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Transcriptome of Aphanomyces euteiches: new oomycete putative pathogenicity factors and metabolic pathways.

ABSTRACT: Aphanomyces euteiches is an oomycete pathogen that causes seedling blight and root rot of legumes, such as alfalfa and pea. The genus Aphanomyces is phylogenically distinct from well-studied oomycetes such as Phytophthora sp., and contains species pathogenic on plants and aquatic animals. To provide the first foray into gene diversity of A. euteiches, two cDNA libraries were constructed using mRNA extracted from mycelium grown in an artificial liquid medium or in contact to plant roots. A unigene set of 7,977 sequences was obtained from 18,864 high-quality expressed sequenced tags (ESTs) and characterized for potential functions. Comparisons with oomycete proteomes revealed major differences between the gene content of A. euteiches and those of Phytophthora species, leading to the identification of biosynthetic pathways absent in Phytophthora, of new putative pathogenicity genes and of expansion of gene families encoding extracellular proteins, notably different classes of proteases. Among the genes specific of A. euteiches are members of a new family of extracellular proteins putatively involved in adhesion, containing up to four protein domains similar to fungal cellulose binding domains. Comparison of A. euteiches sequences with proteomes of fully sequenced eukaryotic pathogens, including fungi, apicomplexa and trypanosomatids, allowed the identification of A. euteiches genes with close orthologs in these microorganisms but absent in other oomycetes sequenced so far, notably transporters and non-ribosomal peptide synthetases, and suggests the presence of a defense mechanism against oxidative stress which was initially characterized in the pathogenic trypanosomatids.

SUBMITTER: Gaulin E

PROVIDER: S-EPMC2248709 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Aphanomyces euteiches is an oomycete pathogen with a broad host-range on legumes that causes devastating root rot disease in many pea-growing countries and especially in France. Genetic resistance is a promising way to manage the disease since consistent QTL controlling partial resistance have been identified in near isogenic lines of pea. However, there are still no resistant pea varieties cultivated in France. This study aimed to evaluate the phenotypic and genetic diversity of A. euteiches populations from the major pea-growing regions in France. A collection of 205 isolates, from soil samples collected in infested pea fields located in five French regions, was established and genotyped using 20 SSR markers. Thirteen multilocus genotypes were found among the 205 isolates which displayed a low genotypic richness (ranged from 0 to 0.333). Two main clusters of isolates were identified using PCoA and STRUCTURE, including a predominant group comprising 88% of isolates and another group representing 12% of isolates mainly from the Bourgogne region. A subset of 34 isolates, representative of the fields sampled, was phenotyped for aggressiveness on a set of resistant and susceptible varieties of four legume hosts (pea, faba bean, vetch, alfalfa). Significant differences in disease severity were found among isolates and three groups of aggressiveness comprising 16, 17, and 2 isolates, respectively, were identified using HCA analysis. A higher diversity in pathogen aggressiveness was observed among isolates from Bourgogne, which included different legumes in its crop history. Little relationship was observed between genetic clusters and pathogenicity in the subset of 34 isolates, as expected using neutral markers. This study provides useful knowledge on the current state of low to moderate diversity among A. euteiches populations before resistant pea varieties are grown in France. New insights and hypotheses about the major factors shaping the diversity and evolution of A. euteiches are also discussed.

Project description:Polyphenols comprise the largest group of plant secondary metabolites and have critical roles in plant physiology and response to the biotic and abiotic environment. Changes in the content of polyphenols in the root extracts and root tissues of wild (Lens ervoides) and cultivated (Lens culinaris) lentil genotypes were examined in response to infection by Aphanomyces euteiches using liquid chromatography mass spectrometry (LC-MS). Genotype, infection and their interaction determined the composition of polyphenols in lentil roots. The levels of several polyphenols were lower in the root extract of the low-tannin genotype L. culinaris ZT-4 compared to L. ervoides L01-827A. Kaempferol derivatives including kaempferol dirutinoside and kaempferol 3-robinoside 7-rhamnoside were more concentrated in the healthy root tissues of L. ervoides L01-827A than in L. culinaris genotypes. Infection increased the concentration of kaempferol, apigenin, and naringenin in the root tissues of all genotypes, but had no effect on some polyphenols in the low-tannin genotype L. culinaris ZT-4. The concentrations of apigenin, naringenin, apigenin 4-glucoside, naringenin7-rutinoside, diosmetin, and hesperetin 7-rutinoside were higher in the infected root tissues of L. ervoides L01-827A compared with the L. culinaris genotypes. Organic acids including coumaric acid, vanillic acid, 4-aminosalicylic acid, 4-hydroxybenzoic acid, and 3,4-dihydroxybenzoic acid effectively suppressed the in-vitro hyphal growth of A. euteiches. Some of these bioactive polyphenols were more concentrated in roots of L. ervoides L01-827A but were low to undetectable in ZT-4. This study shows that genotypic differences exist in the composition of root polyphenols in lentil, and is related to the response to infection caused by A. euteiches. Polyphenols, particularly the organic acid content could be useful for selection and breeding of lentil genotypes that are resistant to Aphanomyces root rot (ARR) disease.

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Transcriptome of Aphanomyces euteiches: new oomycete putative pathogenicity factors and metabolic pathways.

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