An Exploration of the Chemical Signals and Neural Pathways Driving the Attraction of Meloidogyne incognita and Caenorhabditis elegans to Favorable Bacteria

Root-knot nematodes (RKNs: Meloidogyne sp.) are among the most devastating plant pathogens. Their chemotaxis-driven host-seeking activity is critical for RKNs&rsquo: infection success. Using attractants derived from bacterial volatile organic compounds (BVOCs) to interrupt the host-seeking is promising for the management of RKNs. However, little is known about how BVOCs contribute to the attractiveness of RKNs. Here, we provide a first evaluation of the attractive potential of taxonomically diverse bacteria from different environments and assemble a previously unidentified repertoire of bi-attractive bacteria to M. incognita and Caenorhabditis elegans. We found that the attraction strength of the preferred bacteria to the nematodes was positively correlated with the abundance and amounts of ketones in the BVOC profiles. This suggested that ketones are key for BVOC-mediated attraction. In our behavioral experiments using ketone compounds, we provide evidence that the attractiveness of the nematodes to the preferred bacteria arises specifically from ketone odor cues, a phenomenon not reported previously. This study demonstrates for the first time that a specific ketone blend naturally occurring within the BVOC profiles from the preferred bacteria serves as a key odorant regulating their enhanced attraction toward the nematodes. We used genetic methods to show that the AWCON neurons are important for worms to sense the ketones derived from the preferred bacteria and drive attraction to these bacteria. Our study may serve as a platform for a better understanding of the chemical and neuronal basis for ketone-mediated bacteria&ndash:nematode interactions and the development of new BVOCs as attractants in RKNs&rsquo: management.