Insertion of non-intron sequence into maize introns interferes with splicing.

Transposable element (TE) insertion into or near plant introns can cause intron skipping and alternative splicing events, resulting in reduced expression. To explore the impact of inserted sequences on splicing, we added non-intron sequence to two maize introns and tested these chimeric introns in a maize transient expression assay. Non-intron sequence inserted into Adh1-S intron 1 and actin intron 3 decreased expression from the luciferase reporter gene; the insertion sites tested were not in intron regions thought to be essential for splicing. Alternatively spliced mRNAs were not observed in transcripts derived from the insertion variants. In contrast, addition of an internal segment of an intron to Adh1-S intron 1 resulted in normal splice site selection and efficient processing. Because the normal intron sequence (including the conserved splice junctions) was retained in all constructs, we hypothesize that added non-intron sequence can interfere with intron recognition and/or splicing.