engleski

Interplay of selective pressure and stochastic events directs evolution of the MEL172 satellite DNA library in root-knot nematodes

According to the library model, related species can have in common satellite DNA families amplified in differing abundances, but reasons for persistence of particular sequences in the library during long periods of time are poorly understood. In this paper we characterize three related satellite DNAs coexisting in the form of a library in mitotic parthenogenetic root-knot nematodes of the genus Meloidogyne. Due to sequence similarity and conserved monomer length of 172 bp, this group of satellite DNAs is named MEL172. Analysis of sequence variability patterns among monomers of three MEL172 satellites revealed two low variable domains highly reluctant to sequence changes, two moderately variable domains characterized by limited number of mutations, and one highly variable domain. The latter domain is prone to rapid spread and homogenization of changes. Comparison of the three MEL172 consensus sequences shows that the low variable domains have 6 % changed nucleotide positions, the moderately variable domains have 48 %, while 78 % divergence is concentrated in the highly variable domain. Conserved distribution of intersatellite variability might indicate a complex pattern of interactions in heterochromatin which limits the range and phasing of allowed changes, implying a possible selection imposed on monomer sequences. The lack of fixed species-diagnostic mutations in each of the examined MEL172 satellites suggests that they existed in unaltered form in a common ancestor of extant species. Consequently, the evolution of these satellites seems to be driven by interplay of selective constraints and stochastic events. We propose that new satellites were derived from an ancestral progenitor sequence by nonrandom accumulation of mutations due to selective pressure on particular sequence segments. In the library of particular taxa, established satellites might be subject to differential amplification at chance due to stochastic mechanisms of concerted evolution.

satellite DNA library; sequence variability; concerted evolution; selective pressure; parthenogenesis; root-knot nematode

doi: 10.1093/molbev/msl119