Biosynthesis of Fusapyrone Depends on the H3K9 Methyltransferase, FmKmt1, in Fusarium mangiferae

Abstract

The phytopathogenic fungus Fusarium mangiferae belongs to the Fusarium fujikuroi species complex (FFSC). Members of this group cause a wide spectrum of devastating diseases on diverse agricultural crops. F. mangiferae is the causal agent of the mango malformation disease (MMD) and as such detrimental for agriculture in the southern hemisphere. During plant infection, the fungus produces a plethora of bioactive secondary metabolites (SMs), which most often lead to severe adverse defects on plants health. Changes in chromatin structure achieved by posttranslational modifications (PTM) of histones play a key role in regulation of fungal SM biosynthesis. Posttranslational tri-methylation of histone 3 lysine 9 (H3K9me3) is considered a hallmark of heterochromatin and established by the SET-domain protein Kmt1. Here, we show that FmKmt1 is involved in H3K9me3 in F. mangiferae. Loss of FmKmt1 only slightly though significantly affected fungal hyphal growth and stress response and is required for wild type-like conidiation. While FmKmt1 is largely dispensable for the biosynthesis of most known SMs, removal of FmKMT1 resulted in an almost complete loss of fusapyrone and deoxyfusapyrone, γ-pyrones previously only known from Fusarium semitectum. Here, we identified the polyketide synthase (PKS) FmPKS40 to be involved in fusapyrone biosynthesis, delineate putative cluster borders by co-expression studies and provide insights into its regulation.

Ten decadal advances in fungal biology leading towards human well-being

“…In F. fujikuroi the ortholog of KMT6 appears to be essential (Studt et al 2016a , b ), but similarly to F. graminearum , down-regulation of KMT6 by RNA interference resulted in up-regulation of several otherwise silent secondary metabolite genes, a phenotype that was accompanied by reduced H3K27me3 levels at the respective gene loci and the production of novel compounds (Studt et al 2016a , b ). Notably, H3K9me3 established by Kmt1 appears to be essential for biosynthesis of fusapyrone in Fusarium mangiferae associated with mango malformation (Atanasoff-Kardjalieff et al 2021 ). Another histone mark that has received little attention in filamentous fungi is H4K20me3 associated with gene silencing in higher eukaryotes (Kourmouli et al 2004 ; Schotta et al 2004 ).…”

Biosynthesis of the Isocoumarin Derivatives Fusamarins is Mediated by the PKS8 Gene Cluster in Fusarium

“…We have previously shown that the cryptic FmPKS8 is expressed in low nitrogen conditions, and that its expression depends on a functional ortholog of FmKmt1 [17] . To identify possible FmPKS8‐derived products, an untargeted metabolomics approach was used.…”

“…We have previously shown that FmPKS8 expression greatly depends on the nitrogen source and concentration i. e., FmPKS8 expression is specifically induced in liquid ICI medium with 6 mM NaNO 3 as sole nitrogen source ( FmPKS8 ‐inducing conditions). While only low or no transcripts are detectable when either 6 or 60 mM glutamine or 120 mM NaNO 3 is used [17] . To further validate the FmPKS8 origin of compound 1 – 9 , FmWT was grown for seven days under these different nitrogen supply conditions, and culture filtrates were subsequently analyzed by targeted chemical analysis via HPLC‐HRMS.…”

“…H3K9me3 is in general associated with heterochromatin formation and as such with gene silencing as shown for the fission yeast Schizosaccharomyces pombe (SpClr4) [15] or Neurospora crassa (NcDIM5) [16] . H3K9me3 is established by FmKmt1 in F. mangiferae [17] . The role of H3K9me3 in fungal development and virulence is diverse, not only in the genus Fusarium but in the fungal kingdom in general.…”

“…Notably, not much is known about the role of H3K9me3 in SM‐gene regulation in filamentous fungi thus far. Previously, we have shown that FmKmt1 is crucial for wild type‐like expression of selected BGCs in F. mangifera e i. e., FmNRPS22 and FmPKS40 involved in beauvericin and fusapyrone biosynthesis, respectively, as well as the cryptic FmPKS8 BGC [17] …”