Transcriptomic Evidence of Base and Nucleotide Excision Repair Mechanisms in Response to UV-B Radiation in an Arctic Fungus Pseudogymnoascus australis Strain HNDR4

Polar micro-fungi are known to have developed protective mechanisms and responses against the harmful effects of UV radiation. In this study, physiological, cellular, and transcriptomic responses of an Arctic fungal strain of Pseudogymnoascus australis towards UV-B radiation were examined. Fungal isolate was cultured on 0.45μm nylon membranes overlayed on Czapex-Dox agar (CDA) at 15ºC for 10 d in dark condition to reach the mid-log phase. To assess DNA damage and recovery, the isolates were exposed to UV-B radiation (UV dosage of 6.1 kj m-2 d-1) for 130 min, followed by 0, 2 and 6 hr incubation under light condition. Differential gene expression in DNA repair after UV-B treatment at these time points was analysed based on RNA-Seq data output of 40 million reads per sample from an Illumina NovaSeq 6000 system platform. The results revealed that radiation-repair (RAD) genes were upregulated and the photoreactivation (PHR1) gene was downregulated after UV-B exposure in light condition. Downregulation of oxidoreductase activity was observed from the GO enrichment analysis. The KEGG pathway enrichment analysis exhibited upregulation of base excision repair (BER) genes and nucleotide excision repair (NER) genes upon UV-B exposure. This is the fi rst RNASeq transcriptomic study on the DNA repair mechanisms employed by a polar fungus to mitigate UV-induced DNA damage.