Antifungal drug resistance (click to expand)
Recent annual global estimates of fungal infections in humans have indicated 3M cases of chronic pulmonary aspergillosis, ~220K cases of cryptococcal meningitis associated with HIV/AIDS, ~700K cases of invasive candidiasis, ~500K cases of Pneumocystis jirovecii-caused pneumonia, ~250K cases of invasive aspergillosis, ~100K cases of disseminated histoplasmosis, more than 10M cases of fungal-triggered asthma and ~1M cases of fungal keratitis 1-3. Fungal diseases have been leading to major social and economic costs in food systems 4,5, pushing animal species to the brink of extinction 6,7, and are on the rise due to global warming 8. A restricted number of therapeutic options against human fungal infections are available, including polyene (amphotericin B), echinocandin and azole compounds 9. In agriculture, fungicides include ethyl benzimidazole carbamates, succinate dehydrogenase inhibitors, anilinopyrimidines, quinone outside inhibitors, morpholines and azoles 10. Antifungal drug resistance due to the long term exposure to fungicides and concomitant cellular adaptation occurs because of the acquisition of genetic instability, target modification, overexpression of efflux pump genes, detoxification by metabolic enzymes, or hot spot amino acid substitutions 11,12.
Our project intends to explore the natural diversity in antifungal drug resistance using natural populations of the microbial eukaryote Neurospora crassa. We are also interested in studying transcription factors that regulate fungal sensitivity to drugs. We anticipate that our research will lead us to relevant data towards the understanding of antifungal drug resistance, a dramatic public health problem with worldwide ramifications.
Evolution of fungal allorecognition (click to expand)
Sociality is not restricted to the so-called ‘higher organisms’. In some filamentous fungi, somatic cell-cell fusion typifies a cooperative behavior that is essential for the formation of the multicellular hyphal network 1,2. It is the syncytial nature of the fungal mycelium that allows these organisms to translocate nutrients and organelles across the colony and efficiently grow and colonize substrates 3; hence, it is unsurprising that somatic cell fusion is beneficial for fitness in Neurospora crassa 4. Intercellular cooperation in N. crassa depends greatly on genetic similarity and conflict can arise from inopportune fusion between genetically nonidentical partners due to the transmission of infectious elements, assimilation of harmful genotypes or selection of cheaters, individuals that gain the benefit of social traits (e.g., enjoy public goods such as nutrients) while contributing less to their production 5. As microbes are evidently unable to use visual, olfactory or tactile cues to recognize their kin and socially evaluate potential fusion partners, cooperation versus competition is dictated by genetic relatedness at certain genomic loci, a phenomenon known as allorecognition. In multicellular colonies, hyphal fusion of strains carrying dissimilar het loci triggers a rapid response that leads to cell death 6. Importantly, this allorecognition reaction, known as heterokaryon incompatibility, is accompanied by septal plugging of the incompatible fusion compartment in a way that cell death is restricted to that particular area 6. This phenomenon has, thus, been portrayed as having an altruistic character, since part of the mycelium perishes for the benefit of the colonial community. Notably, heterokaryon incompatibility is inactive in germinated spores (germlings). However, genetic analyses of germling fusion in a wild population of N. crassa revealed that nonself recognition can occur at distance 7, during cell-cell adhesion 8 and after cytoplasmic mixing 9,10, resulting in various phenotypes that hinder the success of incompatible cell fusion events 11,12.
Since all of these allorecognition checkpoints are active and suppressed during asexual and sexual reproduction, respectively, our hypothesis is that genetic diversification in N. crassa (and potentially other heterothallic fungi) occurs preferentially via outbreeding. Our laboratory aims to analyze the evolution of fungal self/nonself recognition by undertaking an in silico approach. We intend to integrate our findings in the context of species within the Neurospora genus and their diverse sexual and asexual lifestyles.
Project 3 (click to expand)