Posttranscriptional gene silencing of gn1 in tobacco triggers accumulation of truncated gn1-derived RNA species.

Posttranscriptional silencing of basic beta-1,3-glucanase genes in the tobacco line T17 is manifested by reduced transcript levels of the gn1 transgene and homologous, endogenous basic beta-1,3-glucanase genes. An RNA ligation-mediated rapid amplification of cDNA ends (RLM-RACE) technique was used to compare the 3' termini of gn1 RNAs present in expressing (hemizygous and young homozygous) and silenced (mature homozygous) T17 plants. Full-length, polyadenylated gn1 transcripts primarily accumulated in expressing plants, whereas in silenced T17 plants, mainly 3'-truncated, nonpolyadenylated gn1 RNAs were detected. The relative abundance of these 3'-truncated gn1 RNA species gradually increased during the establishment of silencing in homozygous T17 plants. Similar 3'-truncated, nonpolyadenylated gn1 RNA products were observed in an independent case of beta-1,3-glucanase posttranscriptional gene silencing. This suggests that these 3'-truncated gn1 RNAs are a general feature of tobacco plants showing posttranscriptional silencing of the gn1 transgene.