DNA methylation and expression of NPT II in transgenic petunias and progeny.

The expression and inheritance of the NPT II (neomycin phosphotransferase II) gene was studied in four transgenic petunia (Petunia hybrida Vilm.) plants and their progeny. The four transgenic plants, each of which had more than one site of insertion, were different from each other in the level of foreign gene expression. Transmission of one or more NPT II alleles to progeny as deteceted by DNA hybridization did not lead to consistant or predictable patterns of NPT II expression. All transgenic plants and their progeny displaying NPT II enzyme activity contained unmethylated SstII (methylation-sensitive restriction enzyme) sites in the nopaline synthase (NOS) promoter (controlling NPT II gene transcription); whereas, 13 of 17 plants which contained the NPT II gene and which showed no NPT II activity had methylated SstII sites. Two progeny of 1 transgenic plant appeared to have some unmethylated SstII sites, but no NPT II enzyme activity was found in leaf tissue samples. DNA methylation of the SstII site in the NOS promoter is strongly correlated with a decrease in NPT II gene expression in transgenic petunia plants and their progeny. However, DNA methylation alone could not account for the variability seen in NPT II gene expression.

Expression and inheritance pattern of two foreign genes in petunia.

Transgenic petunia (Petunia hybrida Vilm.) plants were obtained from Agrobacterium-mediated shoot apex transformation. Studies at the phenotypic as well as molecular level established both the presence of the NPT II (neomycin phosphotransferase II) and GUS (ß-glucuronidase) genes and their level of activity. Twenty-nine primary transformed plants showed varying patterns of phenotype expression of both genes. NPT II and GUS expression in 7 primary plants over a 4-month interval showed varying levels of gene expression within and among individual plants. All primary transgenic plants were self-pollinated and backcrossed to establish the inheritance patterns of both genes. Mendelian and non-Mendelian inheritance patterns for both genes were observed. Analysis of the progeny showed poor transmission of the foreign genes through the pollen especially when two or more bands were present in the Southern hybridization. Most plants whose progeny segregated in Mendelian ratios for either the NPT II or GUS gene had just one copy of the gene. In this study where both foreign genes were examined in both self and test crosses, no transgenic plant showed Mendelian patterns of inheritance for both foreign traits.