SummaryThe COP9 signalosome complex (CSN) is a crucial regulator of ubiquitin ligases. Defects in CSN result in embryonic impairment and death in higher eukaryotes, whereas the filamentous fungus Aspergillus nidulans survives without CSN, but is unable to complete sexual development. We investigated overall impact of CSN activity on A. nidulans cells by combined transcriptome, proteome and metabolome analysis. Absence of csn5/csnE affects transcription of at least 15% of genes during development, including numerous oxidoreductases. csnE deletion leads to changes in the fungal proteome indicating impaired redox regulation and hypersensitivity to oxidative stress. CSN promotes the formation of asexual spores by regulating developmental hormones produced by PpoA and PpoC dioxygenases. We identify more than 100 metabolites, including orsellinic acid derivatives, accumulating preferentially in the csnE mutant. We also show that CSN is required to activate glucanases and other cell wall recycling enzymes during development. These findings suggest a dual role for CSN during development: it is required early for protection against oxidative stress and hormone regulation and is later essential for control of the secondary metabolism and cell wall rearrangement.

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.

Various starvation conditions cause adhesive growth of haploid cells or pseudohyphae formation of diploid cells of Saccharomyces cerevisiae. For the genetic Sigma1278b background, these morphological changes depend on the expression of the gene encoding the cell wall glycoprotein Flo11p, which is increased during nutritional limitations. Deletion of the genes encoding the transcriptional coactivators Rsc1p or Gcn5p impairs FLO11 transcription, which consequently leads to a loss of both haploid invasive growth and diploid pseudohyphae development upon glucose and nitrogen limitation, respectively. In contrast, amino acid starvation induces FLO11-dependent adhesive growth of the rsc1Delta and gcn5Delta strains although FLO11 transcription remains very low. The double deletion strain rsc1Deltaflo11Delta, however, does not grow adhesively, suggesting that the adhesion of the rsc1Delta strain at amino acid starvation is still FLO11-dependent. The FLO11prom-lacZ-encoded beta-galactosidase activities of the rsc1Delta and gcn5Delta mutant strains increase manifold upon amino acid starvation. It is therefore concluded that low levels of FLO11 transcripts are essential and sufficient for derepression of FLO11 expression and adhesive growth during amino acid starvation. A posttranscriptional control is assumed to be behind this phenomenon that permits the increased FLO11 expression from low FLO11 transcript abundances.

Particularly 90% of plants have some kind of mycorrhizal relationship with various fungi and are dependent upon this relationship for their survival (Smith & Read, 1997). For instance, mycorrhiza is specifically employed to give roses an excellent start for their growth. In this symbiosis fungi enhance the uptake of water and minerals for the plant and get sugar compounds in return. A successful growth and development of many orchids also requires symbiosis with specific fungi.The Agaricomycetes Amanita muscaria is capable to undergo symbiosis with different et al., 2011, Ba, et al., 2012, Zambare & Christopher, 2012. Saprophytic fungiFungal growth and differentiation are very energy consuming processes and require exploitation of external energy sources. Along with fungi numerous saprophytic pro-and eukaryotic organism genomes contain and express several genes encoding enzymes secreted for the hydrolysis of cell wall material derived from dead animals, plants, fungi and bacteria.Cell wall composition of the different organisms is specific for the kingdoms. Plant cell wall degraded by saprophytic organisms like A. nidulans is primarily composed of a primary, secondary layer and middle lamella (Buchanan, et al., 2000). The primary layer consists of pectins, cellulose, hemicellulose and glycoproteins. Xylan belongs to hemicelluloses and is also part of the primary plant cell wall. The epidermis an outer part of the primary plant cell wall consists of cutin and wax generating the plant cuticle a permeability barrier. Waxes protect the plant from drying-out. Suberin or cutin two epidermal polyester-like polymers protect the cell from herbivores (Moire, et al., 1999). The secondary plant cell wall named cuticula consists of microfibrilcellulose and hemicellulose which strengthen and waterproof the wall additionally. Plant cell wall hydrolysis requires specific enzymes. Among them are xylanases, pectinases, cutinases, polygalacturonase etc. In contrast, bacterial cell walls are mainly composed of peptidoglycan which is also called murein (van Heijenoort, 2001).Muramidases are able to hydrolyse murein.Polysaccharides like starch and lichenin which assure energy storage in plants are also at fungal disposal. Thereby lichenin is mainly synthesized in moos and lichen for long-term energy storage. Saprophytic fungi contain and secret enzymes like amylases and licheninase for the utilization of such external polysaccharides. Hydrolysis of starch requires amylases.The A. nidulans genome comprises seven known amylase genes (amyA -amyF, glaA, glaB) (Nakamura, et al., 2006). Beside starch, lichenin presents a further polysaccharide with an immense meaning for the survival of countless organisms since licheninases are conserved from prokaryotes to eukaryotes. For instance, the eng2 orthologue xgeA (AN2385) from A. nidulans is also thought to be a putative GPI anchored endo-1,3(4)-beta-glucanase (Bauer, et al., 2006, de Groot, et al., 2009. XgeA possesses also licheninase activity. Licheninases are Secondary metabolites can be gro...