One possible mechanism suggested for somaclonal variation is the activation of transposable elements. The activation of retrotransposons by stresses and external changes is commonly observed in plants. In previous study, we isolated the reverse transcriptase (RT) gene sequences of Ty1-copia retrotransposons from tissue culture strawberry (Fragaria × ananassa) plant, but not the transcriptionally active sequence. For further understanding the relationship between retrotransposon and somaclonal varation, in this study, we isolated the transcriptionally active RT gene sequences from strawberry plants subjected to different abiotic stresses. These retrotransposons were activated by spraying strawberry leaves with 2 mmol L-1 salicylic acid (SA), 50 mmol L-1 methyl jasmonate (MeJA), 50 mmol L-1 abscisic acid (ABA), 50 mmol L-1 2,4-dichlorophenoxyacetic acid (2,4-D) or by inducing callus growth in 2 types of MS media: first medium supplemented with 0.5 mg L-1 6-benzylaminopurine (6-BA), 0.5 mg L-1 gibberellic acid (GA3), 1.0 mg L-1 thidiazuron (TDZ), and 0.1 mg L-1 2,4-D, and the second medium supplemented with 0.5 mg L-1 6-BA, 0.5 mg L-1 GA3, 2.0 mg L-1 TDZ, and 0.02 mg L-1 indole butyric acid (IBA). Analysis of gene sequences of 17 RTs revealed that none of them contained stop codons and/or indels disrupting the reading frame. These different stress-origin transcriptionally active RTs were remarkably similar to each other-FATEXP2-8 and FATEYS9-7 showed 100% sequence identity. Analysis of pylogenetic of these transcriptionally active RTs and the RT sequences from genome showed that there were close phylogenetic relationships of most of the transcriptionally active RTs. The results of this study have contributed to the background information necessary for future studies for evaluating the relationship between retrotransposons and somaclonal variation.
MA YueHE PingSUN Hai-yueZHAO Gui-lingDAI Hong-yanZHANG Zhi-hong
