Organization of 5S ribosomal DNA of Poa pratensis L.

Abstract

5S rDNA, which belongs to the class of repeated sequences, represents a convenient model for studying the molecular evolution of plants. The 5S rDNA repeated unit consists of a conserved region encoding 5S rRNA and variable intergenic spacer (IGS) that contains the motifs required for initiation and termination of transcription. The IGS sequences can be used as a molecular marker for elucidation of the phylogenetic relationships of low-ranking taxa. Today, the molecular organization of 5S rDNA in species of the Poaceae family, which includes many economically important crops, is still poorly understood. Therefore, the aim of the study was to investigate the organization and polymorphism of 5S rDNA IGS in the genome of Poa pratensis L., a member of one of the largest genera of the Poaceae family. Using PCR amplification, cloning, sequencing and analysis of the SRA database, two variants of the 5S rDNA repeated units were found in the genome of P. pratensis. The two variants possess 119 bp-long coding regions, whereas the length of IGS ranges from 169 to 185 bp. At the beginning of IGS, the oligo-T sequence of the RNA polymerase III transcription terminator is present. In members of the Poaceae family, the putative external elements of the 5S rDNA promoter differ from those in previously studied groups of plants.