Large vs small genomes in Passiflora: the influence of the mobilome and the satellitome

Ancient hybridization and repetitive element proliferation in the evolutionary history of the monocot genus Amomum (Zingiberaceae)

Genome size variation is a crucial aspect of plant evolution, influenced by a complex interplay of factors. Repetitive elements, which are fundamental components of genomic architecture, often play a role in genome expansion by selectively amplifying specific repeat motifs. This study focuses on Amomum, a genus in the ginger family (Zingiberaceae), known for its 4.4-fold variation in genome size. Using a robust methodology involving PhyloNet reconstruction, RepeatExplorer clustering, and repeat similarity-based phylogenetic network construction, we investigated the repeatome composition, analyzed repeat dynamics, and identified potential hybridization events within the genus. Our analysis confirmed the presence of four major infrageneric clades (A-D) within Amomum, with clades A-C exclusively comprising diploid species (2n = 48) and clade D encompassing both diploid and tetraploid species (2n = 48 and 96). We observed an increase in the repeat content within the genus, ranging from 84% to 89%, compared to outgroup species with 75% of the repeatome. The SIRE lineage of the Ty1-Copia repeat superfamily was prevalent in most analyzed ingroup genomes. We identified significant difference in repeatome structure between the basal Amomum clades (A, B, C) and the most diverged clade D. Our investigation revealed evidence of ancient hybridization events within Amomum, coinciding with a substantial proliferation of multiple repeat groups. This finding supports the hypothesis that ancient hybridization is a driving force in the genomic evolution of Amomum. Furthermore, we contextualize our findings within the broader context of genome size variations and repeatome dynamics observed across major monocot lineages. This study enhances our understanding of evolutionary processes within monocots by highlighting the crucial roles of repetitive elements in shaping genome size and suggesting the mechanisms that drive these changes.

Multi-integrated genomic data for Passiflora foetida provides insights into genome size evolution and floral development in Passiflora

Passiflora is a plant genus known for its extremely distinctive and colorful flowers and a wide range of genome size variation. However, how genome characteristics are related to flower traits among Passiflora species remains poorly understood. Here, we assembled a chromosome-scale genome of P. foetida, which belongs to the same subgenus as the commercial passionfruit P. edulis. The genome of P. foetida is smaller (424.16 Mb) and contains fewer copies of long terminal repeat retrotransposons (LTR-RTs). The disparity in LTR-RTs is one of the main contributors to the differences in genome sizes between these two species and possibly in floral traits. Additionally, we observed variation in insertion times and copy numbers of LTR-RTs across different transposable element (TE) lineages. Then, by integrating transcriptomic data from 33 samples (eight floral organs and flower buds at three developmental stages) with phylogenomic and metabolomic data, we conducted an in-depth analysis of the expression, phylogeny, and copy number of MIKC-type MADS-box genes and identified essential biosynthetic genes responsible for flower color and scent from glandular bracts and other floral organs. Our study pinpoints LRT-RTs as an important player in genome size variation in Passiflora species and provides insights into future genetic improvement.

The spread of satellite DNAs in euchromatin and insights into the multiple sex chromosome evolution in Hemiptera revealed by repeatome analysis of the bug Oxycarenus hyalinipennis

Satellite DNAs (satDNAs) are highly repeated tandem sequences primarily located in heterochromatin, although their occurrence in euchromatin has been reported. Here, our aim was to advance the understanding of satDNA and multiple sex chromosome evolution in heteropterans. We combined cytogenetic and genomic approaches to study, for the first time, the satDNA composition of the genome in an Oxycarenidae bug, Oxycarenus hyalinipennis. The species exhibits a male karyotype of 2n = 19 (14A + 2 m + X1 X2 Y), with a highly differentiated Y chromosome, as demonstrated by C-banding and comparative genomic hybridization, revealing an enrichment of repeats from the male genome. Additionally, comparative analysis between males and females revealed that the 26 identified satDNA families are significantly biased towards male genome, accumulating in discrete regions in the Y chromosome. Exceptionally, the OhyaSat04-125 family was found to be distributed virtually throughout the entire extension of the Y chromosome. This suggests an important role of satDNA in Y chromosome differentiation, in comparison of other repeats, which collectively shows similar abundance between sexes, about 50%. Furthermore, chromosomal mapping of all satDNA families revealed an unexpected high spread in euchromatic regions, covering the entire extension, irrespective of their abundance. Only discrete regions of heterochromatin on the Y chromosome and of the m-chromosomes (peculiar chromosomes commonly observed in heteropterans) were enriched with satDNAs. The putative causes of the intense enrichment of satDNAs in euchromatin are discussed, including the possible existence of burst cycles similar to transposable elements and as a result of holocentricity. These data challenge the classical notion that euchromatin is not enriched with satDNAs.

