Journal
HEREDITY
Volume 127, Issue 5, Pages 475-483Publisher
SPRINGERNATURE
DOI: 10.1038/s41437-021-00470-5
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Funding
- Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior-Brasil (CAPES)
- Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [2014/11763-8, 2015/16661-1]
- Conselho Nacional de Desenvolvimento Cientifiico e Tecnolo'gico (CNPq)
- Conselho Nacional de Desenvolvimento Cientifico e Tecnologico-CNPq [308290/2020-8]
- Junta de Andalucia fellowship (Spain)
- Marie Skodowska-Curie Individual Fellowship (European Commission) [875732]
- Sven och Lilly Lawskis fond (Sweden)
- Marie Curie Actions (MSCA) [875732] Funding Source: Marie Curie Actions (MSCA)
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The study analyzed the B chromosome of the grasshopper Abracris flavolineata in depth and found its DNA repeat content to be highly similar to that of A chromosomes, with little enrichment for high-copy repeats. The few satellite DNAs on the B chromosome were mainly restricted to centromeric and telomeric regions, displaying smaller bands than on the A chromosomes. The data supported the intraspecific origin of the B chromosome and suggested that it may have recently emerged and could be undergoing a process of heterochromatinization.
In addition to the normal set of standard (A) chromosomes, some eukaryote species harbor supernumerary (B) chromosomes. In most cases, B chromosomes show differential condensation with respect to A chromosomes and display dark C-bands of heterochromatin, and some of them are highly enriched in repetitive DNA. Here we perform a comprehensive NGS (next-generation sequencing) analysis of the repeatome in the grasshopper Abracris flavolineata aimed at uncovering the molecular composition and origin of its B chromosome. Our results have revealed that this B chromosome shows a DNA repeat content highly similar to the DNA repeat content observed for euchromatic (non-C-banded) regions of A chromosomes. Moreover, this B chromosome shows little enrichment for high-copy repeats, with only a few elements showing overabundance in B-carrying individuals compared to the 0B individuals. Consequently, the few satellite DNAs (satDNAs) mapping on the B chromosome were mostly restricted to its centromeric and telomeric regions, and they displayed much smaller bands than those observed on the A chromosomes. Our data support the intraspecific origin of the B chromosome from the longest autosome by misdivision, isochromosome formation, and additional restructuring, with accumulation of specific repeats in one or both B chromosome arms, yielding a submetacentric B. Finally, the absence of B-specific satDNAs, which are frequent in other species, along with its euchromatic nature, suggest that this B chromosome arose recently and might still be starting a heterochromatinization process. On this basis, it could be a good model to investigate the initial steps of B chromosome evolution.
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