[The frequency of reversion of the opaque2 locus mutable alleles controlled by the Bg-rbg system of mobile elements...

Maize lines differing in the frequency of reversion of the opaque2 (o2) mutable alleles controlled by the system of Bg-rbg transportable elements were studied. In the presence of the Bg regulatory element, these alleles can revert to normal. When reversion occurs prior to the first division of the primary endosperm nucleus, either phenotypically normal kernels or whole endosperm revertants (WER) develop. Low frequency of whole endosperm revertant formation may be produced by different genetic mechanisms. The frequency of WER formation was shown to nonlinearly depend on the dose of the Bg-hf regulatory element. A dose increase from two to three failed to cause an essential increase in the number of revertants. The regulatory elements Bg-lf and Bg-hf differed in ability to induce excision of the receptor element at the same dose. The frequency of reversion of the receptive alleles was shown to be regulated by epigenetic mechanisms so that high frequency of reversion of receptive alleles requires preliminary premeiotic association between the regulatory and receptor elements. The inheritance of the maize alleles o2-hf and o2-lf proved to be similar to that an3 mutable alleles in petunia.