Repeat-based phylogenomics shed light on unclear relationships in the monocentric genus Juncus L. (Juncaceae)

The repetitive fraction (repeatome) of eukaryotic genomes is diverse and usually fast evolving, being an important tool for clarify plant systematics. The genus Juncus L. comprises 332 species, karyotypically recognized by having holocentric chromosomes. However, four species were recently described as monocentric, yet our understanding of their genome evolution is largely masked by unclear phylogenetic relationships. Here, we reassess the current Juncus systematics using low-coverage genome skimming data of 33 taxa to construct repeats, nuclear rDNA and plastome-based phylogenetic hypothesis. Furthermore, we characterize the repeatome and chromosomal distribution of Juncus-specific centromeric repeats/CENH3 protein to test the monocentricity reach in the genus. Repeat-base phylogenies revealed topologies congruent with the rDNA tree, but not with the plastome tree. The incongruence between nuclear and plastome chloroplast dataset suggest an ancient hybridization in the divergence of Juncotypus and Tenageia sections 40 Myr ago. The phylogenetic resolution at section level was better fitted with the rDNA/repeat-based approaches, with the recognition of two monophyletic sections (Stygiopsis and Tenageia). We found specific repeatome trends for the main lineages, such as the higher abundances of TEs in the Caespitosi and Iridifolii + Ozophyllum clades. CENH3 immunostaining confirmed the monocentricity of Juncus, which can be a generic synapomorphy for the genus. The heterogeneity of the repeatomes, with high phylogenetic informativeness, identified here may be correlated with their ancient origin (56 Mya) and reveals the potential of comparative genomic analyses for understanding plant systematics and evolution.

Genome-wide analysis of transposable elements and satellite DNA in Humulus scandens, a dioecious plant with XX/XY1Y2 chromosomes

Transposable elements (TEs) and satellite DNAs, two major categories of repetitive sequences, are expected to accumulate in non-recombining genome regions, including sex-linked regions, and contribute to sex chromosome evolution. The dioecious plant, Humulus scandens, can be used for studying the evolution of the XX/XY1Y2 sex chromosomes. In this study, we thoroughly examined the repetitive components of male and female H. scandens using next-generation sequencing data followed by bioinformatics analysis and florescence in situ hybridization (FISH). The H. scandens genome has a high overall repetitive sequence composition, 68.30% in the female and 66.78% in the male genome, with abundant long terminal repeat (LTR) retrotransposons (RTs), including more Ty3/Gypsy than Ty1/Copia elements, particularly two Ty3/Gypsy lineages, Tekay and Retand. Most LTR-RT lineages were found dispersed across the chromosomes, though CRM and Athila elements were predominately found within the centromeres and the pericentromeric regions. The Athila elements also showed clearly higher FISH signal intensities in the Y1 and Y2 chromosomes than in the X or autosomes. Three novel satellite DNAs were specifically distributed in the centromeric and/or telomeric regions, with markedly different distributions on the X, Y1, and Y2 chromosomes. Combined with FISH using satellite DNAs to stain chromosomes during meiotic diakinesis, we determined the synapsis pattern and distinguish pseudoautosomal regions (PARs). The results indicate that the XY1Y2 sex chromosomes of H. scandens might have originated from a centric fission event. This study improves our understanding of the repetitive sequence organization of H. scandens genome and provides a basis for further analysis of their chromosome evolution process.

