Gene regulatory networks (GRNs) drive developmental and cellular differentiation, and variation in their architectures gives rise to morphological diversity. Pioneering studies in Aspergillus fungi, coupled with subsequent work in other filamentous fungi, have shown that the GRN governed by the BrlA, AbaA, and WetA proteins controls the development of the asexual fruiting body, or conidiophore. A specific aspect of conidiophore development is the production of phialides, conidiophore structures that are under the developmental control of AbaA and function to repetitively generate spores. Fungal genome sequencing has revealed that some filamentous fungi lack abaA, and also produce asexual structures that lack phialides, raising the hypothesis that abaA loss is functionally linked to diversity in asexual fruiting body morphology. To examine this hypothesis, we carried out an extensive search for the abaA gene across 241 genomes of species from the fungal subphylum Pezizomycotina. We found that abaA was independently lost in four lineages of Eurotiomycetes, including from all sequenced species within the order Onygenales, and that all four lineages that have lost abaA also lack the ability to form phialides. Genetic restoration of abaA from Aspergillus nidulans into Histoplasma capsulatum, a pathogenic species from the order Onygenales that lacks an endogenous copy of abaA, did not alter Histoplasma conidiation morphology but resulted in a marked increase in spore viability. We also discovered that species lacking abaA contain fewer AbaA binding motifs in the regulatory regions of orthologs of some AbaA target genes, suggesting that the asexual fruiting body GRN of organisms that have lost abaA has likely been rewired. Our results provide an illustration of how repeated losses of a key regulatory transcription factor have contributed to the diversity of an iconic fungal morphological trait.

中文翻译：

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ABAA（丝状真菌无性发育的主要调节者）的反复流失与基因组和形态特征的变化有关。

基因调控网络（GRN）推动发育和细胞分化，其结构的变异引起形态多样性。曲霉真菌的开创性研究以及其他丝状真菌的后续研究表明，由BrlA，AbaA和WetA蛋白控制的GRN控制着无性子实体或分生孢子的发育。分生孢子发育的一个特定方面是phialides的生产，其是在AbaA的发育控制下并具有重复产生孢子的功能的分生孢子结构。真菌基因组测序表明，某些丝状真菌缺乏abaA，并且还产生缺乏phialides的无性结构，这提出了abaA丧失与无性子实体形态上的功能相关的假说。为了检验这一假设，我们对真菌亚纲Pezizomycotina的241个物种的基因组进行了广泛的搜索。我们发现abaA在欧洲丝菌的四个谱系中独立丢失，包括从Onygenales顺序中的所有测序物种中丢失，并且丢失abaA的所有四个谱系也都缺乏形成phialides的能力。从构巢曲霉将abaA遗传还原到荚膜组织胞浆菌中（一种来自Onygenales的病原体，缺乏内源性abaA拷贝），并没有改变组织胞浆分生形态，但导致了孢子活力的显着增加。我们还发现，缺乏abaA的物种在某些AbaA目标基因直系同源物的调控区中含有较少的AbaA结合基序，这表明丢失了abaA的生物体的无性子实体GRN可能已被重新布线。我们的结果提供了一个例证，说明关键调节转录因子的反复缺失如何导致标志性真菌形态特征的多样性。