Effect of RNA interference targeting chemosensory genes on chemotactic host-seeking in Meloidogyne graminicola

Pre-parasitic second-stage juveniles (pre-J2s) of Meloidogyne graminicola are non-feeding in soil, and their migration, localization and successful invasion of host roots are essential for survival. Chemotaxis is thought to play a central role in host localization, but the mechanisms of chemotaxis are poorly understood. In this study, we cloned and evaluated the molecular characteristics and functions of four chemosensory genes, including Mg-odr-3 , Mg-odr-1 , Mg-tax-4 , and Mg-osm-9 . Quantitative real-time PCR (qRT‒PCR) analysis revealed that Mg-odr-3 and Mg-osm-9 tended to be expressed in pre-J2s and parasitic J2s (par-J2s), while Mg-odr-1 and Mg-tax-4 were expressed in par-J2s, consistent with their functions during the host-seeking period and establishment of suitable feeding sites in root tips. Root signals from eight plant root extracts, namely, rice, barnyard grass ( Echinochloa crus-galli ), wheat, soybean, pepper, tomato, eggplant, and marigold, were repulsive to J2s of M. graminicola . Moreover, RNAi silencing of Mg-odr-3 , Mg-odr-1 , Mg-tax-4 , and Mg-osm-9 in J2s attenuated their repulsion to the rice root extract. Furthermore, we found that the response of J2s to root exudates was concentration-dependent, with high concentrations of root exudates repelling J2s. Silenced J2s also showed reduced repulsion in response to high concentrations of rice root exudates. Conversely, M. graminicola J2s were attracted to the root tips of the eight plants, while RNAi-J2s showed defective attraction to root tips. In conclusion, our results showed that chemosensory genes are crucial for the chemotactic host-seeking behaviour of M. graminicola .