|DEJONGE, RONNIE - Utrecht University|
|EBERT, MALAIKA - Wageningen University|
|HUITT-ROEHL, CALLIE - Johns Hopkins University|
|PAL, PARAMITA - Johns Hopkins University|
|SPANNER, REBECCA - North Dakota State University|
|STOTT, KARINA - North Dakota State University|
|SECOR, GARY - North Dakota State University|
|THOMMA, BART - Wageningen University|
|VAN DE PEER, YVES - Ghent University|
|TOWNSEND, CRAIG - Johns Hopkins University|
Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2018
Publication Date: 6/12/2018
Citation: Dejonge, R., Ebert, M., Huitt-Roehl, C., Pal, P., Suttle, J.C., Spanner, R.E., Neubauer, J., Jurick II, W.M., Stott, K.A., Secor, G.A., Thomma, B.P., Van De Peer, Y., Townsend, C.A., Bolton, M.D. 2018. Gene cluster conservation provides insight into cercosporin biosynthesis and extends production to the genus Colletotrichum. Proceedings of the National Academy of Sciences. 115(24):E5459-E5466.
Interpretive Summary: Species in the fungal genus Cercospora cause economically devastating diseases in sugar beet, maize, rice, soy bean and other major food crops throughout the world. Sugar beet is the primary source of sugar in the United States. The most important disease of sugar beet is Cercospora leaf spot, which is caused by Cercospora beticola. Despite the global importance of this pathogen, little is known on how this fungus is able to cause disease. To gain insight into pathogenicity, we sequenced the Cercospora beticola genome and identified a large number of gene clusters that enable the fungus to produce a suite of toxins that are likely important for disease. One such gene cluster is responsible for production of cercosporin, a toxin that has been studied for nearly 60 years. We noticed that the gene cluster responsible for cercosporin production was found twice in the Cercospora beticola genome. Since duplication of gene clusters is not a well-studied phenomenon, we looked for similar duplication events in the genomes of other plant pathogens. Surprisingly, we identified the cercosporin gene cluster in a number of species not known to produce this toxin. By analyzing the cercosporin gene clusters in these species, we gained additional understanding of how cercosporin is produced in Cercospora beticola. Importantly, we confirmed that the apple fruit pathogen Colletotrichum fioriniae can produce cercosporin. Since cercosporin has been shown to be highly toxic to mice, the production of cercosporin in a very common pathogen of apple fruit has implications for human health. Our studies provide new insight into the evolution and biology of a toxin critical to agriculture and broaden the production of cercosporin to another fungal genus containing many plant pathogens of important crops worldwide.
Technical Abstract: Species in the genus Cercospora cause economically devastating diseases in sugar beet, maize, rice, soy bean and other major food crops. Here we sequenced the genome of the sugar beet pathogen C. beticola and found it encodes 63 putative secondary metabolite gene clusters, including the cercosporin toxin biosynthesis (CTB) cluster. We show that the CTB gene cluster has experienced multiple duplications and horizontal transfers across a spectrum of plant pathogenic fungi, including the wide-host range Colletotrichum genus as well as the rice pathogen Magnaporthe oryzae. Although cercosporin biosynthesis has been thought to-date to rely on an eight gene CTB cluster, our phylogenomic analysis revealed gene collinearity adjacent to the established cluster in all CTB cluster-harboring species. We demonstrate that the CTB cluster is larger than previously recognized and includes cercosporin facilitator protein (CFP) previously shown to be involved with cercosporin auto-resistance, and four additional genes required for cercosporin biosynthesis including the final pathway enzymes that install the unusual cercosporin methylenedioxy bridge. Finally, we demonstrate production of cercosporin by Colletotrichum fioriniae, the first known cercosporin producer within this agriculturally important genus. Thus, our results provide new insight into the intricate evolution and biology of a toxin critical to agriculture and broaden the production of cercosporin to another fungal genus containing many plant pathogens of important crops worldwide.