The Genetic Basis of Abiotic Stress Resistance in Extremophilic Fungi: The Genes Cloning and Application

Abstract

In eukaryotic organisms, many genera of fungi have successfully colonized various extreme environments known on earth. For example, some species thrive in hypersaline environments and some uniquely inhabit bare rock surface niches in hot or cold deserts where other eukaryotes such as plants can hardly survive under these conditions. Therefore, extremophilic fungi are excellent models to provide understanding in the resistant mechanisms that allow higher organisms to overcome stress; these fungi present valuable resources for isolation of resistance genes to be applied in genetic engineering and biotechnology. As a model fungus, the unicellular yeast Saccharomyces cerevisiae exhibits characteristics responses to a variety of stressors, it is a practical genetic tool to identify and validate abiotic stress resistant genes. In addition, it has led to the discovery of two significant osmotic-resistance pathways: the high-osmolarity glycerol response (HOG1) pathway and calcineurin-dependent pathway. With the increasing number of fungal species being characterized and sequenced, extremophilic fungi are found to be better systems to reveal the complex extremo-resistant mechanisms, and for the isolation of abiotic stress resistance and related genes. A series of environmental stress-related genes have been investigated in diverse groups of fungi, and no doubt these specific resistance genes could be valuable for the improvement of crop tolerance to single or multiple stresses. Interestingly, several ribosomal proteins recently isolated from the extremophilic fungi have been reported to possess abiotic stress resistant functions (moonlighting functions). Collectively, a tremendous amount of tolerant genes (e.g., HOG1) cloned from extremophilic fungi appeared to be more resistant to abiotic stress than their homologs or orthologs cloned from non-extremophilic fungi, though these proteins are highly conserved and exist in a wide variety of organisms. Taking into account the special characteristics/mechanisms of genes from extremophilic fungi in stress responses, the application of these types of genes might be more valuable and reliable for biotechnological applications.