Sawers Ruairidh J H, Viney Joanne, Farmer Phyllis R, Bussey Rhiannon R, Olsefski Gregory, Anufrikova Katya, Hunter C Neil, Brutnell Thomas P
Boyce Thompson Institute, Cornell University, Tower Road, Ithaca, NY 14853, USA.
Plant Mol Biol. 2006 Jan;60(1):95-106. doi: 10.1007/s11103-005-2880-0.
Semi-dominant Oil yellow1 (Oy1) mutants of maize (Zea mays) are deficient in the conversion of protoporphyrin IX to magnesium protoporphyrin IX, the first committed step of chlorophyll biosynthesis. Using a candidate gene approach, a cDNA clone was isolated that was predicted to encode the I subunit of magnesium chelatase (ZmCHLI) and mapped to the same genetic interval as Oy1. Allelic variation was identified at ZmCHLI between wild-type plants and plants carrying semi-dominant alleles of Oy1. These differences revealed putative amino acid substitutions that could account for the alterations in protein function. Candidate lesions were tested by introduction of homologous changes into the Synechocystis magnesium chelatase I gene (SschlI) and characterization of the activity of mutant protein variants in an in vitro enzyme activity assay. The results of these analyses suggest that SsChlI protein variants containing the substitutions identified in the dominant Oy1 maize alleles lack activity necessary for magnesium chelation and confer a semi-dominant phenotype via competitive inhibition of wild-type SsChlI.
玉米（Zea mays）的半显性油黄1（Oy1）突变体在原卟啉IX向镁原卟啉IX的转化过程中存在缺陷，这是叶绿素生物合成的第一步关键反应。采用候选基因法，分离出一个cDNA克隆，预测其编码镁螯合酶的I亚基（ZmCHLI），并将其定位到与Oy1相同的遗传区间。在野生型植株和携带Oy1半显性等位基因的植株之间，鉴定出ZmCHLI存在等位基因变异。这些差异揭示了可能导致蛋白质功能改变的氨基酸替换。通过将同源变化引入集胞藻镁螯合酶I基因（SschlI），并在体外酶活性测定中对突变蛋白变体的活性进行表征，对候选损伤进行了测试。这些分析结果表明，含有在显性Oy1玉米等位基因中鉴定出的替换的SsChlI蛋白变体缺乏镁螯合所需的活性，并通过对野生型SsChlI的竞争性抑制赋予半显性表型。
