Abstract: Using degenerate oligonucleotide primers corresponding to the conserved domains of the Ty1-copia retrotransposon reverse transcriptase，a fragment of 260 bp was amplified by polymerase chain reaction（PCR）from genomic DNA of Hylocereus undatus. The amplicons were recovered and cloned，then sequenced and analyzed. Twenty-three DNA sequences of reverse transcriptase were obtained from  normal or somaclonal variant of Hylocereus undatus in vitro plants. The sequences can be classified into  five groups with high heterogeneity through phylogenic analysis. The DNA sequences displayed mutation including deletion，frameshift or stop codon. A phylogenic tree was constructed based on the amino acid sequences from other species，indicating that they might share the common origin and that horizontal transmission of retrotransposons has occurred among the plants in the past.

Key words: Hylocereus undatus, variation, Ty1-copia-like retrotransposon, reverse transcriptase, heterogeneity