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The molecular mechanism by which plants defend against plant root-knot nematodes (RKNs) is largely unknown. The plant receptor kinase FERONIA and its peptide ligands, rapid alkalinization factors (RALFs), regulate plant immune responses and cell expansion, which are two important factors for successful RKN parasitism. In this study, we found that mutation of FERONIA in Arabidopsis thaliana resulted in plants showing low susceptibility to the RKN Meloidogyne incognita. To identify the underlying mechanisms associated with this phenomenon, we identified 18 novel RALF-likes from multiple species of RKNs and showed that two RALF-likes (i.e., MiRALF1 and MiRALF3) from M. incognita were expressed in the esophageal gland with high expression during the parasitic stages of nematode development. These nematode RALF-likes also possess the typical activities of plant RALFs and can directly bind to the extracellular domain of FERONIA to modulate specific steps of nematode parasitism-related immune responses and cell expansion. Genetically, both MiRALF1/3 and FERONIA are required for RKN parasitism in Arabidopsis and rice. Collectively, our study suggests that nematode-encoded RALFs facilitate parasitism via plant-encoded FERONIA and provides a novel paradigm for studying host–pathogen interactions. Eighteen novel RALF-likes were identified from multiple species of root-knot nematodes (RKNs). Both nematode RALF-likes and the plant receptor kinase FERONIA were found to be required for RKN parasitism in Arabidopsis and rice. Nematode RALF-likes are expressed in the esophageal gland and serve as ligands of FERONIA to modulate the immune response and facilitate parasitism, providing a novel paradigm for studying host–pathogen interactions. [ABSTRACT FROM AUTHOR]

The cereal cyst nematodes Heterodera avenae and Heterodera filipjevi are recognized as cyst nematodes that infect cereal crops and cause severe economic losses worldwide. Rapid, visual detection of cyst nematodes is essential for more effective control of this pest. In this study, recombinase polymerase amplification (RPA) combined with clustered regularly interspaced short palindromic repeats (CRISPR)/Cas12a (formerly known as cpf1) was developed for the rapid detection of H. avenae and H. filipjevi from infested field samples. The RPA reaction was performed at a wide range of temperatures from 35 to 42°C within 15 min. There was no cross-reactivity between H. avenae , H. filipjevi , and the common closely related plant-parasitic nematodes, indicating the high specificity of this assay. The detection limit of RPA-Cas12a was as low as 10 -4 single second-stage juvenile (J2), 10 -5 single cyst, and 0.001 ng of genomic DNA, which is 10 times greater than that of RPA-lateral flow dipstick (LFD) detection. The RPA-Cas12a assay was able to detect 10 -1 single J2 of H. avenae and H. filipjevi in 10 g of soil. In addition, the RPA-LFD assay and RPA-Cas12a assays could both quickly detect H. avenae and H. filipjevi from naturally infested soil, and the entire detection process could be completed within 1 h. These results indicated that the RPA-Cas12a assay developed herein is a simple, rapid, specific, sensitive, and visual method that can be easily adapted for the quick detection of H. avenae and H. filipjevi in infested fields., Competing Interests: The author(s) declare no conflict of interest.