Together But Different: The Subgenomes of the Bimodal Eleutherine Karyotypes Are Differentially Organized

Abstract

Bimodal karyotypes are characterized by the presence of two sets of chromosomes of contrasting size. Eleutherine bulbosa (2n = 12) presents a bimodal karyotype with a large chromosome pair, which has a pericentric inversion in permanent heterozygosity with suppressed recombination, and five pairs of three to four times smaller chromosomes. Aiming to understand whether high copy number sequence composition differs between both chromosome sets, we investigated the repetitive DNA fraction of E. bulbosa and compared it to the chromosomal organization of the related Eleutherine latifolia species, not containing the pericentric inversion. We also compared the repetitive sequence proportions between the heteromorphic large chromosomes of E. bulbosa and between E. bulbosa and E. latifolia to understand the influence of the chromosome inversion on the dynamics of repetitive sequences. The most abundant repetitive families of the genome showed a similar chromosomal distribution in both homologs of the large pair and in both species, apparently not influenced by the species-specific inversions. The repeat families Ebusat1 and Ebusat4 are localized interstitially only on the large chromosome pair, while Ebusat2 is located in the centromeric region of all chromosomes. The four most abundant retrotransposon lineages are accumulated in the large chromosome pair. Replication timing and distribution of epigenetic and transcriptional marks differ between large and small chromosomes. The differential distribution of retroelements appears to be related to the bimodal condition and is not influenced by the nonrecombining chromosome inversions in these species. Thus, the large and small chromosome subgenomes of the bimodal Eleutherine karyotype are differentially organized and probably evolved by repetitive sequences accumulation on the large chromosome set.

Analysis of the small chromosomal Prionium serratum (Cyperid) demonstrates the importance of reliable methods to differentiate between mono- and holocentricity

“…The application of these antibodies in a wide range of species is possible due to the evolutionarily conserved amino acid sequence of histone H3. However, in some monocentric species, the application of anti-H2AT120ph resulted in additional non-pericentromeric signals (Baez et al 2019 ; Sousa et al 2016 ).…”

High Chromosomal Reorganization and Presence of Microchromosomes in Chactidae Scorpions from the Brazilian Amazon

“…Several studies have shown that the recombination rate tends to differ between the chromosome sets of a bimodal karyotype over time [ 22 , 68 ]. This characteristic is necessary to maintain the asymmetry of a bimodal karyotype after its formation [ 69 ].…”

“…Fusion/fission events can originate bimodal karyotypes, which are characterized by the existence of classes of chromosomes with divergent sizes [ 20 ]. The origin of the bimodal karyotype can be related to fusion/fission-type chromosomal rearrangements, the hybridization process with subsequent polyploidy [ 21 ] or differential accumulation of repetitive sequences in certain chromosomes [ 22 ]. In bimodal karyotypes of some monocotyledonous plants and vertebrate animals, microchromosomes were recorded, which are extremely small in size, similar to dots, whose morphology is not possible to determine [ 21 , 23 ].…”

Analysis of the small chromosomalPrionium serratum(Cyperid) demonstrates the importance of a reliable method to differentiate between mono- and holocentricity

“…The application of these antibodies in a wide range of species is possible due to the evolutionarily conserved amino acid sequence of histone H3. However, in some monocentric species, the application of anti-H2AT120ph resulted in additional non-pericentromeric signals (Baez et al, 2019;Sousa et al, 2016).…”