The chlorophyll-deficient golden leaf mutation in cucumber is due to a single nucleotide substitution in CsChlI for magnesium chelatase I subunit

Authors: GAO, MEILING - University Of Wisconsin; HU, LIANGLIANG - Northwest Agricultural & Forestry University; LI, YUHONG - Northwest Agricultural & Forestry University; Weng, Yiqun

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2016
Publication Date: 7/19/2016
Publication URL: http://handle.nal.usda.gov/10113/63174
Citation: Gao, M., Hu, L., Li, Y., Weng, Y. 2016. The chlorophyll-deficient golden leaf mutation in cucumber is due to a single nucleotide substitution in CsChlI for magnesium chelatase I subunit. Theoretical and Applied Genetics. 129(10):1961-1973. doi: 10.1007/s00122-016-2752-9.

Interpretive Summary: 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 1,757-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.

Technical Abstract: The chlorophyll gives the green color in plants. Any mutations in chloroplhyll biosynthesis or regulation may result in colr changes. Leaf color mutants are common in higher plants, which can be used as markers in crop breeding or as a tool in understanding regulatory mechanisms in chlorophyll biosynthesis and chloroplast development. 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 1,757-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.