Cloning and characterization of two satellite DNAs in the low-C-value genome of the nematode Meloidogyne spp

Two highly reiterated StyI satellite DNAs have been cloned from two nematode species: one from Meloidogyne hapla and another from M. incognita. The monomeric units of these two satellites have a repeat length of 169 and 295 bp, respectively. These StyI repeated element families constitute 5% of the M. hapla and 2.5% of the M. incognita haploid genomes. The A + T content is elevated in both families (i.e., 68% and 77%, respectively). Nucleotide methylation and transcriptional activity are negative. No similarity was found between the two satellites, nor to other known highly repetitive elements. These StyI satellite DNAs are quite homogenous in sequence, showing on average 3% and 3.5% divergence from their respective calculated consensus sequence. An internal subrepeating unit of about 11 bp is observed in the StyI satellite monomer sequences of M. hapla, suggesting that it could have evolved from a shorter sequence. Because of the small size of the Meloidogyne genome (51 Mb) and the abundance of repeated sequences, this genus approaches a limit in terms of coding fraction.