Cell Wall Degrading Enzymes in HST-Producing Fungal Pathogens

Abstract

Although best known for elaboration of a host-specific toxin, HC-toxin, the fungal maize pathogen Cochliobolus carbonum also produces a large number of cell wall degrading enzymes (CWDEs) capable of depolymerizing various components of the host cell wall. C. carbonum genes have been cloned that encode endo-polygalacturonase, exo-polygalacturonase, pectin methylesterase, four endo-xylanases, β-xylosidase, cellobiohydrolase, endo-β-1,4 glucanase, two exo-β-1,3-glucanases, two β-1,3-1,4 glucanases, two alkaline proteases and cutinase. Using a transformation-mediated gene disruption strategy, many of these genes have been mutated singly in pathogenic wild-type C. carbonum strains. In every case, the disruption of the CWDE gene and the concomitant loss of CWDE activity did not cause any detectable change in the pathogenicity or virulence of the mutant strain. Strains of C. carbonum that contain multiple mutations in related CWDEs are being constructed in order to examine whether the inability to degrade a particular cell wall component will affect disease development.