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Functional characterization of polyketide synthase genes in the biocontrol fungus Clonostachys rosea

Mukesh Dubey: Dept. Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences

<div>Polyketides, a group of secondary metabolites produced both by prokaryotes and eukaryotes, are vital for various biological functions required for ecological and evolutionary adaptation in microorganisms. These metabolites are biosynthesized by large, multi-domain enzymes called polyketide synthases (PKSs). The aim of this study was to investigate the biological functions of PKSs in the biocontrol fungus <em>Clonostachys rosea</em>, with emphasis on their role in biocontrol interactions. The <em>C</em>. <em>rosea</em> genome contains 31 PKS genes, significantly higher compared with the number found in the more studied <em>Trichoderma</em> fungal biocontrol agents. Seventy-five percent of the <em>C. rosea</em> PKSs are arranged in biosynthetic gene clusters, and gene expression analysis during <em>C</em>. <em>rosea</em> interactions with the fungal pathogens <em>Botrytis</em> <em>cinerea</em> and <em>Fusarium</em> <em>graminearum</em> showed common and species-specific induction of PKS genes. There was a positive correlation between PKS gene expression and antagonism in <em>C</em>. <em>rosea</em>. The <em>pks22</em> and <em>pks29</em> genes were highly induced during fungal-fungal interactions, and gene deletion studies revealed that PKS29 was required for full antagonism against <em>B</em>. <em>cinerea</em>, and for biocontrol of fusarium foot rot on barley. Metabolite analysis of <em>C</em>. <em>rosea</em> wildtype and deletion strains using LC-MS and NMR revealed that Δ<em>pks22</em> strains lost the ability to produce a previously unknown polyketide with the molecular formula C<sub>14</sub>H<sub>25</sub>NO<sub>3</sub>, while Δ<em>pks29</em> strains showed a significant (P = 0.001) 50% reduction in production of another unknown polyketide with the molecular formula C<sub>15</sub>H<sub>28</sub>O<sub>3</sub>. This study shows the involvement of PKSs in fungal biocontrol, and led to the identification of previously unknown polyketides in <em>C</em>. <em>rosea</em>.</div>

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