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 first enzyme of the flavonoid pathway, is under developmental control as well as affected by external stimuli such as light. Varying fragments of the 1 kb upstream region of the CHS1 gene from white mustard (Sinapis alba L.) were fused to the GUS-coding region, and the light-regulated expression of these constructs was analysed in transgenic Arabidopsis and tobacco plants. Studies performed with Arabidopsis seedlings indicate the presence of two elements within the CHS1 promoter mediating light responses via different photoreceptors. One element, located about 150 bp upstream of the transcription start site, is homologous to Unit 1 of the parsley CHS gene, the second, far more upstream element carries sequences similar to Unit 2 of the same gene. Detailed studies on Unit 1-driven expression indicate that this element transfers the expression characteristics of the original gene to both Arabidopsis and tobacco. Although the expression characteristics of Unit 1 are indistinguishable from those of the full-length promoter within the same species, we observed differences in mustard CHS promoter regulation between Arabidopsis and tobacco plants transgenic for the identical construct. The difference in photoreceptor usage by the same promoter element in different transgenic species (Unit 1 from mustard in Arabidopsis vs. tobacco) was also observed for different but homologous promoter elements in the same transgenic species (Unit 1 from mustard and parsley in tobacco). We therefore conclude that the same promoter and even the same promoter element (Unit 1) can mediate different spatial patterns of expression and modes of light regulation in different transgenic species.

An amino-terminal deletion of rice phytochrome A results in a dominant negative suppression of tobacco phytochrome A activity in transgenic tobacco seedlings.

Overexpression of phytochrome A results in an increased inhibition of hypocotyl elongation under red and far-red light. We used this approach to assay for the function of N-terminal mutations of rice (Oryza sativa L.) phytochrome A. Transgenic tobacco seedlings that express the wild-type rice phytochrome A (RW), a rice phytochrome A lacking the first 80 amino acids (NTD) or a rice phytochrome A with a conversion of the first 10 serines into alanine residues (S/A) were compared with untransformed wild-type tobacco (Nicotiana tabacum L. cv. Xanthi) seedlings. Experiments under different fluence rates showed that RW and, even more strongly, S/A increased the response under both red and far-red light, whereas NTD decreased the response under far-red light but hardly altered the response under red light. These results indicate that NTD not only lacks residues essential for an increased response under red light but also distorts the wild-type response under far-red light. Wild-type rice phytochrome A and, even more so, S/A mediate an enhanced phytochrome A as well as phytochrome B function, whereas NTD interferes with the function of endogenous tobacco phytochrome A as well as that of rice phytochrome A when co-expressed in a single host. Experiments with seedlings of different ages and various times of irradiation under far-red light demonstrated that the effect of NTD is dependent on the stage of development. Our results suggest that the lack of the first 80 amino acids still allows a rice phytochrome A to interact with the phytochrome transduction pathway, albeit non-productively in tobacco seedlings.