UV-inducible transient expression in parsley protoplasts identifies regulatory cis-elements of a chimeric Antirrhinum majus chalcone synthase gene.

It was shown previously that parsley protoplasts retain differential responsiveness to external stimuli, e.g. UV light. This opened the way for the development of transient expression assays to identify DNA sequences acting as regulatory cis-elements in the transcriptional activation of UV-inducible plant genes. The chalcone synthase (chs) gene of Antirrhinum majus (Snapdragon) is inducible by visible and by UV light. We demonstrate that the kinetics of light induction of a chimeric A.majus chs-nptII gene observed during transient expression in the parsley protoplasts reflect the kinetics of UV-induced CHS expression in A.majus seedlings in vivo. We define three regulatory sequence regions, each differing qualitatively and quantitatively in their effects on gene expression. Immediately upstream of the TATA box (-34) a sequence, with coordinates -39 to -197, functions as an orientation independent UV-light responsive element. The complete 1.1 kb promoter or three tandem copies of this element are capable of rendering a heterologous minimal promoter UV responsive. The next upstream region (-197 to -357) contains sequences that do not by themselves cause UV-induced expression, but specifically potentiate the level of UV-induced expression when combined with the TATA-box proximal UV-responsive element. A third element (-661 to -564) has the properties of a general enhancer since it increases the level of both uninduced and UV-induced expression.