Expression in transgenic tobacco of the bacterial neomycin phosphotransferase gene modified by intron insertions of various sizes.

A plant selectable marker gene consisting of cauliflower mosaic virus expression signals and the protein-coding sequence of bacterial neomycin phosphotransferase was modified by insertion of an intron sequence from a storage protein gene, phaseolin. Correct and efficient splicing of the resulting mosaic RNA was observed in transgenic tobacco plants. The insertion of various linkers or gradual increase of intron size by addition in both orientations of internal intron sequences from another plant gene (parsley, 4-coumarate ligase) had little or no effect on the precision of slicing. The gene activity measured by selectability assay in the protoplast transformation showed that only introns enlarged to 1161 bases and longer caused decreased selectability. The suitability of such mosaic marker genes for studies of RNA splicing, DNA recombination and early events after infection of plants with Agrobacterium is discussed.