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Open Access Research article

Drechslerella stenobrocha genome illustrates the mechanism of constricting rings and the origin of nematode predation in fungi

Keke Liu12, Weiwei Zhang12, Yiling Lai12, Meichun Xiang1, Xiuna Wang1, Xinyu Zhang1 and Xingzhong Liu1*

  • * Corresponding author: Xingzhong Liu liuxz@im.ac.cn

  • † Equal contributors

Author Affiliations

1 State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, No 3 1st Beichen West Rd., Chaoyang District, Beijing 100101, China

2 University of Chinese Academy of Sciences, Beijing 100039, China

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BMC Genomics 2014, 15:114  doi:10.1186/1471-2164-15-114

Published: 8 February 2014

Abstract

Background

Nematode-trapping fungi are a unique group of organisms that can capture nematodes using sophisticated trapping structures. The genome of Drechslerella stenobrocha, a constricting-ring-forming fungus, has been sequenced and reported, and provided new insights into the evolutionary origins of nematode predation in fungi, the trapping mechanisms, and the dual lifestyles of saprophagy and predation.

Results

The genome of the fungus Drechslerella stenobrocha, which mechanically traps nematodes using a constricting ring, was sequenced. The genome was 29.02 Mb in size and was found rare instances of transposons and repeat induced point mutations, than that of Arthrobotrys oligospora. The functional proteins involved in nematode-infection, such as chitinases, subtilisins, and adhesive proteins, underwent a significant expansion in the A. oligospora genome, while there were fewer lectin genes that mediate fungus-nematode recognition in the D. stenobrocha genome. The carbohydrate-degrading enzyme catalogs in both species were similar to those of efficient cellulolytic fungi, suggesting a saprophytic origin of nematode-trapping fungi. In D. stenobrocha, the down-regulation of saprophytic enzyme genes and the up-regulation of infection-related genes during the capture of nematodes indicated a transition between dual life strategies of saprophagy and predation. The transcriptional profiles also indicated that trap formation was related to the protein kinase C (PKC) signal pathway and regulated by Zn(2)–C6 type transcription factors.

Conclusions

The genome of D. stenobrocha provides support for the hypothesis that nematode trapping fungi evolved from saprophytic fungi in a high carbon and low nitrogen environment. It reveals the transition between saprophagy and predation of these fungi and also proves new insights into the mechanisms of mechanical trapping.

Keywords:
Nematode-trapping fungi; Comparative genomic analysis; Origin of nematode predation; Transcriptomes; Trapping mechanism