Molecular studies of NAD- and NADP-glutamate dehydrogenases decipher the conundrum of yeast–hypha dimorphism in zygomycete Benjaminiella poitrasii

ABSTRACT Benjaminiella poitrasii, a zygomycete, shows glucose- and temperature-dependent yeast (Y)–hypha (H) dimorphic transition. Earlier, we reported the biochemical correlation of relative proportion of NAD- and NADP-glutamate dehydrogenases (GDHs) with Y–H transition. Further, we observed the presence of one NAD-GDH and two form-specific NADP-GDH isoenzymes in B. poitrasii. However, molecular studies are necessary to elucidate the explicit role of GDHs in regulating Y–H reversible transition. Here, we report the isolation and characterization of one NAD (BpNADGDH, 2.643 kb) and two separate genes, BpNADPGDH I (Y-form specific, 1.365 kb) and BpNADPGDH II (H-form specific, 1.368 kb) coding for NADP-GDH isoenzymes in B. poitrasii. The transcriptional profiling during Y–H transition showed higher BpNADPGDH I expression in Y cells while expression of BpNADPGDH II was higher in H cells. Moreover, the yeast-form monomorphic mutant (Y-5) did not show BpNADPGDH II expression under normal dimorphism triggering conditions. Transformation with H-form specific BpNADPGDH II induced the germ tube formation in Y-5, which confirmed the cause–effect relationship between BpNADPGDH genes and morphological outcome in B. poitrasii. Interestingly, expression of H-form specific BpNADPGDH II also induced germ tube formation in human pathogenic, non-dimorphic yeast Candida glabrata, which further corroborated our findings. There is a cause-effect relationship between the genes coding for NADP-GDH isoenzymes (BpNADPGDHs) and morphological outcome in B. poitrasii with the expression of BpNADPGDH I necessary for yeast-like budding whereas expression of BpNADPGDH II is required for germ tube formation.