Article

Genetica

, Volume 107, Issue 1, pp 271-287

First online:

Host defenses to parasitic sequences and the evolution of epigenetic control mechanisms

  • M.A. MatzkeAffiliated withInstitute of Molecular Biology, Austrian Academy of Sciences
  • , M.F. MetteAffiliated withInstitute of Molecular Biology, Austrian Academy of Sciences
  • , W. AufsatzAffiliated withInstitute of Molecular Biology, Austrian Academy of Sciences
  • , J. JakowitschAffiliated withInstitute of Molecular Biology, Austrian Academy of Sciences
  • , A.J.M. MatzkeAffiliated withInstitute of Molecular Biology, Austrian Academy of Sciences

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Abstract

The analysis of transgene silencing effects in plants and other eukaryotic organisms has revealed novel mechanisms of epigenetic regulation that are based on recognition of nucleic acid sequence homology. These homology-dependent gene silencing phenomena are characterized by an inverse relationship between copy number of a particular sequence and expression levels. Depending on whether promoter regions or transcribed sequences are repeated, silencing occurs at the transcriptional or post-transcriptional level, respectively. Different silencing effects involving DNA–DNA or RNA–DNA associations in the nucleus, and RNA–RNA interactions in the cytoplasm appear to reflect distinct host defense responses to parasitic sequences, including transposable elements (TEs), viroids and RNA viruses. Natural epigenetic phenomena that resemble transgene silencing effects often involve endogenous genes comprising recognizable TE sequences or rearrangements generated by TEs and can thus be interpreted in terms of host defense systems. A genome defense that inactivates TEs by methylation might have been recruited during evolution to regulate the transcription of plant and vertebrate genes that contain remnants of TE insertions in promoter regions.

DNA methylation epigenetic silencing genome evolution polyploidy transgenic plants transposable elements viroids