Environmental pH plays an important role in the growth and differentiation of microorganisms. In fungi, one well-studied pH-response pathway is controlled by the transcriptional regulator PacC. The PacC(KLAP2) gene of the citrus pathogen Colletotrichum acutatum is required for virulence. Here, the phenotypes of C. acutatum mutants obtained by targeted disruption of PacC(KLAP2) are characterized. The PacC(KLAP2) null mutants displayed hypersensitivity to a wide range of compounds but were more tolerant than wild type to cell wall-degrading enzymes (CWDEs). The null mutants have lower cell-wall chitin content as well as lower cellulase, cutinase, xylanase, and catalase activities, but markedly increased pecteolytic activities. Expression of the genes encoding endo-polygalacturonase and cellulase is higher in the null mutants compared with wild type, whereas expression of the gene for cutinase is almost completely abolished, suggesting that cutinase and other CWDEs may play a role in fungal pathogenicity.