Autophagy is required for trap formation in the nematode-trapping fungus Arthrobotrys oligospora

Nematode-trapping fungi live mainly as saprobes in soil environments. When encountering nematodes, these fungi become carnivorous' and develop specialized trapping devices to attack their hosts for extracting nutrients, especially nitrogen source. Thus, nematode-trapping fungi are model organisms for understanding the molecular mechanism of the switch between saprobic and parasitic phases of pathogen life cycles. Arthrobotrys oligospora, one of the best-studied nematode-trapping fungi, mainly lives as a saprobe. In the presence of nematodes, A.oligospora enters the parasitic stage by forming adhesive reticulate traps to capture nematodes. In filamentous fungi, autophagy has been shown to be involved in morphogenesis and morphology. In this study, we demonstrate that autophagy is induced by nematodes during the early stage of trap formation in A.oligospora. Disruption of atg8 gene not only abolishes the nematode-induced autophagy, but also suppresses trap formation and reduces pathogenicity for nematodes. During the early stage of trap formation, the expression of genes involved in amino acid biosynthesis is upregulated and the transcriptional activity of GCN4 is induced in A.oligospora, suggesting that nematodes induce autophagy probably by triggering intracellular amino acid starvation. Autophagy is thus crucial for trap formation in A.oligospora during infection of nematodes.

捕食线虫真菌主要在土壤环境中作为腐生菌生存。当遇到线虫时，这些真菌会变成“肉食性”的，并发育出特殊的捕食装置来攻击其宿主以获取营养，尤其是氮源。因此，捕食线虫真菌是了解病原体生命周期中腐生阶段和寄生阶段转换的分子机制的模式生物。少孢节丛孢（Arthrobotrys oligospora）是研究最为深入的捕食线虫真菌之一，主要作为腐生菌生存。在有线虫存在的情况下，少孢节丛孢通过形成粘性网状陷阱来捕获线虫从而进入寄生阶段。在丝状真菌中，自噬已被证明与形态发生和形态有关。在这项研究中，我们证明在少孢节丛孢陷阱形成的早期阶段，自噬是由线虫诱导的。atg8基因的破坏不仅消除了线虫诱导的自噬，还抑制了陷阱的形成并降低了对线虫的致病性。在陷阱形成的早期阶段，少孢节丛孢中参与氨基酸生物合成的基因表达上调，GCN4的转录活性被诱导，这表明线虫可能通过引发细胞内氨基酸饥饿来诱导自噬。因此，自噬对于少孢节丛孢在线虫感染过程中陷阱的形成至关重要。