Adenylosuccinate synthase negatively controls <italic>Metarhizium robertsii</italic> pathogenicity

Adenylosuccinate synthetase (ADSS) plays an important role in cellular energy metabolism and signal transduction. However, ADSS had not been reported in entomopathogenic fungi. In this study, function of ADSS family protein MrADSS-1 to the growth, stress resistance and pathogenicity in the entomopathogenic fungus Metarhizium robertsii was characterized by investigating the protein subcellular localization and gene disruption, complementation and over-expression. Results showed that MrADSS-1 is exclusively localized within the vacuole. Disruption of the MrADSS-1 resulted in marked reduction of radial growth of the fungus on maltose medium and a significant decrease in UV-B tolerance, but unexpectedly enhanced thermotolerance. Bioassays revealed that loss of MrADSS-1 led to a pronounced increase in appressorium formation and penetration efficiency through cicada wings, resulting in elevated pathogenicity toward Galleria mellonella larvae. Conversely, over-expression of MrADSS-1 attenuated fungal virulence. These findings demonstrated that MrADSS-1 functions as a repressor of both thermotolerance and virulence in M. robertsii.