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 LAURA; SEBASTIÁN SAMOLUK; AGOSTINI FEDERICO; GERMAN ROBLEDO; GUILLERMO SEIJO

Saly

Conferencia; AAGB 2018 Conference; 2018

The ribosomal DNA repeats are an important fraction of the repetitive DNA of the genomes, which have a significant and direct role in the expression of genes. 45S rDNA repeat unit contains the sequence for the 26S, 5.8S and 18S rRNA genes, as well as two transcribed spacers (the ITS1 and ITS2) and a large intergenic spacer (IGS). In the same way, the 5S rDNA is organized in a transcribable region and a non-transcribable (NTS) region. Both rDNA repeats are organized into arrays at one or more chromosomal locations; and each array 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 sequence and representation in the allotetraploids, and to make inferences in relation to homogenization process and possible influences in the differential expression of the two genomes. 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. ipaensis. 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. That is, the structure of the loci analyzed in the Arachis AABB allopolyploids seem to be directly inherited from their corresponding diploid ancestors without any detectable structural change. Thus, we can infer a quiescent and additive genomic behavior in the allotetraploids.