Comparative analysis of repetitive DNA in dysploid and non-dysploid Phaseolus beans

Structural karyotype changes result from ectopic recombination events frequently associated with repetitive DNA. Although most Phaseolus species present relatively stable karyotypes with 2n = 22 chromosomes, the karyotypes of species of the Leptostachyus group show high rates of structural rearrangements, including a nested chromosome fusion that led to the dysploid chromosome number of the group (2n = 20). We examined the roles of repetitive landscapes in the rearrangements of species of the Leptostachyus group using genome-skimming data to characterize the repeatome in a range of Phaseolus species and compared them to species of that group (P. leptostachyus and P. macvaughii). LTR retrotransposons, especially the Ty3/gypsy lineage Chromovirus, were the most abundant elements in the genomes. Differences in the abundance of Tekay, Retand, and SIRE elements between P. macvaughii and P. leptostachyus were reflected in their total amounts of Ty3/gypsy and Ty1/copia. The satellite DNA fraction was the most divergent among the species, varying both in abundance and distribution, even between P. leptostachyus and P. macvaughii. The rapid turnover of repeats in the Leptostachyus group may be associated with the several rearrangements observed.

Abundance of distal repetitive DNA sequences in Capsicum L. (Solanaceae) chromosomes

Chili peppers (Solanaceae family) have great commercial value. They are commercialized in natura and used as spices and for ornamental and medicinal purposes. Although three whole genomes have been published, limited information about satellite DNA sequences, their composition, and genomic distribution has been provided. Here, we exploited the noncoding repetitive fraction, represented by satellite sequences, that tends to accumulate in blocks along chromosomes, especially near the chromosome ends of peppers. Two satellite DNA sequences were identified (CDR-1 and CDR-2), characterized and mapped in silico in three Capsicum genomes (C. annuum, C. chinense, and C. baccatum) using data from the published high-coverage sequencing and repeats finding bioinformatic tools. Localization using FISH in the chromosomes of these species and in two others (C. frutescens and C. chacoense), totaling five species, showed signals adjacent to the rDNA sites. A sequence comparison with existing Solanaceae repeats showed that CDR-1 and CDR-2 have different origins but without homology to rDNA sequences. Satellites occupied subterminal chromosomal regions, sometimes collocated with or adjacent to 35S rDNA sequences. Our results expand knowledge about the diversity of subterminal regions of Capsicum chromosomes, showing different amounts and distributions within and between karyotypes. In addition, these sequences may be useful for future phylogenetic studies.

Satellite DNAs-From Localized to Highly Dispersed Genome Components

According to the established classical view, satellite DNAs are defined as abundant non-coding DNA sequences repeated in tandem that build long arrays located in heterochromatin. Advances in sequencing methodologies and development of specialized bioinformatics tools enabled defining a collection of all repetitive DNAs and satellite DNAs in a genome, the repeatome and the satellitome, respectively, as well as their reliable annotation on sequenced genomes. Supported by various non-model species included in recent studies, the patterns of satellite DNAs and satellitomes as a whole showed much more diversity and complexity than initially thought. Differences are not only in number and abundance of satellite DNAs but also in their distribution across the genome, array length, interspersion patterns, association with transposable elements, localization in heterochromatin and/or in euchromatin. In this review, we compare characteristic organizational features of satellite DNAs and satellitomes across different animal and plant species in order to summarize organizational forms and evolutionary processes that may lead to satellitomes' diversity and revisit some basic notions regarding repetitive DNA landscapes in genomes.

Differential Repeat Accumulation in the Bimodal Karyotype of Agave L

The genus Agave presents a bimodal karyotype with x = 30 (5L, large, +25S, small chromosomes). Bimodality within this genus is generally attributed to allopolyploidy in the ancestral form of Agavoideae. However, alternative mechanisms, such as the preferential accumulation of repetitive elements at the macrochromosomes, could also be important. Aiming to understand the role of repetitive DNA within the bimodal karyotype of Agave, genomic DNA from the commercial hybrid 11648 (2n = 2x = 60, 6.31 Gbp) was sequenced at low coverage, and the repetitive fraction was characterized. In silico analysis showed that ~67.6% of the genome is mainly composed of different LTR retrotransposon lineages and one satellite DNA family (AgSAT171). The satellite DNA localized at the centromeric regions of all chromosomes; however, stronger signals were observed for 20 of the macro- and microchromosomes. All transposable elements showed a dispersed distribution, but not uniform across the length of the chromosomes. Different distribution patterns were observed for different TE lineages, with larger accumulation at the macrochromosomes. The data indicate the differential accumulation of LTR retrotransposon lineages at the macrochromosomes, probably contributing to the bimodality. Nevertheless, the differential accumulation of the satDNA in one group of macro- and microchromosomes possibly reflects the hybrid origin of this Agave accession.

