## 3 Discussion
The actin cytoskeleton can facilitate immune signalling, playing roles in the maintenance, surveillance, activation, execution, and possibly de-escalation of plant immunity [6]. The actin-depolymerizing factor proteins are important for actin turnover, and play diverse roles in plant immunity. For example, the localisation of AtADF4 to the nucleus is related to the decreased expression of the PTI defence gene _FRK1_ in _A. thaliana_[61]. Additionally, the _Pst_ PAMP elf26 elicitor can directly increase the abundance of actin filaments in _A. thaliana_ cells, which is inhibited when AtADF4 is knocked out [8; 61; 62]. These results directly prove that the turnover of the actin cytoskeleton can be used as a marker, and that the ADF protein family may play key regulatory roles in the PTI of plants. In addition, it has been reported that both _A. thaliana adf3_ and _adf4_ mutants can inhibit the cell wall-strengthening process of callose deposition [8; 42]. Studies on the function and mechanism of FARs in the inhibition of plant defences have been reported. The potato cyst nematode _Globodenz pallida_ Gp-FAR-1 binds to two lipids (linolenic and linoleic acids), which are precursors of plant defence compounds and the jasmonic acid signalling pathway [29]. Protein Mj-FAR-1 produced by the root-knot nematode _M. javanica_ regulates the expression of lipid-, cell wall-, stress-, and phenylpropanol-related genes during nematode infection in tomatoes, as determined by transcriptome analysis [31]. ProteinBx-FAR-1 secreted by the pine wood nematode _Bursaphelenchus xylophilus_, interacts with the F-box protein of pines to mediate the jasmonic acid pathway and facilitate parasitism of the nematodes in pines [24]. In this study, the process of callose deposition and ROS bursts and the transcriptional activation of two genes _PHII_ and _NHLI0_ of CDPK pathway and _CYP81_ gene of MAPK pathway were both inhibited in _A. thaliana_ overexpressing Ab-FAR-1\({}^{\mathrm{Asp}}\) and _adf3_ mutant after flg22 treatment. These results showed that Ab-FAR-1\({}^{\mathrm{Asp}}\) and AtADP3 were involved in PTI immune signal transduction in the plants. In addition, the _FRK1_ gene was also inhibited in _A. thaliana_ overexpressing Ab-FAR-1\({}^{\mathrm{Asp}}\), but not in the _adf3_ mutant, indicating that Ab-FAR-1 has other complex pathways and functions in plant defence responses. In conclusion, Ab-FAR-1 may not only have the previously reported function of helping nematodes to obtain fatty acids and retinols but may also affect the distribution and turnover of actin filaments in plants by interacting with AtADP3, suppressing the plant PTI, and promoting the parasitism of RWTNs. In addition, the current study also enriches our understanding of the relationship between the actin cytoskeleton and defence responses in plants. The knockout of AtADF2 affects the development of giant cells and inhibits the infection of root-knot nematodes [55]. This study confirmed that the knockout AtADF2 was more susceptible to RWTNs. Whether these results are related to the different parasitic pathways to hosts of sedentary and migratory plant-parasitic nematodes is an interesting question. Therefore, further studies on the function of FAR and the relationship between the actin cytoskeleton, nematode parasitism, and pathogenicity may be of great significance for understanding and controlling different plant-parasitic nematodes.