Longevity of 5-azacytidine-mediated gene expression and re-establishment of silencing in transgenic rice.

Epigenetic silencing of a bialaphos resistance (bar) gene in R1 progeny of a transgenic rice line was found to be meiotically stable since selfed (R2) progeny were also susceptible and the bar locus highly methylated. A high proportion of R2 seedlings germinated in the presence of 5-azacytidine (AzaC) were herbicide-resistant and also contained at least one unmethylated copy of the bar gene, further establishing the relationship between silencing and methylation. Restored bar gene expression was typically maintained for 20-50 days, but eventual methylation and silencing of the bar locus underscores the ability of the recipient genome to recognize and inactivate intrusive DNA.