A Polymorphism in npr-1 Is a Behavioral Determinant of Pathogen Susceptibility in C. elegans

Abstract

The nematode Caenorhabditis elegans responds to pathogenic bacteria with conserved innate immune responses and pathogen avoidance behaviors. We investigated natural variation in C. elegans resistance to pathogen infection. With the use of quantitative genetic analysis, we determined that the pathogen susceptibility difference between the laboratory wild-type strain N2 and the wild isolate CB4856 is caused by a polymorphism in the npr-1 gene, which encodes a homolog of the mammalian neuropeptide Y receptor. We show that the mechanism of NPR-1-mediated pathogen resistance is through oxygen-dependent behavioral avoidance rather than direct regulation of innate immunity. For C. elegans, bacteria represent food but also a potential source of infection. Our data underscore the importance of behavioral responses to oxygen levels in finding an optimal balance between these potentially conflicting cues.Microbes, including commensal organisms and pathogens, profoundly influence the immune and metabolic physiology of host organisms (1). We used the nematode Caenorhabditis elegans as an experimental host to dissect the molecular basis of interactions between host species and microorganisms. C. elegans exhibits diverse behaviors in response to bacteria provided as a nutrient source (2-4). Feeding behavior can be modulated by environmental conditions, including oxygen concentration (5). Some bacterial species are pathogenic to C. elegans (6), and C. elegans responds by activating conserved innate immune pathways (7-9) and by avoiding pathogens (10).We found that the standard laboratory strain N2 (isolated in Bristol, England) and strain CB4856 (isolated in Hawaii, U.S.A.) exhibited a marked difference in susceptibility to the human opportunistic pathogen Pseudomonas aeruginosa strain PA14 (Fig. 1A). The mean time to 50% lethality (LT50) for CB4856 was shorter (50±7.8 hours) than that for N2 (90±13 hours). Using a collection of recombinant inbred lines (11), we mapped the pathogen susceptibility trait to a 774-kb region of the X chromosome (LGX) containing npr-1, which encodes a G protein-coupled receptor related to the mammalian neuropeptide Y receptor (Fig. 1B). The 215V npr-1 allele in N2 has increased NPR-1 activity relative to the 215F npr-1 allele in CB4856, and the 215V allele confers behavioral differences that are dominant to those conferred by the 215F allele (12). To test the possibility that npr-1 causes the difference in pathogen susceptibility between the N2 and CB4856 strains, we used npr-1 loss-of-function mutants isolated in the N2 background. Like the CB4856 strain, the npr-1 presumptive null †To whom correspondence should be addressed., leonid@genomics.princeton.edu (L.K.)or dhkim@mit.edu (D.H.K.). * These authors contributed equally to this work. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript alleles ad609 and ky13, along with the reduction-of-function alleles ur89 and n1353, had enhanced susceptibility to killing by PA14 ( Fig. 1C and fig. S1). The enha...

Caenorhabditis elegans NPR-1–mediated behaviors are suppressed in the presence of mucoid bacteria

“…The previously reported characterization of mucoid P. aeruginosa PA14 mucD included the killing of C. elegans N2 (26). We have shown that a marked difference in susceptibility between C. elegans N2 wild type and strains with diminished NPR-1 activity, such as npr-1(lf) mutants and wild strains such as CB4856, results from the effects of NPR-1 on C. elegans behavioral avoidance (17). Because mucoid strains do not elicit NPR-1-mediated behavior, we anticipated that N2 and CB4856 strains should exhibit the same susceptibility to killing by a lawn of mucoid P. aeruginosa.…”

“…In contrast, npr-1(lf) mutants and strains carrying the 215F allele of npr-1 do not leave the lawn of P. aeruginosa because of an overriding hyperoxia avoidance (Fig. S1) (17). This NPR-1-dependent behavioral difference in the presence of pathogenic bacteria underlies the difference in susceptibility between N2 and npr-1 mutants (17).…”

“…These observations suggest that the integration of oxygen sensing and bacteria sensing may aid C. elegans in striking a balance between the need for food and the risk of infection (17). Recent studies suggest that the 215V allele of npr-1 likely emerged through a mutation during the laboratory domestication of the Bristol N2 strain (20,21).…”

“…The NPR-1-dependent influence of bacteria on the aerotaxis behavior of C. elegans N2 facilitates avoidance of pathogenic bacteria (17). In the presence of a lawn of pathogenic Pseudomonas aeruginosa PA14, C. elegans N2 exhibits aversive learning behavior that results in animals leaving the lawn (7,11,18,19).…”

Genetic mapping of variation in dauer larvae development in growing populations of Caenorhabditis elegans

“…This locus is of interest as the lab-derived (McGrath et al, 2009), N2 allele of npr-1 has been found to be important in a number of phenotypes (for example, Doroszuk et al, 2009;McGrath et al, 2009;Reddy et al, 2009;Gaertner et al, 2012). This locus was therefore investigated using the isolate DA650, which contains the g320 npr-1 allele from RC301 backcrossed 10 times into an N2 background (Gloria-Soria and Azevedo, 2008), and isolates DA609 and DA508, which contain different npr-1 loss-offunction alleles (de Bono and Bargmann, 1998).…”