Identification of Genomewide Alternative Splicing Events in Sequential, Isogenic Clinical Isolates of Candida albicans Reveals a Novel Mechanism of Drug Resistance and Tolerance to Cellular Stresses.

Alternative splicing (AS)-a process by which a single gene gives rise to different protein isoforms in eukaryotes-has been implicated in many basic cellular processes, but little is known about its role in drug resistance and fungal pathogenesis. The most common human fungal pathogen, , has introns in 4 to 6% of its genes, the functions of which remain largely unknown. Here, we report AS regulating drug resistance in Comparative RNA-sequencing of two different sets of sequential, isogenic azole-sensitive and -resistant isolates of revealed differential expression of splice isoforms of 14 genes. One of these was the superoxide dismutase gene , which contains a single intron. The Δ/Δ mutant was susceptible to the antifungals amphotericin B (AMB) and menadione (MND). While AMB susceptibility was rescued by overexpression of both the spliced and unspliced isoforms, only the spliced isoform could overcome MND susceptibility, demonstrating the functional relevance of this splicing in developing drug resistance. Furthermore, unlike AMB, MND inhibits splicing and acts as a splicing inhibitor. Consistent with these observations, MND exposure resulted in increased levels of unspliced isoform that are unable to scavenge reactive oxygen species (ROS), resulting in increased drug susceptibility. Collectively, these observations suggest that AS is a novel mechanism for stress adaptation and overcoming drug susceptibility in The emergence of resistance in , an opportunistic pathogen, against the commonly used antifungals is becoming a major obstacle in its treatment. The necessity to identify new drug targets demands fundamental insights into the mechanisms used by this organism to develop drug resistance. has introns in 4 to 6% of its genes, the functions of which remain largely unknown. Using the RNA-sequencing data from isogenic pairs of azole-sensitive and -resistant isolates of , here, we show how uses modulations in mRNA splicing to overcome antifungal drug stress.