The Discovery And Function Mechanism Of MilRNA In Nematode-trapping Fungus Arthrobotrys Oligospora

Non-coding RNAs widely exist in procaryotic organisms and various kinds of eukaryotic organisms, and they play very important roles in regulation of multiple biological processes. MicroRNA (miRNA) is one of the best studied small non-coding RNAswith length of around 21nt. The biogenesis and regulation of miRNAs in plants and animals have been systemically studied. So far they have been applied in research of biological mechanisms and the treatment of various human diseases. MiRNA were previously thought to be absent from fungi until microRNA-like RNA (milRNA) were identified recently. However, the physiological importance of milRNA in fungi remains to be determined.Here we show that milRNA exist in the representative nematode-trapping fungus Arthrobotrys oligospora.We found that milR289 could target qde-2which plays an important role in the lifestyle transition of the fungi to carnivores indicated by developing adhesive networks to trap and consume nematodes. MilRNA were identified by small RNA sequencing and confirmed by northern blot analysis. The biogenesis and structures showed they resembled miRNAs. RNA immunoprecipitation (RIP) analysis has shown that milR289 was associated with the argonaute protein QDE-2. In addition, as the core component in RISC, disruption of qde-2 gene led to serious defect in trap induction by urea, nematode extraction (NE) and live nematode. Putative target genes were predicted, and three of them have been found by RIP-RT-PCR in immunoprecipitation (IP) product of QDE-2. Interestingly, the mRNA of argonaute gene qde-2 itself was detected to be associated with QDE-2 and the interaction between milR289 and qde-2 mRNA has been verified in transient gene expression system in tobacco.To our knowledge, it is the first time to identify milRNA in nematode-trapping fungi. Our work is a pioneer attempt to study physiological function and mechanism of milRNA in fungi, and this mechanism plays an important role in trap induction. Our results suggest a regulatory loop between milRNA and QDE-2/RNAi pathways. The similar pathway has also been found in plants, suggesting a conservative regulation in fungi and plants.