Analysis of the rDNA loci variability by next generation sequencing in a wild diploid Arachis species

CHALUP, LAURA M. I.; SAMOLUK SS; AGOSTINI F; ROBLEDO G.; SEIJO JG

Congreso; 8vo Congreso Argentino de Bioinformática y Biología Computacional; 2017

The ribosomal DNA repeats are an extensively studied repetitive gene family. Generally, each repeat unit contains three ribosomal DNA 26S, 5.8S and 18S, 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 region transcribable and another no- transcribable (NTS). Generally, rDNA is organized into arrays at one or more chromosomal locations. Each array contains hundreds to thousands of identical to near-identical repeats. These repeats are homogenized by evolutionary forces as unequal crossing-over, gene conversion those are collectively referred to as concerted evolution. Although concerted evolutionary forces have long been known to homogenize repeats within individual loci, there are few robust demonstrations of concerted evolution among repeats from different loci. Moreover, it is thought that the loci located near the centromere are less exposed to the evolutionary forces that lead to the concerted evolution. This is the reason why we analyze to Arachis glandulifera, this species presents a large difference between the number of 5S rDNA and 45S rDNA loci. A single pair of 5S rDNA and 5 pairs of 45S rDNA loci has been observed. The first pair is located in a subterminal position in long arms of the chromosomal pair #8 and the last ones present a complex pattern. Three of these pairs were located proximally on the long arms of pairs #2, #4 and #7. The fourth pair of loci located in an interstitial position on the long arms of chromosomes #10, while the fifth was observed in a subtelomeric position on the short arms of the chromosomes of pair #1. In this species, 45S rDNA loci carried by the chromosomes of pairs #2, #4 and #10 showed the highest intensity hybridization signals of the karyotype, while the others showed lower intensity hybridization signals. These marked differences make A. glandulifera a good model for the study of evolutionary processes in ribosomal genes.