Meiotic Reestablishment of Post-Transcriptional Gene Silencing is Regulated by Aberrant RNA Formation in Tomato (Lycopersicon esculentum cv. Mill.)

Although post-transcriptional gene silencing (PTGS) resulting from introduced transgenes has been shown in plant species, the mechanisms regulating initiation and maintenance of silencing are not yet understood. We report here multi-generational characterization of two independent transgenic tomato lines expressing a truncated pectin methylesterase (pme) gene. Transgenic lines 607-1 had multiple transgene insertions, whereas C92-1 had a single copy of the transgene. Multigenerational analyses of these lines showed that PTGS was stably inherited in line 607-1 but was unstable in line C92-1 indicating a role of the transgene copy number in transgene induced phenotype during sexual propagation. The instability of PTGS in the C92-1 line was independent of genetic backgrounds or maternal/paternal effects. The non-silenced homozygous progeny accumulate transgene transcripts confirming that the transgene transcript accumulation is not sufficient for PTGS. The aberrant pme transgene RNAs are present in all homozygous lines exhibiting PTGS, but are not detectable in the non-silenced lines suggesting its role in gene silencing. Taken together these results suggest a role for meiosis in the formation of transgene aberrant RNAs in erasure and reestablishment of PTGS.