Peroxisomal metabolic function is required for appressorium-mediated plant infection by Colletotrichum lagenarium

Peroxisomes are organelles that perform a wide range of metabolic functions in eukaryotic cells. However, their role in fungal pathogenesis is poorly understood. Here we report that ClaPEX6, an ortholog of PEX6, is required for the fungus Colletotrichum lagenarium to infect host plants. ClaPEX6 was identified in random insertional mutagenesis experiments aimed at elucidating genes involved in pathogenesis. Functional analysis, using a green fluorescent protein cassette containing the peroxisomal targeting signal1 (PTS1), revealed that import of PTS1-containing proteins is impaired in clapex6 mutants generated by targeted gene disruption. Failure of growth on fatty acids shows an inability of fatty acid beta-oxidation in these mutants. These results indicate that disruption of ClaPEX6 impairs peroxisomal metabolism, even though clapex6 mutants show normal growth and conidiation in nutrient-rich conditions. The clapex6 mutants formed small appressoria with severely reduced melanization that failed to form infectious hyphae. These data indicate that peroxisomes are necessary for appressorium-mediated penetration of host plants. The addition of glucose increased the pathogenicity of clapex6 mutants, suggesting that the glucose metabolic pathway can compensate partially for peroxisomes in phytopathogenicity.