The nitrate assimilation pathway is involved in the trap formation of Arthrobotrys oligospora, a nematode-trapping fungus

• Nitrate can induce trap formation in Arthrobotrys oligospora.
• Nitrate can significantly promote trap formation in A. oligospora induced by nematodes.
• Nitrate assimilation pathway play a role in trap formation.

Nutrient conditions are important for trap formation and a switch from saprophytic to predacious lifestyle in nematode-trapping fungi. Arthrobotrys oligospora is a typical nematode-trapping fungus which can capture and kill nematodes by means of traps formed in response to the presence of their prey. A nutrient-limited environment was previously shown to be important for trap formation, which was induced by several inferior nitrogen sources, such as sodium nitrate, in the absence of the cell wall protein AoMad1 in A. oligospora. To characterize the role of nitrate in trap formation, we knocked out four genes in the nitrate assimilation pathway and assessed possible effect of nitrate, host nematode or both on the trap formation in the mutants and the wild type. The results showed that trap induction by nitrate used a distinct pathway that differed from induction by nematodes. Moreover, the nitrate facilitated trap formation in the presence of nematodes. Our findings revealed that the trap formation induced by nematodes or nitrate is influenced by the nitrate assimilation pathway.