The AreA Nitrogen Catabolite Repression Activator Balances Fungal Nutrient Utilization and Virulence in the Insect Fungal Pathogen Beauveria bassiana

In many fungi, the AreA GATA-type transcription factor mediates nitrogen catabolite repression affecting fungal development and, where applicable, virulence. Here, we investigated the functions of AreA in the fungal entomopathogen and plant endophyte Beauveria bassiana using knockdown of gene expression. The antiAreA mutants were impaired in nitrogen utilization and showed increased sensitivities to osmotic stressors but increased tolerances to oxidative/hypoxia stresses. Repression of BbAreA caused overall minimal effects on fungal virulence. The minor effects on virulence appeared to be due in part to competing secondary effects where host defense phenoloxidase activity was significantly decreased, but production of the fungal metabolite oosporein was increased and hyphal body development was impaired. Knockdown of BbAreA expression also resulted in impairment in ability of the fungus to associate with host plants. These data implicate that BbAreA likely acts as a regulator to balance fungal nutrient utilization, pathogenicity, and mutualism, facilitating the fungal occupation of host niches.在多数真菌中，AreA GATA型转录因子（GATA-type transcription factor）可介导氮代谢物阻遏（nitrogen catabolite repression），调控真菌生长发育，且在适用场景下影响其致病力。本研究通过基因沉默（gene knockdown）技术，探究了昆虫病原真菌兼植物内生真菌——球孢白僵菌（Beauveria bassiana）中AreA的功能。经AreA敲低的突变体（antiAreA mutants）在氮源利用能力上存在缺陷，对渗透压胁迫的敏感性升高，但对氧化/低氧胁迫的耐受性增强。BbAreA的基因沉默对真菌致病力整体影响极小，这种微弱影响部分源于相互拮抗的次级效应：宿主防御性酚氧化酶（phenoloxidase）活性显著降低，同时真菌代谢产物卵孢霉素（oosporein）的合成量升高，且虫菌体发育受阻。此外，BbAreA的表达沉默还会削弱真菌与宿主植物的定殖能力。上述研究结果表明，BbAreA大概率作为调控因子，平衡真菌的营养利用、致病力与共生互作，助力真菌占据宿主生态位。