Characterizing the Role of AosfgA and AofluG in Mycelial and Conidial Development in Arthrobotrys oligospora and Their Role in Secondary Metabolism.

Arthrobotrys oligospora , a widespread nematode-trapping fungus which can produce conidia for asexual reproduction and form trapping devices (traps) to catch nematodes. However, little is known about the sporulation mechanism of A. oligospora . This research characterized the functions and regulatory roles of the upstream spore-producing regulatory genes, AosfgA and AofluG , in A. oligospora . Our analysis showed that AosfgA and AofluG interacted with each other. Meanwhile, the AofluG gene was downregulated in the Δ AosfgA mutant strain, indicating that AosfgA positively regulates AofluG . Loss of the AosfgA and AofluG genes led to shorter hyphae and more septa, and the Δ AosfgA strain responded to heat and chemical stresses. Surprisingly, the number of nuclei was increased in the mycelia but reduced in the conidia of the Δ AosfgA and Δ AofluG mutants. In addition, after nematode induction, the number and volume of vacuoles were remarkably increased in the Δ AosfgA and Δ AofluG mutant strains. The abundance of metabolites was markedly decreased in the Δ AosfgA and Δ AofluG mutant strains. Collectively, the AosfgA and AofluG genes play critical roles in mycelial development, and they are also involved in vacuole assembly, the stress response, and secondary metabolism. Our study provides distinct insights into the regulatory mechanism of sporulation in nematode-trapping fungi.