# MaNrtB, a Putative Nitrate Transporter, Contributes to Stress Tolerance and Virulence in the Entomopathogenic Fungus Metarhizium acridum

## TL;DR

This study explores how a nitrate transporter gene in a fungus affects its ability to tolerate stress and infect insects.

## Contribution

The study identifies MaNrtB as a key gene in stress tolerance and virulence in the entomopathogenic fungus Metarhizium acridum.

## Key findings

- Disruption of MaNrtB delays conidial germination without affecting conidial production.
- MaNrtB disruption increases vulnerability to UV-B and osmotic stress but improves heat resistance.
- Loss of MaNrtB reduces virulence by impairing appressorium formation and growth in insect hemolymph.

## Abstract

Nitrogen is an essential nutrient that frequently determines the growth rate of fungi. Nitrate transporter proteins (Nrts) play a crucial role in the cellular absorption of nitrate from the environment. Entomopathogenic fungi (EPF) have shown their potential in the biological control of pests. Thus, comprehending the mechanisms that govern the pathogenicity and stress tolerance of EPF is helpful in improving the effectiveness and practical application of these fungal biocontrol agents. In this study, we utilized homologous recombination to create MaNrtB deletion mutants and complementation strains. We systematically investigated the biological functions of the nitrate transporter protein gene MaNrtB in M. acridum. Our findings revealed that the disruption of MaNrtB resulted in delayed conidial germination without affecting conidial production. Stress tolerance assays demonstrated that the MaNrtB disruption strain was more vulnerable to UV-B irradiation, hyperosmotic stress, and cell wall disturbing agents, yet it exhibited increased heat resistance compared to the wild-type strain. Bioassays on the locust Locusta migratoria manilensis showed that the disruption of MaNrtB impaired the fungal virulence owing to the reduced appressorium formation on the insect cuticle and the attenuated growth in the locust hemolymph. These findings provide new perspectives for understanding the pathogenesis of EPF.