Diversidade e distribuição de sequências repetitivas em tandem em espécies de Cynodon rich. (Poaceae)

Abstract

The genus Cynodon (Poaceae) comprises species widely distributed in tropical and subtropical regions, exhibiting morphological, cytogenetic, and genomic variability. Despite its agronomic and ecological importance, studies on the organization and evolution of its repetitive elements remain limited, especially satellite DNAs (satDNAs), which may act as chromosomal markers and provide insights into the evolutionary history of the group. In this study, a comparative cytogenomic characterization of diploid and polyploid Cynodon species was performed, focusing on the identification and mapping of satDNAs. In silico analyses, conducted using genomic data, enabled the identification of satDNA families, which were subsequently validated by Fluorescent in situ hybridization (FISH). Chromosomal distribution patterns, the presence of heteromorphisms, and the potential of these sequences as cytogenetic markers were evaluated. Comparative analysis of the idiograms revealed heteromorphism patterns between homologous chromosomes, possibly associated with the reorganization of repetitive sequences. Greater genomic proximity was observed between C. dactylon and C. nlemfuensis, which shared four satellite families and exhibited highly syntenic idiograms, whereas C. incompletus showed a higher number of species-specific sequences in the in silico analyses and an idiogram distinct from the other species. Difficulties were encountered in proposing an idiogram model based solely on the markings detected in tetraploid C. transvaalensis, mainly due to the high number of chromosomes with similar sizes and labeling patterns, as well as differences observed among homologous chromosomes themselves, attributed to the high heterozygosity of the genus. The results obtained in this thesis reinforce the importance of satDNAs as a valuable tool for chromosome identification, while also highlighting the genomic complexity of the tandem repetitive fraction in the genus Cynodon.