Evolution of satDNAs on holocentric chromosomes: insights from hemipteran insects of the genus Mahanarva

Satellite DNAs (satDNAs) constitute one of the main components of eukaryote genomes and are involved in chromosomal organization and diversification. Although largely studied, little information was gathered about their evolution on holocentric species, i.e., diffuse centromeres, which, due to differences in repeat organization, could result in different evolutionary patterns. Here, we combined bioinformatics and cytogenetic approaches to evaluate the evolution of the satellitomes in Mahanarva holocentric insects. In two species, de novo identification revealed a high number of satDNAs, 110 and 113, with an extreme monomer length range of 18-4228 bp. The overall abundance of satDNAs was observed to be 6.67% in M. quadripunctata and 1.98% in M. spectabilis, with different abundances for the shared satDNAs. Chromosomal mapping of the most abundant repeats of M. quadripunctata and M. spectabilis on other Mahanarva reinforced the dynamic nature of satDNAs. Variable patterns of chromosomal distribution for the satDNAs were noticed, with the occurrence of clusters on distinct numbers of chromosomes and at different positions and the occurrence of scattered signals or nonclustered satDNAs. Altogether, our data demonstrated the high dynamism of satDNAs in Mahanarva with the involvement of this genomic fraction in chromosome diversification of the genus. The general characteristics and patterns of evolution of satDNAs are similar to those observed on monocentric chromosomes, suggesting that the differential organization of genome compartments observed on holocentric chromosomes compared with monocentric chromosomes does not have a large impact on the evolution of satDNAs. Analysis of the satellitomes of other holocentric species in a comparative manner will shed light on this issue.

Annotation of the Turnera subulata (Passifloraceae) Draft Genome Reveals the S-Locus Evolved after the Divergence of Turneroideae from Passifloroideae in a Stepwise Manner

A majority of Turnera species (Passifloraceae) exhibit distyly, a reproductive system involving both self-incompatibility and reciprocal herkogamy. This system differs from self-incompatibility in Passiflora species. The genetic basis of distyly in Turnera is a supergene, restricted to the S-morph, and containing three S-genes. How supergenes and distyly evolved in Turnera, and the other Angiosperm families exhibiting distyly remain largely unknown. Unraveling the evolutionary origins in Turnera requires the generation of genomic resources and extensive phylogenetic analyses. Here, we present the annotated draft genome of the S-morph of distylous Turnera subulata. Our annotation allowed for phylogenetic analyses of the three S-genes' families across 56 plant species ranging from non-seed plants to eudicots. In addition to the phylogenetic analysis, we identified the three S-genes' closest paralogs in two species of Passiflora. Our analyses suggest that the S-locus evolved after the divergence of Passiflora and Turnera. Finally, to provide insights into the neofunctionalization of the S-genes, we compared expression patterns of the S-genes with close paralogs in Arabidopsis and Populus trichocarpa. The annotation of the T. subulata genome will provide a useful resource for future comparative work. Additionally, this work has provided insights into the convergent nature of distyly and the origin of supergenes.

Satellitome Analysis on Talpa aquitania Genome and Inferences about the satDNAs Evolution on Some Talpidae

In the genus Talpa a new species, named Talpa aquitania, has been recently described. Only cytogenetic data are available for the nuclear genome of this species. In this work, we characterize the satellitome of the T. aquitania genome that presents 16 different families, including telomeric sequences, and they represent 1.24% of the genome. The first satellite DNA family (TaquSat1-183) represents 0.558%, and six more abundant families, including TaquSat1-183, comprise 1.13%, while the remaining 11 sat-DNAs represent only 0.11%. The average A + T content of the SatDNA families was 50.43% and the median monomer length was 289.24 bp. The analysis of these SatDNAs indicated that they have different grades of clusterization, homogenization, and degeneration. Most of the satDNA families are present in the genomes of the other Talpa species analyzed, while in the genomes of other more distant species of Talpidae, only some of them are present, in accordance with the library hypothesis. Moreover, chromosomal localization by FISH revealed that some satDNAs are localized preferentially on centromeric and non-centromeric heterochromatin in T. aquitania and also in the sister species T. occidentalis karyotype. The differences observed between T. aquitania and the close relative T. occidentalis and T. europaea suggested that the satellitome is a very dynamic component of the genomes and that the satDNAs could be responsible for chromosomal differences between the species. Finally, in a broad context, these data contribute to the understanding of the evolution of satellitomes on mammals.

