAs of the 42 samples have been sequenced with an average of 126 ± 5 million reads (mean ± SE) per sample, and aligned to the reference transcriptome. We detail the quality assessment of the datasets and the complete annotation procedure, providing the possibility to investigate daily gene expression of this ecologically important species at high Arctic latitudes, and to compare gene expression according to latitude and sea ice-coverage.

The contribution of ancient admixture to reproductive isolation between European sea bass lineages.

Understanding how new species arise through the progressive establishment of reproductive isolation (RI) barriers between diverging populations is a major goal in Evolutionary Biology. An important result of speciation genomics studies is that genomic regions involved in RI frequently harbor anciently diverged haplotypes that predate the reconstructed history of species divergence. The possible origins of these old alleles remain much debated, as they relate to contrasting mechanisms of speciation that are not yet fully understood. In the European sea bass (Dicentrarchus labrax), the genomic regions involved in RI between Atlantic and Mediterranean lineages are enriched for anciently diverged alleles of unknown origin. Here, we used haplotype-resolved whole-genome sequences to test whether divergent haplotypes could have originated from a closely related species, the spotted sea bass (Dicentrarchus punctatus). We found that an ancient admixture event between D. labrax and D. punctatus is responsible for the presence of shared derived alleles that segregate at low frequencies in both lineages of D. labrax. An exception to this was found within regions involved in RI between the two D. labrax lineages. In those regions, archaic tracts originating from D. punctatus locally reached high frequencies or even fixation in Atlantic genomes but were almost absent in the Mediterranean. We showed that the ancient admixture event most likely occurred between D. punctatus and the D. labrax Atlantic lineage, while Atlantic and Mediterranean D. labrax lineages were experiencing allopatric isolation. Our results suggest that local adaptive introgression and/or the resolution of genomic conflicts provoked by ancient admixture have probably contributed to the establishment of RI between the two D. labrax lineages.

Characterization of a Y-specific duplication/insertion of the anti-Mullerian hormone type II receptor gene based on a chromosome-scale genome assembly of yellow perch, Perca flavescens.

Yellow perch, Perca flavescens, is an ecologically and economically important species native to a large portion of the northern United States and southern Canada and is also a promising candidate species for aquaculture. However, no yellow perch reference genome has been available to facilitate improvements in both fisheries and aquaculture management practices. By combining Oxford Nanopore Technologies long-reads, 10X Genomics Illumina short linked reads and a chromosome contact map produced with Hi-C, we generated a high-continuity chromosome-scale yellow perch genome assembly of 877.4 Mb. It contains, in agreement with the known diploid chromosome yellow perch count, 24 chromosome-size scaffolds covering 98.8% of the complete assembly (N50 = 37.4 Mb, L50 = 11). We also provide a first characterization of the yellow perch sex determination locus that contains a male-specific duplicate of the anti-Mullerian hormone type II receptor gene (amhr2by) inserted at the proximal end of the Y chromosome (chromosome 9). Using this sex-specific information, we developed a simple PCR genotyping assay which accurately differentiates XY genetic males (amhr2by+ ) from XX genetic females (amhr2by- ). Our high-quality genome assembly is an important genomic resource for future studies on yellow perch ecology, toxicology, fisheries and aquaculture research. In addition, characterization of the amhr2by gene as a candidate sex-determining gene in yellow perch provides a new example of the recurrent implication of the transforming growth factor beta pathway in fish sex determination, and highlights gene duplication as an important genomic mechanism for the emergence of new master sex determination genes.

Author Correction: De novo phased assembly of the Vitis riparia grape genome.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

De novo phased assembly of the Vitis riparia grape genome.

