Presence of wheat retrotransposons in Gramineae species and the origin of wheat retrotransposon families.

Distribution of wheat retrotransposon families (families 1 to 7) was examined in 11 Gramineae species by the use of representative reverse transcriptase domain clones selected from six of the seven wheat retrotransposon families previously identified as probes. The homologues of families 3, 4, 5, and 7 retrotransposons were detectable only in the Pooideae species, suggesting that the distribution of the retrotransposons related to these families is restricted to the Pooideae subfamily. The representatives of families 1 and 2, distantly related to families 3 to 7, revealed homologues additionally in the species outside the Pooideae subfamily including rice. These results suggest that the retrotransposons related to the former families have wider distribution than those related to families 3, 4, 5, and 7. Analysis of a wheat genomic clone confirmed that the family 1 representative reverse transcriptase domain clone is a Ty1-copia group retrotransposon derivative, which we have named Tar1. On the basis of these results, the origin of wheat retrotransposon families is discussed.