Chromatin-level regulation of biosynthetic gene clusters

Abstract

Loss-of-function Aspergillus nidulans CclA, a Bre2 ortholog involved in histone H3 lysine 4 methylation, activated the expression of cryptic secondary metabolite clusters in A. nidulans. One new cluster generated monodictyphenone, emodin and emodin derivatives, whereas a second encoded two anti-osteoporosis polyketides, F9775A and F9775B. Modification of the chromatin landscape in fungal secondary metabolite clusters allows for a simple technological means to express silent fungal secondary metabolite gene clusters.

Figure 1

Identification of monodictyphenone and its gene cluster. (a) HPLC profiles (UV 254 nm) of A. nidulans strains. Ethyl acetate extract of stcJΔ mutant, stcJΔ, cclAΔ double mutant, stcJΔ, cclAΔ, AN0150Δ triple mutant, and stcJΔ, alcA(p)-AN0148 mutant under inducing conditions. (b) Chemical structures of compounds 7 – 14 isolated from A. nidulans. (c) Top: Gene cluster expression in cclAΔ. mRNAs from liquid shake cultures grown for 24, 48 and 60 hr were examined for expression in wild type and cclAΔ strains. Bottom: Histone 3 lysine 4 trimethylation (K4M3), dimethylation (K4M2) and histone 3 lysine 9 trimethylation (K9M3) of 3 genes in wild type (white bars) and cclAΔ (black bars) at 48 hr correlating with mRNA in top. Raw data is presented in Supplementary Fig. 1. (d) Proposed biosynthetic pathway of monodictyphenone (9) and emodin analogs (10 – 14).

Figure 2

Identification of F9775 and its gene cluster. (a) EIC profiles at m/z 395 (negative mode) of A. nidulans strains. Ethyl acetate extract after acidification of stcJΔ mutant, stcJΔ, cclAΔ double mutant, and stcJΔ, cclAΔ, AN7909Δ triple mutant analyzed by LCMS. (b) Chemical structures of F9775B (17) and F9775A (18). (c) Gene cluster expression in cclAΔ. mRNAs from liquid shake cultures grown for 24, 48 and 60 hr were examined for expression in wild type and cclAΔ strains. Genes AN7909 – AN7915 are predicted to be required for F9775 biosynthesis.