Grapevine is one of the most important fruit species in the world. In order to better understand genetic basis of traits variation and facilitate the breeding of new genotypes, we sequenced, assembled, and annotated the genome of the American native Vitis riparia, one of the main species used worldwide for rootstock and scion breeding. A total of 164 Gb raw DNA reads were obtained from Vitis riparia resulting in a 225X depth of coverage. We generated a genome assembly of the V. riparia grape de novo using the PacBio long-reads that was phased with the 10x Genomics Chromium linked-reads. At the chromosome level, a 500 Mb genome was generated with a scaffold N50 size of 1 Mb. More than 34% of the whole genome were identified as repeat sequences, and 37,207 protein-coding genes were predicted. This genome assembly sets the stage for comparative genomic analysis of the diversification and adaptation of grapevine and will provide a solid resource for further genetic analysis and breeding of this economically important species.

Whole-genome sequencing of Aspergillus tubingensis G131 and overview of its secondary metabolism potential.

BACKGROUND: Black Aspergilli represent one of the most important fungal resources of primary and secondary metabolites for biotechnological industry. Having several black Aspergilli sequenced genomes should allow targeting the production of certain metabolites with bioactive properties. RESULTS: In this study, we report the draft genome of a black Aspergilli, A. tubingensis G131, isolated from a French Mediterranean vineyard. This 35 Mb genome includes 10,994 predicted genes. A genomic-based discovery identifies 80 secondary metabolites biosynthetic gene clusters. Genomic sequences of these clusters were blasted on 3 chosen black Aspergilli genomes: A. tubingensis CBS 134.48, A. niger CBS 513.88 and A. kawachii IFO 4308. This comparison highlights different levels of clusters conservation between the four strains. It also allows identifying seven unique clusters in A. tubingensis G131. Moreover, the putative secondary metabolites clusters for asperazine and naphtho-gamma-pyrones production were proposed based on this genomic analysis. Key biosynthetic genes required for the production of 2 mycotoxins, ochratoxin A and fumonisin, are absent from this draft genome. Even if intergenic sequences of these mycotoxins biosynthetic pathways are present, this could not lead to the production of those mycotoxins by A. tubingensis G131. CONCLUSIONS: Functional and bioinformatics analyses of A. tubingensis G131 genome highlight its potential for metabolites production in particular for TAN-1612, asperazine and naphtho-gamma-pyrones presenting antioxidant, anticancer or antibiotic properties.

High-throughput sequencing of kDNA amplicons for the analysis of Leishmania minicircles and identification of Neotropical species.

Leishmania kinetoplast DNA contains thousands of small circular molecules referred to as kinetoplast DNA (kDNA) minicercles. kDNA minicircles are the preferred targets for sensitive Leishmania detection, because they are present in high copy number and contain conserved sequence blocks in which polymerase chain reaction (PCR) primers can be designed. On the other hand, the heterogenic nature of minicircle networks has hampered the use of this peculiar genomic region for strain typing. The characterization of Leishmania minicirculomes used to require isolation and cloning steps prior to sequencing. Here, we show that high-throughput sequencing of single minicircle PCR products allows bypassing these laborious laboratory tasks. The 120 bp long minicircle conserved region was amplified by PCR from 18 Leishmania strains representative of the major species complexes found in the Neotropics. High-throughput sequencing of PCR products enabled recovering significant numbers of distinct minicircle sequences from each strain, reflecting minicircle class diversity. Minicircle sequence analysis revealed patterns that are congruent with current hypothesis of Leishmania relationships. Then, we show that a barcoding-like approach based on minicircle sequence comparisons may allow reliable identifications of Leishmania spp. This work opens up promising perspectives for the study of kDNA minicercles and a variety of applications in Leishmania research.

Estimating virus effective population size and selection without neutral markers.

