Distribuição de DNA repetitivo em cromossomos de acessos de Urochloa humidicola (Rendle) Morrone & Zuloaga e as contribuições da meiose para análise genômica

Abstract

Polyploidy plays a central role in plant evolution, involving either the duplication of a single genome or the combination of distinct genomes, which affects the chromosome pairing and segregation. The use of cytomolecular techniques, such as fluorescent in situ hybridization (FISH) and genomic in situ hybridization (GISH), has expanded the understanding of genomic composition and meiotic behavior in polyploid species. Urochloa humidicola is an agronomically important forage species, characterized by a polyploid series and predominantly apomictic accessions. The accession H031, the only known sexual genotype and widely used in breeding programs, was recently identified as an aneuploid, highlighting the need for additional cytogenetic studies. In this context, the aim of the study was to compare the distribution of genomic DNA (gDNA) probe signals and a centromeric probe on chromosomes of two U. humidicola accessions to discriminate chromosomes belonging to ancestral genomes. A second approach aimed to characterize pairing configurations and meiotic irregularities using satDNA FISH probes. Double GISH combined with centromeric FISH enabled the discrimination of some chromosomes derived from ancestral genomes. The colocalization of UroSat-1a probe with the strongest gDNA signals from species of the Brizantha complex reflects close phylogenetic relationships and the inheritance of satellite sequences from a common ancestor, in agreement with the satellite library model. The identification of a chromosome showing a terminal UroSat-1a signal in accession H016 suggests the occurrence of structural rearrangements throughout the evolutionary history of the species. Meiotic analyses using satellite DNA (satDNA) probes improved chromosome characterization, enabling the identification of preferential homologous and homeologous pairings and facilitating the detection of chromosomes with irregular behavior. The predominance of bivalents and homologous pairings in both accessions indicates that the species is undergoing cytological diploidization. However, some chromosomes participate more frequently in multivalent configurations, indicating that this process is not uniform. The expansion of the set of cytomolecular probes and the analysis of meiosis II are essential to further advance the understanding of chromosome organization in U. humidicola.