Molecular analysis of arthrosporol, ascaroside and nutritional signaling during the interaction of the nematode-trapping fungus Duddingtonia flagrans with Caenorhabditis elegans

生物间的相互作用对地球上的生命至关重要。这种相互作用通常非常复杂，并且是在进化过程中形成的。在真菌相互作用的情况下，它们的范围可以从共生到致病再到掠食性。我们正在研究捕获线虫的掠食性真菌，它们产生不同的捕获装置，引诱线虫进入陷阱，用穿透性菌丝侵入线虫，随后在线虫体内定植。我们的模型是在实验室中生长良好并产生粘性陷阱网络的旗鱼。该菌还可作为家畜养殖中的生物防治剂，并可进一步开发用于植物病原线虫的防治。与其他捕获线虫的真菌不同，它产生抗性衣原体孢子，可用于土壤中的应用。真菌-线虫相互作用的第一步是真菌对线虫的感知和陷阱形成的开始。因为陷阱的形成只有在一定数量的线虫存在而其他营养物质不可用的情况下才有意义，一种基于低分子量化合物的有趣的生物间通信系统进化了。次生代谢物、不同的关节孢子素和6-甲基水杨酸抑制陷阱的形成。这种真菌能够感知蛔虫苷——一种重要的线虫分子——从而感知到线虫的存在。蛔虫苷抑制真菌衍生的负信号分子的产生，从而导致诱捕诱导。该系统类似于群体感应机制，能够感应到线虫的密度。在目前的研究计划中，将分析陷阱诱导和形态发生的信号级联。初步数据表明，g蛋白和g蛋白偶联膜受体（gpcr）参与了线虫的营养状况和存在的整合。信号级联将通过基因缺失和过表达实验来解决。我们将验证在线虫进化过程中是否通过水平基因转移（HGT）获得了一些真菌蛔虫苷传感gpcr的假设。除了通过基因缺失、基因过表达和使用构成型活性g - α等位基因来阐明信号级联的组成外，还将通过双分子荧光互补（BiFC）、酵母双杂交和FRET分析在时间和空间上研究g蛋白与其gpcr的相互作用。为了进一步阐明陷阱诱导和陷阱形态发生的过程，我们将通过全基因组转录分析分离和表征信号级联的靶基因。

Organismic interactions are crucial for live on earth. Such interactions are often very sophisticated and have been shaped during evolution. In the case of fungal interactions, they can range from symbiotic to pathogenic to predatory. We are studying nematode-trapping, predatory fungi, which produce different trapping devices, lure nematodes into the traps, invade the nematodes with penetrating hyphae and subsequently colonize the entire worm body. Our model is Duddintonia flagrans, which grows well in the lab and produces adhesive trap networks. D. flagrans is also used as a biocontrol agent in livestock farming, and may be further developed against plant pathogenic nematodes in the future. As a difference to other nematode-trapping fungi, it produces resistant chlamydospores, which may be used for its application in soil. One of the first steps of the fungal-nematode interaction is the fungal sensing of the nematodes and the initiation of trap formation. Because trap formation only makes sense, if a certain number of nematodes is present and other nutrients are not available, an interesting interorganismic communication system based on low-molecular weight compounds evolved. Trap formation is inhibited by secondary metabolites, different arthrosporols and 6-methyl salicylic acid. The fungi are able to sense ascarosides – important nematode molecules – and thereby the presence of nematodes. Ascarosides inhibit the production of the fungal-derived, negative signaling molecules, which leads to trap induction. The system resembles a quorum sensing mechanism, enabling the sensing of the nematode density.In the current research proposal, the signaling cascades underlying trap induction and morphogenesis will be analyzed. Preliminary data suggest the involvement of G-proteins and G-protein coupled membrane receptors (GPCRs) in the integration of the nutritional status and the presence of nematodes. The signaling cascades will be resolved by gene deletion and overexpression experiments. We will test the hypothesis if some fungal ascaroside-sensing GPCRs were acquired by horizontal gene transfer (HGT) from nematodes during evolution.Besides the elucidation of the components of the signaling cascades by gene deletion, gene overexpression and the use of constitutive-active G-alpha alleles, the interaction of the G-proteins with their GPCRs will be studied in time and space by bimolecular fluorescence complementation (BiFC), yeast-two-hybrid and FRET analyses.To further elucidate the process of trap induction and trap morphogenesis, target genes of the signaling cascades will be isolated and characterized after genome-wide transcription analyses.