Most parasitic and free-living species exhibit species-specific host-seeking behavior, oftentimes triggered by chemoattraction to host-secreted odors, such as pheromones. Although chemosensation is important for host-seeking, the corresponding pathways are only defined at the molecular level in C. elegans. To further explore the genes responsible for chemoattraction, we investigated the interaction between the entomophilic Pristionchus pacificus and its host beetle pheromone, ZTDO, which acts as an attractant, but also paralyzes the worm in high concentrations. We investigated a ZTDO-hypersensitive mutant,
Ppa-obi-1(
tu404), a gene which is highly expressed in amphid neuron sheaths and encodes lipid-binding domains that are hypothesized to have a role in mediating ZTDO reception and preventing J4 larvae hypersensitivity. To identify other factors involved in the reception of ZTDO, we conducted a mutagenesis of 52,000 F1 genomes to isolate mutants that suppress the
Ppa-obi-1 J4 hypersensitivity to ZTDO. We isolated three mutants:
csu61,
csu63, and
csu64, all of which display incomplete penetrance for the suppression of paralysis to ZTDO in the J4 stage. Like PS312 wildtype,
csu63 is also mildly attracted to ZTDO and thus suppressing the ZTDO chemotaxis defect exhibited by
obi-1 mutants. Combining the
csu61 and
csu63 suppressors enhanced the resistance to ZTDO. Additionally,
csu64 can also suppress the
Ppa-obi-1 hypersensitivity to betaine - a potent nematocide mediated by ACR-23, a nicotinic acetylcholine receptor - suggesting overlap between the pathways for ZTDO-induced paralysis and an ancient nematocide. We detected candidate mutations on the left arm of Chromosome X in
csu63 using whole genome sequencing and mapping. Although we did not find nonsynonymous or splice mutations, we found two mutations that reside in potential regulatory regions, including those of sulfatases and a dopamine receptor. We are currently conducting transgenic rescue to further pinpoint the gene responsible for the
csu63 suppression phenotype. Ultimately, the goal of our research is to understand the mechanisms underlying ZTDO chemoregulation to provide better insight into the entomophilic host-seeking behavior.