The protein, OxO , also known as Oxalate Oxidase, is an enzyme which breaks down oxalic acid. The chestnut fungus (Cryphonectria parasitica) produces oxalic acid which is damaging to the chestnut tree. The American chestnut does not express much OxO, while other species of chestnut including the Chinese Chestnut have higher levels of the enzyme. Zhang et al.1 found in 2013 that if the production of the OxO protein is increased ~50x in American Chestnuts, then the oxalic acid secreted by the fungus will no longer be lethal to the tree.