Analysis of genes negatively regulated by phytochrome action in Lemna gibba and identification of a promoter region required for phytochrome responsiveness.

As a step to understanding how the photoreceptor phytochrome acts to change the transcription of specific nuclear genes in Lemna gibba, we wish to compare promoter elements involved in negative regulation by phytochrome with those involved in positive regulation. We have isolated three genes negatively regulated by phytochrome, designated NR (negatively phytochrome regulated) genes (P.A. Okubara, E.M. Tobin [1991] Plant Physiol 96:1237-1245), and we have now sequenced two of these. The promoters of both contain some sequence motifs that are identical with motifs from other genes. We used a transient assay in L. gibba to demonstrate that approximately 1.7 kb pairs of the NPR1 promoter and 1.1 kb pairs of the NPR2 promoter could confer negative phytochrome regulation to a luciferase reporter gene. Deletion analysis of the NPR2 promoter showed that sequences between -208 and -82 from the transcription start were necessary for negative phytochrome regulation. However, this region was not sufficient to confer negative regulation by phytochrome to another promoter. Additionally, we noted that this region showed no similarity to a region identified as important for the negative regulation of the oat phyA promoter (W.B. Bruce, X.-W. Deng, P.H. Quail [1991] EMBO J 10:3015-3024), but it does contain a sequence element found in several other kinds of genes, including ones positively regulated by phytochrome. The deduced amino acid sequences of NPR1 and NPR2 were found to share similarities with many abscisic acid-induced or seed-abundant proteins. Thus, these genes, like other phytochrome-regulated genes, might respond to multiple regulatory signals.