By combining high-throughput sequencing (HTS) with experimental evolution, we can observe the within-host dynamics of pathogen variants of biomedical or ecological interest. We studied the evolutionary dynamics of five variants of Potato virus Y (PVY) in 15 doubled-haploid lines of pepper. All plants were inoculated with the same mixture of virus variants and variant frequencies were determined by HTS in eight plants of each pepper line at each of six sampling dates. We developed a method for estimating the intensities of selection and genetic drift in a multi-allelic Wright-Fisher model, applicable whether these forces are strong or weak, and in the absence of neutral markers. This method requires variant frequency determination at several time points, in independent hosts. The parameters are the selection coefficients for each PVY variant and four effective population sizes Ne at different time-points of the experiment. Numerical simulations of asexual haploid Wright-Fisher populations subjected to contrasting genetic drift (Ne ∈ [10, 2000]) and selection (|s| ∈ [0, 0.15]) regimes were used to validate the method proposed. The experiment in closely related pepper host genotypes revealed that viruses experienced a considerable diversity of selection and genetic drift regimes. The resulting variant dynamics were accurately described by Wright-Fisher models. The fitness ranks of the variants were almost identical between host genotypes. By contrast, the dynamics of Ne were highly variable, although a bottleneck was often identified during the systemic movement of the virus. We demonstrated that, for a fixed initial PVY population, virus effective population size is a heritable trait in plants. These findings pave the way for the breeding of plant varieties exposing viruses to stronger genetic drift, thereby slowing virus adaptation.

iDNA screening: Disease vectors as vertebrate samplers.

In the current context of global change and human-induced biodiversity decline, there is an urgent need for developing sampling approaches able to accurately describe the state of biodiversity. Traditional surveys of vertebrate fauna involve time-consuming and skill-demanding field methods. Recently, the use of DNA derived from invertebrate parasites (leeches and blowflies) was suggested as a new tool for vertebrate diversity assessment. Bloodmeal analyses of arthropod disease vectors have long been performed to describe their feeding behaviour, for epidemiological purposes. On the other hand, this existing expertise has not yet been applied to investigate vertebrate fauna per se. Here, we evaluate the usefulness of hematophagous dipterans as vertebrate samplers. Blood-fed sand flies and mosquitoes were collected in Amazonian forest sites and analysed using high-throughput sequencing of short mitochondrial markers. Bloodmeal identifications highlighted contrasting ecological features and feeding behaviour among dipteran species, which allowed unveiling arboreal and terrestrial mammals of various body size, as well as birds, lizards and amphibians. Additionally, lower vertebrate diversity was found in sites undergoing higher levels of human-induced perturbation. These results suggest that, in addition to providing precious information on disease vector host use, dipteran bloodmeal analyses may represent a useful tool in the study of vertebrate communities. Although further effort is required to validate the approach and consider its application to large-scale studies, this first work opens up promising perspectives for biodiversity monitoring and eco-epidemiology.

Vector soup: high-throughput identification of Neotropical phlebotomine sand flies using metabarcoding.

Phlebotomine sand flies are haematophagous dipterans of primary medical importance. They represent the only proven vectors of leishmaniasis worldwide and are involved in the transmission of various other pathogens. Studying the ecology of sand flies is crucial to understand the epidemiology of leishmaniasis and further control this disease. A major limitation in this regard is that traditional morphological-based methods for sand fly species identifications are time-consuming and require taxonomic expertise. DNA metabarcoding holds great promise in overcoming this issue by allowing the identification of multiple species from a single bulk sample. Here, we assessed the reliability of a short insect metabarcode located in the mitochondrial 16S rRNA for the identification of Neotropical sand flies, and constructed a reference database for 40 species found in French Guiana. Then, we conducted a metabarcoding experiment on sand flies mixtures of known content and showed that the method allows an accurate identification of specimens in pools. Finally, we applied metabarcoding to field samples caught in a 1-ha forest plot in French Guiana. Besides providing reliable molecular data for species-level assignations of phlebotomine sand flies, our study proves the efficiency of metabarcoding based on the mitochondrial 16S rRNA for studying sand fly diversity from bulk samples. The application of this high-throughput identification procedure to field samples can provide great opportunities for vector monitoring and eco-epidemiological studies.

Genetic diversity, linkage disequilibrium and power of a large grapevine (Vitis vinifera L) diversity panel newly designed for association studies.

