The repetitive DNA landscape in the 'brizantha' agamic complex of Urochloa P. Beauv.

Abstract

Urochloa P. Beauv. (formerly classified as Brachiaria (Trin.) Griseb.) is a genus of African perennial grasses that is extensively cultivated in tropical countries for cattle nutrition. Three of the most economically relevant species, Urochloa brizantha, U. decumbens, and U. ruziziensis, form the 'brizantha' agamic complex, which includes allopolyploid series with distinct subgenomes. Investigating the composition and organization of repetitive DNA, a major component of grass genomes, can provide insights into their genomic relationships and evolutionary history. This study aimed to characterize the repetitive DNA landscape of selected Urochloa species belonging to the 'brizantha' agamic complex; identify and compare major repeat classes across species and evaluate their potential as cytogenetic markers on mitotic chromosomes using fluorescent in situ hybridization (FISH). Clustering analysis revealed that repetitive DNA constitutes 56-65% of the genomes, with Ty3/Gypsy retrotransposons, particularly the Athila and Retand lineages, representing the most abundant repeat class. U. decumbens exhibited the highest proportion of Ty3/Gypsy retrotransposons, while U. ruziziensis had the highest satellite DNA content. The chromosomal location of representative satellites (UroSat-1a, UroSat-2a, and UroSat-3) was determined in all three species via FISH. UroSat-1a was detected in all centromeres, while UroSat-2a and UroSat-3 signals varied in number and position. Our findings validate the use of satDNA as cytogenetic markers in the Urochloa 'brizantha' agamic complex and revealed genomic relationships among different species and ploidy levels.