Genomics of Cercospora

Cercospora, a widely distributed genus of plant pathogenic fungi, includes species that infect cereals, vegetables, and ornamental plants. Gray leaf spot of corn (caused by C. zeae-maydis and C. zeina), frogeye leaf spot of soybean (caused by C. sojina), and Cercospora leaf blight of soybean (caused by C. cf. flagellaris and other species) are of particular importance to U.S. agriculture. Many Cercospora species form appressoria before penetrating leaves through stomata, and subsequently cause latent infections before inducing necrosis. Foliar necrosis among Cercospora spp. is associated with cercosporin, a polyketide-derived phytotoxin. To elucidate fundamental mechanisms of pathogenicity among Cercospora spp., we have focused on dissecting pathogenesis in C. zeae-maydis, C. zeina, C. sojina, and C. cf. flagellaris. To complement the recently released genome sequence of C. zeae-maydis, we sequenced and assembled the genomes of C. zeina, C. sojina, and C. cf. flagellaris. Comparative analyses identified novel potential components of pathogenesis among these Cercospora spp., including genes undergoing diversifying selection and genes that are unique at the genus or species level. The cercosporin biosynthetic cluster was highly conserved, including in C. zeina and C. sojina, which were not previously known to produce cercosporin. However, the polyketide synthase gene within the cluster (CTB1) is dispensable for pathogenesis in C. zeae-maydis, which requires re-evaluation of whether cercosporin is universally important for pathogenesis among Cercospora spp. Although many questions remain, findings thus far have led to new hypotheses and working models describing the complex dynamics underlying pathogenesis in Cercospora spp.