RESUMO
Eukaryotic genome expansion/retraction caused by LTR-retrotransposon activity is dependent on the expression of full length copies to trigger efficient transposition and recombination-driven events. The Tnt1 family of retrotransposons has served as a model to evaluate the diversity among closely related elements within Solanaceae species and found that members of the family vary mainly in their U3 region of the long terminal repeats (LTRs). Recovery of a full length genomic copy of Retrosol was performed through a PCR-based approach from wild potato, Solanum oplocense. Further characterization focusing on both LTR sequences of the amplified copy allowed estimating an approximate insertion time at 2 million years ago thus supporting the occurrence of transposition cycles after genus divergence. Copy number of Tnt1-like elements in Solanum species were determined through genomic quantitative PCR whereby results sustain that Retrosol in Solanum species is a low copy number retrotransposon (1-4 copies) while Retrolyc1 has an intermediate copy number (38 copies) in S. peruvianum. Comparative analysis of retrotransposon content revealed no correlation between genome size or ploidy level and Retrosol copy number. The tetraploid cultivated potato with a cellular genome size of 1,715 Mbp harbours similar copy number per monoploid genome than other diploid Solanum species (613-884 Mbp). Conversely, S. peruvianum genome (1,125 Mbp) has a higher copy number. These results point towards a lineage specific dynamic flux regarding the history of amplification/activity of Tnt1-like elements in the genome of Solanum species.
Assuntos
DNA de Plantas/genética , Retroelementos/genética , Solanum/genética , Sequência de Aminoácidos , Sequência de Bases , Primers do DNA/genética , Dosagem de Genes , Genes de Plantas , Variação Genética , Genoma de Planta , Modelos Genéticos , Dados de Sequência Molecular , Proteínas de Plantas/genética , Ploidias , Reação em Cadeia da Polimerase , Homologia de Sequência de Aminoácidos , Homologia de Sequência do Ácido Nucleico , Solanum/classificação , Especificidade da EspécieRESUMO
Retrolycl, a Ty1/copia-like element, was originally isolated from the Lycopersicon peruvianum genome and shown to be present also in other Lycopersicon species. It shares extensive similarities with Tntl, except in its U3 regulatory region. In order to evaluate Retrolycl diversity, we analyzed partial sequences including both coding domains and the U3 regulatory region in four different species of the Lycopersicon genus. Two Retrolycl subfamilies defined by different U3 regions were identified. RetrolyclA is most abundant in L. peruvianum and L. hirsutum, while Retrolyc1B is distributed in all four species studied here. The RetrolyclA U3 region contains tandemly repeated elements of 53 bp. Transient expression analysis suggests that Retrolyc1A is a transcriptionally active family, and that the repeated motifs found in its U3 region are important transcriptional regulatory elements.
Assuntos
Sequências Reguladoras de Ácido Nucleico , Retroelementos , Solanum lycopersicum/genética , Sequências Repetidas Terminais/genética , Sequência de Bases , DNA de Plantas , Dados de Sequência Molecular , Filogenia , Regiões Promotoras Genéticas , Homologia de Sequência do Ácido Nucleico , Transcrição GênicaRESUMO
Retrotransposons are ubiquitous mobile genetic elements that transpose through an RNA intermediate. One of the best known plant retrotransposon, Tnt1, was isolated from tobacco and showed an extensive distribution in the Nicotiana genus. We investigated the presence of related sequences in the Lycopersicon genus, another member of the Solanaceae family. Hybridization experiments performed using Tnt1 probes indicated that homologous sequences were present in all Lycopersicon species, indicating that these Tnt1-related sequences, that we named Retrolyc1, are distributed throughout the Lycopersicon genus. Different distribution patterns were detected between species, demonstrating a potential use of Retrolyc1 elements as molecular markers. An incomplete Retrolyc1 sequence, that we named Retrolyc1-1, was isolated from an L. peruvianum genomic library. Retrolyc1-1 shows extensive homology with Tnt1 sequences except in the LTR U3 region. Since this region is known to be involved in the control of transcription, this strongly suggests the existence of different patterns of regulation for Tnt1 and Retrolyc1 elements. The study of these two elements within the Solanaceae family may provide interesting models for retrotransposon evolution within this group and transmission in host genomes.