Maize Oxalyl-CoA Decarboxylase1 Degrades Oxalate and Affects the Seed Metabolome and Nutritional Quality.

The organic acid oxalate occurs in microbes, animals, and plants; however, excessive oxalate accumulation in vivo is toxic to cell growth and decreases the nutritional quality of certain vegetables. However, the enzymes and functions required for oxalate degradation in plants remain largely unknown. Here, we report the cloning of a maize () opaque endosperm mutant that encodes oxalyl-CoA decarboxylase1 (EC4.1.1.8; OCD1). is generally expressed and is specifically induced by oxalate. The mutant seeds contain a significantly higher level of oxalate than the wild type, indicating that the mutants have a defect in oxalate catabolism. The maize classic mutant () was initially cloned for its high lysine trait, although the gene function was not understood until its homolog in was found to encode an oxalyl-CoA synthetase (EC 6.2.1.8), which ligates oxalate and CoA to form oxalyl-CoA. Our enzymatic analysis showed that ZmOCD1 catalyzes oxalyl-CoA, the product of O7, into formyl-CoA and CO for degradation. Mutations in caused dramatic alterations in the metabolome in the endosperm. Our findings demonstrate that ZmOCD1 acts downstream of O7 in oxalate degradation and affects endosperm development, the metabolome, and nutritional quality in maize seeds.