Identification of laccase-like multicopper oxidases from the pathogenic fungus Setosphaeria turcica and their expression pattern during growth and infection

Abstract

Setosphaeria turcica (syn. Exserohilum turcicum) is the pathogenic fungus of maize (Zea mays) causing northern leaf blight, which is a major maize disease worldwide. Laccase-like multicopper oxidases (LMCOs) are generally found in different fungi and play important physiological roles during growth and pathogenesis of the fungus. Nine LMCOs were found in the S. turcica genome using a Hidden Markov Model for three Pfam copper oxidase families. They shared a low homology of 19.79%–48.70% and were classified into five LMCO super families, but had conserved amino acid residues in the Cu-binding sites. Transcription levels of LMCOs were detected by quantitative real-time PCR during different stages of invasion, i.e. in non-germinated conidia, during formation of germ tubes, appressoria and penetration pegs as well as during hyphal growth after penetration. StLAC6 and StLAC8 were highly expressed in mycelium and expression of StLAC2 was significant in non-germinated conidia. During infection, the expression of StLAC1 and StLAC8 was high during appressorium formation and the expression of StLAC6 was high during penetration peg formation. The laccase activity and gene expression of LMCOs cultivated with the laccase inducers CuSO4, ABTS and resveratrol was detected. When treated with Cu2+, the laccase activity significantly increased. Furthermore, the expression of all genes was significantly increased, except that of StLAC7. In the presence of the phenolic phytoalexin resveratrol, laccase activity did not increase, but the expression levels of StLAC2, StLAC4 and StLAC5 were up-regulated. These results suggest that LMCOs in S. turcica play different roles during fungal growth and infection processes.