Molecular structure and chromosomal localization of major repetitive DNA families in the chickpea (Cicer arietinum L.) genome

Three major repetitive DNA sequences were isolated from a genomic library of chickpea (Cicer arietinum L.) and characterized with respect to their genomic organization and chromosomal localization. All repetitive elements are genus-specific and mostly located in the AT-rich pericentric heterochromatin. Two families are organized as satellite DNAs with repeat lengths of 162-168 bp (CaSat1) and 100 bp (CaSat2). CaSat1 is mainly located adjacent to the 18S rDNA clusters on chromosomes A and B, whereas CaSat2 is a major component of the pericentric heterochromatin on all chromosomes. The high abundance of these sequences in closely related species of the genus Cicer as well as their variation in structure and copy number among the annual species provide useful tools for taxonomic studies. The retrotransposon-like sequences of the third family (CaRep) display a more complex organization and are represented by two independent sets of clones (CaRep1 and CaRep2) with homology to different regions of Ty3-gypsy-like retrotransposons. They are distributed over the pericentric heterochromatin block on all chromosomes with extensions into euchromatic regions. Conserved structures within different crossability groups of related Cicer species suggest independent amplification or transposition events during the evolution of the annual species of the genus.