Abstract
Fungal Hülle cells with nuclear storage and developmental backup functions are reminiscent of multipotent stem cells. In the soil, Hülle cells nurse the overwintering fruiting bodies of Aspergillus nidulans. The genome of A. nidulans harbors genes for the biosynthesis of xanthones. We show that enzymes and metabolites of this biosynthetic pathway accumulate in Hülle cells under the control of the regulatory velvet complex, which coordinates development and secondary metabolism. Deletion strains blocked in the conversion of anthraquinones to xanthones accumulate emodins and are delayed in maturation and growth of fruiting bodies. Emodin represses fruiting body and resting structure formation in other fungi. Xanthones are not required for sexual development but exert antifeedant effects on fungivorous animals such as springtails and woodlice. Our findings reveal a novel role of Hülle cells in establishing secure niches for A. nidulans by accumulating metabolites with antifeedant activity that protect reproductive structures from animal predators.
Highlights
Fungi are sessile organisms and cannot escape when they are attacked by predators or competitors
We showed in a food choice experiment that the mdp/xpt cluster metabolites present in wildtype protect A. nidulans from soil animal predators
These results suggest that the mdp/xpt metabolites produced in wildtype Hülle cells protect the sexual fruiting body of A
Summary
Fungi are sessile organisms and cannot escape when they are attacked by predators or competitors. Whereas vertebrates have a protective immune system, which is regulated by Rel homology domain transcription factors, fungi have developed chemical defense strategies by producing protective secondary metabolites (SMs), which are regulated by the structurally similar velvet domain proteins (Ahmed et al, 2013). These small molecule (< 1000 Da) fungal SMs are not directly involved in the normal growth of the producing organisms but play important roles in the organism's survivability in nature.
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