BACKGROUND: As for many crops, new high-quality grapevine varieties requiring less pesticide and adapted to climate change are needed. In perennial species, breeding is a long process which can be speeded up by gaining knowledge about quantitative trait loci linked to agronomic traits variation. However, due to the long juvenile period of these species, establishing numerous highly recombinant populations for high resolution mapping is both costly and time-consuming. Genome wide association studies in germplasm panels is an alternative method of choice, since it allows identifying the main quantitative trait loci with high resolution by exploiting past recombination events between cultivars. Such studies require adequate panel design to represent most of the available genetic and phenotypic diversity. Assessing linkage disequilibrium extent and panel power is also needed to determine the marker density required for association studies. RESULTS: Starting from the largest grapevine collection worldwide maintained in Vassal (France), we designed a diversity panel of 279 cultivars with limited relatedness, reflecting the low structuration in three genetic pools resulting from different uses (table vs wine) and geographical origin (East vs West), and including the major founders of modern cultivars. With 20 simple sequence repeat markers and five quantitative traits, we showed that our panel adequately captured most of the genetic and phenotypic diversity existing within the entire Vassal collection. To assess linkage disequilibrium extent and panel power, we genotyped single nucleotide polymorphisms: 372 over four genomic regions and 129 distributed over the whole genome. Linkage disequilibrium, measured by correlation corrected for kinship, reached 0.2 for a physical distance between 9 and 458 Kb depending on genetic pool and genomic region, with varying size of linkage disequilibrium blocks. This panel achieved reasonable power to detect associations between traits with high broad-sense heritability (> 0.7) and causal loci with intermediate allelic frequency and strong effect (explaining > 10 % of total variance). CONCLUSIONS: Our association panel constitutes a new, highly valuable resource for genetic association studies in grapevine, and deserves dissemination to diverse field and greenhouse trials to gain more insight into the genetic control of many agronomic traits and their interaction with the environment.

The Characterization of Novel Tissue Microbiota Using an Optimized 16S Metagenomic Sequencing Pipeline.

BACKGROUND: Substantial progress in high-throughput metagenomic sequencing methodologies has enabled the characterisation of bacteria from various origins (for example gut and skin). However, the recently-discovered bacterial microbiota present within animal internal tissues has remained unexplored due to technical difficulties associated with these challenging samples. RESULTS: We have optimized a specific 16S rDNA-targeted metagenomics sequencing (16S metabarcoding) pipeline based on the Illumina MiSeq technology for the analysis of bacterial DNA in human and animal tissues. This was successfully achieved in various mouse tissues despite the high abundance of eukaryotic DNA and PCR inhibitors in these samples. We extensively tested this pipeline on mock communities, negative controls, positive controls and tissues and demonstrated the presence of novel tissue specific bacterial DNA profiles in a variety of organs (including brain, muscle, adipose tissue, liver and heart). CONCLUSION: The high throughput and excellent reproducibility of the method ensured exhaustive and precise coverage of the 16S rDNA bacterial variants present in mouse tissues. This optimized 16S metagenomic sequencing pipeline will allow the scientific community to catalogue the bacterial DNA profiles of different tissues and will provide a database to analyse host/bacterial interactions in relation to homeostasis and disease.

Emergence shapes the structure of the seed microbiota.

Seeds carry complex microbial communities, which may exert beneficial or deleterious effects on plant growth and plant health. To date, the composition of microbial communities associated with seeds has been explored mainly through culture-based diversity studies and therefore remains largely unknown. In this work, we analyzed the structures of the seed microbiotas of different plants from the family Brassicaceae and their dynamics during germination and emergence through sequencing of three molecular markers: the ITS1 region of the fungal internal transcribed spacer, the V4 region of 16S rRNA gene, and a species-specific bacterial marker based on a fragment of gyrB. Sequence analyses revealed important variations in microbial community composition between seed samples. Moreover, we found that emergence strongly influences the structure of the microbiota, with a marked reduction of bacterial and fungal diversity. This shift in the microbial community composition is mostly due to an increase in the relative abundance of some bacterial and fungal taxa possessing fast-growing abilities. Altogether, our results provide an estimation of the role of the seed as a source of inoculum for the seedling, which is crucial for practical applications in developing new strategies of inoculation for disease prevention.