Suppressors of transcriptional transgenic silencing in Chlamydomonas are sensitive to DNA-damaging agents and reactivate transposable elements.
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.
Jeong Br
Byeong-ryool
BR
School of Biological Sciences and Plant Science Initiative, University of Nebraska, E211 Beadle Center, Post Office Box 880666, Lincoln, NE 68588-0666, USA.
Wu-Scharf
Dancia
D
Zhang
Chaomei
C
Cerutti
Heriberto
H
D000818:Animals; D005075:Biological Evolution; D001761:Bleomycin / Q000633:toxicity; D016825:Chlamydomonas reinhardtii / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D004249:DNA Damage; D004260:DNA Repair; D004251:DNA Transposable Elements / Q000235:genetics; D020868:Gene Silencing; D017343:Genes, Plant; D017125:Genes, Protozoan; D008741:Methyl Methanesulfonate / Q000633:toxicity; D009154:Mutation; D013489:Suppression, Genetic; D014158:Transcription, Genetic
D004251:DNA Transposable Elements; D001761:Bleomycin; D008741:Methyl Methanesulfonate