Molecular Pathogens, 2025, Vol.16, No.6, 257-265 http://microbescipublisher.com/index.php/mp 259 2.3 Molecular and physiological responses of potato to viral stress The potato is not a plant that "stands and gets beaten". In the face of viruses, it has several sets of defense mechanisms. The first step is the intervention of the R gene. Like the Ny gene, once it recognizes the virus, it will trigger local cell death, which is known as an allergic reaction (HR). The Ry gene is even more potent, directly blocking the replication and spread of the virus without even showing any symptoms. Secondly, there is a major adjustment in gene expression. Once infected, pathogen-associated proteins (PR), various stress regulatory factors, and genes related to the salicylic acid signaling pathway will all be "awakened". Meanwhile, the cell walls of plants will also be "reinforced" - synthesizing more glycoproteins and regulating the activity of cellulase to prevent the further spread of viruses (Otulak-Koziel et al., 2018). Furthermore, the antioxidant system also comes into play. For instance, enzymes like SOD, POD, and CAT, which act as "scavengers", rapidly enhance their activity during an infection, thereby alleviating oxidative stress. In addition, the metabolism of carbohydrates, amino acids and fatty acids in plants will also change. Behind these changes, there are actually genetic differences in resistance among different varieties. Some reactions are evident in strongly resistant varieties, while others are only temporary regulatory responses. The final outcome can also vary depending on the virus strain and environmental conditions, ranging from completely sensitive to highly resistant. 3 Classification and Characteristics of Potato Resistance Genes 3.1 NBS-LRR type resistance genes and their virus recognition mechanisms These NB-LRR genes, in essence, are a type of receptor that "stands guard" in cells, capable of recognizing specific viral proteins and triggering an immune response. The Rx and Rysto genes in potatoes can be regarded as the "stars" in this regard. The former works against PVX, and the latter has a significant resistance effect against PVY (Kondrak et al., 2019; Torrance et al., 2020; Liu et al., 2021). But how do they identify viruses? Structurally speaking, the NBS section is responsible for energy operations (in combination with ATP/GTP), while the LRR segment is more like a "face recognition expert", determining which pathogens can be identified. Once matched, plants may choose to "cut off one arm of their own", that is, trigger an allergic reaction (HR) to cause local cell death to prevent the spread. There is also a more straightforward approach, which is to directly prevent the virus from replicating (ER) in the body, with almost no symptoms throughout the process. It should be noted that even minor sequence changes in the LRR region can affect the recognition range - this can also be seen from the domain swap experiments. Therefore, the "adaptability" of such genes is actually very strong and they can keep up with the changing rhythm of the virus. 3.2 Distribution of natural resistance resources in ecotypes and cultivars The "origin" of resistance genes is actually mainly concentrated in wild Solanaceous plants. These resources, after breeding, were transferred into cultivated potatoes, such as Rysto from the creeping tomato and Ry(o)phu from the Phureja group, which are located on chromosomes 12 and 9 respectively, and can provide broad-spectrum resistance to PVY (Akai et al., 2023). However, many commercial varieties do not carry these resistance genes at present, which can be seen from the results of molecular marker screening. On the other hand, the latest research also shows that more than 55 different Rysto-like sequences can be found in some wild relatives (Guo and Wang, 2025), and their genetic diversity far exceeds that of cultivated species. This also explains why they are often regarded as an important "gene pool" for resistance breeding (Paluchowska et al., 2024). 3.3 Expression regulation and signal transduction of resistance genes Genes not only need to be "present", but also "utilized". The expression of the R gene is not as simple as a light switch. It is regulated at multiple levels, including the joint participation of transcription, post-transcription and even epigenetic mechanisms. Some promoter regions carry cis-elements related to stress, such as sequences involved in salicylic acid or abscisic acid pathways, which become active when viruses invade (Karimipour et al., 2025). Once the R gene is activated, it will trigger a long series of signaling pathways, including protein kinases, transcription factors, and a cascade reaction involving multiple hormones. These pathways will eventually activate
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