Fine mapping of lcm1, a gene conferring chlorophyll-deficient golden leaf in Chinese cabbage (Brassica rapa ssp. pekinensis)

Leaf color mutants are valuable resources for studying regulatory mechanisms of photosynthetic pigment metabolism. In this study, a chlorophyll-deficient golden leaf mutant lcm1 of Chinese cabbage was identified from its wild-type FT by ethyl methanesulfonate (EMS) mutagenesis. The phenotype of the golden leaf mutant lcm1 was that the leaves remained golden throughout development. Pigment measurements showed that the chlorophyll content of the mutant lcm1 was less than that of the wild-type FT. There were no obvious grana lamellae observed in the chloroplast microstructure of the mutant lcm1. Genetic analysis revealed that the mutant lcm1 phenotype was controlled by a single recessive nuclear gene, lcm1 (BrChlH). The MutMap method and Kompetitive Allele Specific PCR genotyping were used to predict that Bra006208 encoding a Mg-chelatase H subunit, the candidate gene for the mutant lcm1. The 4249-bp lcm1 gene had five exons and a single nucleotide substitution (G to A) in the third exon that resulted in an amino acid substitution (A to V). This SNP2523351 occurred in the highly conserved CobN-Mg_chel domain of the LCM1 (BrCHLH) protein. This study suggests that lcm1 gene plays an important role in the function of CHLH and provides a solid foundation for further studies on the development of plant leaf color.