ARS | Publication request: Oxalate catabolism in Arabidopsis

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 14, 2012
Publication Date: N/A

Technical Abstract: Oxalic acid is found in most plant species and can serve beneficial roles that protect the plant from a variety of environmental stresses. Excessive amounts of oxalate, however, can be detrimental to plant health. Thus, careful coordination of oxalate metabolism is needed. Despite the important impact of oxalate on plant health, little is known about the pathways regulating oxalate metabolism. The best characterized pathway of oxalate catabolism is via oxalate oxidase, but many species, including Arabidopsis, do not contain oxalate oxidase activity. Here we present evidence supporting the existence of a novel pathway of oxalate catabolism (oxalate>oxalyl-CoA>CO2+formyl-CoA>formate>CO2), in Arabidopsis, through the identification and cloning of two genes that encode enzymes capable of catalyzing the first two steps of this proposed pathway. The first enzyme, Acyl-activating enzyme 3 (AAE3), was found capable of catalyzing the formation of oxalyl-CoA from oxalate and CoA. Characterization of allelic aae3 mutants revealed that each lacked oxalyl-CoA synthetase activity and were unable to degrade oxalate into CO2. Seeds of mutants accumulated oxalate to levels three-fold higher than wild-type, resulting in the formation of oxalate crystals. Crystal formation was associated with seed-coat defects and substantially reduced germination of mutant seeds. Leaves of mutants were damaged by exogenous oxalate and more susceptible than wild-type to infection by the oxalate-secreting fungus, Sclerotinia sclerotiorum, that produces acid as a pathogenicity factor. The second enzyme, oxalyl-CoA decarboxylase (OCD), was found to be capable of catalyzing the conversion of oxalyl-CoA to formyl-CoA and CO2. HPLC analysis revealed a putative oxalyl-CoA peak that was present in OCD dsRNA lines and absent in WT. Seed germination was also found to be reduced in the knockdown lines with the severity of this phenotype increasing with increasing oxalyl-CoA levels. Overall, our results support the existence of a novel pathway of oxalate catabolism in plants.