INTRODUCTION: Satellite DNA (satDNA) is a rapidly evolving component of plant genomes, typically found in (peri)centromeric, (sub)telomeric, and other heterochromatic regions. Due to their variability and species- or population-specific distribution, satDNA serves as valuable cytogenetic markers for studying chromosomal rearrangements and karyotype evolution among closely related species. Previous studies have identified species-specific subtelomeric repeats CS-1 in Cannabis sativa, HSR1 in Humulus lupulus, and HJSR in Humulus japonicus. These satellites have been used to differentiate sex chromosomes from autosomes, however, their evolutionary origins, sequence variation and conservation pattern across related species remain largely unexplored. METHODS: In this study, we analyze sequence similarity among these satellites and assess their interspecific chromosomal localization using fluorescence in situ hybridization (FISH). RESULTS: Our results reveal that the HSR1 and HJSR satellites are shared across all studied species, suggesting their common origin from a shared pool of satDNA in their common ancestor. In contrast, the CS-1 satellite exhibits higher sequence divergence. DISCUSSION: Although all three satellites are predominantly localized in subtelomeric regions, we identified species-specific exceptions. These findings provide new insight into the evolutionary dynamics of satDNA within the Cannabaceae family and offer further support for the divergence of Humulus species.

• Keywords
• Humulus, metaphase chromosomes, phylogenetics, satellite divergence, subtelomeric repeats,
• Publication type
• Journal Article MeSH

The genus Chenopodium L. is characterized by its wide geographic distribution and ecological adaptability. Species such as quinoa (Chenopodium quinoa Willd.) have served as domesticated staple crops for centuries. Wild Chenopodium species exhibit diverse niche adaptations and are important genetic reservoirs for beneficial agronomic traits, including disease resistance and climate hardiness. To harness the potential of the wild taxa for crop improvement, we developed a Chenopodium pangenome through the assembly and comparative analyses of 12 Chenopodium species that encompass the eight known genome types (A-H). Six of the species are new chromosome-scale assemblies, and many are polyploids; thus, a total of 20 genomes were included in the pangenome analyses. We show that the genomes vary dramatically in size with the D genome being the smallest (∼370 Mb) and the B genome being the largest (∼700 Mb) and that genome size was correlated with independent expansions of the Copia and Gypsy LTR retrotransposon families, suggesting that transposable elements have played a critical role in the evolution of the Chenopodium genomes. We annotated a total of 33,457 pan-Chenopodium gene families, of which ∼65% were classified as shell (2% private). Phylogenetic analysis clarified the evolutionary relationships among the genome lineages, notably resolving the taxonomic placement of the F genome while highlighting the uniqueness of the A genome in the Western Hemisphere. These genomic resources are particularly important for understanding the secondary and tertiary gene pools available for the improvement of the domesticated chenopods while furthering our understanding of the evolution and complexity within the genus.

• MeSH
• Chenopodium * genetics   MeSH
• Genome Size MeSH
• Phylogeny MeSH
• Genome, Plant * MeSH
• Terminal Repeat Sequences * genetics   MeSH
• Evolution, Molecular * MeSH
• Retroelements MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Retroelements MeSH

Multiple sex chromosomes usually arise from chromosomal rearrangements which involve ancestral sex chromosomes. There is a fundamental condition to be met for their long-term fixation: the meiosis must function, leading to the stability of the emerged system, mainly concerning the segregation of the sex multivalent. Here, we sought to analyze the degree of differentiation and meiotic pairing properties in the selected fish multiple sex chromosome system present in the wolf-fish Hoplias malabaricus (HMA). This species complex encompasses seven known karyotype forms (karyomorphs) where the karyomorph C (HMA-C) exhibits a nascent XY sex chromosomes from which the multiple X1X2Y system evolved in karyomorph HMA-D via a Y-autosome fusion. We combined genomic and cytogenetic approaches to analyze the satellite DNA (satDNA) content in the genome of HMA-D karyomorph and to investigate its potential contribution to X1X2Y sex chromosome differentiation. We revealed 56 satDNA monomers of which the majority was AT-rich and with repeat units longer than 100 bp. Seven out of 18 satDNA families chosen for chromosomal mapping by fluorescence in situ hybridization (FISH) formed detectable accumulation in at least one of the three sex chromosomes (X1, X2 and neo-Y). Nine satDNA monomers showed only two hybridization signals limited to HMA-D autosomes, and the two remaining ones provided no visible FISH signals. Out of seven satDNAs located on the HMA-D sex chromosomes, five mapped also to XY chromosomes of HMA-C. We showed that after the autosome-Y fusion event, the neo-Y chromosome has not substantially accumulated or eliminated satDNA sequences except for minor changes in the centromere-proximal region. Finally, based on the obtained FISHpatterns, we speculate on the possible contribution of satDNA to sex trivalent pairing and segregation.

