State Key Laboratory of Crop Stress Biology for Arid Areas, College of Plant Protection, Northwest A&F University, Yangling, Shaanxi 712100, China.
Mol Plant Pathol. 2018 Jun;19(6):1353-1363. doi: 10.1111/mpp.12619. Epub 2017 Dec 28.
Apple Valsa canker, 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 with 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 with the wild-type, three of the seven FAE single-deletion mutants showed significantly reduced pathogenicity and three of the six FAE double-deletion mutants exhibited greater reductions in pathogenicity, suggesting the joint action of 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.
苹果腐烂病菌（Valsa mali）引起的苹果溃疡病是东亚地区苹果树最具破坏性的病害之一。阿魏酸酯酶（FAE）属于羧酸酯酶亚类，可以切断植物细胞壁中连接羟基肉桂酸和阿拉伯木聚糖或某些果胶的酯键。然而，FAE 在植物病原真菌中的致病作用尚未得到证实。本研究在苹果腐烂病菌中鉴定出包括一个 A 型、一个 B 型、三个 C 型和两个 D 型 FAE 基因在内的 FAE 基因家族。与在无菌培养中生长的菌丝相比，7 个 FAE 基因中有 5 个在苹果腐烂病菌-苹果树树皮互作中转录水平显著升高。酵母信号序列捕获实验证实了 VmFAEs 的信号肽。为了研究 FAE 是否是苹果腐烂病菌致病性所必需的，生成了 7 个单基因缺失突变体和 6 个双基因缺失突变体。与野生型相比，7 个 FAE 单基因缺失突变体中有 3 个的致病性显著降低，6 个 FAE 双基因缺失突变体中有 3 个的致病性降低更明显，表明 FAEs 在苹果腐烂病菌-苹果树互作中共同发挥作用。大多数表现出致病性显著降低的 FAE 突变体的 FAE 活性明显低于野生型真菌。这些结果表明，分泌型 FAEs 是植物病原真菌苹果腐烂病菌完全致病性所必需的。
