title: Reduced chlorophyll biosynthesis in heterozygous barley magnesium chelatase mutants.
abstract: Chlorophyll biosynthesis is initiated by magnesium chelatase, an enzyme composed of three proteins, which catalyzes the insertion of Mg2+ into protoporphyrin IX to produce Mg-protoporphyrin IX. In barley (Hordeum vulgare L.) the three proteins are encoded by Xantha-f, Xantha-g and Xantha-h. Two of the gene products, XanH and XanG, belong to the structurally conserved family of AAA+ proteins (ATPases associated with various cellular activities) and form a complex involving six subunits of each protein. The complex functions as an ATP-fueled motor of the magnesium chelatase that uses XanF as substrate, which is the catalytic subunit responsible for the insertion of Mg2+ into protoporphyrin IX. Previous studies have shown that semi-dominant Xantha-h mutations result in non-functional XanH subunits that participate in the formation of inactive AAA complexes. In the present study, we identify severe mutations in the barley mutants xantha-h.38, -h.56 and -h.57. A truncated form of the protein is seen in xantha-h.38, whereas no XanH is detected in xantha-h.56 and -h.57. Heterozygous mutants show a reduction in chlorophyll content by 14-18% suggesting a slight semi-dominance of xantha-h.38, -h.56 and -h.57, which otherwise have been regarded as recessive mutations.
authors.affiliation: Carlsberg Laboratory, Gamle Carlsberg Vej 10, 1799 Copenhagen V, Denmark.
authors.forename: Ilka
authors.initials: I
authors.lastname: Braumann
authors.affiliation: Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), D-06466 Seeland OT Gatersleben, Germany.
authors.forename: Nils
authors.initials: N
authors.lastname: Stein
authors.affiliation: Carlsberg Laboratory, Gamle Carlsberg Vej 10, 1799 Copenhagen V, Denmark. Electronic address: mats.hansson@carlsberglab.dk.
authors.forename: Mats
authors.initials: M
authors.lastname: Hansson
mesh_terms: D015153:Blotting, Western; D002734:Chlorophyll / Q000096:biosynthesis*; D005799:Genes, Dominant / Q000235:genetics; D006579:Heterozygote; D001467:Hordeum / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D008190:Lyases / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D016133:Polymerase Chain Reaction; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D021122:Protein Subunits; D002734:Chlorophyll; D008190:Lyases; C086788:magnesium chelatase
keywords: AAA; BchI; ChlI; Hordeum vulgare; Mg-chelatase