Cloning and characterization of an extremely conserved satellite DNA family from the root-knot nematode Meloidogyne arenaria

A new satellite DNA family, named pMaE, has been cloned from the genome of the phytoparasitic nematode, Meloidogyne arenaria (Nematoda: Tylenchida). I t is represented as tandemly repeated sequences with a monomeric unit of 17 2 bp. The monomers are present at approximately 15 700 copies per haploid g enome, and represent about 5.3% of the total genomic DNA. Twenty-seven inde pendent monomers have been cloned and sequenced. The deduced consensus sequ ence is 70.9% A + T rich, with frequent stretches of A and (or) T. Several direct or inverted sub-repeats are present in the sequence, which may allow the formation of a dyad structure, suggesting some potential role of this repetitive sequence in heterochromatin condensation. The monomers are very homogeneous in sequence, showing on average 1.8% divergence from their cons ensus sequence. Moreover, Southern blot experiments and sequence analysis o f homologous monomers from the genome of geographically distinct M. arenari a populations have shown that this satellite DNA is uniformly distributed a nd highly conserved within the species. Therefore, it is hypothesized that this unusually low level of variability, either within the genome of a give n population or between populations, could be achieved as the result of som e highly effective homogenization mechanism acting upon the nematode genome .