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ARS Home » Midwest Area » West Lafayette, Indiana » Crop Production and Pest Control Research » Research » Publications at this Location » Publication #147440
Title: CZK3, A MAP KINASE KINASE KINASE HOMOLOG IN CERCOSPORA ZEAE-MAYDIS, REGULATES CERCOSPORIN BIOSYNTHESIS, FUNGAL DEVELOPMENT, AND PATHOGENESIS

Author
item SHIM, WON BO - PURDUE UNIVERSITY
item Dunkle, Larry

Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2003
Publication Date: 9/1/2003
Citation: Shim, W., Dunkle, L.D. 2003. CZK3, A map kinase kinase kinase homolog in cercospora zeae-maydis, regulates cercosporin biosynthesis, fungal development, and pathogenesis. Molecular Plant-Microbe Interactions. 16:760-768.

Interpretive Summary: The fungus Cercospora zeae-maydis causes gray leaf spot of corn and produces cercosporin, a secondary metabolite that is toxic to a broad spectrum of organisms. However, little is known about how this toxin is produced or the factors that influence its production. In this work, we discovered a gene, which we designated CZK3, that is very similar to genes that respond to environmental cues in other fungi. When we abolished the function of CZK3 by targeted disruption, the mutants were unable to produce cercosporin, could not form spores, and caused considerably less severe disease symptoms on corn compared to the wild type pathogen. When the wild-type copy of the gene was put back into the mutants, this complemented strain was able once again to produce wild-type amounts of cercosporin and spores and incite the same disease symptoms on inoculated corn leaves as the wild type. The results suggest that the CZK3 gene regulates a variety of functions that are important for the fungus to damage the corn plant and cause gray leaf spot. This information is important to determine the features that are important for resistance of corn to gray leaf spot.

Technical 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, but 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 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 4119-bp open reading frame devoid of introns and encodes a 1373-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 to 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.