Cloning and Molecular Characterization of CmOxdc3 Coding for Oxalate Decarboxylase in the Mycoparasite Coniothyrium minitans .

Coniothyrium minitans ( Cm ) is a mycoparasitic fungus of Sclerotinia sclerotiorum ( Ss ), the causal agent of Sclerotinia stem rot of oilseed rape. Ss can produce oxalic acid (OA) as a phytotoxin, whereas Cm can degrade OA, thereby nullifying the toxic effect of OA. Two oxalate decarboxylase (OxDC)-coding genes, CmOxdc1 and CmOxdc2 , were cloned, and only CmOxdc1 was found to be partially responsible for OA degradation, implying that other OA-degrading genes may exist in Cm . This study cloned a novel OxDC gene ( CmOxdc3 ) in Cm and its OA-degrading function was characterized by disruption and complementation of CmOxdc3 . Sequence analysis indicated that, unlike CmOxdc1 , CmOxdc3 does not have the signal peptide sequence, implying that CmOxDC3 may have no secretory capability. Quantitative RT-PCR showed that CmOxdc3 was up-regulated in the presence of OA, malonic acid and hydrochloric acid. Deletion of CmOxdc3 resulted in reduced capability to parasitize sclerotia of Ss . The polypeptide (CmOxDC3) encoded by CmOxdc3 was localized in cytoplasm and gathered in vacuoles in response to the extracellular OA. Taken together, our results demonstrated that CmOxdc3 is a novel gene responsible for OA degradation, which may work in a synergistic manner with CmOxdc1 .