Genome and transcriptome sequences reveal the specific parasitism of the nematophagous Purpureocillium lilacinum 36-1

Purpureocillium lilacinum is a promising nematophagous ascomycete able to adapt diverse environments and it is also an opportunistic fungus that infects humans. A microbial inoculant of P. lilacinum has been registered to control plant parasitic nematodes. However, the molecular mechanism of the toxicological processes is still unclear because of the relatively few reports on the subject. In this study, using Illumina paired-end sequencing, the draft genome sequence and the transcriptome of P. lilacinum strain 36-1 infecting nematode-eggs were determined. Whole genome alignment indicated that P. lilacinum 36-1 possessed a more dynamic genome in comparison with P. lilacinum India strain. Moreover, a phylogenetic analysis showed that the P. lilacinum 36-1 had a closer relation to entomophagous fungi. The protein-coding genes in P. lilacinum 36-1 occurred much more frequently than they did in other fungi, which was a result of the depletion of repeat-induced point mutations (RIP). Comparative genome and transcriptome analyses revealed the genes that were involved in pathogenicity, particularly in the recognition, adhesion of nematode-eggs, downstream signal transduction pathways and hydrolase genes. By contrast, certain numbers of cellulose and xylan degradation genes and a lack of polysaccharide lyase genes showed the potential of P. lilacinum 36-1 as an endophyte. Notably, the expression of appressorium-formation and antioxidants-related genes exhibited similar infection patterns in P. lilacinum strain 36-1 to those of the model entomophagous fungi Metarhizium spp. These results uncovered the specific parasitism of P. lilacinum and presented the genes responsible for the infection of nematode-eggs

Dihydroxyacetone of wheat root exudates serves as an attractant for Heterodera avenae.

Heterodera avenae, as an obligate endoparasite, causes severe yield loss in wheat (Triticum aestivum). Investigation on the mechanisms how H. avenae perceives wheat roots is limited. Here, the attractiveness of root exudates from eight plant genotypes to H. avenae were evaluated on agar plates. Results showed that the attraction of H. avenae to the root exudates from the non-host Brachypodium distachyon variety Bd21-3 was the highest, approximately 50 infective second-stage juveniles (J2s) per plate, followed by that from three H. avenae-susceptible wheat varieties, Zhengmai9023, Yanmai84 and Xiangmai25, as well as the resistant one of Xinyuan958, whereas the lowest attractive activity was observed in the two H. avenae-resistant wheat varieties, Xianmai20 (approximately 12 J2s/plate) and Liangxing66 (approximately 11 J2s/plate). Then Bd21-3, Zhengmai9023 and Heng4399 were selected for further assays as their different attractiveness and resistance to H. avenae, and attractants for H. avenae in their root exudates were characterized to be heat-labile and low-molecular compounds (LM) by behavioral bioassay. Based on these properties of the attractants, a principle of identifying attractants for H. avenae was set up. Then LM of six root exudates from the three plants with and without heating were separated and analyzed by HPLC-MS. Finally, dihydroxyacetone (DHA), methylprednisolone succinate, embelin and diethylpropionin in the root exudates were identified to be putative attractants for H. avenae according to the principle, and the attraction of DHA to H. avenae was validated by behavioral bioassay on agar. Our study enhances the recognition to the orientation mechanism of H. avenae towards wheat roots

The Zn(II)2Cys6 putative transcription factor is involved in the regulation of leucinostatin production and pathogenicity of the nematophagous fungus <i>Paecilomyces lilacinus</i>

<div><p></p><p>Zn(II)2Cys6 transcription factor genes encode transcription regulators that manage the infection potential and production of secondary metabolites such as toxins in fungi. In this study, a gene named <i>rolP</i> that encodes a putative Zn(II)2Cys6 transcription factor regulating leucinostatin production in the filamentous fungus <i>Paecilomyces lilacinus</i> was characterized by a gene knockout approach. The deduced proprotein consists of 705 amino acids and is highly homologous to the Zn(II)2Cys6 transcription factor of the entomopathogenic fungus <i>Metarhizium brunneum</i>. Predictive analysis of the secondary structure of the proportion showed that it has two domains. <i>Paecilomyces lilacinus</i> can produce nematotoxins leucinostatins A and B. Deletion of <i>rolP</i> from the <i>P. lilacinus</i> wild-type strain Pl36-1 leads to the absence of leucinostatin A, while a large increase in the leucinostatin A level was achieved in the <i>rolP</i> overexpression strain Ov-Pl36-1. During the process of nematode infection, <i>rolP</i> showed high expression levels at 48–72 h and peaked at 48 h. Bioassay tests confirmed the requirement of <i>rolP</i> for leucinostatin production. However, the root-knot second-stage juvenile-toxicity was minimized to 35.3% in Δ<i>rolP</i>; toxicity was 97.2% with Ov-Pl36-1 compared with 68.4% with the wild type strain Pl36-1. Interestingly, neither knockout nor overexpression of the <i>rolP</i> gene affected the growth or sporulation of <i>P. lilacinus</i>. Additionally, fungal nutrition and acidic media might stimulate the <i>rolP</i> activity of the wild type strain against nematodes. These findings suggested that the <i>rolP</i> gene is required for the induction and production of leucinostatins and is considered a leucinostatin regulatory gene in <i>P. lilacinus</i>.</p></div