Effect of location, organization, and repeat-copy number in satellite-DNA evolution.
Here, we analyze the evolutionary dynamics of a satellite-DNA family in an attempt to understand the effect of factors such as location, organization, and repeat-copy number in the molecular drive process leading to the concerted-evolution pattern found in this type of repetitive sequences. The presence of RAE180 satellite-DNA in the dioecious species of the plant genus Rumex is a noteworthy feature at this respect, as RAE180 satellite repeats have accumulated differentially, showing a distinct distribution pattern in different species. The evolution of dioecious Rumex gave rise to two phylogenetic clades: one clade composed of species with an ancestral XX/XY sex chromosome system and a second, derived clade of species with a multiple sex-chromosome system XX/XY(1)Y(2). While in the XX/XY dioecious species, the RAE180 satellite-DNA is located only in a small autosomal locus, the RAE180 repeats are present also in a small autosomal locus and additionally have been massively amplified in the Y chromosomes of XX/XY(1)Y(2) species. Here, we have found that the RAE180 repeats of the autosomal locus of XX/XY species are characterized by intra-specific sequence homogeneity and inter-specific divergence and that the comparison of individual nucleotide positions between related species shows a general pattern of concerted evolution. On the contrary, both in the autosomal and the Y-linked loci of XX/XY(1)Y(2) species, ancestral variability has remained with reduced rates of sequence homogenization and of evolution. Thus, this study demonstrates that molecular mechanisms of non-reciprocal exchange are key factors in the molecular drive process; the satellite DNAs in the non-recombining Y chromosomes show low rates of concerted evolution and intra-specific variability increase with no inter-specific divergence. By contrast, freely recombining loci undergo concerted evolution with genetic differentiation between species as occurred in the autosomal locus of XX/XY species. However, evolutionary periods of rapid sequence change might alternate with evolutionary periods of stasis with variability remaining by the reduced action of molecular mechanisms of non-reciprocal exchange as occurred in XX/XY(1)Y(2) species, which could depend on repeat-copy number and the processes involved in their amplification.
Navajas-Pérez
R
R
Departamento de Genética, Universidad de Granada, Granada 18071, Spain.
Quesada del Bosque
M E
ME
Garrido-Ramos
M A
MA
D002874:Chromosome Mapping; D032461:Chromosomes, Plant; D004276:DNA, Satellite / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D019143:Evolution, Molecular; D018628:Gene Dosage / Q000502:physiology*; D023061:Gene Order / Q000502:physiology*; D017343:Genes, Plant; D010802:Phylogeny; D031804:Rumex / Q000235:genetics*; D017422:Sequence Analysis, DNA; D012730:Sex Chromosomes / Q000737:chemistry / Q000235:genetics; D013045:Species Specificity
D004276:DNA, Satellite