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

Ampelomyces quisqualis, a mycoparasite of fungi causing powdery mildews, exhibited high levels of extracellular exo-β-1,3-glucanase activity in culture 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 examination. A gene encoding an exo-β-1,3-glucanase in A. quisqualis, designated exgA, was isolated and sequenced. The predicted polypeptide deduced from exgA had 46, 42, and 30% identity with amino acid sequences of Trichoderma harzianum exo-β-1,3-glucanase and Cochliobolus carbonum EXG1 (both encoding exo-β-1,3-glucanase) and T. harzianum bng13.1 (encoding an endo-β-1,3-glucanase), respectively. The exgA gene had a predicted molecular mass of 84 kDa and a pI of 4.79. The gene was expressed during the late stages of growth in culture, and transcription was induced by fungal cell wall components. Transcript levels for exgA were present during late stages of hyperparasitism and were abundant along A. quisqualis mycelium and were slightly less abundant in A. quisqualis pycnidia.