Diaporthe helianthi is a fungus pathogenic to sunflower. Virulent strains of this fungus cause stem canker with important yield losses and reduction of oil content. Here we present the first draft whole-genome sequence of the highly virulent isolate D. helianthi strain 7/96, thus providing a useful platform for future research on stem canker of sunflower and fungal genomics. The genome sequence of the D. helianthi isolate 7/96 was deposited at DDBJ/ENA/GenBank under the accession number MAVT00000000 (BioProject PRJNA327798).
BackgroundThe early phases of Diaporthe helianthi pathogenesis on sunflower are characterized by the production of phytotoxins that may play a role in host colonisation. In previous studies, phytotoxins of a polyketidic nature were isolated and purified from culture filtrates of virulent strains of D. helianthi isolated from sunflower. A highly aggressive isolate (7/96) from France contained a gene fragment of a putative nonaketide synthase (lovB) which was conserved in a virulent D. helianthi population.ResultsIn order to investigate the role of polyketide synthases in D. helianthi 7/96, a draft genome of this isolate was examined. We were able to find and phylogenetically analyse 40 genes putatively coding for polyketide synthases (PKSs). Analysis of their domains revealed that most PKS genes of D. helianthi are reducing PKSs, whereas only eight lacked reducing domains. Most of the identified PKSs have orthologs shown to be virulence factors or genetic determinants for toxin production in other pathogenic fungi. One of the genes (DhPKS1) corresponded to the previously cloned D. helianthi lovB gene fragment and clustered with a nonribosomal peptide synthetase (NRPS) -PKS hybrid/lovastatin nonaketide like A. nidulans LovB. We used DhPKS1 as a case study and carried out its disruption through Agrobacterium-mediated transformation in the isolate 7/96. D. helianthi DhPKS1 deleted mutants were less virulent to sunflower compared to the wild type, indicating a role for this gene in the pathogenesis of the fungus.ConclusionThe PKS sequences analysed and reported here constitute a new genomic resource that will be useful for further research on the biology, ecology and evolution of D. helianthi and generally of fungal plant pathogens.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-017-4405-z) contains supplementary material, which is available to authorized users.
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