The effect of altered codon usage on luciferase activity in tobacco, maize and wheat

A comparison of the wild-type firefly luciferase reporter gene to a codon-modified gene, available from Promega, demonstrates that in tobacco cell cultures, an increase in G+C content of 1.8%, as a consequence of 36 A/T→G/C synonymous codon alterations and removal of the lysosomal targeting sequence, has no significant effect on expression. In maize Black Mexican Sweet cells and wheat scutellum, increases in activity of 14- to 23-fold and 53- to 59-fold, respectively, are obtained using the codon-modified luciferase with the UBI1 promoter and its leader intron. The observed increase in luc+ expression is most likely a consequence of differences in codon usage reflecting tRNA abundance rather than an increase in the efficiency of intron splicing resulting from the small increase in the G+C content of the coding sequence. This difference in light emission between the wild-type and codon-modified luciferases can be clearly visualised in a low-light imaging camera, making the latter a much more sensitive and useful reporter gene for detecting luciferase activity in vivo.