Endosome motility controls light-responsive reproductive development and secondary metabolite production in Aspergillus

Filamentous fungi, such as Aspergillus species, use microtubule transport to move early endosomes. Other cargos, such as peroxisomes and mRNAs, “hitchhike” on early endosomes to move throughout the long hyphae of these organisms. In Aspergillus nidulans, peroxisomes hitchhike on early endosomes using the endosomal protein PxdA and the peroxisomal protein AcbdA. The HookA adaptor protein links endosomes to microtubule motors. Here, we set out to explore the physiological functions of peroxisome hitchhiking and endosome motility. Aspergillus nidulans has a complex life cycle that includes asexual and sexual reproduction. A. nidulans and other fungi within the Pezizomycotina subphylum are also notable for the vast number of secondary metabolites they produce. Light and other environmental conditions influence developmental decisions and secondary metabolite production. Here, we found that sexual reproduction is favored in the absence of endosome motility, even in the light, which normally promotes asexual reproduction. RNA sequencing of strains lacking endosome motility showed altered expression of genes involved in development. Unexpectedly, we observed altered expression of genes involved in secondary metabolism in strains lacking endosome motility and peroxisome hitchhiking. Using mass spectrometry, we found that the loss of endosome motility affected the biosynthesis of secondary metabolites, including sterigmatocystin, a carcinogenic mycotoxin that is a food contaminant. Finally, in a pathogenic species, Aspergillus fumigatus, we found that deletion of its PxdA homolog also significantly altered secondary metabolite production. Our work uncovers an unexpected link between organelle motility, developmental decisions in response to light, and secondary metabolite production in filamentous fungi.丝状真菌（Filamentous fungi）如曲霉属（Aspergillus）物种，借助微管运输（microtubule transport）转运早期内体（early endosomes）。包括过氧化物酶体（peroxisomes）与信使RNA（mRNA）在内的其他货物，会“搭便车”于早期内体之上，在这类生物的细长菌丝（hyphae）中完成全域转运。在构巢曲霉（Aspergillus nidulans）中，过氧化物酶体通过内体蛋白PxdA与过氧化物酶体蛋白AcbdA，搭乘早期内体实现转运。HookA衔接蛋白（HookA adaptor protein）可将内体与微管马达蛋白（microtubule motors）相连。本研究旨在探究过氧化物酶体搭便车转运与内体运动的生理功能。构巢曲霉拥有包含无性生殖与有性生殖的复杂生命周期。盘菌亚门（Pezizomycotina subphylum）的构巢曲霉与其他同类真菌，还因可产生海量次级代谢产物（secondary metabolites）而广受关注。光照及其他环境条件会调控真菌的发育决策与次级代谢产物的合成。本研究发现，即便在通常促进无性生殖的光照条件下，缺失内体运动的菌株更倾向于开展有性生殖。对缺失内体运动的菌株进行RNA测序（RNA sequencing）后，结果显示其发育相关基因的表达发生显著改变。出乎意料的是，同时缺失内体运动与过氧化物酶体搭便车转运的菌株，其次级代谢相关基因的表达同样出现异常。通过质谱分析法（mass spectrometry），我们证实内体运动的缺失会影响多种次级代谢产物的生物合成，其中包括杂色曲霉素（sterigmatocystin）——一种具有致癌性的真菌毒素（mycotoxin），同时也是常见的食品污染物。最后，在致病物种烟曲霉（Aspergillus fumigatus）中，我们发现其PxdA同源蛋白的敲除同样会显著改变次级代谢产物的合成。本研究揭示了丝状真菌中细胞器运动、光照响应的发育决策与次级代谢产物合成之间此前未被发现的内在关联。