title: Suppressors of transcriptional transgenic silencing in Chlamydomonas are sensitive to DNA-damaging agents and reactivate transposable elements.
abstract: 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.
authors.affiliation: School of Biological Sciences and Plant Science Initiative, University of Nebraska, E211 Beadle Center, Post Office Box 880666, Lincoln, NE 68588-0666, USA.
authors.forename: Byeong-ryool
authors.initials: BR
authors.lastname: Jeong Br
authors.forename: Dancia
authors.initials: D
authors.lastname: Wu-Scharf
authors.forename: Chaomei
authors.initials: C
authors.lastname: Zhang
authors.forename: Heriberto
authors.initials: H
authors.lastname: Cerutti
mesh_terms: 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
chemical_list: D004251:DNA Transposable Elements; D001761:Bleomycin; D008741:Methyl Methanesulfonate