|Zeng, Li-mei - Huazhong Agricultural University|
|Zhang, Jin - Huazhong Agricultural University|
|Han, Yong-chao - Huazhong Agricultural University|
|Yang, Long - Huazhong Agricultural University|
|Wu, Ming-de - Huazhong Agricultural University|
|Jiang, Daohong - Huazhong Agricultural University|
|Li, Guo-qing - Huazhong Agricultural University|
Submitted to: Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2013
Publication Date: 3/4/2014
Citation: Zeng, L., Zhang, J., Han, Y., Yang, L., Wu, M., Jiang, D., Chen, W., Li, G. 2014. Degradation of oxalic acid by the mycoparasite Coniothyrium minitans plays an important role in interacting with Sclerotinia sclerotiorum. Environmental Microbiology. 16(8):2591–2610.
Interpretive Summary: Sclerotinia sclerotiorum causes white mold on many economically important crops including bean, canola, chickpea, lentil, pea, soybean and sunflower. White mold is difficult to manage because crop resistance is inadequate and the pathogen can persist in soil for many years as sclerotia. A mycoparasitic fungus Coniothyrium minitans has been used as a biocontrol agent in reducing damage caused by white mold. The white mold pathogen produces oxalic acid (OA) as a virulence factor, which is also toxic to the biocontrol agent C. minitans. The mechanisms of the mycoparasitism are not completely understood. This research is aimed at discovering the mechanisms of C. minitans in parasitizing S. sclerotiorum. It was found that C. minitans produces oxalate decarboxylase which can degrade oxalate produced by the white mold pathogen. The ability to degrade or detoxify oxalate by C. minitans is related to its ability to elevate the ambient pH and colonize colonies of S. sclerotiorum. In the meantime, C. minitans also produces antifungal factors in interacting with S. sclerotiorum. This study provides direct genetic evidence of OA degradation regulating mycoparasitism and antibiosis of C. minitans against S. sclerotiorum, and sheds light on the sophisticated strategies of C. minitans in interacting with metabolically active mycelia and dormant sclerotia of Sclerotinia sclerotiorum.
Technical Abstract: Coniothyrium minitans is a mycoparasite of the phytopathogenic fungus Sclerotinia sclerotiorum. Sclerotinia sclerotiorum produces a virulence factor oxalic acid (OA) which is toxic to plants and also to C. minitans, and C. minitans detoxifies OA by degradation. In this study, two oxalate decarboxylase genes, Cmoxdc1 and Cmoxdc2, were cloned from C. minitans strain Chy-1. OA and low pH induced expression of Cmoxdc1, but not Cmoxdc2. Cmoxdc1 was partially responsible for OA degradation, whereas Cmoxdc2 had no effect on OA degradation. Disruption of Cmoxdc1 in C. minitans reduced its ability to infect S. sclerotiorum in dual cultures where OA accumulated. Compared to wild type strain Chy-1, the Cmoxdc1-disrupted mutants in the presence of OA had reduced expression levels of two mycoparasitism-related genes chitinase (Cmch1) and ß-1,3-glucanase (Cmg1), and had no detectable activity of extracellular proteases. On the other hand, the cultural filtrates of the Cmoxdc1-disrupted mutants in OA-amended media showed enhanced antifungal activity, possibly due to increased production of antifungal substances under acidic pH condition resulted from reduced Cmoxdc1-mediated OA degradation. This study provides direct genetic evidence of OA degradation regulating mycoparasitism and antibiosis of C. minitans against S. sclerotiorum, and sheds light on the sophisticated strategies of C. minitans in interacting with metabolically active mycelia and dormant sclerotia of Sclerotinia sclerotiorum.