The Satellite DNA Catalogues of Two Serrasalmidae (Teleostei, Characiformes): Conservation of General satDNA Features over 30 Million Years

Satellite DNAs (satDNAs) are tandemly repeated sequences that are usually located on the heterochromatin, and the entire collection of satDNAs within a genome is called satellitome. Primarily, these sequences are not under selective pressure and evolve by concerted evolution, resulting in elevated rates of divergence between the satDNA profiles of reproductive isolated species/populations. Here, we characterized two additional satellitomes of Characiformes fish (Colossoma macropomum and Piaractus mesopotamicus) that diverged approximately 30 million years ago, while still retaining conserved karyotype features. The results we obtained indicated that several satDNAs (50% of satellite sequences in P. mesopotamicus and 43% in C. macropomum) show levels of conservation between the analyzed species, in the nucleotide and chromosomal levels. We propose that long-life cycles and few genomic changes could slow down rates of satDNA differentiation.

Comparative repeatome analysis reveals new evidence on genome evolution in wild diploid Arachis (Fabaceae) species

Opposing changes in the abundance of satellite DNA and long terminal repeat (LTR) retroelements are the main contributors to the variation in genome size and heterochromatin amount in Arachis diploids. The South American genus Arachis (Fabaceae) comprises 83 species organized in nine taxonomic sections. Among them, section Arachis is characterized by species with a wide genome and karyotype diversity. Such diversity is determined mainly by the amount and composition of repetitive DNA. Here we performed computational analysis on low coverage genome sequencing to infer the dynamics of changes in major repeat families that led to the differentiation of genomes in diploid species (x = 10) of genus Arachis, focusing on section Arachis. Estimated repeat content ranged from 62.50 to 71.68% of the genomes. Species with different genome composition tended to have different landscapes of repeated sequences. Athila family retrotransposons were the most abundant and variable lineage among Arachis repeatomes, with peaks of transpositional activity inferred at different times in the evolution of the species. Satellite DNAs (satDNAs) were less abundant, but differentially represented among species. High rates of evolution of an AT-rich superfamily of satDNAs led to the differential accumulation of heterochromatin in Arachis genomes. The relationship between genome size variation and the repetitive content is complex. However, largest genomes presented a higher accumulation of LTR elements and lower contents of satDNAs. In contrast, species with lowest genome sizes tended to accumulate satDNAs in detriment of LTR elements. Phylogenetic analysis based on repetitive DNA supported the genome arrangement of section Arachis. Altogether, our results provide the most comprehensive picture on the repeatome dynamics that led to the genome differentiation of Arachis species.

Genomes shed light on the evolution of Begonia, a mega-diverse genus

Clarifying the evolutionary processes underlying species diversification and adaptation is a key focus of evolutionary biology. Begonia (Begoniaceae) is one of the most species-rich angiosperm genera with c. 2000 species, most of which are shade-adapted. Here, we present chromosome-scale genome assemblies for four species of Begonia (B. loranthoides, B. masoniana, B. darthvaderiana and B. peltatifolia), and whole genome shotgun data for an additional 74 Begonia representatives to investigate lineage evolution and shade adaptation of the genus. The four genome assemblies range in size from 331.75 Mb (B. peltatifolia) to 799.83 Mb (B. masoniana), and harbor 22 059-23 444 protein-coding genes. Synteny analysis revealed a lineage-specific whole-genome duplication (WGD) that occurred just before the diversification of Begonia. Functional enrichment of gene families retained after WGD highlights the significance of modified carbohydrate metabolism and photosynthesis possibly linked to shade adaptation in the genus, which is further supported by expansions of gene families involved in light perception and harvesting. Phylogenomic reconstructions and genomics studies indicate that genomic introgression has also played a role in the evolution of Begonia. Overall, this study provides valuable genomic resources for Begonia and suggests potential drivers underlying the diversity and adaptive evolution of this mega-diverse clade.

