|EBERT, MALAIKA - Wageningen University
|SPANNER, REBECCA - North Dakota State University
|DE JONGE, RONNIE - Utrecht University
|SECOR, GARY - North Dakota State University
|THOMMA, BART - Wageningen University
Submitted to: Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2018
Publication Date: 3/13/2019
Citation: Ebert, M.K., Spanner, R.E., De Jonge, R., Smith, D.J., Holthusen, J.E., Secor, G.A., Thomma, B.P., Bolton, M.D. 2019. Gene cluster conservation identifies melanin and perylenequinone biosynthesis pathways in multiple plant pathogenic fungi. Environmental Microbiology. 21(3):913-927. https://doi.org/10.1111/1462-2920.14475.
Interpretive Summary: Plant pathogens utilize a variety of molecular ‘weapons’ to cause disease. One common type of weapon used by fungi are special toxins that cause damage to plant cells in the presence of light. Such toxins have a unique DNA signature associated with them. In this research, we took advantage of this DNA signature to identify similar toxins in two unrelated plant pathogens. A variety of techniques were utilized that provide conclusive evidence that the identified genes responsible for the production of these toxins. We believe that this manuscript describes a useful tool for identifying such toxins that can be applied to a wide variety of plant pathogenic fungi.
Technical Abstract: Perylenequinones are a family of structurally related fungal toxins with nearly universal toxicity to a wide spectrum of organisms. These photosynthesizing compounds absorb light energy which enables them to produce reactive oxygen species in the presence of oxygen. This potent mechanism serves as an effective weapon for plant pathogens in disease establishment. The foliar sugar beet pathogen Cercospora beticola secretes the perylenequinone cercosporin during infection. Recent studies have shown that the cercosporin toxin biosynthesis (CTB) gene cluster is present in several phytopathogenic fungal species outside of the genus Cercospora, prompting the search for biosynthetic gene clusters (BGCs) of structurally-similar perylenequinones in other fungi. Here, we report the identification of the elsinochrome and phleichrome biosynthetic clusters of Elsinoë fawcettii and Cladosporium phlei, respectively, based on gene cluster conservation with the CTB and hypocrellin gene clusters. Targeted gene replacement of putative perylenequinone and melanin polyketide synthesis (PKS) genes in C. beticola and E. fawcettii provided proof of concept. We show that previous studies aiming to identify the elsinochrome BGC from E. fawcettii and the phleichrome BGC from C. phlei likely were the result of misannotation and that the BGCs in question are involved in melanin production. Phylogenetic analysis of the corresponding melanin PKSs as well as alignment of putative melanin BGCs revealed high conservation between the established melanin BGCs and newly identified C. beticola, E. fawcettii, and C. phlei melanin pathways. Our results emphasize the high conservation level between BGCs of structurally related secondary metabolites and how this conservation can be utilized as a reliable method to identify biosynthetic pathways.