Characterization of a highly conserved satellite DNA from the parasitoid wasp Trichogramma brassicae

An EcoRI satellite DNA has been isolated, cloned and sequenced from Trichog ramma brassicae, a minute parasitic wasp. This repeated family represents 1 6% of the genome. The monomer is 385 base pairs (bp) long and has an A+T co ntent of 64.5%. The average nucleotide sequence variability among 12 random ly chosen monomers is extremely low (0.5%), suggesting that. the amplificat ion of the monomer into a high-copy-number family occurred recently. An Eco RI satellite DNA probe has been developed and used, at high stringency, as an identification tool to unambiguously discriminate T. brassicae from nine other Trichogramma species. However, at a lower stringency, a hybridizatio n signal can be detected in two closely related Trichogramma species, and, using PCR assay, the presence of the T. brassicae EcoRI monomer has been de tected in several other species of Trichogramma. These results argue in fav or of the 'library' model of satellite DNA evolution that predicts that rel ated species share a number of low-copy satellite sequences, some of which could be amplified into a major satellite family in each of the species. Fu rthermore, this T. brassicae EcoRI satellite DNA sequence exhibits particul ar internal features such as a long inverted repeat that can form a dyad st ructure. Such sequence motifs seem to be a common characteristic of satelli te DNAs, suggesting that they could result from selective forces acting on repetitive DNA. (C) 2000 Elsevier Science B.V. All rights reserved.