Partners and International Organizations
(English)
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Plant Genetic Systems, Gent (B), U. of Gent (B), John Innes Centre, Norwich (UK), U. of Nottingham (UK), Free University, Amsterdam (NL), Universitá 'La Sapienza', Rome (I), Austrian Academy of Sciences, Salzburg (A), Friedrich Miescher Institute, Basel (CH), U. of Leeds (UK), Inst. Jacques Monod-CNRS, Paris (F), Zeneca Agrochemicals, Bracknell (UK), INRA, Versailles (F), Agricultural University, Wageningen (NL)
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Abstract
(English)
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'Gene silencing' refers to the complete or partial inactivation of transgenes and homologous endogenous genes and is a frequently reported phenomenon in transgenic plants. Transcriptional silencing, characterized by a lack of transcript initiation and DNA methylation at promoter sequences, is very stable during mitotic and meiotic transmission. These epigenetic changes in gene expression are a risk for the successful application of gene transfer techniques in agriculture. In addition, they may be also relevant for differentiation and evolution in plants and represent an interesting mechanism of gene regulation.
We have studied transcriptional gene silencing (TGS) in Nicotiana tabacum and in Arabidopsis thaliana. The main achievements of the project were
· to demonstrate that DNA methylation in the promoter region at the conventional acceptor sites CG and CNG is not a prerequisite for the initiation of transcriptional silencing. Therefore, methylation at symmetrical sites is likely to be a consequence rather than the cause of silencing.
· to generate the first plant mutants which release TGS from previously silent loci. These mutations were linked to mutants affected in DNA methylation and to a gene having similarity with a chromatin remodelling factor (Jeddeloh et al. 1999).
· to show that changes in ploidy can cause significant and durable changes in gene expression. The formation of epialleles and their allelic interaction might be significant for the generation of new gene expression patterns in the course of the frequent polyploidization in higher plants.
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