title: Characterization of mutations in barley fch2 encoding chlorophyllide a oxygenase.
abstract: The barley (Hordeum vulgare L.) mutants fch2 and clo-f2 comprise an allelic group of 14 Chl b-deficient lines. The genetic map position of fch2 corresponds to the physical map position of the gene encoding chlorophyllide a oxygenase. This enzyme converts chlorophyllide a to chlorophyllide b and it is essential for Chl b biosynthesis. The fch2 and clo-f2 barley lines were shown to be mutated in the gene for chlorophyllide a oxygenase. A five-base insertion was found in fch2 and base deletions in clo-f2.101, clo-f2.105, clo-f2.2800 and clo-f2.3613. In clo-f2.105 and clo-f2.108, nonsense base exchanges were discovered. All of these mutations led to a premature stop of translation and none of the mutants formed Chl b. The mutant clo-f2.2807 was transcript deficient and formed no Chl b. Missense mutations in clo-f2.102 (leading to the amino acid exchange D495N) and clo-f2.103 (G280D) resulted in a total lack of Chl b, whereas in the missense mutants clo-f2.107 (P419L), clo-f2.109 (A94T), clo-f2.122 (C320Y), clo-f2.123 (A94T), clo-f2.133 (A376V) and clo-f2.181 (L373F) intermediate contents of Chl b were determined. The missense mutations affect conserved residues, and their effect on chlorophyllide a oxygenase is discussed. The mutations in clo-f2.102, clo-f2.103, clo-f2.133 and clo-f2.181 may influence electron transfer as illustrated in the active site of a structural model protein. The changes in clo-f2.107, clo-f2.109, clo-f2.122 and clo-f2.123 may lead to Chlb deficiency by interfering with the regulation of chlorophyllide a oxygenase. The correlation of mutations and phenotypes strongly supports that the barley locus fch2 encodes chlorophyllide a oxygenase.
authors.affiliation: Carlsberg Laboratory, Gamle Carlsberg Vej 10, 1799 Copenhagen V, Denmark. andrem@stanford.edu
authors.forename: Andre Hubertus
authors.initials: AH
authors.lastname: Mueller
authors.forename: Christoph
authors.initials: C
authors.lastname: Dockter
authors.forename: Simon Peter
authors.initials: SP
authors.lastname: Gough
authors.forename: Udda
authors.initials: U
authors.lastname: Lundqvist
authors.forename: Diter
authors.initials: D
authors.lastname: von Wettstein
authors.forename: Mats
authors.initials: M
authors.lastname: Hansson
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D020134:Catalytic Domain; D002734:Chlorophyll / Q000235:genetics / Q000378:metabolism; D002874:Chromosome Mapping; D032461:Chromosomes, Plant / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D018389:Codon, Nonsense / Q000235:genetics / Q000378:metabolism; D004579:Electron Transport; D016368:Frameshift Mutation; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D001467:Hordeum / Q000201:enzymology / Q000235:genetics*; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D010105:Oxygenases / Q000235:genetics* / Q000378:metabolism; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D026801:Synteny
chemical_list: D018389:Codon, Nonsense; D010940:Plant Proteins; D002734:Chlorophyll; C037184:chlorophyll b; D010105:Oxygenases; C115272:chlorophyll a oxygenase