Mycoparasitic fungi can be utilized as biocontrol agents (BCAs) of many plant pathogens. Deciphering the molecular mechanisms of mycoparasitism may improve biocontrol efficiency. This work reports the first functional genetic studies in Ampelomyces, widespread mycoparasites and BCAs of powdery mildew fungi, and a molecular genetic toolbox for future works. The nitrate reductase (euknr) gene was targeted to reveal the biological function of nitrate assimilation in Ampelomyces. These mycoparasites live in an apparently nitrate-free environment, i.e. inside the hyphae of powdery mildew fungi that lack any nitrate uptake and assimilation system. Homologous recombination-based gene knock-out (KO) was applied to eliminate the euknr gene using Agrobacterium tumefaciens-mediated transformation. Efficient KO of euknr was confirmed by PCR, and visible phenotype caused by loss of euknr was detected on media with different nitrogen sources. Mycoparasitic ability was not affected by knocking out euknr as a tested transformant readily parasitized Blumeria graminis and Podosphaera xanthii colonies on barley and cucumber, respectively, and the rate of mycoparasitism did not differ from the wild type. These results indicate that euknr is not involved in mycoparasitism. Dissimilatory processes, involvement in nitric oxide metabolism, or other, yet undiscovered processes may explain why a functional euknr is maintained in Ampelomyces.

真菌寄生真菌可用作许多植物病原体的生物防治剂 (BCA)。破译真菌寄生的分子机制可以提高生物防治效率。这项工作报告了Ampelomyces、广泛存在的支原体和白粉病真菌的BCA的首次功能遗传研究，以及用于未来工作的分子遗传工具箱。以硝酸还原酶（euknr）基因为靶点，揭示了链霉菌中硝酸盐同化的生物学功能。这些真菌寄生物生活在明显不含硝酸盐的环境中，即在缺乏任何硝酸盐吸收和同化系统的白粉病真菌的菌丝内。应用基于同源重组的基因敲除 (KO) 来消除euknr基因使用根癌农杆菌介导的转化。通过 PCR 证实了euknr 的有效 KO，在不同氮源的培养基上检测到euknr丢失引起的可见表型。真菌寄生能力不受敲除euknr 的影响，因为测试的转化体容易分别寄生在大麦和黄瓜上的禾本科和黄花球藻菌落，并且真菌寄生率与野生型没有区别。这些结果表明euknr不参与真菌寄生。异化过程、参与一氧化氮代谢或其他尚未发现的过程可以解释为什么在Ampelomyces中保持功能性euknr。