Chlorophyll Deficiency in the Soybean Mutant ‘MinnGold’ Is Caused by a Nonsynonymous Substitution in a Magnesium Chelatase Subunit

A spontaneous chlorophyll deficient soybean mutant, MinnGold, characterized by its golden colored leaves, was identified in the University of Minnesota Soybean Breeding Program in 2008.  Since then, efforts have been underway to map and clone the causal gene.  Two populations were developed and used for fine mapping the gene to a 165.3-kb interval on Chromosome 13.  This region contains 22 gene models, according to the most current soybean genome annotation.  A literature search of similar phenotypes led to the identification of a Mg-Chelatase subunit candidate gene.  Sequencing of the candidate gene identified a Single Nucleotide Polymorphism (SNP) in the middle of the third exon that causes a nonsynonymous amino acid change.  Subsequent sequencing of the candidate gene from a panel of 29 diverse soybean lines showed that the wild-type allele is highly conserved and that the SNP associated with the MinnGold phenotype is unique to the mutant line.  Whole plant transformation of MinnGold with a genomic clone of the wild-type allele resulted in the restoration of the wild-type phenotype.  Therefore, we conclude that the MinnGold phenotype was caused by a spontaneous nonsynonymous mutation in the coding region of a Mg-Chelatase subunit gene.  To our knowledge, this is the first report on the cloning of a yellow foliage gene in soybean.