Dataset Information

Chromosome Number and Genome Size Evolution in Brasolia and Sobralia (Sobralieae, Orchidaceae).

ABSTRACT: Despite the clear circumscription of tribe Sobralieae (Orchidaceae), its internal relationships are still dubious. The recently delimited genus Brasolia, based on previous Sobralia species, is now assumed to be paraphyletic, with a third genus, Elleanthus, nested in it. The morphology of these three genera is significantly different, indicating the necessity of new data for a better genera delimitation. Though morphology and molecular data are available, cytogenetics data for Sobralieae is restricted to two Sobralia and one Elleanthus species. Aiming to evaluate the potential of cytogenetic data for Brasolia-Elleanthus-Sobralia genera delimitation, we present chromosome number and genome size data for 21 and 20 species, respectively, and used such data to infer the pattern of karyotype evolution in these genera. The analysis allowed us to infer x = 24 as the base chromosome number and genome size of average 1C-value of 5.0 pg for the common ancestor of Brasolia-Elleanthus-Sobralia. The recurrent descending dysploidy in Sobralieae and the punctual genome upsize suggest a recent diversification in Sobralieae but did not allow differing between Brasolia and Sobralia. However, the basal position of tribe Sobralieae in the subfamily Epidendroideae makes this tribe of interest to further studies clarifying the internal delimitation and pattern of karyotype evolution.

SUBMITTER: Baranow P

PROVIDER: S-EPMC8999598 | biostudies-literature | 2022 Apr

REPOSITORIES: biostudies-literature

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Publications

Chromosome Number and Genome Size Evolution in Brasolia and Sobralia (Sobralieae, Orchidaceae).

Baranow Przemysław P Rojek Joanna J Dudek Magdalena M Szlachetko Dariusz D Bohdanowicz Jerzy J Kapusta Małgorzata M Jedrzejczyk Iwona I Rewers Monika M Moraes Ana Paula AP

International journal of molecular sciences 20220401 7

Despite the clear circumscription of tribe Sobralieae (Orchidaceae), its internal relationships are still dubious. The recently delimited genus Brasolia, based on previous Sobralia species, is now assumed to be paraphyletic, with a third genus, Elleanthus, nested in it. The morphology of these three genera is significantly different, indicating the necessity of new data for a better genera delimitation. Though morphology and molecular data are available, cytogenetics data fo ...[more]

PMID: 35409308

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Project description:Background and aimsSome species of Genlisea possess ultrasmall nuclear genomes, the smallest known among angiosperms, and some have been found to have chromosomes of diminutive size, which may explain why chromosome numbers and karyotypes are not known for the majority of species of the genus. However, other members of the genus do not possess ultrasmall genomes, nor do most taxa studied in related genera of the family or order. This study therefore examined the evolution of genome sizes and chromosome numbers in Genlisea in a phylogenetic context. The correlations of genome size with chromosome number and size, with the phylogeny of the group and with growth forms and habitats were also examined.MethodsNuclear genome sizes were measured from cultivated plant material for a comprehensive sampling of taxa, including nearly half of all species of Genlisea and representing all major lineages. Flow cytometric measurements were conducted in parallel in two laboratories in order to compare the consistency of different methods and controls. Chromosome counts were performed for the majority of taxa, comparing different staining techniques for the ultrasmall chromosomes.Key resultsGenome sizes of 15 taxa of Genlisea are presented and interpreted in a phylogenetic context. A high degree of congruence was found between genome size distribution and the major phylogenetic lineages. Ultrasmall genomes with 1C values of <100 Mbp were almost exclusively found in a derived lineage of South American species. The ancestral haploid chromosome number was inferred to be n = 8. Chromosome numbers in Genlisea ranged from 2n = 2x = 16 to 2n = 4x = 32. Ascendant dysploid series (2n = 36, 38) are documented for three derived taxa. The different ploidy levels corresponded to the two subgenera, but were not directly correlated to differences in genome size; the three different karyotype ranges mirrored the different sections of the genus. The smallest known plant genomes were not found in G. margaretae, as previously reported, but in G. tuberosa (1C ≈ 61 Mbp) and some strains of G. aurea (1C ≈ 64 Mbp).ConclusionsGenlisea is an ideal candidate model organism for the understanding of genome reduction as the genus includes species with both relatively large (∼1700 Mbp) and ultrasmall (∼61 Mbp) genomes. This comparative, phylogeny-based analysis of genome sizes and karyotypes in Genlisea provides essential data for selection of suitable species for comparative whole-genome analyses, as well as for further studies on both the molecular and cytogenetic basis of genome reduction in plants.

Project description:BackgroundGenome size is influenced by natural selection and genetic drift acting on variations from polyploidy and repetitive DNA sequences. We hypothesized that centromere drive, where centromeres compete for inclusion in the functional gamete during meiosis, may also affect genome and chromosome size. This competition occurs in asymmetric meiosis, where only one of the four meiotic products becomes a gamete. If centromere drive influences chromosome size evolution, it may also impact post-polyploid diploidization, where a polyploid genome is restructured to function more like a diploid through chromosomal rearrangements, including fusions. We tested if plant lineages with asymmetric meiosis exhibit faster chromosome size evolution compared to those with only symmetric meiosis, which lack centromere drive as all four meiotic products become gametes. We also examined if positive selection on centromeric histone H3 (CENH3), a protein that can suppress centromere drive, is more frequent in these asymmetric lineages.MethodsWe analysed plant groups with different meiotic modes: asymmetric in gymnosperms and angiosperms, and symmetric in bryophytes, lycophytes and ferns. We selected species based on available CENH3 gene sequences and chromosome size data. Using Ornstein-Uhlenbeck evolutionary models and phylogenetic regressions, we assessed the rates of chromosome size evolution and the frequency of positive selection on CENH3 in these clades.ResultsOur analyses showed that clades with asymmetric meiosis have a higher frequency of positive selection on CENH3 and increased rates of chromosome size evolution compared to symmetric clades.ConclusionsOur findings support the hypothesis that centromere drive accelerates chromosome and genome size evolution, potentially also influencing the process of post-polyploid diploidization. We propose a model which in a single framework helps explain the stability of chromosome size in symmetric lineages (bryophytes, lycophytes and ferns) and its variability in asymmetric lineages (gymnosperms and angiosperms), providing a foundation for future research in plant genome evolution.

Dataset Information

Chromosome Number and Genome Size Evolution in Brasolia and Sobralia (Sobralieae, Orchidaceae).

Publications

Chromosome Number and Genome Size Evolution in <i>Brasolia</i> and <i>Sobralia</i> (Sobralieae, Orchidaceae).

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