Análise comparativa do DNA repetitivo nuclear e do genoma cloroplastidial de espécies de Cenchrus L. (Poaceae)

Abstract

Cenchrus L. is an important genus of the Poaceae family that comprises several species of high agronomic importance, mainly forage prominent in national livestock, such as Cenchrus purpureus, Cenchrus americanus and, Cenchrus ciliaris. Several breeding programs explore the production capacity and quality of these forages. Besides, they are interesting for genomic-evolutionary studies, since they have relatively large genomes and complex polyploid combinations. Genomic studies using next-generation sequencing (NGS) with low coverage are an interesting tool for the characterization of germplasm and studies of genomic evolution. These studies allow characterization of the repetitive fraction of the genome and assembly of its chloroplastidial genome. Therefore, the objective of the present work is the comparative genomic analysis of the repetitive fraction of the genome of Cenchrus purpureus and Cenchrus americanus, as well as of the chloroplastidial genome of Cenchrus purpureus, Cenchrus americanus and, Cenchrus ciliaris. For that, the genomes of C. purpureus and C. americanus were sequenced on the Illumina HiSeq ™ 4000 platform and analyzed using tha plattform RepeatExplorer. For the analysis and assembly of the chloroplastidial genome, in addition to sequenced genomes, the chloroplastidial genome of C. ciliaris deposited under access MH286942 in the NCBI database was also used. The assembly and comparative analysis of the cpDNA was performed using tools implemented in the Geneious Prime 2020.1.1 software and in specific platforms such as CHLOROBOX - GeSeq. The repetitive fraction of C. purpureus and C. americanus corresponds to 52.23 and 76.82% of the genome, respectively, and the most abundant repetitive elements in both are the LTRs. Satellite DNA sequences were also identified in both genomes that correspond to 2.55 and 4.17% of the genome of each species, respectively. The ancestral relationship, as well as the cycles of polyploidization-diploidization involved in evolution of both species, played a fundamental role in the composition of their repetitive fraction. The evolutionary processes inherent to satellite DNA sequences are the basis for the differentiation and amplification of this genomic fraction of Cenchrus purpureus and Cenchrus americanus. The chloroplastidial genomes of Cenchrus purpureus, Cenchrus americanus and, Cenchrus ciliaris are very similar either in length and or composition, corroborating to the close phylogenetic relationship among these species, as well as to the well-known conservability of its genome among grass species, mainly in Cenchrus species.