The feruloyl esterase genes are required for full pathogenicity of the apple tree canker pathogen Valsa mali

SUMMARY Apple Valsa canker, which is caused by the fungus Valsa mali, is one of the most destructive diseases of apple trees in East Asia. Feruloyl esterases (ferulic acid esterases, FAEs), which belong to a subclass of carboxylic esterases, can cleave ester bonds that crosslink hydroxycinnamic acids and arabinoxylans or certain pectins in plant cell walls. However, a pathogenic role of FAE has not been demonstrated in plant pathogenic fungi. In this study, the FAE gene family, including one type A, one type B, three type C and two type D FAE genes, was identified in V. mali. Five of the seven FAE genes had highly elevated transcript levels in V. mali-apple tree bark interactions compared to mycelia grown in axenic culture. Signal peptides of the VmFAEs were confirmed using yeast signal sequence trap assays. To examine whether FAEs are required for the pathogenicity of V. mali, seven single- and six double-gene deletion mutants were generated. Compared to the wild type, three of the seven FAE single deletion mutants had significantly reduced pathogenicity and three of the six FAE double deletion mutants exhibited greater reductions in pathogenicity, which suggests the joint action regarding FAEs in the V. mali-apple tree interaction. Most of the FAE mutants that exhibited a significant reduction in pathogenicity had significantly lower FAE activity than the wild type fungus. These results indicate that secreted FAEs are required for the full pathogenicity of the phytopathogenic fungus V. mali. This article is protected by copyright. All rights reserved.