CRISPR-Cas9 genome editing inSteinernemaentomopathogenic nematodes

Abstract

Molecular tool development in traditionally non-tractable animals opens new avenues to study gene functions in the relevant ecological context. Entomopathogenic nematodes (EPN)Steinernemaand their symbiotic bacteria ofXenorhabdusspp are a valuable experimental system in the laboratory and are applicable in the field to promote agricultural productivity. The infective juvenile (IJ) stage of the nematode packages mutualistic symbiotic bacteria in the intestinal pocket and invades insects that are agricultural pests. The lack of consistent and heritable genetics tools in EPN targeted mutagenesis severely restricted the study of molecular mechanisms underlying both parasitic and mutualistic interactions. Here, I report a protocol for CRISPR-Cas9 based genome-editing that is successful in two EPN species,S. carpocapsaeandS. hermaphroditum. I adapted a gonadal microinjection technique inS. carpocapsae, which created on-target modifications of a homologueSc-dpy-10(cuticular collagen) by homology-directed repair. A similar delivery approach was used to introduce various alleles inS. hermaphroditumincludingSh-dpy-10andSh-unc-22(a muscle gene), resulting in visible and heritable phenotypes of dumpy and twitching, respectively. Using conditionally dominant alleles ofSh-unc-22as a co-CRISPR marker, I successfully modified a second locus encoding Sh-Daf-22 (a homologue of human sterol carrier protein SCPx), predicted to function as a core enzyme in the biosynthesis of nematode pheromone that is required for IJ development. As a proof of concept,Sh-daf-22null mutant showed IJ developmental defectsin vivo(in insecta). This research demonstrates thatSteinernemaspp are highly tractable for targeted mutagenesis and has great potential in the study of gene functions under controlled laboratory conditions within the relevant context of its ecological niche.

Analyses ofXenorhabdus griffiniaegenomes reveal two distinct sub-species that display intra-species variation due to prophages

“…As part of their symbiotic and entomopathogenic lifecycle, all Xenorhabdus must colonize and be transported by a nematode host, suppress insect immunity, establish a community within and consume the cadaver, and support reproduction of the nematode to ensure future transport [10]. Many will also compete or cooperate with other resident or transient hermaphroditum, currently the most genetically tractable steinernematid [24,120,25].…”