Alterations in gene expression and secondary metabolite production during development of Aspergillus nidulans

Abstract

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...