The mysterious role of the C.elegans nuclear hormone receptor NPR-1 in pathogen defense

The nematode Caenorhabditis elegans feeds on microbes inits natural environment. Some of these microbes are pathogenic and thus harmful to C. elegans.Tominimize resulting fitness reductions,C. elegans has evolved various defence mechanisms including behavioural responses (e.g. avoidance behaviour) that reduce contact with the infectious microbes. In this study, we characterized the genetic architecture of natural variation in C. elegans avoidancebehaviour against the infectious stages of the Gram-positive bacterium Bacillus thuringiensis. We performed an analysis of quantitative trait loci (QTLs) using recombinant inbred lines (RILs) and introgression lines (ILs) generated from a cross of two genetically as well as phenotypically distinct natural isolates N2 and CB4856. The analysis identified several QTLs that underlie variation in the behavioural response to pathogenic and/or non-pathogenic bacteria. One of the candidates is the npr-1gene. This gene encodes a homolog of the mammalian neuropeptide receptor.Npr-1was previously indicated to fully contribute to behavioural defence against the Gram-negative bacterium Pseudomonas aeruginosa and food patch-leaving behaviour on Escherichia coli. Interestingly, inour study, npr-1is not the only gene mediating avoidance behaviour toward Bacillus thuringiensis. Moreover, our functional analyses show that npr-1alleles appear to influence survival and avoidance behaviour toward Bacillus thuringiensis inexactly the opposite way than toward Pseudomonas aeruginosa. Our findings highlight the role of npr-1infine-tuning nematode behaviourinan ecological context depending on the microbe to whichC. elegans is exposed.