The DUG Pathway Governs Degradation of Intracellular Glutathione in Aspergillus nidulans

Abstract

Glutathione (GSH) is an abundant tripeptide that plays a crucial role in shielding cellular macromolecules from various reactive oxygen and nitrogen species in fungi. Understanding GSH metabolism is of vital importance to deciphering redox regulation in these microorganisms. In the present study, to better understand the GSH metabolism in filamentous fungi, we investigate functions of the dugB and dugC genes in the model fungus Aspergillus nidulans. These genes are orthologues of dug2-3 involved in cytosolic GSH degradation in the yeast. The deletion (Δ) of dugB, dugC, or both resulted in a moderate increase in the GSH content in the mycelia grown on glucose, reduced conidia production, and disturbed sexual development. In agreement with these observations, transcriptome data showed that genes encoding MAP kinase pathway elements (e.g. steC, sskB, hogA, mkkA) or regulatory proteins of conidiogenesis and sexual differentiation (e.g. flbA,C,E, nosA, rosA, nsdC,D) were down-regulated in the ΔdugBΔdugC mutant. Deletion of dugB and/or dugC slowed down the depletion of GSH pools under carbon starvation. It also reduced accumulation of reactive oxygen species, decreased autolytic cell wall degradation and enzyme secretion but increased sterigmatocystin formation. Transcriptome data demonstrated that enzyme secretions - in contrast to mycotoxin production - were controlled at post-transcriptional level. We suggest that GSH connects starvation and redox regulation to each other: Cells utilize GSH as stored carbon source during starvation. The reduction of GSH content alters the redox state activating regulatory pathways responsible for carbon starvation stress responses. Importance Glutathione (GSH) is a widely distributed tripeptide in both eukaryotes and prokaryotes. Owing to its very low redox potential, antioxidative character and high intracellular concentration, GSH profoundly shapes the redox status of cells. Our observations suggest that GSH metabolism and/or the redox status of cells plays a determinative role in several important aspects of fungal life, including oxidative stress defense, protein secretion, secondary metabolite production (including mycotoxin formation) as well as sexual and asexual differentiations. We demonstrated that even a slightly elevated GSH level can substantially disturb the homeostasis of fungi. This information could be important for development of new GSH producing strains or for any biotechnologically relevant processes where the GSH content, antioxidant capacity or oxidative stress tolerance of a fungal strain is manipulated.

AtfA-Independent Adaptation to the Toxic Heavy Metal Cadmium in Aspergillus nidulans

“…In contrast, specific catalase activities remained unchanged (Table 1), which can be explained with multiple, differentially regulated catalase genes [55] affecting catalase activities [55]. Similar behavior of the "Antioxidative enzyme" genes (i.e., stress-dependent remodeling of their activity) was observed under oxidative stress induced by carbon starvation earlier [57,58].…”

“…In contrast to oxidative, osmotic or carbon starvation stress [ 23 , 58 ] the applied cadmium stress had minor effect on the transcription of “Secondary metabolite cluster” genes ( Table 3 and Table S5 ). A few clusters, however, showed up-regulation (inp cluster) or down-regulation (microperfuranone cluster, AN1242 cluster) ( Table 3 and Table S5 ).…”

Exogenous inoculation of endophyte Penicillium sp. alleviated pineapple internal browning during storage

“…Cells synthesized more ascorbic acids and antioxidants to balance ROS [ 64 ]. Under normal and healthy conditions, the ROS molecules were scavenged by various antioxidative defense mechanisms [ 65 ]. These included enzymatic antioxidant systems, such as SOD, POD, GR (glutathione reductase), and CAT (catalase), and nonenzymatic low molecular metabolites, such as ascorbic acids (AsA) and glutathione (GSH) [ [65] , [66] , [67] , [68] ].…”

Strategies Shaping the Transcription of Carbohydrate-Active Enzyme Genes in Aspergillus nidulans

“…The A. nidulans THS30 (pyrG89; AfupyrG + ; pyroA4; pyroA + ) reference strain [27] was used in this study. It was maintained on Barratt's minimal agar plates at 37 • C [28] and only freshly collected conidia from 6 d cultures were used for inoculation in all experiments.…”

“…In carbon-starved cultures, utilization of stored compounds (e.g., glycogen or even glutathione [27]), autophagy, and autolytic cell wall degradation (Table 3 and Table S2) [2,42] can provide energy sources. Besides the detection of potential carbon sources, autolytic cell wall degradation also needs intensive production of extracellular enzymes.…”