The fate of plastic waste and a sustainable use of synthetic polymers is one of the major challenges of the twenty first century. Waste valorization strategies can contribute to the solution of this problem. Besides chemical recycling, biological degradation could be a promising tool. Among the high diversity of synthetic polymers, polyurethanes are widely used as foams and insulation materials. In order to examine bacterial biodegradability of polyurethanes, a soil bacterium was isolated from a site rich in brittle plastic waste. The strain, identified as Pseudomonas sp. by 16S rRNA gene sequencing and membrane fatty acid profile, was able to grow on a PU-diol solution, a polyurethane oligomer, as the sole source of carbon and energy. In addition, the strain was able to use 2,4-diaminotoluene, a common precursor and putative degradation intermediate of polyurethanes, respectively, as sole source of energy, carbon, and nitrogen. Whole genome sequencing of the strain revealed the presence of numerus catabolic genes for aromatic compounds. Growth on potential intermediates of 2,4-diaminotoluene degradation, other aromatic growth substrates and a comparison with a protein data base of oxygenases present in the genome, led to the proposal of a degradation pathway.

The phytopathogenic fungusFusarium mangiferaebelongs to theFusarium fujikuroispecies complex (FFSC). Members of this group cause a wide spectrum of devastating diseases on diverse agricultural crops.F. mangiferaeis 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 inF. 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 ofFmKMT1resulted in an almost complete loss of fusapyrone and deoxyfusapyrone, γ-pyrones previously only known fromFusarium 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.

Fusarium is a species-rich group of mycotoxigenic plant pathogens that ranks as one of the most economically important fungal genera in the world. During growth and infection, they are able to produce a vast spectrum of low-molecular-weight compounds, so-called secondary metabolites (SMs). SMs often comprise toxic compounds (i.e., mycotoxins) that contaminate precious food and feed sources and cause adverse health effects in humans and livestock. In this context, understanding the regulation of their biosynthesis is crucial for the development of cropping strategies that aim at minimizing mycotoxin contamination in the field. Nevertheless, currently, only a fraction of SMs have been identified, and even fewer are considered for regular monitoring by regulatory authorities. Limitations to exploit their full chemical potential arise from the fact that the genes involved in their biosynthesis are often silent under standard laboratory conditions and only induced upon specific stimuli mimicking natural conditions in which biosynthesis of the respective SM becomes advantageous for the producer. This implies a complex regulatory network. Several components of these gene networks have been studied in the past, thereby greatly advancing the understanding of SM gene regulation and mycotoxin biosynthesis in general. This review aims at summarizing the latest advances in SM research in these notorious plant pathogens with a focus on chromatin structure.

Facultative heterochromatin marked by histone H3 lysine 27 trimethylation (H3K27me3) is an important regulatory layer involved in secondary metabolite (SM) gene silencing and crucial for fungal development in the genus Fusarium. While this histone mark is essential in some (e.g., the rice pathogen Fusarium fujikuroi), it appears dispensable in other fusaria. Here, we show that deletion of FpKMT6 is detrimental but not lethal in the plant pathogen Fusarium proliferatum, a member of the Fusarium fujikuroi species complex (FFSC). Loss of FpKmt6 results in aberrant growth, and expression of a large set of previously H3K27me3-silenced genes is accompanied by increased H3K27 acetylation (H3K27ac) and an altered H3K36me3 pattern. Next, H3K9me3 patterns are affected in Δfpkmt6, indicating crosstalk between both heterochromatic marks that became even more obvious in a strain deleted for FpKMT1 encoding the H3K9-specific histone methyltransferase. In Δfpkmt1, all H3K9me3 marks present in the wild-type strain are replaced by H3K27me3, a finding that may explain the subtle phenotype of the Δfpkmt1 strain which stands in marked contrast to other filamentous fungi. A large proportion of SM-encoding genes is allocated with H3K27me3 in the wild-type strain and loss of H3K27me3 results in elevated expression of 49% of them. Interestingly, genes involved in the biosynthesis of the phytohormones gibberellins (GA) are among the most upregulated genes in Δfpkmt6. Although several FFSC members harbor GA biosynthetic genes, its production is largely restricted to F. fujikuroi, possibly outlining the distinct lifestyles of these notorious plant pathogens. We show that H3K27me3 is involved in GA gene silencing in F. proliferatum and at least one additional FFSC member, and thus, may serve as a regulatory layer for gene silencing under non-favoring conditions.

Fusarium head blight is a destructive disease of grains resulting in reduced yields and contamination of grains with mycotoxins worldwide; Fusarium graminearum is its major causal agent. Chromatin structure changes play key roles in regulating mycotoxin biosynthesis in filamentous fungi. Using a split-marker approach in three F. graminearum strains INRA156, INRA349 and INRA812 (PH-1), we knocked out the gene encoding H2A.Z, a ubiquitous histone variant reported to be involved in a diverse range of biological processes in yeast, plants and animals, but rarely studied in filamentous fungi. All ΔH2A.Z mutants exhibit defects in development including radial growth, sporulation, germination and sexual reproduction, but with varying degrees of severity between them. Heterogeneity of osmotic and oxidative stress response as well as mycotoxin production was observed in ΔH2A.Z strains. Adding-back wild-type H2A.Z in INRA349ΔH2A.Z could not rescue the phenotypes. Whole genome sequencing revealed that, although H2A.Z has been removed from the genome and the deletion cassette is inserted at H2A.Z locus only, mutations occur at other loci in each mutant regardless of the genetic background. Genes affected by these mutations encode proteins involved in chromatin remodeling, such as the helicase Swr1p or an essential subunit of the histone deacetylase Rpd3S, and one protein of unknown function. These observations suggest that H2A.Z and the genes affected by such mutations are part or the same genetic interaction network. Our results underline the genetic plasticity of F. graminearum facing detrimental gene perturbation. These findings suggest that intergenic suppressions rescue deleterious phenotypes in ΔH2A.Z strains, and that H2A.Z may be essential in F. graminearum. This assumption is further supported by the fact that H2A.Z deletion failed in another Fusarium spp., i.e., the rice pathogen Fusarium fujikuroi. The function of histone variant H2A.Z has been widely studied in Saccharomyces cerevisiae and higher eukaryotes. However, there is a significant lack of knowledge of the role of H2A.Z and its regulation in filamentous fungi. Here we demonstrate for the first time that deleterious consequences of complete removal of H2A.Z from the genome of F. graminearum are mitigated by genetic suppression. The suppressors detected open new possibilities to investigate in more depth the network linking H2A.Z and other genes in F. graminearum and used to decipher unresolved questions concerning H2A.Z.

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 IC₅₀ values between 1 and 50 μM depending on the compound.