Suppressors of transcriptional transgenic silencing in Chlamydomonas are sensitive to DNA-damaging agents and reactivate transposable elements

Byeong Ryool Jeong, Dancia Wu-Scharf, Chaomei Zhang, Heriberto Cerutti

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In the unicellular green alga Chlamydomonas reinhardtii, the epigenetic silencing of transgenes occurs, as in land plants, at both the transcriptional and posttranscriptional levels. In the case of single-copy transgenes, transcriptional silencing takes place without detectable cytosine methylation of the introduced DNA. We have isolated two mutant strains, Mut-9 and Mut-11, that reactivate expression of a transcriptionally silenced single-copy transgene. These suppressors are deficient in the repression of a DNA transposon and a retrotransposon-like element. In addition, the mutants show enhanced sensitivity to DNA-damaging agents, particularly radiomimetic chemicals inducing DNA double-strand breaks. All of these phenotypes are much more prominent in a double mutant strain. These observations suggest that multiple partly redundant epigenetic mechanisms are involved in the repression of transgenes and transposons in eukaryotes, presumably as components of a system that evolved to preserve genomic stability. Our results also raise the possibility of mechanistic connections between epigenetic transcriptional silencing and DNA double-strand break repair.

Original languageEnglish (US)
Pages (from-to)1076-1081
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number2
StatePublished - Jan 22 2002


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