A recent study of transgene expression in plants revisits themes that recur in the literature every so often. Namely, that “alternative polyadenylation” and low-level transcription well beyond a plant polyadenylation signal are common occurrences in plants. These phenomena are not limited to just transgenes, but are seen with most (if not all) genes.
Why the scare quotes? Because, while the events documented in this study are formally occurrences of alternative polyadenylation, they reflect the inherent 3′ end microheterogeneity that is seen in almost all plant genes, and probably involves subtly different handling of a single polyadenylation signal. This sort of poly(A) site heterogeneity should be distinguished from the occurrence of clearly distinct polyadenylation signals, separated by hundreds or thousands of nucleotides along a transcript.
In any case, this short report reinforces the notion that transcriptional readthrough from transgenes can impact the expression of “host” genes via posttranscriptional gene silencing.