College of Life Science, Agriculture and Forestry, Qiqihar University, Qiqihar, 161006, China.
Horticulture Department, University of Wisconsin, Madison, WI, 53706, USA.
Theor Appl Genet. 2016 Oct;129(10):1961-73. doi: 10.1007/s00122-016-2752-9. Epub 2016 Jul 19.
The cucumber chlorophyll-deficient golden leaf mutation is due to a single nucleotide substitution in the CsChlI gene for magnesium chelatase I subunit which plays important roles in the chlorophyll biosynthesis pathway. The Mg-chelatase catalyzes the insertion of Mg(2+) into the protoporphyrin IX in the chlorophyll biosynthesis pathway, which is a protein complex encompassing three subunits CHLI, CHLD, and CHLH. Chlorophyll-deficient mutations in genes encoding the three subunits have played important roles in understanding the structure, function and regulation of this important enzyme. In an EMS mutagenesis population, we identified a chlorophyll-deficient mutant C528 with golden leaf color throughout its development which was viable and able to set fruits and seeds. Segregation analysis in multiple populations indicated that this leaf color mutation was recessively inherited and the green color showed complete dominance over golden color. Map-based cloning identified CsChlI as the candidate gene for this mutation which encoded the CHLI subunit of cucumber Mg-chelatase. The 1757-bp CsChlI gene had three exons and a single nucleotide change (G to A) in its third exon resulted in an amino acid substitution (G269R) and the golden leaf color in C528. This mutation occurred in the highly conserved nucleotide-binding domain of the CHLI protein in which chlorophyll-deficient mutations have been frequently identified. The mutant phenotype, CsChlI expression pattern and the mutated residue in the CHLI protein suggested the mutant allele in C528 is unique among mutations identified so far in different species. This golden leaf mutant not only has its potential in cucumber breeding, but also provides a useful tool in understanding the CHLI function and its regulation in the chlorophyll biosynthesis pathway as well as chloroplast development.
黄瓜叶绿素缺乏的金黄叶突变是由于镁螯合酶 I 亚基的 CsChlI 基因中的一个单核苷酸替换引起的，该基因在叶绿素生物合成途径中发挥重要作用。Mg-螯合酶催化将 Mg(2+)插入到叶绿素生物合成途径中的原卟啉 IX 中，该酶是一个包含三个亚基 CHLI、CHLD 和 CHLH 的蛋白质复合物。编码三个亚基的叶绿素缺乏突变在理解该重要酶的结构、功能和调控方面发挥了重要作用。在 EMS 诱变群体中，我们鉴定出一个叶绿素缺乏的突变体 C528，其整个发育过程中叶片呈金黄色，具有活力且能够结实和结籽。在多个群体中的分离分析表明，该叶色突变是隐性遗传的，绿色对金黄色完全显性。基于图谱的克隆将 CsChlI 鉴定为该突变的候选基因，该基因编码黄瓜 Mg-螯合酶的 CHLI 亚基。1757bp 的 CsChlI 基因有三个外显子，其第三个外显子中的一个单核苷酸变化（G 到 A）导致一个氨基酸取代（G269R），并导致 C528 中的金黄色叶片。该突变发生在 CHLI 蛋白高度保守的核苷酸结合域中，该区域经常鉴定出叶绿素缺乏的突变。突变体表型、CsChlI 表达模式和 CHLI 蛋白中的突变残基表明，C528 中的突变等位基因在迄今为止在不同物种中鉴定出的突变中是独特的。这个金黄叶突变体不仅在黄瓜育种中有其潜力，而且为理解 CHLI 功能及其在叶绿素生物合成途径以及叶绿体发育中的调控提供了有用的工具。
