## 3 Discussion
The current study demonstrated that Ab-FAR-1 interacts with AtADF3 in _A. thaliana_ and that this interaction occurs in the cytoplasm and nucleus of the plant cells. _A. thaliana_ ADF3 expression is the strongest among the ADF family of genes in _A. thaliana_[52]. Gene expression data available in the _Arabidopsis_ eFP Browser ([[http://bbc.botany.utoronto.ca/efp/cgi-bin/efpWeb.cgi](http://bbc.botany.utoronto.ca/efp/cgi-bin/efpWeb.cgi)]([http://bbc.botany.utoronto.ca/efp/cgi-bin/efpWeb.cgi](http://bbc.botany.utoronto.ca/efp/cgi-bin/efpWeb.cgi)), accessed on 20 July 2022) revealed that ADF3 is expressed throughout the development of _A. thaliana_ in most organs, except pollen. Our results showed that the expression level of AtADF3 in leaf veins of _A. thaliana_ infected with RWTN was higher than that of healthy _A. thaliana_, which indicated thatAtADF3 might be involved in the nematode infection process. Phloem, duct, and sieve tubes accumulate in the veins of plants and contain a large amount of water and nutrients that can be used by nematodes during feeding. According to the literature, the actin filament turnover process mediated by the ADF protein family is involved in the interaction between the host and pathogens such as nematodes, bacteria, viruses, and fungi [9]. _A. thaliana adf4_ mutants were more susceptible to the DC3000 population of _Pseudomonas syringae_ pv. Tomato (_Pst_) because actin remodelling and single-filament dynamics in _adf4_ are insensitive to the peptide mimics (elf26) of bacterial elongation factor Tu treatment [7; 8]. The RPS5-AvrPphB-mediated ETI signal transduction pathway in _A. thaliana_ requires phosphorylation and dephosphorylation of AtADF4 to regulate the participation of dynamic rearrangements of the cell actin network [7]. In addition, the _Soybean mosaic virus_-encoded P3 protein can directly interact with soybean ADF2, promoting movement and replication along actin microfilaments of the P3 protein and the spread of the virus [53]. Additionally, _A. thaliana_ AtADF3 mutants are more susceptible to aphids, which may be related to the loss of AtADF3-mediated actin filament depolymerisation [42]. In contrast, AtADF2 knockout inhibits root-knot nematode parasitism [54; 55], and knockout of AtADF4 enhances resistance to powdery mildew fungi [56]. Therefore, different ADF proteins play different roles in plant defences or susceptibility to pathogens. In this study, compared with WT _A. thaliana_, the symptoms were significantly aggravated and the number of nematodes was significantly increased after RWTN infection in the _adf3_ mutant. Thus, Ab-FAR-1 secreted by RWTNs may promote parasitism and pathogenicity of nematodes by interacting with the AtADF3 protein. It has been reported that cytoskeletal rearrangement of actin filaments is necessary for the development of giant cells formed in hosts infected by root-knot nematodes [57]. Knockout of AtADF2 stabilises the actin cytoskeleton, which prevents normal giant cell maturation in root-knot nematodes and leads to a significant reduction in the number of nematode invasions [55]. In general, ADFs bind to both monomeric globular (G-) and filamentous (F-) actin to increase actin dynamics by severing microfilaments and increasing the dissociation rate of actin monomers [58; 59; 60]. In this study, we found that the interaction between AAb-FAR-1\({}^{\text{asp}}\) and rAtADF3 inhibits the function of AtADF3 in depolymerising F-actin. The state, distribution, and turnover of the actin cytoskeleton were altered in _A. thaliana_ overexpressing Ab-FAR-1\({}^{\text{asp}}\). Therefore, RWTNs may affect the function of AtADF3 by secreting Ab-FAR-1, which indirectly affects the actin cytoskeleton and promotes the pathogenic process of RWTNs. Results also indicated that the plant actin cytoskeleton could be used as an important target to prevent nematode infection or as an important structure of plant defences against nematode infection. In recent years, the actin cytoskeleton has been shown to play a key role in plant immune signalling.