Abstract
Carbon Catabolite Repression (CCR) has fascinated scientists and researchers around the globe for the past few decades. This important mechanism allows preferential utilization of an energy-efficient and readily available carbon source over relatively less easily accessible carbon sources. This mechanism helps microorganisms to obtain maximum amount of glucose in order to keep pace with their metabolism. Microorganisms assimilate glucose and highly favorable sugars before switching to less-favored sources of carbon such as organic acids and alcohols. In CCR of filamentous fungi, CreA acts as a transcription factor, which is regulated to some extent by ubiquitination. CreD-HulA ubiquitination ligase complex helps in CreA ubiquitination, while CreB-CreC deubiquitination (DUB) complex removes ubiquitin from CreA, which causes its activation. CCR of fungi also involves some very crucial elements such as Hexokinases, cAMP, Protein Kinase (PKA), Ras proteins, G protein-coupled receptor (GPCR), Adenylate cyclase, RcoA and SnfA. Thorough study of molecular mechanism of CCR is important for understanding growth, conidiation, virulence and survival of filamentous fungi. This review is a comprehensive revision of the regulation of CCR in filamentous fungi as well as an updated summary of key regulators, regulation of different CCR-dependent mechanisms and its impact on various physical characteristics of filamentous fungi.
Highlights
Fungi are responsible for causing devastating diseases of fauna and flora
CreA activity is regulated via ubiquitination and deubiquitination [5]
The roles of CreB, CreC and CreD are well established in relation to CreA activation, some ambiguities still exist regarding the functions of HulA and ApyA in ubiquitination of CreA [73]
Summary
Fungi are responsible for causing devastating diseases of fauna and flora. Pathogenic fungi have developed genetic mechanisms and molecular strategies to survive unpredictable scenarios and establish effective disease conditions in their hosts [1,2,3]. Carbon Catabolite Repression helps microorganisms to precisely adapt their physiology to the environment. The importance of this fine tuning is illustrated by the finding that within populations there may be balancing selections for individuals with fast and slow rates of reprogramming [2,4,5]. CCR has been studied extensively in Saccharomyces cerevisiae, which serves as a model organism for understanding the complexity of repression, derepression and induction of gene expression in response to glucose [2,6]. Mutants of CCR in A. nidulans have been mapped to define the genes CreA (Cre = catabolite responsive elements), CreB, CreC and CreD [8,9,10,11]. In order to develop biotechnological processes, for plant biomass deconstruction for conversion to high-value products, a more complete understanding of CCR in a wide variety of fungal species is needed [17,18,19]
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