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

Abstract

Fusarium mangiferae causes the mango malformation disease (MMD) on young mango trees and seedlings resulting in economically significant crop losses. In addition, F. mangiferae produces a vast array of secondary metabolites (SMs), including mycotoxins that may contaminate the harvest. Their production is tightly regulated at the transcriptional level. Here, we show that lack of the H3 K9-specific histone methyltransferase, FmKmt1, influences the expression of the F. mangiferae polyketide synthase (PKS) 8 (FmPKS8), a so far cryptic PKS. By a combination of reverse genetics, untargeted metabolomics, bioinformatics and chemical analyses including structural elucidation, we determined the FmPKS8 biosynthetic gene cluster (BGC) and linked its activity to the production of fusamarins (FMN), which can be structurally classified as dihydroisocoumarins. Functional characterization of the four FMN cluster genes shed light on the biosynthetic pathway. Cytotoxicity assays revealed moderate toxicities with IC 50 values between 1 and 50 μM depending on the compound.

H3K27me3 is vital for fungal development and secondary metabolite gene silencing, and substitutes for the loss of H3K9me3 in the plant pathogen Fusarium proliferatum

“…For most of these, expression was generally very low suggesting that additional factors are required to induce their transcription. This is most prominent in the case of the two PKS-encoding genes, PKS17 (FPRN2_14992) and PKS18 (FPRN2_15000), and the remnant of PKS8 (FPRN_15017) [32], all located in close proximity to one another on chromosome 11. None of those genes is derepressed upon relief of H3K27me3 in Δfpkmt6 (Fig 5, highlighted with an asterisk).…”

“…Next to H3K27me3, another heterochromatic mark i.e., histone H3 lysine 9 trimethylation (H3K9me3), appears to be required for wild type-like SM gene expression in several fungi including Fusarium spp. [22,28,32]. H3K9me3 is a hallmark for constitutive heterochromatin and typically associated with centromeric and gene-poor regions.…”

Activation of a Silent Polyketide Synthase SlPKS4 Encoding the C7-Methylated Isocoumarin in a Marine-Derived Fungus Simplicillium lamellicola HDN13-430

“…Several biosynthetic gene and gene clusters responsible for coumarins and isocoumarins have been discovered [ 23 , 32 , 33 , 34 , 35 ]. In fungi, isocoumarin derivatives are primarily derived from the polyketide pathways, which are typically catalyzed by nonreducing polyketide synthase (nrPKS), containing domains such as starter unit ACP transacylase (SAT), β-ketoacyl synthase (KS), acyl transferase (AT), product template (PT), acyl carrier protein (ACP), methyltransferase (MT), and thioesterase (TE) [ 22 , 23 , 32 ].…”

Recent advances in the discovery, biosynthesis, and therapeutic potential of isocoumarins derived from fungi: a comprehensive update

“…Although it was reported 50 years ago, the biosynthetic pathway has not been revealed yet. Indeed, Atanasoff-Kardjalieff et al , 55 managed to investigate the gene cluster involved in fusamarins biosynthesis. They showed that the FmPKS8 biosynthetic gene cluster (FMN BGC) leads the biosynthesis, which is composed of FmPKS8 (FmFMN1), followed by FmFMN2, FmFMN3, and FmFMN4.…”