Natural genetic variation in Drosophila melanogaster reveals genes associated with Coxiella burnetii infection

Authors: GUZMAN, ROSA - Washington State University; HOWARD, ZACHARY - Washington State University; LIU, ZIYING - Washington State University; OLIVEIRA, R - Washington State University; MASSA, ALISHA - Washington State University; OMSLAND, ANDERS - Washington State University; White, Stephen; GOODMAN, ALAN - Washington State University

Submitted to: Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2021
Publication Date: 3/1/2021
Citation: Guzman, R.M., Howard, Z.P., Liu, Z., Oliveira, R.D., Massa, A.T., Omsland, A., White, S.N., Goodman, A.G. 2021. Natural genetic variation in Drosophila melanogaster reveals genes associated with Coxiella burnetii infection. Genetics. 217(3). Article iyab005. https://doi.org/10.1093/genetics/iyab005.
DOI: https://doi.org/10.1093/genetics/iyab005

Interpretive Summary: Coxiella burnetii is a zoonotic bacterium that can cause coxiellosis in livestock and Q Fever in humans. Coxiellosis in livestock is estimated to cost in the millions of dollars per year and often results in abortions and even abortion storms with severe economic and animal health consequences. Livestock have often been blamed for human Q Fever outbreaks, which can include fever, aches, pneumonia, hepatitis, pregnancy complications, and potentially fatal swelling of the heart. A large human Q Fever outbreak in the U.S. could have costs in excess of $1 billion. While a genetic basis for susceptibility to coxiellosis and Q Fever have been demonstrated in livestock, humans, and other species, the specific genes involved have remained largely unexplored. Here we report the first genome-wide association study of C. burnetii susceptibility in any species. We used a special fruit fly genetics resource - the Drosophila Genetics Reference Panel (DGRP) - to scan the entire genome for genetic variants and genes associated with C. burnetii susceptibility. Of 25 genes identified, more than half (15) had their roles in C. burnetii susceptibility validated by either fruit flies with knockout genes or by gene knockdown experiments. Many of these genes play roles in innate immune responses to C. burnetii, including through regulation of key cells (macrophages) that C. burnetii targets. This is the first report of association associating many of these genes with C. burnetii traits. The clear equivalence of these genes with livestock and human genes suggests new avenues for research into genetic control of susceptibility to C. burnetii not only in livestock, but also in human medicine. Further work based on these results will be required to better understand C. burnetii infection and produce future DNA tests for C. burnetii susceptibility. Breeding ruminant livestock that do not shed C. burnetii could be a powerful tool to limit risks of both coxiellosis in livestock and human Q Fever.

Technical Abstract: The Gram-negative bacterium Coxiella burnetii is the causative agent of Query (Q) fever in humans and coxiellosis in livestock. Association between host genetic background and C. burnetii pathogenesis has been demonstrated both in humans and animals; however, specific genes associated with severity of infection remain unknown. We employed the Drosophila Genetics Reference Panel (DGRP) to perform a genome-wide association study (GWAS) and identify host genetic variants that regulate C. burnetii infection. The analysis resulted in 64 genome-wide suggestive (P < 10-5) single nucleotide polymorphisms (SNPs) in 25 unique genes. We examined the role of each gene in C. burnetii infection using flies carrying a null mutation or RNAi knockdown of each gene and monitoring survival. Of the 25 candidate genes, 15 validated in at least one system (6 validated in null mutants only, 5 in RNAi knockdown only, and 4 in both null mutants and RNAi). For many, this is the first report establishing involvement of these genes or their homologs with C. burnetii susceptibility in any system. Among the validated genes, FER and tara play roles in the JAK-STAT, JNK, and decapentaplegic/TGF-ß signaling pathways which are associated with the innate immune response to C. burnetii infection. Two other validated genes, CG42673 and DIP-e, play roles in bacterial infection and synaptic signaling but no previous association with C. burnetii pathogenesis. Furthermore, since the mammalian ortholog of CG13404 (PLGRKT) is an important regulator of macrophage function, CG13404 could play a role in C. burnetii susceptibility through haemocyte regulation. These insights provide a foundation for further investigation of genetics of C. burnetii susceptibility across a wide variety of hosts.