The Loss of Rad3 Induces the Diploidization of <i>Tor2</i><i>-287</i> Mutant to Promote the Cell Survival

Maintenance of genomic integrity is essential for all organism that help to maintain the number of chromosomes during cell division. In yeast and other organisms, the diploidization of genome serves as a key survival strategy under changing environmental conditions. Fission yeast ATR homolog Rad3 and TOR complex protein Tor2 are phosphatidylinositol 3-kinase-related protein kinases (PIKKs) and are involved in various functions. Rad3 is a key regulator of DNA damage signaling pathway and is involved in the maintenance of genomic integrity. The TOR complex, TORC1 and TORC2, contain Tor2 and Tor1 protein kinase respectively as their major component are involved in regulating eukaryotic cell growth, metabolism, and survival, in response to nutrient, energy, and environmental cues. In this study, we observed the suppression of temperature sensitive phenotype of a tor2-287 mutation in rad3Δ background. The presence of azygotic asci and tetrad dissection analysis revealed the diploid nature of rad3Δ tor2-287 double mutant cells, which was further confirmed by flow cytometry (FACS) analysis. In addition, the tor2-287/tor2-287 homozygous and tor-287/tor2+ heterozygous diploid exhibit temperature sensitive and resistant phenotypes, respectively. The tetrad dissection analysis revealed that a wild type copy of the tor2+ and rad3+ genes was present in tor2-287 rad3Δ strain due to the diploid nature of these cells, thereby suppressing the temperature sensitive phenotype. Overall, our results demonstrate that the absence of rad3 suppresses the temperature sensitivity of tor2-287 mutant by maintaining the diploid nature of cells.