Abstract:

To provide theoretical basis for genetic evolution and diversity of Osmanthus fragrans，reverse transcriptase（RT）sequences of Ty1-copia and Ty3-gypsy-like retrotransposon were cloned and analyzed in the genome. Using degenerate oligonucleotide primers corresponding to conserved domains of Ty1-copia and Ty3-gypsy LTR retrotransposon RT sequence，fragments of 260 bp and 430 bp were amplified by polymerase chain reaction（PCR）from genomic DNA of leaves，respectively. Then，the products were purified and sub-cloned to pMD-19-T vector. Subsequently，49 RT sequences of Ty1-copia-like retrotransposon and 20 of Ty3-gypsy-like retrotransposon were obtained through sequencing and related bioinformatics analysis. RT sequences of Ty1-copia-like retrotransposon were classified into four groups after cluster and alignment analyses of their nucleotide sequences. The length of the nucleotide sequences varied from 255 to 271 bp，and homology ranged from 32.0% to 96.9%. When RT nucleotide sequences translated into amino acids，two sequences showed frameshift mutation，and sixteen sequences presented stop codon mutation. Four groups were clustered by alignment analyses of RT nucleotide sequences of Ty3-gypsy-like retrotransposon. The length of the nucleotide sequences varied from 408 to 449 bp，and homology ranged from 54.7% to 98.8%. The deduction of amino acids revealed that 8 sequences presented frameshift mutation and 10 sequences presented stop codon mutation. Phylogenic trees were constructed based on the amino acid sequences from other species，indicating that Osmanthus fragrans had homologies with Prunus mume，Prunus salicina as well as Ziziphus jujuba. The RT nucleotide sequence of Ty1-copia and Ty3-gypsy retrotransposon were highly heterogeneous. Phylogenetic analysis demonstrated that Osmanthus fragrans showed a common origin with other species，and a horizontal transmission of retrotransposons occurred among different species in the process of evolution.

Key words: Osmanthus fragrans, retrotransposon, Ty1-copia, Ty3-gypsy, reverse transcriptase, heterogeneity