Plant Science Innovation, Center for


Date of this Version

June 1997


Published in THE PLANT CELL, Vol 9, Issue 6 (June 1997), pp. 925-945. Copyright © 1997 by American Society of Plant Biologists. The American Society of Plant Biologists does not allow its publications to be archived in an institutional repository. It does, however, provide a free link to full-text content on its own site. Please use the link below to access this article:


The unstable expression of introduced genes poses a serious problem for the application of transgenic technology in plants. In transformants of the unicellular green alga Chlamydomonas reinhardtii, expression of a eubacterial aadA gene, conferring spectinomycin resistance, is transcriptionally suppressed by a reversible epigenetic mechanism(s). Variations in the size and frequency of colonies surviving on different concentrations of spectinomycin as well as the levels of transcriptional activity of the introduced transgene(s) suggest the existence of intermediate expression states in genetically identical cells. Gene silencing does not correlate with methylation of the integrated DNA and does not involve large alterations in its chromatin structure, as revealed by digestion with restriction endonucleases and DNase I. Transgene repression is enhanced by lower temperatures, similar to position effect variegation in Drosophila. By analogy to epigenetic phenomena in several eukaryotes, our results suggest a possible role for (hetero)chromatic chromosomal domains in transcriptional inactivation.

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