PgmNr P2106: Virulence QTLs and Genome-wide Recombination Rates in Cryptococcus.

Authors:
Cullen Roth 1 ; Sheng Sun 2 ; R. Blake Billmyre 2 ; Joseph Heitman 2 ; Paul M. Magwene 1,3


Institutes
1) University Program in Genetics and Genomics, Duke University, Durham, NC; 2) Department of Molecular Genetics and Microbiology, Duke University, Durham, NC; 3) Department of Biology, Duke University, Durham, NC.


Abstract:

Cryptococcal disease is estimated to affect 1 million people and kill approximately 600,000 annually. Environmental isolates of Cryptococcus neoformans, and its relative Cryptococcus deneoformans, vary in their pathogenicity, ranging from benign to hyper-virulent. Key traits that contribute to virulence, such as the ability to grow at human body temperature (37°C), have been identified. However, little is known about the genetic basis of this phenotypic variation. Here we investigate the genetic basis of virulence-related traits using quantitative trait locus (QTL) mapping in C. deneoformans. We crossed strains of two different genetic backgrounds (approximately 5 SNPs/kb), generated haploid segregants via bisexual and unisexual mating, and obtained genotypes for 100 segregants using short-read sequencing. We inferred recombination breakpoints using SNP genotype data and calculated a genome wide average recombination frequency of ~7 kb/cM. Five virulence related traits were phenotyped: high temperature growth (at 39°, 40°, 41°, and 42°C), growth at high pH, melanin production, amphotericin B resistance, and fluconazole resistance. We used a marker regression framework to identify QTL underlying variation in these virulence phenotypes. QTLs with major effects were identified for high temperature growth (chromosomes 2 and 12), amphotericin B resistance (chromosome 2), and fluconazole resistance (chromosome 2 and 7). Interestingly, we observed several candidate pleiotropic QTLs, one is located on chromosome 2 and appears to mediate both high temperature growth and amphotericin B resistance, and another is located on chromosome 12 and plays a role in both high temperature growth and melanin production. These results provide novel genome wide estimates of recombination and advance our understanding of the genetic basis underlying virulence in Cryptococcus.