DNA
methylation of the Ac in transgenic tobacco plants
--Birgit Nelsen-Salz and Hans-Peter
Doring
Transgenic tobacco plants carrying the
complete Ac element from maize or an inactive deletion derivative
of Ac were studied. Plants were transformed via direct DNA transfer
methods or via A. tumefaciens. DNA of the transgenic plants was
examined with a number of different restriction enzymes whose activity
is sensitive for C methylation in their target sequence. Thirty CpGs and
26 CpXpGs were analysed up to now. In four different transgenic plants
the Ac or Ds sequences remain completely unmethylated at
those methylatable sites which were examined. There was one plant which
showed partial methylation at the XhoI site. It is interesting to
note that the PvuI site at the 5' end of the Ac sequence
and at least one of three closely spaced HpaII sites at the 3' end
of the Ac sequence are cleaved and thus are unmodified in complete
Ac sequences as well as in the internally deleted, inactive Ac
element. This is different from what has been found for Ac or Ds
elements in maize (Schwartz and Dennis, Mol. Gen. Genet. 205:476-482, 1986;
Schwartz, Proc. Natl. Acad. Sci. USA 86:2789-2793, 1989). We conclude that
the Ac sequence is not a good target for the de novo methylation
activity of the tobacco methyltransferase. If the Ac sequence used
for transformation is methylated at the EcoRII sites, this preimposed
methylation pattern is not recovered in the transgenic plant. The methylated
EcoRII sequences are not recognized by the methyltransferase which
confers maintenance of methylation patterns.
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