Dominant negative suppression of arabidopsis photoresponses by mutant phytochrome A sequences identifies spatially discrete regulatory domains in the photoreceptor.
We used the exaggerated short hypocotyl phenotype induced by oat phytochrome A overexpression in transgenic Arabidopsis to monitor the biological activity of mutant phytochrome A derivatives. Three different mutations, which were generated by removing 52 amino acids from the N terminus (delta N52), the entire C-terminal domain (delta C617), or amino acids 617-686 (delta 617-686) of the oat molecule, each caused striking dominant negative interference with the ability of endogenous Arabidopsis phytochrome A to inhibit hypocotyl growth in continuous far-red light ("far-red high irradiance response" conditions). By contrast, in continuous white or red light, delta N52 was as active as the unmutagenized oat phytochrome A protein in suppressing hypocotyl elongation, while delta C617 and delta 617-686 continued to exhibit dominant negative behavior under these conditions. These data suggest that at least three spatially discrete molecular domains coordinate the photoregulatory activities of phytochrome A in Arabidopsis seedlings. The first is the chromophore-bearing N-terminal domain between residues 53 and 616 that is apparently sufficient for the light-induced initiation but not the completion of productive interactions with transduction chain components. The second is the C-terminal domain between residues 617 and 1129 that is apparently necessary for completion of productive interactions under all irradiation conditions. The third is the N-terminal 52 amino acids that are apparently necessary for completion of productive interactions only under far-red high irradiance conditions and are completely dispensable under white and red light regimes.
Boylan
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University of California-Berkeley/U.S. Department of Agriculture, Plant Gene Expression Center, Albany 94710.
Douglas
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Quail
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D017360:Arabidopsis / Q000187:drug effects / Q000254:growth & development* / Q000528:radiation effects*; D001664:Biliverdine / Q000494:pharmacology; D004252:DNA Mutational Analysis; D002523:Edible Grain / Q000235:genetics*; D008027:Light; D008954:Models, Biological; D010834:Phytochrome / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism* / Q000528:radiation effects; D030821:Plants, Genetically Modified / Q000187:drug effects / Q000254:growth & development / Q000528:radiation effects; D017384:Sequence Deletion; D013053:Spectrophotometry; D013329:Structure-Activity Relationship
D010834:Phytochrome; D001664:Biliverdine