PcchiB1, encoding a class V chitinase, is affected by PcVelA and PcLaeA, and is responsible for cell wall integrity in Penicillium chrysogenum

Abstract

Penicillin production inPenicillium chrysogenumis controlled by PcVelA and PcLaeA, two components of the regulatoryvelvet-like complex. Comparative microarray analysis with mutants lacking PcVelA or PcLaeA revealed a set of 62 common genes affected by the loss of both components. A downregulated gene in both knockout strains isPcchiB1, potentially encoding a class V chitinase. Under nutrient-depleted conditions, transcript levels ofPcchiB1are strongly upregulated, and the gene product contributes to more than 50 % of extracellular chitinase activity. Functional characterization by generatingPcchiB1-disruption strains revealed that PcChiB1 is responsible for cell wall integrity and pellet formation inP. chrysogenum.Further, fluorescence microscopy with a DsRed-labelled chitinase suggests a cell wall association of the protein. An unexpected phenotype occurred when knockout strains were grown on media containingN-acetylglucosamine as the sole C and N source, where, in contrast to the recipient, a penicillin producer strain, the mutants and an ancestral strain show distinct mycelial growth. We discuss the relevance of this class V chitinase for morphology in an industrially important fungus.