Molecular requirements for <i>C. elegans</i> transgenerational epigenetic inheritance of pathogen avoidance.

Abstract

Bacteria are <i>Caenorhabditis elegans'</i> food, and worms are naturally attracted to many bacteria, including pathogenic <i>Pseudomonas</i>, preferring PA14 over laboratory <i>Escherichia coli</i> (OP50). Despite this natural attraction to PA14, prior PA14 exposure causes the worms to instead avoid PA14. This behavioral switch can happen quickly - even within the duration of the choice assay. We show that accurate assessment of the animals' true first choice requires the use of a paralytic (azide) to trap the worms at their initial choice, preventing the switch from attraction to avoidance of PA14 within the assay period. We previously discovered that exposure of <i>C. elegans</i> to 25°C plate-grown PA14 at 20°C for 24 hr not only leads to PA14 avoidance, but also to four generations of naïve progeny avoiding PA14, while other PA14 paradigms only cause P0 and/or F1 avoidance. We also showed that the transgenerational (P0-F4) epigenetic avoidance is mediated by P11, a small RNA produced by PA14. P11 is both necessary and sufficient for TEI of learned avoidance. P11 is highly expressed in our standard growth conditions (25°C on surfaces), but not in other conditions, suggesting that the reported failure to observe F2-F4 avoidance is likely due to the absence of P11 expression in PA14 in the experimenters' growth conditions. Additionally, we tested ~35 genes for involvement in TEI of learned pathogen avoidance. The conservation of multiple components of this sRNA TEI mechanism across <i>C. elegans</i> strains and in multiple <i>Pseudomonas</i> species suggests that this TEI behavior is likely to be physiologically important in wild conditions.