IMPRINTING OF DNA AND HISTONE MODIFICATIONS IN ARACHIS HYPOGAEA AND THEIR RELATIONSHIP WITH THE CHROMOSOMAL DISTRIBUTION OF SOME REPETITIVE SEQUENCES

SAMOLUK S.; GUERRA M.; SEIJO G.

Brasília- DF

Congreso; VIII Encontro Latinoamericano de Especialistas em Arachis; 2013

Embrapa Recursos Genéticos e Biotecnologia

Twenty nine diploid species (2n=2x=18, 20) belonging to six different genomes (A, B, D, G, F and K) and two allotetraploid species (2n=4x=40) with genome constitution AABB are included in the Arachis section of the homonymous genus. Peanut (A. hypogaea) is a cultivated allotetraploid species and constitute an important source of proteins and edible oil. Based on molecular markers, physical mapping of ribosomal genes and GISH analysis it have been determined that A. duranensis (A genome) and A. ipäensis (B genome) are the most probable progenitors of the cultigen. Even though, qualitative and quantitative changes in the repetitive fraction of DNA would have been the principal forces for genome differentiation in Arachis section, the studies based on repetitive sequences showed that the processes of hybridization and genome doubling that gave rise to peanut occurred without significative changes in the repetitive fraction of DNA. However, no information is available concerning the epigenetic states of the genomes neither in the diploid nor in the tetraploid species yet. In order to provide the first information on this subject, in this study we established the distribution patterns of covalent modifications of DNA (5- methylcytosine) and histones (H3K4 me2 and H2AT120 ph) by inmunostaining and their relationships with the distribution patterns of the known retroelements (LINEs and Ty3- gypsy) and the satellite sequence A-TR2 established by FISH in the chromosomes of the A and B genomes of peanut. All the chromosomes of the B complement showed signals of 5- methylcytosine generally localized along the whole chromosome length. The A complement presented weaker signals than those observed in the B complement, which were preferentially localized in the interstitial regions and absent from the centromeric regions. The H3K4 me2 signals were detected in the interstitial and distal regions of the chromosomes, but no signals were observed in the centromeres. The inmunodetection of H2AT120 ph revealed strong signals in all chromosome centromeres of the A and B complements. Notably, in the A genome, the signals covered the whole heterochromatic bands. The pattern of the FISH hybridization of LINES did not correspond with any of the patterns analyzed for epigenetic modifications. The Ty3 Gypsy distribution followed the patterns observed for the 5- methylcytosine and for the euchromatic marker H3K4-me2 observed in the A genome. The distribution of ATR-2 sequences located in the DAPI positive pericentromeric bands of the A genome overlaps with the inmunodetection of the H2AT120 ph and with the low DNA methylation registered at the centromeric regions. This data evidenced different epigenetic patterns in the A and B genomes of the tetraploid A. hypogaea.