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.

译文

苹果Valsa溃疡病,由真菌Valsa mali引起,是东亚苹果树最具破坏性的疾病之一。阿魏酸酯酶 (阿魏酸酯酶,FAEs),属于羧酸酯酶的一个亚类,可以在植物细胞壁中裂解交联羟基肉桂酸和阿拉伯木聚糖或某些果胶的酯键。然而,在植物病原真菌中尚未证明FAE的致病作用。在这项研究中,在马里V中鉴定了FAE基因家族,包括一个a型,一个b型,三个C型和两个D型FAE基因。与在无菌培养中生长的菌丝体相比,七个FAE基因中的五个在马里V-苹果树树皮相互作用中的转录水平高度升高。使用酵母信号序列陷阱测定法确认了vmfae的信号肽。为了检查马里V的致病性是否需要fae,产生了七个单基因和六个双基因缺失突变体。与野生型相比,七个FAE单缺失突变体中的三个显示出明显降低的致病性,而六个FAE双缺失突变体中的三个显示出更大的致病性降低,这表明FAE在V. mali-苹果树中的共同作用相互作用。大多数致病性显着降低的FAE突变体的FAE活性明显低于野生型真菌。这些结果表明,植物病原真菌V. mali的完全致病性需要分泌的fae。

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