The RNA helicase Ski2 in the fungal pathogen Cryptococcus neoformans highlights key roles in azoles resistance and stress tolerance

The yeast SKI (superkiller) complex was originally identified from cells that were infected by the M 'killer' virus. Ski2, as the core of the SKI complex, is a cytoplasmic cofactor and regulator of RNA-degrading exosome. The putative RNA helicase Ski2 was highly conserved from yeast to animals and has been demonstrated to play a key role in the regulation of RNA surveillance, temperature sensitivity, and growth in several yeasts but not yet in Cryptococcus neoformans (C. neoformans). Here, we report the identification of a gene encoding an equivalent Ski2 protein, named SKI2, in the fungal pathogen C. neoformans. To obtain insights into the function of Ski2, we created a mutant strain, ski2 Delta, with the CRISPR-Cas9 editing tool. Disruption of SKI2 impaired cell wall integrity. Further investigations revealed the defects of the ski2 Delta mutant in resistance to osmotic stresses and extreme growth temperatures. However, significantly, the ability to undergo invasive growth under nutrient-depleted conditions was increased in the ski2 Delta mutant. More importantly, our results showed that the ski2 Delta mutant exhibited slightly lower virulence and severe susceptibility to anti-ribosomal drugs by comparison to the wild type, but it developed multidrug resistance to azoles and flucytosine. By constructing the double deletion strain ski2 Delta afr1 Delta, we verified that increased Afr1 in ski2 Delta contributed to the azole resistance, which might be influenced by nonclassical small interfering RNA. Our work suggests that Ski2 plays critical roles in drug resistance and regulation of gene transcription in the yeast pathogen C. neoformans.