Transcriptome Analysis of the Entomopathogenic Oomycete Lagenidium giganteum Reveals Putative Virulence Factors

Abstract

A combination of 454 pyrosequencing and Sanger sequencing was used to sample and characterize the transcriptome of the entomopathogenic oomycete Lagenidium giganteum. More than 50,000 high-throughput reads were annotated through homology searches. Several selected reads served as seeds for the amplification and sequencing of full-length transcripts. Phylogenetic analyses inferred from full-length cellulose synthase alignments revealed that L giganteum is nested within the peronosporalean galaxy and as such appears to have evolved from a phytopathogenic ancestor. In agreement with the phylogeny reconstructions, full-length L. giganteum oomycete effector orthologs, corresponding to the cellulose-binding elicitor lectin (CBEL), crinkler (CRN), and elicitin proteins, were characterized by domain organizations similar to those of pathogenicity factors of plantpathogenic oomycetes. Importantly, the L. giganteum effectors provide a basis for detailing the roles of canonical CRN, CBEL, and elicitin proteins in the infectious process of an oomycete known principally as an animal pathogen. Finally, phylogenetic analyses and genome mining identified members of glycoside hydrolase family 5 subfamily 27 (GH5_27) as putative virulence factors active on the host insect cuticle, based in part on the fact that GH5_27 genes are shared by entomopathogenic oomycetes and fungi but are underrepresented in nonentomopathogenic genomes. The genomic resources gathered from the L. giganteum transcriptome analysis strongly suggest that filamentous entomopathogens (oomycetes and fungi) exhibit convergent evolution: they have evolved independently from plant-associated microbes, have retained genes indicative of plant associations, and may share similar cores of virulence factors, such as GH5_27 enzymes, that are absent from the genomes of their plant-pathogenic relatives.

Lagenidium giganteumPathogenicity in Mammals

“…The resent transcriptome analysis of a strain of L. giganteum recovered in nature from mosquito larvae further strengthens the relevance of our findings ( 25 ). The use of varieties or subspecies to name these 2 populations of L. giganteum was avoided until more comprehensive genomic data shed light on their true evolutionary relationships.…”

Genomic innovations linked to infection strategies across emerging pathogenic chytrid fungi

“…Notably we found regions of low-gene density include homologues of a class of virulence effectors termed Crinkler and Necrosis (CRN) genes, previously found in the Phytophthora and Lagenidium genera of Oomycetes1415. CRN-like genes in Bd had long intergenic regions consistent with a gene-poor repeat-rich environment (averaging 1.4 kb; Supplementary Fig.…”

Molecular phylogeny and taxonomy of Lagenidium -like oomycetes pathogenic to mammals

“…This concept is supported by the fact that at least one of these newly described pathogens (L. deciduum) has been isolated from both mammals (cats) and nematodes. Furthermore, recent transcriptome sequencing of L. giganteum f. giganteum has revealed the presence of putative CBEL and CRN effectors that are known as pathogenicity factors in plant pathogens, raising the question of whether this species could also infect and establish pathogenic or endophytic relationships with plants (Quiroz Velasquez et al 2014). Future investigations aimed at environmental sampling of nematodes or insect larvae and plant material in areas where Lagenidium and Paralagenidium infection in mammals is common may help to further characterise the potential role of invertebrate and plant hosts in the life cycle and infectivity of these newly described pathogens.…”