Many plant retrotransposons have been characterized, but only three families (Tnt1, Tto1 and
Tos17) have been demonstrated to be transpositionally competent. We followed a novel approach
that enabled us to identify an active element of the Ty1-copia retrotransposon family with
estimated 400 copies in the sweetpotato genome. DNA sequences of Ty1 -copia reverse
transcriptase (RTase) from the sweetpotato genome were analyzed, and a group of
retrotransposon copies probably formed by recent transposition events was further analyzed.
3’RACE on callus cDNA amplified transcripts containing long terminal repeats (LTR) of this
group. The sequence -specific amplification polymorphism (S-SAP) patterns of the LTR sequence
in the genomic DNA were compared between a normal plant and callus lines derived from it. A
callus -specific S-SAP product was found into which the retrotransposon detected by the 3’RACE
had been transposed apparently during cell culture. We conclude that our approach provides an
effective way to identify active elements of retrotransposons with high copy numbers.</p