The Singular Evolution of Olea Genome Structure

The current view of plant genome evolution proposes that genome size has mainly been determined by polyploidisation and amplification/loss of transposons, with a minor role played by other repeated sequences, such as tandem repeats. In cultivated olive (Olea europaea subsp. europaea var. europaea), available data suggest a singular model of genome evolution, in which a massive expansion of tandem-repeated sequences accompanied changes in nuclear architecture. This peculiar scenario highlights the importance of focusing on Olea genus evolution, to shed light on mechanisms that led to its present genomic structure. Next-generation sequencing technologies, bioinformatics and in situ hybridisation were applied to study the genomic structure of five related Olea taxa, which originated at different times from their last common ancestor. On average, repetitive DNA in the Olea taxa ranged from ~59% to ~73% of the total genome, showing remarkable differences in terms of composition. Among repeats, we identified 11 major families of tandem repeats, with different abundances in the analysed taxa, five of which were novel discoveries. Interestingly, overall tandem repeat abundance was inversely correlated to that of retrotransposons. This trend might imply a competition in the proliferation of these repeat classes. Indeed, O. paniculata, the species closest to the Olea common ancestor, showed very few tandem-repeated sequences, while it was rich in long terminal repeat retrotransposons, suggesting that the amplification of tandem repeats occurred after its divergence from the Olea ancestor. Furthermore, some tandem repeats were physically localised in closely related O. europaea subspecies (i.e., cultivated olive and O. europaea subsp. cuspidata), which showed a significant difference in tandem repeats abundance. For 4 tandem repeats families, a similar number of hybridisation signals were observed in both subspecies, apparently indicating that, after their dissemination throughout the olive genome, these tandem repeats families differentially amplified maintaining the same positions in each genome. Overall, our research identified the temporal dynamics shaping genome structure during Olea speciation, which represented a singular model of genome evolution in higher plants.

Tracing the Evolution of the Angiosperm Genome from the Cytogenetic Point of View

Cytogenetics constitutes a branch of genetics that is focused on the cellular components, especially chromosomes, in relation to heredity and genome structure, function and evolution. The use of modern cytogenetic approaches and the latest microscopes with image acquisition and processing systems enables the simultaneous two- or three-dimensional, multicolour visualisation of both single-copy and highly-repetitive sequences in the plant genome. The data that is gathered using the cytogenetic methods in the phylogenetic background enable tracing the evolution of the plant genome that involve changes in: (i) genome sizes; (ii) chromosome numbers and morphology; (iii) the content of repetitive sequences and (iv) ploidy level. Modern cytogenetic approaches such as FISH using chromosome- and genome-specific probes have been widely used in studies of the evolution of diploids and the consequences of polyploidy. Nowadays, modern cytogenetics complements analyses in other fields of cell biology and constitutes the linkage between genetics, molecular biology and genomics.

A genome sequence resource for the genus Passiflora, the genome of the wild diploid species Passiflora organensis

The genus Passiflora comprises a large group of plants popularly known as passionfruit, much appreciated for their exotic flowers and edible fruits. The species (∼500) are morphologically variable (e.g., growth habit, size, and color of flowers) and are adapted to distinct tropical ecosystems. In this study, we generated the genome of the wild diploid species Passiflora organensis Gardner by adopting a hybrid assembly approach. Passiflora organensis has a small genome of 259 Mbp and a heterozygosity rate of 81%, consistent with its reproductive system. Most of the genome sequences could be integrated into its chromosomes with cytogenomic markers (satellite DNA) as references. The repeated sequences accounted for 58.55% of the total DNA analyzed, and the Tekay lineage was the prevalent retrotransposon. In total, 25,327 coding genes were predicted. Passiflora organensis retains 5,609 singletons and 15,671 gene families. We focused on the genes potentially involved in the locus determining self-incompatibility and the MADS-box gene family, allowing us to infer expansions and contractions within specific subfamilies. Finally, we recovered the organellar DNA. Structural rearrangements and two mitoviruses, besides relics of other mobile elements, were found in the chloroplast and mt-DNA molecules, respectively. This study presents the first draft genome assembly of a wild Passiflora species, providing a valuable sequence resource for genomic and evolutionary studies on the genus, and support for breeding cropped passionfruit species.

