Genome Of Dactylellina Leptospora Reveals The Trap Evolution And Carnivorous Adaptation

Nematode-trapping fungi can develop specific trapping device to capture nematodes, which lead to great agricultural loss in the whole world. Therefore, nematode-trapping fungi can be important resources for development of biocontrol agents.Nematode-trapping fungi belong to orbiliaceae, ascomycete. Compared to other members of orbiliaceae, nematode-trapping fungi has unique lifestyle. Various trapping structures have been developed by nematode-trapping fungi. Among them, the combination of non-constricting rings and adhesive knobs has attracted more interests. The fungi with this kind of traps are mainly coming from genus Dactylellina. It ts interesting to know whether the combination of two traps will improve the hunting efficiency. Previous researches have mainly focused on adhesive networks of Arthrobotrys oligospora, which are quite different from non-constricting rings and adhesive knobs. We hope to reveal the underlying genetic mechanisms with comparative genomic studies.We sequenced the genome of Dactylellina leptospora which develops both non-constricting rings and adhesive knobs, and carried out genomic annotation and comparative genomic research. Since Dactylellina leptospora can form the traps whether or not there are nematodes, we also explored the conditions that will lead nematode-trapping fungi to form traps spontaneously.We got a genome assembly with the size of34Mb. Combined gene prediction have identified10,661protein-coding genes in the genome. Interestingly, there is very few repeat sequences in the genome, which has also been found in other nematode-trapping fungi. Further study showed that positive RIP signals were found in the genome sequences.16other fungal genomes were selected to carry out comparative genomic analysis, including model fungi, plant pathogens, animal pathogens and other nematode-trapping fungi.368orthologous genes were identified and used for phylogenomic analysis. The results showed that Dactylellina leptospora evolved close to the nematode-trapping fungi with adhesive knobs.We selected a few pathogenicity-related gene families for comparative analysis. The results show that some of them had expanded in the nematode-trapping fungi, including cellulase-endoglucanase, pectinesterase, GAS(glycolipid-anchored surface proteins), polygalacturonase and subtilisin. These gene families may play very important roles in trap formation and infection of nematodes.Nutrient deficiency may be the key factor for spontaneous trap formation of Dactylellina leptospora. Compared to the induced trap formation in other nematode-trapping fungi, limitation of carbon source will make Dactylellina leptospora develop traps spontaneously.In this paper, we studied the underlying mechanism of trap formation and infection of nematodes by Dactylellina leptospora by phylogenomic and comparative genomic analyses. We also explored the conditions for Dactylellina leptospora to develop traps spontaneously. The results provide a basis for further studies.