A region of the Arabidopis Lhcb1*3 promoter that binds to CA-1 activity is essential for high expression and phytochrome regulation.
We have previously characterized a protein from Arabidopsis thaliana, called CA-1, that bound to a specific region of the Lhcb1*3 promoter. This binding activity was of interest because the sequence to which it bound is included in a portion of the promoter that is sufficient for phytochrome regulation and because the activity was absent in photomorphogenic mutant det1 seedlings (L. Sun, R.A. Doxsee, E. Harel, E.M. Tobin [1993] Plant Cell 5: 109-121). We have now directly tested whether the nucleotide sequence to which CA-1 binds is required for regulation of the transcription of this gene by phytochrome. A mutation that abolished CA-1 binding in vitro was introduced into a 1.15-kb segment of the Lhcb1*3 promoter, and both the wild-type and mutant promoter fragments were fused to a uidA reporter gene and used to stably transform A. thaliana. Ten different homozygous lines were examined for phytochrome responsiveness for each of the two constructs by assaying beta-glucuronidase activity. The wild-type construct showed normal phytochrome responsiveness. The mutant construct showed no phytochrome response, and the overall level of beta-glucuronidase activity in etiolated seedlings was decreased by about 2 orders of magnitude. We did not detect a response to a B photoreceptor other than phytochrome itself for either the wild-type or mutant construct. We conclude that information essential for both a high level of expression and phytochrome responsiveness is contained in a 27-bp region to which the CA-1 activity binds.
Kenigsbuch
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Biology Department, University of California, Los Angeles 90095-1606, USA.
Tobin
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D017360:Arabidopsis / Q000235:genetics*; D001483:Base Sequence; D018744:DNA, Plant; D004268:DNA-Binding Proteins / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D006720:Homozygote; D008969:Molecular Sequence Data; D010834:Phytochrome / Q000235:genetics*; D010940:Plant Proteins / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D014170:Transformation, Genetic
D018744:DNA, Plant; D004268:DNA-Binding Proteins; D010940:Plant Proteins; D010834:Phytochrome