Changes of global gene expression and secondary metabolite accumulation during light-dependent Aspergillus nidulans development

Abstract

Fungal development and secondary metabolite production are coordinated by regulatory complexes as the trimeric velvet complex. Light accelerates asexual but decreases sexual development of the filamentous fungus Aspergillus nidulans. Changes in gene expression and secondary metabolite accumulation in response to environmental stimuli have been the focus of many studies, but a comprehensive comparison during entire development is lacking. We compared snapshots of transcript and metabolite profiles during fungal development in dark or light. Overall 2.014 genes corresponding to 19% of the genome were differentially expressed when submerged vegetative hyphae were compared to surface development. Differentiation was preferentially asexual in light or preferentially sexual connected to delayed asexual development in dark. Light induces significantly gene expression within the first 24–48h after the transfer to surfaces. Many light induced genes are also expressed in dark after a delay of up to two days, which might be required for preparation of enhanced sexual development. Darkness results in a massive transcriptional reprogramming causing a peak of lipid-derived fungal pheromone synthesis (psi factors) during early sexual development and the expression of genes for cell-wall degradation presumably to mobilize the energy for sexual differentiation. Accumulation of secondary metabolites like antitumoral terrequinone A or like emericellamide start under light conditions, whereas the mycotoxin sterigmatocystin or asperthecin and emodin appear under dark conditions during sexual development. Amino acid synthesis and pool rapidly drop after 72–96h in dark. Subsequent initiation of apoptotic cell-death pathways in darkness happens significantly later than in light. This illustrates that fungal adaptation in differentiation and secondary metabolite production to light conditions requires the reprogramming of one fifth of the potential of its genome.