Epigenetic regulation of the rice retrotransposon Tos17
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Transposable elements are major components of plant genomes. Their activity seems to be epigenetically regulated by gene silencing systems. Here we report epigenetic variation in the retrotransposon Tos17 activity in rice varieties. Of the two copies of Tos17 present in chromosome 7 (Tos17 chr.7) and chromosome 10 (Tos17 chr.10), Tos17 chr.7 is strongly activated by tissue culture in most varieties including Nipponbare except for Moritawase, despite the identity of the DNA sequences in Moritawase and Nipponbare. Tos17 chr.7 activity correlated with its methylation status, and Tos17 chr.7 in Moritawase was heavily methylated and activated by treatment of 5-azacytidine (5-azaC), a DNA methylation inhibitor. Although the original copies of Tos17 are methylated to some extent in all varieties examined, the transposed copies in calli mostly are not methylated. When plants were regenerated from calli, the degree of methylation of the Tos17 DNA increased gradually with the growth of plants, and a significant progress of DNA methylation occurred in the next generation after a completed reproductive cycle. With increasing DNA methylation, the transcription of transposed and original Tos17 copies driven by its own as well as by a flanking gene promoter were suppressed. We conclude that Tos17 DNA methylation controls the transpositional activity of Tos17, and modulates the activity of neighboring genes. Based on the analysis of the inactive Tos17 chr.10, we propose that another mechanism, called transcriptional interference, is involved in the control of Tos17 activity.
KeywordsRetrotransposon Rice Epigenetic regulation DNA methylation Tissue culture
We thank Dr. Akio Miyao for supplying the tissue-culture derived R1 seeds and technical assistance. Dr. Muneo Yamazaki is gratefully acknowledged for technical assistance.
- Fedoroff N (1996) Epigenetic regulation of the maize Spm transposable element. In: Russo VEA et al (eds) Epigenetic mechanisms of gene regulation, Cold Spring Harbor Laboratory Press, Cold Spring Harbour, pp 575–592Google Scholar
- Martienssen RA (1996) Epigenetic silencing of Mu transposable elements in maize. In: Russo VEA et al (eds) Epigenetic mechanisms of gene regulation, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, pp 593–608Google Scholar
- McCarthy EM, Liu J, Lizhi G, McDonald JF (2002) Long terminal repeat retrotransposons of Oryza sativa. Genome Biol 3:research 0053.1–0053.11Google Scholar
- Miyao A, Tanaka K, Murata K, Sawaki H, Takeda S, Abe K, Shinozuka Y, Onosato K, Hirochika H (2003) Target site specificity of the Tos17 retrotransposon shows a preference for insertion within genes and against insertion in retrotransposon-rich regions of the genome. Plant Cell 15:1771–1780PubMedCrossRefGoogle Scholar