Abstract

The NADPH oxidase complex of a sclerotial mycoparasite Coniothyrium minitans, an important biocontrol agent against crop diseases caused by Sclerotinia sclerotiorum, was identified and its functions involved in conidiation and mycoparasitism were studied. Gene knock-out and complementary experiments indicated that CmNox1, but not CmNox2, is necessary for conidiation and parasitism, and its expression could be significantly induced by its host fungus. CmNox1 is regulated by CmRac1-CmNoxR and interacts with CmSlt2, a homolog of Saccharomyces cerevisiae Slt2 encoding cell wall integrity-related MAP kinase. In ΔCmNox1, CmSlt2-GFP fusion protein lost the ability to localize to the cell nucleus accurately. The defect of conidiation in ΔCmRac1 could be partially restored by over-expressing CmSlt2, indicating that CmSlt2 was a downstream regulatory factor of CmNox1 and was involved in conidiation and parasitism. The expressions of mycoparasitism-related genes CmPks1, Cmg1 and CH1 were suppressed in the knock-out mutants of the genes in CmNox1-CmSlt2 signal pathway when cultivated either on PDA. Therefore, our study infers that CmRac1-CmNoxR regulates CmNox1-CmSlt2 pathway in regulating conidiation and pathogenicity of C. minitans.

Highlights

  • Sclerotinia sclerotiorum (Lib.) de Bary is a significant necrotrophic pathogen that could infect more than 400 plant species worldwide and cause huge economic losses every year[1,2]

  • We investigated a fungal cell wall integrity-associated MAP kinase cascade in C. minitans and found that this cascade was required for conidiation and mycoparasitism[13]

  • The role of NADPH oxidases complex of C. minitans on growth, conidiation and mycoparasitism were studied

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Summary

Introduction

Sclerotinia sclerotiorum (Lib.) de Bary is a significant necrotrophic pathogen that could infect more than 400 plant species worldwide and cause huge economic losses every year[1,2]. Coniothyrium minitans is an important mycoparasite of Sclerotinia spp.; it could parasitize and destroy both sclerotium and hypha of its hosts It is an effective agent for controlling crop diseases caused by S. sclerotiorum[3,4,5]. ROS is critical in maintaining a mutualistic interaction between Epichloë festucae and perennial ryegrass[27,28,29,30,31] In saprophytic fungi, such as Aspergillus spp., Neurospora crassa and Podospora anserina, NADPH oxidases are required for growth, cell differentiation, conidiation, and sexual reproduction[32,33,34,35,36]. Jaimes-Arroyo et al found that SrkA kinase could regulate stress responses and development in A. nidulans, and H2O2 could induce mitochondrial fragmentation and relocalize SrkA at the presence of SakA53

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