Homeostasis of Calnexin Is Essential for the Growth, Virulence, and Hypovirus RNA Accumulation in the Chestnut Blight Fungus

Abstract

Calnexin, a calcium-binding protein, promotes correct protein folding and prevents incompletely folded glycopolypeptides from premature oxidation and degradation. Cryphonectria parasitica, an ascomycete fungus responsible for chestnut blight, poses a significant threat to the chestnut forest or orchards worldwide. Although various aspects of calnexin have been investigated, little is known about the impact of fungal viruses. CpCne was identified and characterized in this study, encoding the calnexin in C. parasitica. Strains with deletion or interference of the CpCne gene had a significant reduction in biomass and pathogenicity, and strains with overexpression of the CpCne gene had retarded growth and reduced pathogenicity. Transcriptome analysis showed that the △CpCne mutant had significant changes in the expression of genes related to carbohydrate metabolism, cell wall polysaccharide synthesis and degradation, indicating that CpCne may reduce virulence by affecting the cell wall. Additionally, the △CpCne mutant was sensitive to endoplasmic reticulum (ER) stress, suggesting that CpCne plays an important role in maintaining ER homeostasis. Furthermore, CpCne was also involved in the interaction between C. parasitica and the CHV1-EP713. Deletion or overexpression of the CpCne gene reduced viral RNA accumulation, and deletion of the CpCne gene altered the lipid and carboxylic acid metabolic pathways, thereby interfering with virus replication and assembly. Together, we demonstrated that the homeostasis of calnexin in C. parasitica (CpCne) is essential for hyphal growth and virulence, and revealed its role in viral replication and virulence.