The Nitrogen Regulation Network and its Impact on Secondary Metabolism and Pathogenicity
Philipp Wiemann and Bettina Tudzynski
from: Fusarium: Genomics, Molecular and Cellular Biology (Edited by: Daren W. Brown and Robert H. Proctor). Caister Academic Press, U.K. (2013)
Nitrogen is essential for fungal growth because it is a component of both nucleic acids and proteins. Fungi have two predominant mechanisms to incorporate ammonium into their metabolism: 1) the NADP-dependent, glutamate-dehydrogenase-catalyzed reductive amination of 2-oxoglutarate to form glutamate; and 2) the ATP-dependent, glutamine synthase-catalyzed fusion of ammonium and glutamate to form glutamine. Beside ammonium, fungi can also utilize a broad variety of other nitrogen sources, such as nitrate, proteins, amino acids, uric acid, allantoin and urea. Efficient control mechanisms are needed to coordinate activation/repression of genes and their products that are involved in sensing, transporting and/or metabolizing nitrogen-containing substances. Furthermore, nitrogen availability plays a critical role in how fungi interact with plants as pathogens and endophytes. Thus, nitrogen limitation has been proposed to be a key signal for activating the expression of virulence-associated genes in plant pathogens. Additionally, quality and quantity of nitrogen also affects the formation of a broad range of secondary metabolites. These secondary metabolites often contribute to virulence on the fungus' host and additionally can bare a threat to animal and human health when they occur as contaminants of food and feed. This Chapter will review the genetic basis of the nitrogen regulation network with the focus on the genus Fusarium which contains some of the most devastating plant pathogens read more ...