Inhibition of gene expression in transformed plants by antisense RNA.

We report the successful suppression of nopaline synthase (EC 1.5.1.19) enzymatic activity in the leaves of tobacco plants via the overproduction of RNAs complementary to the nopaline synthase (nos) mRNA. Several different regions of the nos gene were fused, in antisense orientation, to the promoter from a strongly expressed petunia chlorophyll a/b-binding protein gene. These constructions were directly introduced into a tobacco line which contained a single copy of the wild-type nos gene and transgenic plants were regenerated. The degree of nopaline synthase suppression in the leaves of the double transformants ranged up to 85% and was dependent on the particular region of the nos gene present in the antisense RNA. The most effective nos antisense sequences were derived from the 3' half of the nos gene transcript. In addition, we report a new sensitive method for the detection and quantitation of nopaline synthase activity in crude plant extracts.