The mycoparasite Ampelomyces quisqualis expresses exgA encoding an exo-beta-1,3-glucanase in culture and during mycoparasitism

Ampelomyces quisqualis, a mycoparasite of fungi causing powdery mildews, ex hibited high levels of extracellular exo-beta-1,3-glucanase activity in cul ture compared with Neurospora crassa and Gliocladium roseum. A. quisqualis culture filtrates affected powdery mildew caused by Sphaerotheca fusca in a manner indicative of cell wall degradation, as determined by microscopic e xamination. A gene encoding an exo-beta-1,3-glucanase in A. quisqualis, des ignated exgA, was isolated and sequenced. The predicted polypeptide deduced from exgA had 46, 42, and 30% identity with amino acid sequences of Tricho derma harzianum exo-beta-1,3-glucanase and Cochliobolus carbonum EXG1 (both encoding exo-beta-1,3-glucanase) and T. harzianum bng13.1 (encoding an end o-beta-1,3-glucanase), respectively. The exgA gene had a predicted molecula r mass of 84 kDa and a pi of 4.79. The gene was expressed during the late s tages of growth in culture, and transcription was induced by fungal cell wa ll components. Transcript levels for exgA were present during late stages o f hyperparasitism and were abundant along A. quisqualis mycelium and were s lightly less abundant in A. quisqualis pycnidia.