Abstract：
The formation of the trapping device induced by nematodes has been assumed as an indicator for a switch from saprophytic to predacious lifestyles for nematode-trapping fungi. However, fungal nematocidal activity is not completely synonymous with fungal trap formation. We found that the predominant nematode-trapping fungus Arthrobotrys oligospora harbored a rare NRPS (Ao415) gene cluster that was mainly distributed in nematode-trapping fungi. The gene Ao415 putatively encodes a protein with a unique domain organization, distinct from other NRPSs in other fungi. Mutation of the two key biosynthetic genes Ao415 and Ao414 combined with nontarget metabolic analysis revealed that the Ao415 gene cluster was responsible for the biosynthesis of a hydroxamate siderophore, desferriferrichrome (1). Lack of desferriferrichrome (1) and its hydroxamate precursor (3) could lead to significantly increased Fe3+ content, which induced fungal trap formation without a nematode inducer. Furthermore, the addition of Fe3+ strongly improved fungal trap formation but deleteriously caused broken traps. The addition of 1 significantly attenuated trap formation but enhanced fungal nematicidal activity. Our findings indicate that iron is a key factor for trap formation and provide a new insight into the underlying mechanism of siderophores in nematode-trapping fungi.
摘要：
线虫诱导的诱捕装置的形成被认为是线虫诱捕真菌从腐生转变为食欲不振的生活方式的指标。然而,真菌杀线虫活性与真菌陷阱的形成并不完全同义。我们发现，主要的线虫诱捕真菌Arthrobotrys寡孢菌带有一个罕见的NRPS（Ao415）基因簇，该基因簇主要分布在线虫诱捕真菌中。Ao415基因推定编码一种具有独特结构域结构的蛋白质，与其他真菌中的其他NRPS不同。两个关键的生物合成基因Ao415和Ao414的突变结合非靶标代谢分析显示，Ao415基因簇负责异羟肟酸盐铁载体的生物合成，desferriferrichrome(1).脱铁醇(1)及其异羟肟酸盐前体(3)的缺乏可导致Fe3+含量显著增加,在没有线虫诱导剂的情况下诱导真菌陷阱的形成。此外，Fe3的添加大大改善了真菌陷阱的形成，但有害地导致陷阱破裂。添加1可显着减弱陷阱的形成，但增强了杀真菌线虫的活性。我们的发现表明，铁是陷阱形成的关键因素，并为线虫诱捕真菌中铁载体的潜在机制提供了新的见解。
