Molecular Pathogens, 2025, Vol.16, No.6, 257-265 http://microbescipublisher.com/index.php/mp 260 defense genes and induce systemic resistance (Yan et al., 2022; Li et al., 2025). Co-expression analysis further identified many regulatory nodes and key modules, providing valuable targets for resistance breeding (Hajibarat et al., 2024). However, the expression of the R gene is not necessarily the stronger the better. When there is no illness, it should be kept "low-key", otherwise the adaptation cost will be too high and it will instead hinder growth. 4 Molecular Mechanisms of Resistance Gene–Mediated Virus Defense 4.1 ETI (Effector-triggered immunity) mechanisms based on gene recognition Not every time a virus invades, plants can immediately launch a full-scale counterattack. Usually, it is not until R proteins (such as NLR) recognize the "suspicious molecules" of a specific virus - that is, effector proteins - that cells will initiate the ETI immune process. The Ny-1 gene in potatoes operates in this way, specifically responding to PVY infection. Its reaction mode is a bit "ruthless": it directly triggers an allergic reaction (HR), causing the cells around the infected area to die voluntarily, thereby confining the virus within a local area. This reaction is not random. Salicylic acid (SA) plays a key role in timing and regional control. Molecules like NADPH oxidase RBOHD are activated at the edge of the lesion, releasing reactive oxygen species (ROS), which in turn guide SA to accumulate at the appropriate location. If there is a problem with the signaling link of this RBOHD-SA, the defense line will be easily broken through and the virus will spread (Gouveia et al., 2017). 4.2 RNA silencing and its interaction with viral suppressors In addition to protein recognition, potatoes have another "silencing mechanism" to deal with viruses - RNA silencing. This process relies on Dicer-like enzymes to cut the double-stranded RNA produced by the virus into siRNA fragments, and then the Argonaute protein is responsible for using these SiRnas as "navigation" to precisely remove the virus's RNA. However, viruses are not easy to deal with. They have evolved a class of inhibitors called VSR to fight back, such as the P25 protein of PVX, which specifically interferes with the normal operation of the AGO protein and can even promote its degradation. However, the host also has countermeasures. For instance, type I protease inhibitors can target these VSRS, thereby "unblocking" RNA silencing channels and restoring the antiviral mechanism to normal (Shen et al., 2025). This is a back-and-forth contest. Who gains the upper hand largely determines the outcome of this infection (Lopez-Gomollon and Baulcombe, 2022). 4.3 Crosstalk between resistance genes and hormone signaling (SA/JA/ET) After viral infection, the resistance response does not rely solely on a single pathway. The signaling pathways of salicylic acid (SA), jasmonic acid (JA), and ethylene (ET), these three hormones, often work together and cooperate with each other at different stages and sites. Sometimes, this kind of coordination relies on feedback loops like RBOHD-SA. For example, the participation of SA can be seen in the local defense strategy mentioned earlier (Yu, 2025). The problem is that viruses also know how to target from the hormonal level. For instance, some inhibitory factors can directly interfere with the recognition or signal transduction of SA, thereby weakening resistance internally. The pathway on the JA side is more inclined to enhance RNA silencing, which can increase the expression of key factors such as AGO protein (Yang et al., 2020). Hormones are not completely harmonious with each other either. Sometimes, there is even a phenomenon of "competing for resources". So, when dealing with viruses, plants, on the one hand, have to rely on the combined response of these pathways, but on the other hand, they also need to prevent pathogens from exploiting the loopholes in them. 5 Functional Validation and Genetic Tools for Resistance Genes 5.1 Cloning of resistance genes and development of molecular markers To figure out whether a resistance gene is useful or not, it is necessary to first identify and clone it. Genes like Ryadg, Rysto and Rychc were gradually identified through linkage analysis, and then precisely tracked with molecular markers such as RFLP, SNP or KASP (Caruana et al., 2021; Asano and Endelman, 2023). Nowadays, molecular marker-assisted selection (MAS) has become a "standard configuration" for many potato breeding projects. It can quickly introduce resistance genes from wild varieties into commercial varieties, saving a lot of time and manpower (Saidi and Hajibarat, 2021). Some laboratories have also developed multiplex PCR methods that can detect multiple genes at once, which are quite practical tools for breeders (Elison et al., 2020). However,
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