Endogenous siRNAs are required for a learned pathogen avoidance behavior in Caenorhabditis elegans

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The nematode C. elegansis a premier model for the study of learning and exhibits a variety behavioral plasticity phenotypes. For example, worms that are infected by the pathogen Pseudomonas aeruginosa (PA14) early in life associate pathogen odors with infection, and learn to avoid the pathogen as adults when given a choice between PA14 and a nonpathogenic E. coli food source (OP50). This associative learning requires an increase in serotonin in the ADF chemosensory neurons, but the remaining molecular circuitry that allows learned pathogen avoidance is unknown. Based on the known role of small noncoding RNA molecules in regulating other behavioral responses in the worm, we have used a genetic approach to determine the involvement of endogenous small RNAs in pathogen avoidance behavior. Mutants that are defective in small RNA pathways were raised in an environment with both pathogenic PA14 and nonpathogenic OP50, and their pathogen avoidance behavior as adults was compared to that of wild‐type worms using a standard choice assay. For each genotype, we have completed at least three replicate choice assays of at least 71 worms each for the naïve and trained conditions. Briefly, the choice assay involves placing either trained or naïve worms in the center of a standard Nematode Growth Medium plate, and worms are allowed to choose between PA14 and OP50 food sources spotted on opposite sides of the plate. The number of worms found in the PA14 and OP50 spots is counted after an hour, and the proportion of worms on PA14 is compared between naïve and trained worms using a one‐tailed t‐test. As previously published, trained wild‐type worms (raised in the presence of pathogen) show increased avoidance of PA14 when compared with naïve worms (p=0.04369). Interestingly, mut‐7(pk204)animals, which lack a large class of small RNAs known as the endogenous siRNAs, show no change in pathogen avoidance when raised under naïve or trained conditions (p =0.86258), suggesting that endogenous siRNAs are required for learned pathogen avoidance. mut‐7is an upstream component of several functionally and genetically distinct endogenous siRNA pathways, including the 26G‐RNA and 21U RNA‐triggered pathways, the CSR‐1 pathway, and the WAGO pathway. To determine which of these pathways is specifically required for learned pathogen avoidance behavior, we are currently testing learning in mutants that disrupt individual pathways and will report on these results.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.