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

Broad Institute of MIT and Harvard, Cambridge, Massachusetts, United States of America.
PLoS Genetics (Impact Factor: 8.17). 06/2013; 9(6):e1003272. DOI: 10.1371/journal.pgen.1003272
Source: PubMed

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.

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Available from: Berend Snel, Aug 27, 2015
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    • "To identify the ancestral oomycete secretome (AOS) we analyzed the three saprolegnian taxa in comparison with seven sequenced members of the Peronosporaleans. Collectively, these species represent a wide range of oomycete lifestyles, from free-living saprobes to obligate parasites of plants (table 2; Haas et al. 2009; Levesque et al. 2010; Raffaele et al. 2010; Links et al. 2011; Jiang et al. 2013). Using the secretome of the putative sister group of the oomycetes, Hyphochytridiomycete, Hyp. "
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    • "It will be of interest to determine whether SpHtp1 and other host-targeting proteins play a role in Saprolegnia infection of fish, and fish eggs, and whether similar or different infection strategies are used to infect amphibians, crustaceans and/or their eggs. Genome comparisons between S. parasitica (Jiang et al., 2013) and S. diclina might, in the near future, lead to the elucidation of their different infection strategies which in turn will allow the development of effective strategies to reduce the impact of these Oomycetes on natural ecosystems and in particular the aquaculture industry. "
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