Aspergillus nidulans alpha-1,3 glucanase (mutanase), mutA, is expressed during sexual development and mobilizes mutan

We established a subtractive cDNA library of Aspergillus nidulans to identify differentially expressed genes during sexual development. One of the clones displayed homology to fungal alpha-1,3 glucanases (mutanase). Since alpha-1,3 glucan is considered the main reserve material accumulated during vegetative growth as a cell wall component and consumed during sexual development, we analyzed this gene in detail. The gene, mutA, is disrupted by three introns and encodes a putative protein of 48 kDa molecular mass with a signal peptide for secretion at the N terminus. The deduced protein displays amino acids 24-42% identical to mutanases of other fungi. A proposed mutan binding domain characterized in, e.g., Penicillium is not present in A. nidulans. Mutanase transcript and GFP reporter analysis in A. nidulans revealed specific induction of the gene during sexual development in Hülle cells. To study the role of mutA during sexual differentiation, we constructed a mutA deletion strain. Although degradation of mutan was affected in this strain, it was still able to form cleistothecia at a number similar to that of wildtype. These results suggest that additional carbon sources are available during sexual development.