An isolated DNA molecule for enhancing gene expression of a coding sequence, fragment, genetic variant, cassette, vector, cell, plant and seed containing said molecule, wherein the molecule comprises introns for induce an increase in the expression level of a transgene, useful in DNA constructions for transforming plant cells, wherein the cell or plant has a construction containing one of these introns under control of a promoter and upstream of a coding sequence stably integrated in its genome displaying higher expression levels as compared to non-transformed cells or plants, or cells or plants transformed with constructions that lack the inventive intron, wherein the sequences of 5'-non-coding sequences of the genes mentioned above also comprise promoters and exonic sequences in DNA constructions displaying synergism with the effect produced by the intron, and wherein the 5'-non-coding sequences of COX5-c genes lacking said intron promote tissue-specific expression in pollen when they are comprised in DNA constructions for plant transformation.