PacC in the nematophagous fungus Clonostachys rosea controls virulence to nematodes

Nematophagous fungi are commonly used as biological control agents of plant and animal parasitic nematodes. However, relatively little is known of the environmental attributes conferring pathogenicity in these fungi. In this report, we investigated the role of PacC-mediated pH response in the pathogenesis of the nematophagous fungus Clonostachys rosea. We identified a pacC orthologue from this fungus and found that its transcript was elevated in C. rosea during the early stage of its infection of nematode. Disruption of pacC resulted in slowed growth at alkaline pH, altered filamentation, reduced conidiation and attenuated virulence to nematodes. The expression of an extracellular serine protease PrC, a putative virulence factor, was downregulated in the pacC mutants. The PrC transcript levels were significantly higher under alkaline growth conditions than under acidic growth conditions. Promoter activity analysis and electrophoretic mobility shift assay indicated that the regulation of PrC by pH via the PacC pathway occurred at the transcriptional level. In conclusion, PacC functions as a positive regulator of virulence to nematodes in C. rosea.