Identification and characterization of the ergochrome gene cluster in the plant pathogenic fungus Claviceps purpurea

Abstract

Background Claviceps purpurea is a phytopathogenic fungus infecting a broad range of grasses including economically important cereal crop plants. The infection cycle ends with the formation of the typical purple-black pigmented sclerotia containing the toxic ergot alkaloids. Besides these ergot alkaloids little is known about the secondary metabolism of the fungus. Red anthraquinone derivatives and yellow xanthone dimers (ergochromes) have been isolated from sclerotia and described as ergot pigments, but the corresponding gene cluster has remained unknown. Fungal pigments gain increasing interest for example as environmentally friendly alternatives to existing dyes. Furthermore, several pigments show biological activities and may have some pharmaceutical value.ResultsThis study identified the gene cluster responsible for the synthesis of the ergot pigments. Overexpression of the cluster-specific transcription factor led to activation of the gene cluster and to the production of several known ergot pigments. Knock out of the cluster key enzyme, a nonreducing polyketide synthase, clearly showed that this cluster is responsible for the production of red anthraquinones as well as yellow ergochromes. Furthermore, a tentative biosynthetic pathway for the ergot pigments is proposed. By changing the culture conditions, pigment production was activated in axenic culture so that high concentration of phosphate and low concentration of sucrose induced pigment syntheses.ConclusionsThis is the first functional analysis of a secondary metabolite gene cluster in the ergot fungus besides that for the classical ergot alkaloids. We demonstrated that this gene cluster is responsible for the typical purple-black color of the ergot sclerotia and showed that the red and yellow ergot pigments are products of the same biosynthetic pathway. Activation of the gene cluster in axenic culture opened up new possibilities for biotechnological applications like the dye production or the development of new pharmaceuticals.Electronic supplementary materialThe online version of this article (doi:10.1186/s40694-016-0020-z) contains supplementary material, which is available to authorized users.

Fungal secondary metabolism: regulation, function and drug discovery

“…For example, although several genes in the sterigmatocystin BGC are co-regulated during the production of sterigmatocystin, there is no defining phenotype following gene deletion (for example, stcC , stcM and stcR ) 22 . Many of these uncharacterized genes encode hypothetical, fungal and even species-specific proteins such as Cpur_05425 and Cpur_05426 in the ergochrome BGC 23 and AFLA_022990, AFLA_023060 and AFLA_023090 in the aspergillic acid BGC 24 . By contrast, some of the proteins encoded by these other incongruous genes that were once overlooked are now known to provide protection from — or localization and/or destination of — toxic BGC natural products 25 (see below).…”

Chrysoxanthones A–C, Three New Xanthone–Chromanone Heterdimers from Sponge-Associated Penicillium chrysogenum HLS111 Treated with Histone Deacetylase Inhibitor

“…Based on the common tetrahydroxanthones moiety, we proposed that chrysoxanthones A–C shared the same biosynthetic gene cluster and pathway with those of secalonic acids. The biosynthetic gene cluster of secalonic acids in Claviceps purpurea has been confirmed by deleting gene CPUR_05437 , which led to the abolishment of secalonic acid production [ 24 ]. In our effort to find the biosynthetic gene cluster, the gene pc16g10750 of P. chrysogenum wisconsin 54-1255 showed the highest identity with the gene CPUR_05437 (71%) by the NCBI BLAST.…”

“…Pc16g10750 putatively encodes an iterative nonreducing PKS (NR-PKS) and has a domain architecture of KS-AT-PT-ACP, as ascertained by NCBI Conserved Domains. In these special types of NR-PKSs lacking the thioesterase (TE) domain, polyketide is released from the PKS by a metallo-β-lactamase-type thioesterase (MβL-TE) [ 24 ]. The functions of the upstream and downstream genes were also analyzed by BLAST analysis, indicating the integrated gene cluster composed of 23 Open Reading Frames (ORFs) ( Supplementary Materials, Figure S24 ).…”

Ergochromes: Heretofore Neglected Side of Ergot Toxicity

“…Both toxin groups are metabolically independent, but their production in sclerotia is contemporary and seems to be regulated by the same stimuli (phosphate level) [39], which can explain the observed correlation. Fungal pigments typically have a light protection role, and this ability is also expected in the case of ECs [39].…”