A genome-wide survey of the secondary metabolite biosynthesis genes in the wheat pathogen Parastagonospora nodorum

Muria-Gonzalez

Mead

et al. 2015

Appl Environ Microbiol

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b Alternariol (AOH) is an important mycotoxin from the Alternaria fungi. AOH was detected for the first time in the wheat pathogen Parastagonospora nodorum in a recent study. Here, we exploited reverse genetics to demonstrate that SNOG_15829 (SnPKS19), a close homolog of Penicillium aethiopicum norlichexanthone (NLX) synthase gene gsfA, is required for AOH production. We further validate that SnPKS19 is solely responsible for AOH production by heterologous expression in Aspergillus nidulans. The expression profile of SnPKS19 based on previous P. nodorum microarray data correlated with the presence of AOH in vitro and its absence in planta. Subsequent characterization of the ⌬SnPKS19 mutants showed that SnPKS19 and AOH are not involved in virulence and oxidative stress tolerance. Identification and characterization of the P. nodorum SnPKS19 cast light on a possible alternative AOH synthase gene in Alternaria alternata and allowed us to survey the distribution of AOH synthase genes in other fungal genomes. We further demonstrate that phylogenetic analysis could be used to differentiate between AOH synthases and the closely related NLX synthases. This study provides the basis for studying the genetic regulation of AOH production and for development of molecular diagnostic methods for detecting AOH-producing fungi in the future.

Section: Resultsmentioning

confidence: 99%

SnPKS19 Encodes the Polyketide Synthase for Alternariol Mycotoxin Biosynthesis in the Wheat Pathogen Parastagonospora nodorum

Muria-Gonzalez

Mead

et al. 2015

Appl Environ Microbiol

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“…Our previous survey of the P. nodorum genome showed that it encodes at least 38 secondary metabolite gene clusters. The key secondary metabolite backbone biosynthesis genes found in these clusters include 23 polyketide synthase (PKS) genes and 14 non‐ribosomal peptide synthetase (NRPS) genes, four terpene synthases and five prenyltransferases (Chooi et al ., ). Previous transcriptomics data has shown the up‐regulation of several secondary metabolite gene clusters during various stages of in planta growth (Ipcho et al ., ; Chooi and Solomon, ).…”

Section: Introductionmentioning

confidence: 99%

Functional genomics‐guided discovery of a light‐activated phytotoxin in the wheat pathogen Parastagonospora nodorum via pathway activation

Environmental Microbiology

Zhang

et al. 2017

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Parastagonospora nodorum is an important pathogen of wheat. The contribution of secondary metabolites to this pathosystem is poorly understood. A biosynthetic gene cluster (SNOG_08608-08616) has been shown to be upregulated during the late stage of P. nodorum wheat leaf infection. The gene cluster shares several homologues with the Cercospora nicotianae CTB gene cluster encoding the biosynthesis of cercosporin. Activation of the gene cluster by overexpression (OE) of the transcription factor gene (SNOG_08609) in P. nodorum resulted in the production of elsinochrome C, a perelyenequinone phytotoxin structurally similar to cercosporin. Heterologous expression of the polyketide synthase gene elcA from the gene cluster in Aspergillus nidulans resulted in the production of the polyketide precursor nortoralactone common to the cercosporin pathway. Elsinochrome C could be detected on wheat leaves infected with P. nodorum, but not in the elcA disruption mutant. The compound was shown to exhibit necrotic activity on wheat leaves in a light-dependent manner. Wheat seedling infection assays showed that ΔelcA exhibited reduced virulence compared with wild type, while infection by an OE strain overproducing elsinochrome C resulted in larger lesions on leaves. These data provided evidence that elsinochrome C contributes to the virulence of P. nodorum against wheat.

“…Analysis of the SN477 sequence showed that it encodes a typical partially reducing (PR) PKS with ␤-ketosynthase (KS), acyltransferase (AT), dehydratase (DH), ketoreductase (KR), and acyl career protein (ACP) domains (7,(29)(30)(31). Among the characterized fungal PKSs, SN477 was the most similar to the partially reducing PKS ATX from Aspergillus terreus, which synthesizes 6-methylsalicylic acid (6-MSA) (32).…”

Section: Snog_00477 Is the Most Highly Expressed Pks Gene In Plantamentioning

confidence: 99%

“…Along with the tailoring biosynthesis genes, they formed a total of 38 secondary metabolite gene clusters in P. nodorum. So far, none of the products of these secondary metabolite gene clusters have been identified, and only a few secondary metabolites have been identified in this species (7). These metabolites include (R)-mellein and derivatives (8,9), septorines (10,11), mycophenolic acid (8), alternariol (12), and (ϩ)-4=-methoxy-(2S)-methylbutyrophenone (13).…”

mentioning

confidence: 99%

“…Its genome, sequenced in 2007 (6), has revealed a large number of secondary metabolite biosynthetic gene clusters. We recently surveyed the secondary metabolite genes in the P. nodorum genome and identified 23 polyketide synthase (PKS) genes, 14 nonribosomal peptide synthetase (NRPS) genes, 4 terpene synthase genes, and 2 prenyltransferase genes (7). Along with the tailoring biosynthesis genes, they formed a total of 38 secondary metabolite gene clusters in P. nodorum.…”

mentioning

confidence: 99%

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An In Planta -Expressed Polyketide Synthase Produces ( R )-Mellein in the Wheat Pathogen Parastagonospora nodorum

Krill

Barrow

et al. 2015

Appl Environ Microbiol

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dParastagonospora nodorum is a pathogen of wheat that affects yields globally. Previous transcriptional analysis identified a partially reducing polyketide synthase (PR-PKS) gene, SNOG_00477 (SN477), in P. nodorum that is highly upregulated during infection of wheat leaves. Disruption of the corresponding SN477 gene resulted in the loss of production of two compounds, which we identified as (R)-mellein and (R)-O-methylmellein. Using a Saccharomyces cerevisiae yeast heterologous expression system, we successfully demonstrated that SN477 is the only enzyme required for the production of (R)-mellein. This is the first identification of a fungal PKS that is responsible for the synthesis of (R)-mellein. The P. nodorum ⌬SN477 mutant did not show any significant difference from the wild-type strain in its virulence against wheat. However, (R)-mellein at 200 g/ml inhibited the germination of wheat (Triticum aestivum) and barrel medic (Medicago truncatula) seeds. Comparative sequence analysis identified the presence of mellein synthase (MLNS) homologues in several Dothideomycetes and two sodariomycete genera. Phylogenetic analysis suggests that the MLNSs in fungi and bacteria evolved convergently from fungal and bacterial 6-methylsalicylic acid synthases.