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.

禾本科根结线虫的寄生前第二阶段幼虫（pre-J2s）在土壤中不取食，它们的迁移、定位和成功侵入宿主根部对于生存至关重要。趋化性被认为在宿主定位中发挥着核心作用，但人们对趋化性的机制知之甚少。在本研究中，我们克隆并评估了四个化学感应基因的分子特征和功能，包括Mg-odr-3、Mg-odr-1、Mg-tax-4和Mg-osm-9。实时定量 PCR (qRT-PCR) 分析显示，Mg-odr-3和Mg-osm-9倾向于在前 J2 和寄生 J2 (par-J2) 中表达，而Mg-odr-1和Mg- tax-4在par-J2中表达，这与它们在寻找宿主期间的功能以及在根尖建立合适的取食位点一致。来自八种植物根提取物（即水稻、稗草（稗草）、小麦、大豆、胡椒、番茄、茄子和万寿菊）的根信号对M. graminicola的 J2s 是排斥的。此外， J2s 中Mg-odr-3、Mg-odr-1、Mg-tax-4和Mg-osm-9的 RNAi 沉默减弱了它们对稻根提取物的排斥。此外，我们发现J2s对根系分泌物的反应是浓度依赖性的，高浓度的根系分泌物会排斥J2s。沉默的 J2 还表现出对高浓度稻根分泌物的排斥力降低。相反，M. graminicola J2s 被吸引到八株植物的根尖，而 RNAi-J2s 对根尖的吸引力有缺陷。总之，我们的结果表明化学感应基因对于M. graminicola的趋化宿主寻找行为至关重要。