title: CZK3, a MAP kinase kinase kinase homolog in Cercospora zeae-maydis, regulates cercosporin biosynthesis, fungal development, and pathogenesis.
abstract: The fungus Cercospora zeae-maydis causes gray leaf spot of maize and produces cercosporin, a photosensitizing perylenequinone with toxic activity against a broad spectrum of organisms. However, little is known about the biosynthetic pathway or factors that regulate cercosporin production. Analysis of a cDNA subtraction library comprised of genes that are up-regulated during cercosporin synthesis revealed a sequence highly similar to mitogen-activated protein (MAP) kinases in other fungi. Sequencing and conceptual translation of the full-length genomic sequence indicated that the gene, which we designated CZK3, contains a 4,119-bp open reading frame devoid of introns and encodes a 1,373-amino acid sequence that is highly similar to Wis4, a MAP kinase kinase kinase in Schizosaccharomyces pombe. Targeted disruption of CZK3 suppressed expression of genes predicted to participate in cercosporin biosynthesis and abolished cercosporin production. The disrupted mutants grew faster on agar media than the wild type but were deficient in conidiation and elicited only small chlorotic spots on inoculated maize leaves compared with rectangular necrotic lesions incited by the wild type. Complementation of disruptants with the CZK3 open reading frame and flanking sequences restored wild-type levels of conidiation, growth rate, and virulence as well as the ability to produce cercosporin. The results suggest that cercosporin is a virulence factor in C. zeae-maydis during maize pathogenesis, but the pleiotropic effects of CZK3 disruption precluded definitive conclusions.
authors.affiliation: Crop Production and Pest Control Research, U.S. Department of Agriculture-Agricultural Research Service, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907-2054, USA.
authors.forename: Won-Bo
authors.initials: WB
authors.lastname: Shim
authors.forename: Larry D
authors.initials: LD
authors.lastname: Dunkle
mesh_terms: D000595:Amino Acid Sequence; D001203:Ascomycota / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity; D001483:Base Sequence; D017931:DNA Primers; D015966:Gene Expression Regulation, Fungal; D005816:Genetic Complementation Test; D020930:MAP Kinase Kinase Kinases / Q000737:chemistry / Q000502:physiology*; D008969:Molecular Sequence Data; D010569:Perylene / Q000031:analogs & derivatives* / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D010569:Perylene; C026363:cercosporin; D020930:MAP Kinase Kinase Kinases