How dynamic could be the 45S rDNA cistron? An intriguing variability in a grasshopper species revealed by integration of chromosomal and genomic data

Author(s)

Ferretti, Ana B. S. M. ^[1] ; Ruiz-Ruano, Francisco J. ^{[2, 3]} ; Milani, Diogo ^[1] ; Loreto, Vilma ^[4] ; Marti, Dardo A. ^[5] ; Ramos, Erica ^[6] ; Martins, Cesar ^[6] ; Cabral-de-Mello, Diogo C. ^[1]

Affiliation

^[1] UNESP Univ Estadual Paulista, IB, Dept Biol, Rio Claro, SP - Brazil

^[2] UGR Univ Granada, Fac Ciencias, Dept Genet, Granada - Spain

^[3] Uppsala Univ, Evolutionary Biol Ctr, Dept Ecol & Genet, Uppsala - Sweden

^[4] UFPE Univ Fed Pernambuco, CB, Dept Genet, Recife, PE - Brazil

^[5] Consejo Nacl Invest Cient & Tecn, UNaM, IBS, Posadas, Misiones - Argentina

^[6] UNESP Univ Estadual Paulista, IB, Dept Morfol, Botucatu, SP - Brazil

• Document type: Journal article
• Source: CHROMOSOMA; v. 128, n. 2, p. 165-175, JUN 2019.
• Web of Science Citations: 0

Abstract

To better understand the structure and variability of the 45S rDNA cistron and its evolutionary dynamics in grasshoppers, we performed a detailed analysis combining classical and molecular cytogenetic data with whole-genome sequencing in Abracris flavolienata, which shows extraordinary variability in the chromosomal distribution for this element. We found astonishing variability in the number and size of rDNA clusters at intra- and inter-population levels. Interestingly, FISH using distinct parts of 45S rDNA cistron (18S rDNA, 28S rDNA, and ITS1) as probes revealed a distinct number of clusters, suggesting independent mobility and amplification of the 45S rDNA components. This hypothesis is consistent with the higher genomic coverage of almost the entire cistron of 45S rDNA observed in A. flavolineata compared to other grasshoppers, besides coverage variability along the 45S rDNA cistron in the species. In addition, these differences in coverage for distinct components of the 45S rDNA cistron indicate emergence of pseudogenes evidenced by existence of truncated sequences, demonstrating the rDNA dynamics in the species. Although the chromosomal distribution of 18S rDNA was highly variable, the chromosomes 1, 3, 6, and 9 harbored rDNA clusters in all individuals with the occurrence of NOR activity in pair 9, suggesting ancestry or selective pressures to prevent pseudogenization of rDNA sequences in this chromosome pair. Additionally, small NORs and cryptic rDNA loci were observed. Finally, there was no evidence of enrichment and association of transposable elements, at least, inside or nearby rDNA cistron. These findings broaden our knowledge of rDNA dynamics, revealing an independent movement and amplification of segments of 45S rDNA cistron, which in A. flavolineata could be attributed to ectopic recombination. (AU)

• FAPESP's process: 15/16661-1 - Sex and B chromosome enigmas: model systems for the study of chromosome and genome evolution
• Grantee: César Martins
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 14/11763-8 - Contributions to understanding of structure and evolution of sex chromosome systems using as models grashopper and cricket species
• Grantee: Diogo Cavalcanti Cabral de Mello
• Support Opportunities: Regular Research Grants