Regulation and role of a STE12-like transcription factor from the plant pathogen Colletotrichum lindemuthianum

In phytopathogenic fungi, STE12-like genes encode transcription factors essential for appressorium-mediated host penetration. However, their regulation and downstream targets are still unknown. In the present study, a STE12-like gene (CLSTE12) from Colletotrichum lindemuthianum was isolated. We identified a spliced variant whose expression was negatively regulated during early stages of pathogenesis, whereas the correctly spliced mRNA remained expressed up to the penetration step, suggesting distinct roles for these two transcripts. Indeed, the full-length sequence was able to complement a yeast STE12 mutant, whereas overexpression of the transcript variant had a dominant-negative effect on yeast invasive growth and C. lindemuthianum pathogenicity. To further investigate the downstream genes that could be regulated by CLSTE12, disruption mutants were generated. Phenotypic analyses of the mutants revealed reduced pectinase activity and conidial adhesion to polystyrene. Analysis of cell surface proteins allowed the identification of a major protein, Clsp1p, which was absent from the mutants. Clsp1p belongs to a new family of wall-associated proteins only found in euascomycetous fungi. Overall, these results suggest that the activity of CLSTE12 can be modulated by a regulated alternative splicing mechanism and that this factor is involved in the production of cell surface proteins and host cell wall degrading enzymes.