Intron-specific stimulation of anaerobic gene expression and splicing efficiency in maize cells.

Most of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes characterized in plants and algae to date have one intron very close to the 5' end of the gene. To study the functional relevance of some of these introns for gene expression we have analysed the influence of three 5' introns on transient gene expression of the anaerobically inducible maize GapC4 promoter in maize cells. Under aerobic conditions, reporter gene expression is increased in the presence of the first introns of the GapC4 and GapC1 genes, and the first intron of the nuclear encoded chloroplast-specific GapA1 gene. In contrast, the GapC4 intron increases anaerobic gene expression above the level obtained for the intronless construct, while anaerobic expression of constructs harboring the GapA1 and GapC1 introns was similar to the anaerobic expression level of the intronless construct. Splicing analysis revealed that the GapC4 intron is processed more efficiently under anaerobic conditions, while no change in splicing efficiency is observed for the GapC1 and the GapA1 introns when subjected to anaerobic conditions. These results suggest that an increase in splicing efficiency contributes to the anaerobic induction of the maize GapC4 gene.