Biochemical and molecular characterization of NADP‐glutamate dehydrogenase from the ectomycorrhizal fungus Tuber borchii

Abstract

Summary• NADP‐glutamate dehydrogenase (NADP‐GDH) from Tuber borchii was purified and the corresponding gene was cloned in order to elucidate the physiological role of the enzyme in this ectomycorrhizal fungus.• NADP‐GDH was purified using an anion‐exchange column followed by affinity chromatography. The complete gene was cloned from a 30‐d‐old‐mycelium cDNA library and characterized.• T. borchii NADP‐GDH appears to be physically and kinetically similar to those from other fungi and the deduced amino acid sequence of the gdh gene showed a significant similarity to other fungal NADP‐dependent GDHs. Biochemical and Northern blotting analyses carried out with mycelia grown on different nitrogen sources clearly showed that the regulation of T. borchii NADP‐GDH in response to different nitrogen sources was markedly different from the responses of the NADP‐GDHs of other ascomycetes. Northern blotting analyses highlighted that the gdh gene was also expressed in the symbiotic phase.• The biochemical and molecular data suggest that the fungal NADP‐GDH contributes to the primary nitrogen metabolism in the ectomycorrhizal tissues.