hide
Free keywords:
-
Abstract:
To adapt to environmental changes, cells require the ability to sense external signals. Arthrobotrys oligospora, a fungus belonging to a non-monophyletic group known as nematode-trapping fungus (NTF), senses prey signals and initiates trap morphogenesis under starvation. While a previous study has shown that ammonium suppresses trap formation in A. oligospora that the underlying mechanism is still unknown. Ammonium, a major nitrogen source that promotes growth for many microbes, is transported through the Ammonium transporter (Amt)/Methylammonium permease (Mep)/Rhesus protein (Rh) family. Therefore, to investigate how ammonium transport affects trap formation in A. oligospora, we first identified three potential ammonium transporters in A. oligospora, MEP1, MEP2, and MEP3. Phylogenetic analysis revealed that MEP2 and MEP3 are both high-affinity and low-capacity transporters, whereas MEP1 is a low-affinity and high-capacity transporter. MEP gene expression is elevated in response to nematode exposure and subsequently downregulated upon prey capture, indicating their possible roles in the initiation of trap formation. Under low-nutrient conditions, single deletion mutants of mep1 and mep3 show decreased trap numbers, while traps numbers in mep2 remain similar to wildtype. Double mep deletion mutants without enhanced phenotypes and the elevated gene expression of the remaining MEP(s) suggest functional redundancy among the three ammonium transporters. In contrast, upon addition of ammonium, mep1 mutants were the only mep mutants to exhibit normal growth and suppression of trap formation, suggesting that Mep1 is the primary transporter involved in trap formation under ammonium treatment. Together, these results suggest that the Mep transporters are involved in trap formation initiation in A. oligospora. As nematode-trapping fungi (NTF) like A. oligospora have been proposed to be a biocontrol agent, an enhanced understanding of ammonium transport in this fungus is essential as agricultural environments are normally ammonium-rich.