• Keywords
• FISH, Meiosis, Multiple sex chromosomes, Satellitome, Sex trivalent,
• MeSH
• Characiformes * genetics   MeSH
• Y Chromosome genetics   MeSH
• In Situ Hybridization, Fluorescence * MeSH
• Karyotype MeSH
• Meiosis genetics   MeSH
• Evolution, Molecular MeSH
• Sex Chromosomes * genetics   MeSH
• DNA, Satellite * genetics   MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• DNA, Satellite * MeSH

BACKGROUND: Telomeres are the nucleoprotein complexes that physically cap the ends of eukaryotic chromosomes. Most plants possess Arabidopsis-type telomere sequences (TSs). In addition to terminal TSs, more diverse interstitial TSs exists in plants. Although telomeres have been sufficiently studied, the actual diversity of TSs in land plants is underestimated. RESULTS: We investigate genotypes from seven natural populations with contrasting environments of four Chenopodium species to reveal the variability in TSs by analyzing Oxford Nanopore reads. Fluorescent in situ hybridization was used to localize telomeric repeats on chromosomes. We identified a number of derivative monomers that arise in part of both terminal and interstitial telomeric arrays of a single genotype. The former presents a case of block-organized double-monomer telomers, where blocks of Arabidopsis-type TTTAGGG motifs were interspersed with blocks of derivative TTTAAAA motifs. The latter is an integral part of the satellitome with transformations specific to the inactive genome fraction. CONCLUSIONS: We suggested two alternative models for the possible formation of derivative monomers from telomeric heptamer motifs of Arabidopsis-type. It was assumed that derivatization of TSs is a ubiquitous process in the plant genome but occurrence and frequencies of derivatives may be genotype-specific. We also propose that the formation of non-canonical arrays of TSs, especially at chromosomal termini, may be a source for genomic variability in nature.

• Keywords
• Evolution, Oxford nanopore sequencing, Plant, Population, Species, Telomere,
• MeSH
• Arabidopsis * genetics   MeSH
• Eukaryota MeSH
• Genotype MeSH
• In Situ Hybridization, Fluorescence MeSH
• Humans MeSH
• Telomere genetics   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Case Reports MeSH

To provide insights into the fate of transposable elements (TEs) across timescales in a post-polyploidization context, we comparatively investigate five sibling Dactylorhiza allotetraploids (Orchidaceae) formed independently and sequentially between 500 and 100K generations ago by unidirectional hybridization between diploids D. fuchsii and D. incarnata. Our results first reveal that the paternal D. incarnata genome shows a marked increased content of LTR retrotransposons compared to the maternal species, reflected in its larger genome size and consistent with a previously hypothesized bottleneck. With regard to the allopolyploids, in the youngest D. purpurella both genome size and TE composition appear to be largely additive with respect to parents, whereas for polyploids of intermediate ages we uncover rampant genome expansion on a magnitude of multiple entire genomes of some plants such as Arabidopsis. The oldest allopolyploids in the series are not larger than the intermediate ones. A putative tandem repeat, potentially derived from a non-autonomous miniature inverted-repeat TE (MITE) drives much of the genome dynamics in the allopolyploids. The highly dynamic MITE-like element is found in higher proportions in the maternal diploid, D. fuchsii, but is observed to increase in copy number in both subgenomes of the allopolyploids. Altogether, the fate of repeats appears strongly regulated and therefore predictable across multiple independent allopolyploidization events in this system. Apart from the MITE-like element, we consistently document a mild genomic shock following the allopolyploidizations investigated here, which may be linked to their relatively large genome sizes, possibly associated with strong selection against further genome expansions.