Genome Size Doubling Arises From the Differential Repetitive DNA Dynamics in the Genus Heloniopsis (Melanthiaceae)

Plant genomes are highly diverse in size and repetitive DNA composition. In the absence of polyploidy, the dynamics of repetitive elements, which make up the bulk of the genome in many species, are the main drivers underpinning changes in genome size and the overall evolution of the genomic landscape. The advent of high-throughput sequencing technologies has enabled investigation of genome evolutionary dynamics beyond model plants to provide exciting new insights in species across the biodiversity of life. Here we analyze the evolution of repetitive DNA in two closely related species of Heloniopsis (Melanthiaceae), which despite having the same chromosome number differ nearly twofold in genome size [i.e., H. umbellata (1C = 4,680 Mb), and H. koreana (1C = 2,480 Mb)]. Low-coverage genome skimming and the RepeatExplorer2 pipeline were used to identify the main repeat families responsible for the significant differences in genome sizes. Patterns of repeat evolution were found to correlate with genome size with the main classes of transposable elements identified being twice as abundant in the larger genome of H. umbellata compared with H. koreana. In addition, among the satellite DNA families recovered, a single shared satellite (HeloSAT) was shown to have contributed significantly to the genome expansion of H. umbellata. Evolutionary changes in repetitive DNA composition and genome size indicate that the differences in genome size between these species have been underpinned by the activity of several distinct repeat lineages.

Satellitome Analysis of the Pacific Oyster Crassostrea gigas Reveals New Pattern of Satellite DNA Organization, Highly Scattered across the Genome

Several features already qualified the invasive bivalve species Crassostrea gigas as a valuable non-standard model organism in genome research. C. gigas is characterized by the low contribution of satellite DNAs (satDNAs) vs. mobile elements and has an extremely low amount of heterochromatin, predominantly built of DNA transposons. In this work, we have identified 52 satDNAs composing the satellitome of C. gigas and constituting about 6.33% of the genome. Satellitome analysis reveals unusual, highly scattered organization of relatively short satDNA arrays across the whole genome. However, peculiar chromosomal distribution and densities are specific for each satDNA. The inspection of the organizational forms of the 11 most abundant satDNAs shows association with constitutive parts of Helitron mobile elements. Nine of the inspected satDNAs are dominantly found in mobile element-associated form, two mostly appear standalone, and only one is present exclusively as Helitron-associated sequence. The Helitron-related satDNAs appear in more chromosomes than other satDNAs, indicating that these mobile elements could be leading satDNA propagation in C. gigas. No significant accumulation of satDNAs on certain chromosomal positions was detected in C. gigas, thus establishing a novel pattern of satDNA organization on the genome level.

Satellitome Analysis of Rhodnius prolixus, One of the Main Chagas Disease Vector Species

The triatomine Rhodnius prolixus is the main vector of Chagas disease in countries such as Colombia and Venezuela, and the first kissing bug whose genome has been sequenced and assembled. In the repetitive genome fraction (repeatome) of this species, the transposable elements represented 19% of R. prolixus genome, being mostly DNA transposon (Class II elements). However, scarce information has been published regarding another important repeated DNA fraction, the satellite DNA (satDNA), or satellitome. Here, we offer, for the first time, extended data about satellite DNA families in the R. prolixus genome using bioinformatics pipeline based on low-coverage sequencing data. The satellitome of R. prolixus represents 8% of the total genome and it is composed by 39 satDNA families, including four satDNA families that are shared with Triatoma infestans, as well as telomeric (TTAGG)n and (GATA)n repeats, also present in the T. infestans genome. Only three of them exceed 1% of the genome. Chromosomal hybridization with these satDNA probes showed dispersed signals over the euchromatin of all chromosomes, both in autosomes and sex chromosomes. Moreover, clustering analysis revealed that most abundant satDNA families configured several superclusters, indicating that R. prolixus satellitome is complex and that the four most abundant satDNA families are composed by different subfamilies. Additionally, transcription of satDNA families was analyzed in different tissues, showing that 33 out of 39 satDNA families are transcribed in four different patterns of expression across samples.