PROMOTER ELEMENTS OF THE MUSTARD CHS1 GENE ARE SUFFICIENT FOR LIGHT REGULATION IN TRANSGENIC PLANTS

The expression of chalcone synthase (CHS) genes, which encode the firs t enzyme of the flavonoid pathway, is under developmental control as w ell as affected by external stimuli such as light. Varying fragments o f the 1 kb upstream region of the CHS1 gene from white mustard (Sinapi s alba L.) were fused to the GUS-coding region, and the light-regulate d expression of these constructs was analysed in transgenic Arabidopsi s and tobacco plants. Studies performed with Arabidopsis seedlings ind icate the presence of two elements within the CHS1 promoter mediating light responses via different photoreceptors. One element, located abo ut 150 bp upstream of the transcription start site, is homologous to U nit 1 of the parsley CHS gene, the second, far more upstream element c arries sequences similar to Unit 2 Of the same gene. Detailed studies on Unit 1-driven expression indicate that this element transfers the e xpression characteristics of the original gene to both Arabidopsis and tobacco. Although the expression characteristics of Unit 1 are indist inguishable from those of the full-length promoter within the same spe cies, we observed differences in mustard CHS promoter regulation betwe en Arabidopsis and tobacco plants transgenic for the identical constru ct. The difference in photoreceptor usage by the same promoter element in different transgenic species (Unit 1 from mustard in Arabidopsis v s. tobacco) was also observed for different but homologous promoter el ements in the same transgenic species (Unit 1 from mustard and parsley in tobacco). We therefore conclude that the same promoter and even th e same promoter element (Unit 1) can mediate different spatial pattern s of expression and modes of light regulation in different transgenic species.