Variability of gene expression in transgenic tobacco

Variability in the expression of the introduced nptII gene was evaluated in transgenic tobacco. Expression analysis was performed on progeny plants of selfed primary transformants. Three different gene constructs were used, containing the nptII gene expressed by either 35S, heat shock protein (hsp80) or the hsp80 promoter including the TMV (Tobacco Mosaic Virus) omega translational enhancer element. Expression of the nptII gene in leaves collected from different developmental phases, varied up to twelve times. The variation in expression of NPTII between independent transformants, all transformed with the same gene construct was found to vary up to nine times. Expression of the nptII gene in the selfed progeny originating from one transformant varied up to four times. The 35S promoter showed a 50-100 fold higher expression of the nptII gene compared to the hsp80 promoter. The omega element enhanced the expression up to two times when compared to the same promoter without the omega element. Transformants containing multiple T-DNA inserts had generally a lower nptII expression compared to plants containing single T-DNA inserts. Implications of such variation in commercialized transgenic crops are discussed.