An upregulation of all four genes in the Evo strain was confirmed by qRT-PCR after 1 hour of incubation in DMEM+10% FBS at 37C and 5% CO2(Fig. short time-frame, the mutant evolved the ability to escape macrophages by filamentation. In addition, the evolved mutant exhibited hyper-virulence in a murine contamination model and an altered cell wall composition compared to thecph1/efg1 strain. Moreover, the transcriptional regulation of hyphae-associated, and other pathogenicity-related genes became re-responsive to environmental cues in the evolved strain. We went on to identify the causative missense mutation via whole genome- and transcriptome-sequencing: a single nucleotide exchange took place withinSSN3that encodes a component of the Cdk8 module of the Mediator complex, which links transcription factors with the general transcription machinery. This mutation was responsible for the reconnection of the hyphal growth program with environmental signals in the evolved Rabbit Polyclonal to HSP90A strain and was sufficient to bypass Efg1/Cph1-dependent filamentation. These data demonstrate that even central transcriptional networks can be remodeled very quickly under appropriate selection pressure. == Author Summary == Pathogenic microbes often evolve complex traits to adapt to their Dinaciclib (SCH 727965) respective hosts, and this evolution is usually ongoing: for example, microorganisms are developing resistance to antimicrobial compounds in the clinical setting. The ability of the common human pathogenic fungus,Candida albicans, to switch from yeast to hyphal (filamentous) growth is considered a central virulence attribute. For example, hyphal formation allowsC. albicansto escape from macrophages following phagocytosis. A well-investigated signaling network integrates different environmental cues to induce and maintain hyphal growth. In fact, deletion of two central transcription factors in this network results in a mutant that is both nonfilamentous and avirulent. We used experimental evolution to study the adaptation capability of this mutant by continuous co-incubation within macrophages. We found that this selection regime led to a relatively rapid re-connection of signaling between environmental cues and the hyphal growth program. Indeed, the evolved mutant regained the ability to filament and its virulencein vivo. This bypass of central transcription factors was based on a single nucleotide exchange in a gene encoding a component of the general transcription regulation machinery. Our results show that even a complex regulatory network, such as the transcriptional network which governs hyphal growth, can be Dinaciclib (SCH 727965) remodeled via microevolution. == Introduction == The incidence of invasive fungal infections has steadily increased within the past decades, largely because of a growing population of susceptible individuals, reflecting the progress of modern medicine in prolonging life even with severe underlying diseases and the increasing rate of immuno-deficient patients. One of the most frequently isolated fungi isCandida albicans, an ubiquitous and normally harmless commensal of the alimentary tract and mucocutaneous membranes. As an opportunistic pathogen, it can cause superficial infections like oropharyngeal candidiasis, especially in HIV patients, as well as life-threatening systemic infections with mortality rates up to 40%, even with current antifungal treatment options[1]. The transition from the commensal to a pathogenic state depends on the microbiota, the host response, andC. albicansactivities, such as adhesion, secretion of hydrolases, metabolic adaptation, biofilm formation and, importantly, morphological plasticity, which includes the yeast-to-filament transition[2][7]. To survive and thrive in the many different niches inside the host,C. albicansmust be able to adapt to changing environments and different stresses. In the short term, this occurs primarily by changes in gene expression and translation, and via post-translational modifications, but ultimately microevolutionary processes Dinaciclib (SCH 727965) will play an important role. As a prominent example, Whiteet al.[8]have shown that microevolution is the driving force behind the emergence of antifungal drug resistance. They exhibited thede novoappearance of fluconazole resistance in evolvingC. albicansstrainsin vivo[8]. Furthermore, clinical isolates generally exhibit large genetic variations, and microevolution can be observed bothin vitroandin vivo[9],[10], indicating that this process plays an important role in host-pathogen interactions. Therefore, microevolution provides a source of variation for the adaptive response ofC. albicansto challenging (host) environments. Different mechanisms account for the generation of new genotypic variants, including point mutations, amplification or deletion of chromosomal segments, chromosomal translocation or inversion, and whole chromosome aneuploidy. These genetic variations can affect expression of single genes or.