Monocot and dicot pre-mRNAs are processed with different efficiencies in transgenic tobacco.

A gene encoding the small subunit of ribulose 1,5-bisphosphate carboxylase (rbcS) in wheat, a monocot plant, was transferred to tobacco, a dicot plant. The wheat gene is not expressed in transgenic tobacco under the control of its own promoter, but when transcription is driven by a viral promoter, several wheat transcripts accumulate. These include both spliced and unspliced transcripts, which are polyadenylated at multiple novel sites in the wheat 3' flanking region. Another monocot intron, from the maize Adh-1 gene, is also spliced inefficiently in tobacco. These findings contrast results demonstrating efficient processing of different rbcS transcripts from pea, a dicot, in transgenic tobacco. This pattern may reflect general differences in sequences required for RNA processing in monocot and dicot plants.