Gene cluster conservation provides insight into cercosporin biosynthesis and extends production to the genus Colletotrichum

<em>Species in the genus Cercospora cause economically devastating diseases in sugar beet, maize, rice, soy bean and other major food crops</em>. Here we sequenced the genome of the sugar beet pathogen <i>C. beticola<em> and found it </em></i>encodes 63 putative secondary metabolite gene clusters, including the cercosporin toxin biosynthesis (<i>CTB</i>) cluster. We show that the <em>CTB gene cluster</em> has experienced multiple duplications and horizontal transfers across a spectrum of plant pathogenic fungi, including the wide-host range <i>Colletotrichum</i> genus as well as the rice pathogen <i>Magnaporthe oryzae</i>. Although cercosporin biosynthesis has been thought to-date to rely on an eight gene <i>CTB</i> cluster, our phylogenomic analysis revealed gene collinearity adjacent to the established cluster in all <i>CTB </i>cluster-harboring species. We demonstrate that the <i>CTB</i> cluster is larger than previously recognized and includes <i>cercosporin facilitator protein </i>(<i>CFP</i>), 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 <i>Colletotrichum fioriniae</i>, 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.