Identification of QTLs Associated with Virulence Related Traits and Drug Resistance in Cryptococcus neoformans

Abstract

Cryptococcus neoformans is a basidiomycete fungus capable of causing deadly meningoenchephilitis, primarily in immunocompromised individuals. Formerly, C. neoformans was composed of two divergent lineages, but these have recently been elevated to species status, now C. neoformans (formerly C. neoformans var. grubii) and C. deneoformans (formerly C. neoformans var. neoformans). While both species can cause deadly infections in humans, C. neoformans is much more prevalent in clinical settings than C. deneoformans. However, the genetic factors contributing to their significant differences in virulence remain largely unknown. Quantitative trait locus (QTL) mapping is a powerful tool that can be used to identify genomic regions associated with phenotypic differences between strains. Here, we analyzed a hybrid cross between these two species and identified a total of 23 QTL, including five for melanin production, six for cell size, one for cell wall thickness, five for the frequency of capsule production, three for minimal inhibitory concentration (MIC) of fluconazole in broth, and three for MIC on solid medium. For the fluconazole resistance-associated QTL, three showed environment and/or concentration-specific effects. Our results provide a large number of candidate gene regions from which to explore the molecular bases for phenotypic differences between C. neoformans and C. deneoformans.

Patterns of allele distribution in a hybrid population of the Cryptococcus neoformans species complex

“…The increasing prevalence of AD hybrids among clinical samples necessitates a better understanding of the hybridisation process between Cryptococcus species and the potential for increased virulence in resulting hybrids . Transgressive segregation in virulence and virulence‐associated phenotypes has been observed in previous interspecific crosses of Cryptococcus . Our results highlight the significant departure of allele distributions from expected Mendelian ratios in AD hybrids.…”

“…Genomic DNA was extracted from spores that germinated to form colonies on YEPD using standard chloroform‐isoamyl alcohol methodology . Hybrid strains were then genotyped at 33 co‐dominant PCR‐RFLP markers (Table ) taken from a previous study . At least two markers were selected for each of the 14 chromosomes in the genome (Figure ).…”

“…Despite low viability and infertility of sexual spores derived from hybrid crosses, both laboratory‐derived and natural AD hybrids show a remarkable phenotypic diversity in virulence and associated characteristics. While some studies found AD hybrids to show hybrid vigour, others have reported the virulence of AD hybrids to be comparable to that of their more virulent parent . Both the hybrids’ genetic background (including mating type) and the type of host animals used as infection models can influence the in vivo virulence variations .…”

“…While some studies found AD hybrids to show hybrid vigour, others have reported the virulence of AD hybrids to be comparable to that of their more virulent parent. [15][16][17] Both the hybrids' genetic background (including mating type) and the type of host animals used as infection models can influence the in vivo virulence variations. 15,17 Furthermore, a few studies found AD hybrids to exceed both parents in their resistance to UV irradiation and the antifungal drug FK506.…”

“…significantly less than both parents), among laboratory-derived AD hybrids in the expression of virulence factors including capsule production, growth at 37°C and melanin production. 16 The phenotypic diversity found among AD hybrids in clinical, environmental and laboratory settings is indicative of significant genetic diversity present within the hybrid population, a likely product of their novel and unique genetic make-up.…”