Roles of NADPH oxidases in regulating redox homeostasis and pathogenesis of the poplar canker fungus Cytospora chrysosperma

Summary

Poplar trees suffer from a serious fungal disease caused by Cytospora chrysosperma that devastates plantations. Scientists discovered that three genes controlling enzyme complexes called NADPH oxidases are critical for the fungus to cause disease. When these genes are removed, the fungus cannot produce enough of a toxic acid it uses to attack trees, and the fungus cells become stressed and damaged. These findings suggest new ways to control the disease by targeting these enzyme complexes.

Background

Poplar canker caused by Cytospora chrysosperma results in significant losses in poplar plantations in China. NADPH oxidases (NOXs) play important roles in development and pathogenicity of pathogenic fungi. The roles of NOXs in C. chrysosperma and their relationship to redox homeostasis and virulence factors remain unclear.

Objective

To characterize three NOX genes (CcNox1, CcNox2, and CcNoxR) in C. chrysosperma and determine their roles in regulating redox homeostasis, mitochondrial integrity, and pathogenicity. To investigate how NOXs regulate oxalic acid biosynthesis and virulence during poplar infection.

Results

All three NOX genes were highly upregulated during poplar infection, and deletion of any severely reduced virulence. Deletion of CcNox1 or CcNoxR increased endogenous ROS, Ca2+ influx, and disrupted redox homeostasis with compromised mitochondrial integrity. Oxalic acid biosynthesis was defective in mutants, and exogenous supplementation rescued virulence. CcNox2 showed compensatory upregulation when CcNox1 or CcNoxR were deleted.

Conclusion

NOXs play crucial roles in maintaining redox homeostasis, mitochondrial integrity, and pathogenicity in C. chrysosperma through regulation of ROS production and oxalic acid biosynthesis. These findings reveal that NOXs are essential for the pathogenic success of C. chrysosperma and suggest potential targets for disease management strategies.
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