Fig. 3 |. The ecological roles of secondary metabolites.

a | Many fungi produce polyketide-derived melanins, a natural pigment that protects spores from damaging ultraviolet (UV) radiation. b | The bacterium Ralstonia solanacearum secretes the lipopeptide ralsolamycin that induces chlamydospore formation in fungi and expression of the bikaverin gene cluster in Fusarium spp.^7,85. Bikaverin reduces bacterial entry and growth. Both the bikaverin biosynthetic gene cluster (BGC) and ralsolamycin response (that is, protection from bacterial ingress) have been transferred to some Botrytis species. c | For fungi to protect themselves from their own BGC-encoded antifungal secondary metabolites, they have evolved various self-protection strategies, including duplicated, resistant copies of target proteins within a BGC. The diagram of a fungal cell shows the cellular processes that are targeted by six secondary metabolites containing in-cluster resistant genes. Lovastatin interferes with ergosterol biosynthesis and thus cell membrane integrity by inhibiting 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase⁹⁸ (not shown), echinocandin targets cell wall synthesis by inhibiting β−1,3-d-glucan synthase¹⁰⁰ (not shown), fellutamide is a proteasome inhibitor targeting the proteasome subunit C5 (REF.⁹⁹), aspterric acid interferes with protein synthesis by targeting the branched chain amino acid synthesis enzyme dihydroxy-acid dehydratase¹⁰¹ (not shown), fumagillin inhibits RNA synthesis by targeting methionine aminopeptidase²⁶ (not shown) and mycophenolic acid interferes with purine synthesis by inhibiting inosine-5ʹ-monophosphate dehydrogenase¹⁰² (not shown). d | Secondary metabolites can affect developmental processes in fungi. Deletion of a polyketide synthase in the fungus Sordaria macrospora inhibits perithecial formation, whereas its overexpression results in malformed fruiting bodies that lack the usual perithecial neck¹⁰⁶.