Pale green lethal disorder in apple ( Malus ) is caused by a mutation in the PHYLLO gene which is essential for phylloquinone (vitamin K1) biosynthesis
Orcheski, Benjamin ; Parker, Robert ; Brown, Susan
In: Tree Genetics & Genomes, 2015, vol. 11, no. 6, p. 1-11
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- Pale green lethal (PGL) is a recessive genetic disorder of apple (Malus) characterized by severe chlorophyll deficiency and seedling lethality. Following germination, seedlings cannot photosynthesize and do not survive beyond the cotyledon stage. PGL carriers are prevalent in cultivated apple (Malus × domestica Borkh.) germplasm, and a cross between two heterozygotes results in 25% lethality. This high mortality rate represents a significant loss of time, resources, and effort. It also causes segregation distortion which complicates genetic analysis of linked traits. We mapped PGL to the top of Linkage Group 16. Using a combination of genetic and biochemical methods, we identified the apple ortholog of PHYLLO (MdPHYLLO) as the gene responsible for PGL disorder. PHYLLO encodes a multifunctional enzyme that catalyzes key steps in the biosynthesis of phylloquinone (vitamin K1). PGL seedlings do not produce phylloquinone yet can be kept alive and healthy through exogenous application of phylloquinone. The PGL allele of MdPHYLLO contains a mutation that alters a highly conserved amino acid in one of the protein's enzymatic modules. This mutation is present in all PGL carriers tested and absent from all non-carriers. Reasons why the PGL allele of MdPHYLLO is so widespread in cultivated apple are discussed.