Distinctive Expansion of Potential Virulence Genes in the Genome of the Oomycete Fish Pathogen Saprolegnia parasitica

Abstract

Oomycetes in the class Saprolegniomycetidae of the Eukaryotic kingdom Stramenopila have evolved as severe pathogens of amphibians, crustaceans, fish and insects, resulting in major losses in aquaculture and damage to aquatic ecosystems. We have sequenced the 63 Mb genome of the fresh water fish pathogen, Saprolegnia parasitica. Approximately 1/3 of the assembled genome exhibits loss of heterozygosity, indicating an efficient mechanism for revealing new variation. Comparison of S. parasitica with plant pathogenic oomycetes suggests that during evolution the host cellular environment has driven distinct patterns of gene expansion and loss in the genomes of plant and animal pathogens. S. parasitica possesses one of the largest repertoires of proteases (270) among eukaryotes that are deployed in waves at different points during infection as determined from RNA-Seq data. In contrast, despite being capable of living saprotrophically, parasitism has led to loss of inorganic nitrogen and sulfur assimilation pathways, strikingly similar to losses in obligate plant pathogenic oomycetes and fungi. The large gene families that are hallmarks of plant pathogenic oomycetes such as Phytophthora appear to be lacking in S. parasitica, including those encoding RXLR effectors, Crinkler's, and Necrosis Inducing-Like Proteins (NLP). S. parasitica also has a very large kinome of 543 kinases, 10% of which is induced upon infection. Moreover, S. parasitica encodes several genes typical of animals or animal-pathogens and lacking from other oomycetes, including disintegrins and galactose-binding lectins, whose expression and evolutionary origins implicate horizontal gene transfer in the evolution of animal pathogenesis in S. parasitica.

Clotrimazole as a Potent Agent for Treating the Oomycete Fish Pathogen Saprolegnia parasitica through Inhibition of Sterol 14α-Demethylase (CYP51)

“…The SpCYP51 sequence we identified agreed with that published (SPRG_09493.2) by Jiang et al (51) during the course of our work. TargetP predicted the SpCYP51 N-terminal membrane anchor to consist of the first 36 amino acid residues, while WoLF PSORT predicted that SpCYP51 would be located in the endoplasmic reticulum.…”

“…Functional analysis of the lanosterol synthase and ⌬ 5 sterol desaturase candidates (expression, purification, and reconstitution assays) will be required to demonstrate the catalytic function of each protein. The S. parasitica sterol biosynthesis enzymes identified here (Table 4) agree with those identified by Jiang et al (51). However, the sterol pathway proposed by Jiang et al (51) did not relate to the sterols identified in this study.…”

“…The S. parasitica sterol biosynthesis enzymes identified here (Table 4) agree with those identified by Jiang et al (51). However, the sterol pathway proposed by Jiang et al (51) did not relate to the sterols identified in this study. Our pathway (Fig.…”

“…For lanosterol synthase and ⌬ 5 sterol desaturase, two potential candidates were identified for each gene, in agreement with the work of Jiang et al (51). For lanosterol synthase, SPRG_117832.2 (805 amino acids) and SPRG_17895.2 (472 amino acids) shared 99% identity.…”

“…This may be because the S. parasitica ⌬ 3 sterol keto reductase has low sequence identity to mammalian and fungal ⌬ 3 sterol keto reductases or because this chemical reaction is performed by a phylogenetically unrelated enzyme in S. parasitica. Jiang et al (51) were unable to identify a ⌬ 3 sterol keto reductase candidate in S. parasitica, as were Madoui et al (35) in A. euteiches.…”