Unraveling Fungal Radiation Resistance Regulatory Networks through the Genome-Wide Transcriptome and Genetic Analyses of Cryptococcus neoformans

<jats:title>ABSTRACT</jats:title> <jats:p> The basidiomycetous fungus <jats:named-content content-type="genus-species">Cryptococcus neoformans</jats:named-content> has been known to be highly radiation resistant and has been found in fatal radioactive environments such as the damaged nuclear reactor at Chernobyl. To elucidate the mechanisms underlying the radiation resistance phenotype of <jats:named-content content-type="genus-species">C. neoformans</jats:named-content> , we identified genes affected by gamma radiation through genome-wide transcriptome analysis and characterized their functions. We found that genes involved in DNA damage repair systems were upregulated in response to gamma radiation. Particularly, deletion of recombinase <jats:italic>RAD51</jats:italic> and two DNA-dependent ATPase genes, <jats:italic>RAD54</jats:italic> and <jats:italic>RDH54</jats:italic> , increased cellular susceptibility to both gamma radiation and DNA-damaging agents. A variety of oxidative stress response genes were also upregulated. Among them, sulfiredoxin contributed to gamma radiation resistance in a peroxiredoxin/thioredoxin-independent manner. Furthermore, we found that genes involved in molecular chaperone expression, ubiquitination systems, and autophagy were induced, whereas genes involved in the biosynthesis of proteins and fatty acids/sterols were downregulated. Most importantly, we discovered a number of novel <jats:named-content content-type="genus-species">C. neoformans</jats:named-content> genes, the expression of which was modulated by gamma radiation exposure, and their deletion rendered cells susceptible to gamma radiation exposure, as well as DNA damage insults. Among these genes, we found that a unique transcription factor containing the basic leucine zipper domain, named Bdr1, served as a regulator of the gamma radiation resistance of <jats:named-content content-type="genus-species">C. neoformans</jats:named-content> by controlling expression of DNA repair genes, and its expression was regulated by the evolutionarily conserved DNA damage response protein kinase Rad53. Taken together, the current transcriptome and functional analyses contribute to the understanding of the unique molecular mechanism of the radiation-resistant fungus <jats:named-content content-type="genus-species">C. neoformans</jats:named-content> . </jats:p> <jats:p> <jats:bold>IMPORTANCE</jats:bold> Although there are no natural environments under intense radiation, some living organisms have been found to show high radiation resistance. Organisms harboring the ability of radiation resistance have unique regulatory networks to overcome this stress. <jats:named-content content-type="genus-species">Cryptococcus neoformans</jats:named-content> is one of the radiation-resistant fungi and is found in highly radioactive environments. However, it remains elusive how radiation-resistant eukaryotic microorganisms work differentially from radiation-sensitive ones. Here, we performed transcriptome analysis of <jats:named-content content-type="genus-species">C. neoformans</jats:named-content> to explore gene expression profiles after gamma radiation exposure and functionally characterized some of identified radiation resistance genes. Notably, we identified a novel regulator of radiation resistance, named Bdr1 (a <jats:underline>b</jats:underline> ZIP TF for <jats:underline>D</jats:underline> NA damage <jats:underline>r</jats:underline> esponse <jats:underline>1</jats:underline> ), which is a transcription factor (TF) that is not closely homologous to any known TF and is transcriptionally controlled by the Rad53 kinase. Therefore, our work could shed light on understanding not only the radiation response but also the radiation resistance mechanism of <jats:named-content content-type="genus-species">C. neoformans</jats:named-content> . </jats:p>