Evidence for cytosine methylation of non-symmetrical sequences in transgenic Petunia hybrida.

Abstract

A considerable proportion of cytosine residues in plants are methylated at carbon 5. According to a well‐accepted rule, cytosine methylation is confined to symmetrical sequences such as CpG and CpNpG, which provide the signal for faithful transmission of symmetrical methylation patterns by maintenance methylase. Using a genomic sequencing technique, we have analysed cytosine methylation patterns within a hypermethylated and a hypomethylated state of a transgene in Petunia hybrida. Examination of a part of the transgene promoter revealed that in both states m5C residues located within non‐symmetrical sequences could be detected. Non‐symmetrical C residues in the two states were methylated at frequencies of 5.9 and 31.9%, respectively. Methylation appeared to be distributed heterogeneously, but some DNA regions were more intensively methylated than others. Our results show that at least in a transgene, a heterogeneous methylation pattern, which does not depend on symmetry of target sequences, can be established and conserved.

Transgene‐mediated suppression of chalcone synthase expression in Petunia hybrida results from an increase in RNA turnover

“…However, the suppressed chs genes and transgenes are transcribed seemingly unaltered indicating that silencing does not result from a type of DNA modification that prevents transcription initiation. Even though we have not been able to detect differences between the methylation status of suppressed and non-suppressed genes (van Blokland and Stam, unpublished results) we can not exclude the possibility that we missed DNA modifications distinct from CpG or CpNpG methylation (Meyer et al, 1994) which may not affect transcription but which may affect chromatin structure and subsequently RNA processing or transport. Also, we can not exclude the presence of point mutations (Selker, 1991) which may render the transcripts from suppressed genes unstable, however, we consider this possibility unlikely because of the non-clonal suppression patterns in flowers and also because of the inheritance of the suppressed chs genes.…”

Methylation pattern of Activator transposase binding sites in maize endosperm.

“…Recently, the methylation pattern of the maizeA7 gene in transgenic petunia plants has been investigated. In a variant with a silenced, hypermethylated A7 transgene, >90°/o of Cp(Np)G sequences but also 32% of the nonsymmetrical cytosines were methylated (Meyer et al, 1994). Significant methylation of nonsymmetrical cytosines was also observed in an endogenously duplicated, partially silenced copy of the maize R gene (Ronchi et al, 1995).…”

Transgenic Tobacco Plants Expressing the Drosophila Polycomb (Pc) Chromodomain Show Developmental Alterations: Possible Role of Pc Chromodomain Proteins in Chromatin-Mediated Gene Regulation in Plants

“…We were interested in examining the potential role of PCcd proteins in the establishment of chromatin complexes in plants. Transcriptionally silenced transgenes can acquire highly methylated (Matzke et al, 1989;Meyer et al, 1994) (A) and (B) Scanning electron microscopy of a transverse section of a wild-type leaf and a needle leaf, respectively, reveal no significant differences in the anatomy of cells in the midrib, whereas the leaf blade is not formed in the needle phenotype. (C) and (D) Transverse sections through the blade of a wild-type leaf and a broad leaf show disruptions of the tissue context in the broad leaf.…”