Isolation and Characterization of Two Chlorophyll-Deficient Genes in Soybean

We have identified a lethal-yellow and a viable-yellow mutant in soybean. The three phenotypes green, lethal- and viable-yellow were easily distinguished based on their light reflectance indices, chlorophyll abundance and photochemical conversion efficiency. Photochemical conversion efficiency was reduced in the viable-yellow plants, whereas, lethal-yellow plants showed no ability to convert light energy. The lethal-yellow and viable-yellow plants showed significant reduction of chlorophyll A and B. In lethal-yellow plants proplastids did not differentiate into chloroplasts and few membranes were present. The reduction in thylakoid stacking was apparent in the viable-yellow plants. Genetic analysis revealed recessive epistatic interaction between the lethal- and the viable-yellow genes. The lethal-yellow gene was mapped to an 83 kb region on chromosome 3 that contained 13 predicted genes. We have identified and sequenced three potential candidate genes in this region. A single base insertion in the second exon of Glyma.03G230300 resulted in a frame shift that caused an early stop codon. Glyma.03G230300 codes for PsbP that is involved in the development of Photosystem II and is critical for photosynthesis. The viable-yellow gene was mapped to a 58 kb region on chromosome 2. We located 7 predicted genes in this region. A frame shift mutation due to a deletion of a base in Glyma.02g233700 resulted in an early stop codon. Glyma.02g233700 showed homology to a translocon in the inner membrane of chloroplast (Tic110) in Arabidopsis. Tic110 is known to play a critical role in plastid biogenesis and the heterozygous mutants for Tic110 in Arabidopsis exhibited a pale phenotype. Characterization of lethal- and viable-yellow genes may help to better understand the biosynthetic pathways involved in the development of chloroplasts.