Laccases are widely present in bacteria, fungi, plants and invertebrates and involved in a variety of physiological functions. Here, we report that Beauveria bassiana, an economic important entomopathogenic fungus, secretes a laccase 2 (BbLac2) during infection that detoxifies insect immune response‐generated reactive oxygen species (ROS) and interferes with host immune phenoloxidase (PO) activation. BbLac2 is expressed in fungal cells during proliferation in the insect haemocoel and can be found to distribute on the surface of haemolymph‐derived in vivo fungal hyphal bodies or be secreted. Targeted gene‐knockout of BbLac2 increased fungal sensitivity to oxidative stress, decreased virulence to insect, and increased host PO activity. Strains overexpressing BbLac2 showed increased virulence, with reduced host PO activity and lowered ROS levels in infected insects. In vitro assays revealed that BbLac2 could eliminate ROS and oxidize PO substrates (phenols), verifying the enzymatic functioning of the protein in detoxification of cytotoxic ROS and interference with the PO cascade. Moreover, BbLac2 acted as a cell surface protein that masked pathogen associated molecular patterns (PAMPs), enabling the pathogen to evade immune recognition. Our data suggest a multifunctional role for fungal pathogen‐secreted laccase 2 in evasion of insect immune defenses.

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真菌病原体分泌的漆酶2在逃避昆虫免疫防御中的多功能作用

漆酶广泛存在于细菌，真菌，植物和无脊椎动物中，并参与多种生理功能。在这里，我们报道球孢白僵菌，一种经济上重要的致病真菌，在感染过程中分泌漆酶2（BbLac2），该酶解毒昆虫免疫反应产生的活性氧（ROS），并干扰宿主免疫酚氧化酶（PO）的活化。BbLac2在昆虫血细胞中的增殖过程中在真菌细胞中表达，可以发现其分布在血淋巴来源的体内真菌菌丝体的表面或被分泌。BbLac2的靶向基因敲除提高了真菌对氧化应激的敏感性，降低了对昆虫的毒力，并增加了宿主PO的活性。菌株过表达BbLac2显示出增加的毒力，降低了宿主PO活性，并降低了被感染昆虫的ROS水平。体外测定显示，BbLac2可以消除ROS并氧化PO底物（酚），从而验证了该蛋白在细胞毒性ROS解毒和干扰PO级联反应中的酶功能。此外，BbLac2充当细胞表面蛋白，可掩盖病原体相关的分子模式（PAMP），使病原体能够逃避免疫识别。我们的数据表明，真菌病原体分泌的漆酶2在逃避昆虫免疫防御中具有多功能作用。