• Keywords
• allopolyploidy, genome size, genomic shock, marsh orchids, transposable elements,
• MeSH
• Diploidy MeSH
• Genome, Plant MeSH
• Humans MeSH
• Wetlands MeSH
• Orchidaceae * genetics   MeSH
• Polyploidy MeSH
• Siblings * MeSH
• DNA Transposable Elements genetics   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA Transposable Elements MeSH

Djulis (Chenopodium formosanum Koidz.) is a crop grown since antiquity in Taiwan. It is a BCD-genome hexaploid (2n = 6x = 54) domesticated form of lambsquarters (C. album L.) and a relative of the allotetraploid (AABB) C. quinoa. As with quinoa, djulis seed contains a complete protein profile and many nutritionally important vitamins and minerals. While still sold locally in Taiwanese markets, its traditional culinary uses are being lost as diets of younger generations change. Moreover, indigenous Taiwanese peoples who have long safeguarded djulis are losing their traditional farmlands. We used PacBio sequencing and Hi-C-based scaffolding to produce a chromosome-scale, reference-quality assembly of djulis. The final genome assembly spans 1.63 Gb in 798 scaffolds, with 97.8% of the sequence contained in 27 scaffolds representing the nine haploid chromosomes of each sub-genome of the species. Benchmarking of universal, single-copy orthologs indicated that 98.5% of the conserved orthologous genes for Viridiplantae are complete within the assembled genome, with 92.9% duplicated, as expected for a polyploid. A total of 67.8% of the assembly is repetitive, with the most common repeat being Gypsy long terminal repeat retrotransposons, which had significantly expanded in the B sub-genome. Gene annotation using Iso-Seq data from multiple tissues identified 75,056 putative gene models. Comparisons to quinoa showed strong patterns of synteny which allowed for the identification of homoeologous chromosomes, and sub-genome-specific sequences were used to assign homoeologs to each sub-genome. These results represent the first hexaploid genome assembly and the first assemblies of the C and D genomes of the Chenopodioideae subfamily.

• Keywords
• Gypsy, LTR, chromosome-scale, long-read sequencing, polyploid evolution, retrotransposon,
• MeSH
• Chenopodium * genetics   MeSH
• Chromosomes, Plant genetics   MeSH
• Genome, Plant MeSH
• Polyploidy MeSH
• Synteny MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

BACKGROUND: CACTA transposable elements (TEs) comprise one of the most abundant superfamilies of Class 2 (cut-and-paste) transposons. Over recent decades, CACTA elements were widely identified in species from the plant, fungi, and animal kingdoms, but sufficiently studied in the genomes of only a few model species although non-model genomes can bring additional and valuable information. It primarily concerned the genomes of species belonging to clades in the base of large taxonomic groups whose genomes, to a certain extent, can preserve relict and/or possesses specific traits. Thus, we sought to investigate the genomes of Chenopodium (Amaranthaceae, Caryophyllales) species to unravel the structural variability of CACTA elements. Caryophyllales is a separate branch of Angiosperms and until recently the diversity of CACTA elements in this clade was unknown. RESULTS: Application of the short-read genome assembly algorithm followed by analysis of detected complete CACTA elements allowed for the determination of their structural diversity in the genomes of 22 Chenopodium album aggregate species. This approach yielded knowledge regarding: (i) the coexistence of two CACTA transposons subtypes in single genome; (ii) gaining of additional protein conserved domains within the coding sequence; (iii) the presence of captured gene fragments, including key genes for flower development; and (iv)) identification of captured satDNA arrays. Wide comparative database analysis revealed that identified events are scattered through Angiosperms in different proportions. CONCLUSIONS: Our study demonstrated that while preserving the basic element structure a wide range of coding and non-coding additions to CACTA transposons occur in the genomes of C. album aggregate species. Ability to relocate additions inside genome in combination with the proposed novel functional features of structural-different CACTA elements can impact evolutionary trajectory of the host genome.

• Keywords
• CACTA transposons, Chenopodium, Flowering plants, Genome evolution, Next generation sequencing,
• Publication type
• Journal Article MeSH