Graph-based clustering and characterization of rDNA genes of allotetraploid species of Arachis section (peanut and A. monticola) and their diploid parentals by next-generation sequencing

CHALUP L.; SAMOLUK SS.; AGOSTINI F.; ROBLEDO G.; SEIJO G.

Conferencia; Advances in Arachis through Genomics & Biotechnology; 2018

The ribosomal DNA repeats are an important fraction of the repetitive DNA of the genomes, which have a direct role in gene expression. 45S rDNA repeat unit contains the sequence for the 26S, 5.8S and 18S rRNA genes, as well as two transcribed spacers (ITS1 and ITS2) and a large intergenic spacer (IGS). Likewise, the 5S rDNA is organized in a transcribable region and a non-transcribable (NTS) region. Both rDNA repeats are organized into arrays and contains hundreds to thousands of repeats. We characterized the composition of the ribosomal genes in A. hypogaea (AABB), A. monticola (AABB) and their diploid parental species, A. duranensis (AA) and A. ipaënsis (BB), in order to reveal the existing heterogeneity degree in structure and sequence of allotetraploids. The characterization of the structures of the rDNA units of the 5S loci was highly conserved. However, the structure of the 45S loci among the parents showed some species-specific differences. There is a small fraction of 79 bp towards the 5´ end and another 300 bp fraction towards the 3´ end of the promoter that are exclusive of A. ipaënsis. Differences in the composition and structure of a region of repeated sequences were also observed in the ETS portion. Both versions of the structure of the 45S rDNA loci were recognized in the allopolyploids. Based on these results, we would have to quantify the copy number of both versions in the allotetraploids to determine if there was no genetic conversion or if it was partial.