MaMsb2, a signaling mucin, is involved in conidiation, stress tolerances, and virulence in the entomopathogenic fungus Metarhizium acridum

<strong>Background:</strong> The signal transduction mucin Msb2 initiates the signal transduction response in the HOG pathway and participates in the infection and pathogenesis of fungal pathogens. <em>Metarhizium acridum</em>, an entomopathogenic fungus, is a promising biopesticide for agricultural, forestry, and urban pest control. This study focuses on the characterization of MaMsb2 in <em>M. acridum</em>.
<strong>Materials and Methods: </strong>Gene expression profiles of <em>MaMsb2</em> in <em>M. acridum</em> were analyzed using RT-qPCR. Knockout strain of <em>MaMsb2</em> was constructed via homologous recombination, and the Δ<em>MaMsb2</em> complementation strain was constructed via ectopic insertion. Their phenotypic characteristics were examined. The conidial germination rates and conidial yield of different fungal strains were ascertained on 1/4 SDAY. The fungal tolerances to UV-B radiation and heat stress was evaluated. Fungal virulence was evaluated using the fifth instar nymphs of <em>Locusta migratoria manilensis</em>, and infection structures formation and penetration ability were assessed on locust hind wings. 
<strong>Results: </strong>Disruption of <em>MaMsb2</em> resulted in the delayed conidial germination, the increased conidial yield owing to the changed conidiation pattern, the reduced tolerances to multiple stresses, the decreased virulence because of the impairments of appressorium formation and the growth of <em>M. acridum</em> in the hemolymph of locusts. RNA-seq showed that MaMsb2 governed the appressorium formation of <em>M. acridum</em> by mediating the expression of related genes such as conidial adhesion, appressorium formation, and host cuticle penetration.
<strong>Conclusion:</strong> MaMsb2 is crucial for fungal conidiation, stress tolerances, virulence in <em>M. acridum</em>, playing essential roles in infection structures formation, penetration. Understanding its functions provides insights into the pathogenic mechanisms of insect pathogenic fungi.

<strong>背景：</strong>信号转导黏蛋白Msb2可启动HOG通路的信号转导反应，并参与真菌病原体的侵染及致病过程。<em>Metarhizium acridum</em>（金龟子绿僵菌蝗变种）作为一种昆虫病原真菌，是农业、林业及城市害虫防治领域极具应用前景的生物农药。本研究聚焦于<em>M. acridum</em>中MaMsb2的功能表征。
<strong>材料与方法：</strong>采用实时荧光定量聚合酶链式反应（RT-qPCR）分析<em>M. acridum</em>中MaMsb2的基因表达谱；通过同源重组构建MaMsb2敲除菌株，异位插入构建ΔMaMsb2互补菌株，并检测其表型特征。在1/4 SDAY培养基上测定不同菌株的分生孢子萌发率及产量；评估菌株对紫外B辐射和热胁迫的耐受性；以东亚飞蝗五龄若虫（<em>Locusta migratoria manilensis</em>）为对象评价菌株毒力，并在蝗虫后翅上检测侵染结构的形成及穿透能力。
<strong>结果：</strong>MaMsb2缺失导致分生孢子萌发延迟、产孢模式改变引发产量增加、多重胁迫耐受性降低；同时因附着胞形成缺陷及蝗虫血淋巴内生长受阻，菌株毒力下降。转录组测序（RNA-seq）显示，MaMsb2通过调控分生孢子黏附、附着胞形成及宿主表皮穿透等相关基因的表达，介导<em>M. acridum</em>附着胞的形成。
<strong>结论：</strong>MaMsb2对<em>M. acridum</em>的产孢、胁迫耐受性及毒力至关重要，在侵染结构形成与穿透中发挥核心作用。解析其功能可为深入理解昆虫病原真菌的致病机制提供新见解。