Characterization of eight barley xantha-f mutants deficient in magnesium chelatase

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Magnesium chelatase (EC 6.6.1.1) catalyses the insertion of magnesium into protoporphyrin IX, the first unique step of the chlorophyll biosynthetic pathway. The enzyme is composed of three different subunits of approximately 40, 70 and 140 kDa. In barley ( Hordeum vulgare L.) the subunits are encoded by the genes Xantha-h, Xantha-g and Xantha-f. In the 1950s, eight induced xantha-f mutants were isolated. In this work we characterized these mutations at the DNA level and provided explanations for their phenotypes. The xantha-f 10 mutation is a 3 bp deletion, resulting in a polypeptide lacking the glutamate residue at position 424. The leaky mutation xantha-f 26 has a missense mutation leading to a M632R exchange. The xantha-f 27 and - f 40 are deletions of 14 and 2 bp, respectively, resulting in truncated polypeptides of 1104 and 899 amino acid residues, respectively. Mutation xantha-f 41 is an in-frame deletion that removes A439, L440, Q441 and V442 from the resulting protein. Mutation xantha-f 58 is most likely a deletion of the whole Xantha-f gene, as no DNA fragments could be detected by PCR or southern blot experiments. The slightly leaky xantha-f 60 and non-leaky - f 68 mutations each have a missense mutation causing a P393L and G794E exchange in the polypeptide, respectively.