title: Arabidopsis HY8 locus encodes phytochrome A.
abstract: hy8 long hypocotyl mutants of Arabidopsis defective in responsiveness to prolonged far-red light (the so-called "far-red high-irradiance response") are selectively deficient in functional phytochrome A. To define the molecular lesion in these mutants, we sequenced the phytochrome A gene (phyA) in lines carrying one or other of two classes of hy8 alleles. The hy8-1 and hy8-2 mutants that express no detectable phytochrome A each have a single nucleotide change that inserts a translational stop codon in the protein coding sequence. These results establish that phyA resides at the HY8 locus. The hy8-3 mutant that expresses wild-type levels of photochemically active phytochrome A has a glycine-to-glutamate missense mutation at residue 727 in the C-terminal domain of the phyA sequence. Quantitative fluence rate response analysis showed that the mutant phytochrome A molecule produced by hy8-3 exhibited no detectable regulatory activity above that of the phyA-protein-deficient hy8-2 mutant. This result indicates that glycine-727, which is invariant in all sequenced phytochromes, has a function important to the regulatory activity of phytochrome A but not to photoperception.
authors.affiliation: University of California-Berkeley/U.S. Department of Agriculture, Albany 94710.
authors.forename: K
authors.initials: K
authors.lastname: Dehesh
authors.forename: C
authors.initials: C
authors.lastname: Franci
authors.forename: B M
authors.initials: BM
authors.lastname: Parks
authors.forename: K A
authors.initials: KA
authors.lastname: Seeley
authors.forename: T W
authors.initials: TW
authors.lastname: Short
authors.forename: J M
authors.initials: JM
authors.lastname: Tepperman
authors.forename: P H
authors.initials: PH
authors.lastname: Quail
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects; D001483:Base Sequence; D002874:Chromosome Mapping; D004247:DNA / Q000235:genetics; D017343:Genes, Plant; D008027:Light; D008969:Molecular Sequence Data; D009154:Mutation; D010834:Phytochrome / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
chemical_list: D012333:RNA, Messenger; D010834:Phytochrome; D004247:DNA