The chlorophyll-deficient golden leaf mutation in cucumber is due to a single nucleotide substitution in CsChlI for magnesium chelatase I subunit
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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 Mg2+ 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.
KeywordsLeaf Color C528 Mutant Golden Leaf Cucumber Chromosome Yellow Green Leaf
The authors thank Kristin Haider for technical help. MG’s work was supported by the National Natural Science Foundation of China (No. 31401891), the Natural Science Foundation of Heilongjiang Province (C201330) and Young Outstanding Faculty Support Program in General Higher Education Institutions of Heilongjiang Province (1155G65). The work in YL’s lab was supported by the National Natural Science Foundation of China (31171955 and 31471891). The research in YW’s lab was supported by US Department of Agriculture Specialty Crop Research Initiative Grant (Project Number 2011-51181-30661).
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Conflict of interests
The authors declare that they have no competing interests.
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