Molecular Pathogens, 2025, Vol.16, No.5, 207-216 http://microbescipublisher.com/index.php/mp 213 Small RNA also affects immune gene expression by regulating mRNA stability. In addition to using specific resistance genes, disease-resistant breeding should also pay attention to regulatory factors, such as removing negative regulatory TFs through gene editing to improve immunity, but growth and resistance need to be weighed. 6.3 Epigenetic regulation mechanism Increasing evidence shows that plant immune responses to pathogens are also regulated at the epigenetic level, including DNA methylation, histone modifications, and chromatin remodeling. These epigenetic mechanisms can dynamically regulate the expression status of disease resistance-related genes (Ramirez-Prado et al., 2021). In antiviral aspects, a significant epigenetic phenomenon is the silencing of viral DNA/genome by RNA-mediated DNA methylation (RdDM). For DNA viruses such as geminivirus (TYLCV), plants can methylate their genomes to inhibit their transcription, which has been observed during tomato resistance to TYLCV. Even for RNA viruses, siRNA produced by the RdDM pathway can cause methylation changes near host resistance genes, indirectly affecting resistance expression. A study of Arabidopsis resistance to TCV (turnip mosaic virus) found that plants with mutated DNA methyltransferase were more susceptible to the virus, suggesting that DNA methylation contributes to overall resistance. In terms of histone modifications, histone acetylation is usually associated with high gene expression, while histone deacetylation and methylation such as H3K27me3 are associated with gene silencing. In antiviral responses, histone marks in the promoter regions of some defense genes are altered (Ramirez-Prado et al., 2021). 7 Influence of Environmental and Genetic Factors on Viral Resistance 7.1 Adjustment of environmental factors The external environment, especially temperature, light, water and fertilizer conditions, etc., has a significant regulatory effect on plant antiviral immunity. The most prominent example is the temperature effect. The disease resistance of many plants is weakened under high temperatures, making it easier for viruses to infect their hosts under high temperature conditions. The Tswgene of pepper also shows low efficiency in resisting TSWV at high temperatures of 30 °C, and the plants may develop systemic symptoms rather than local restrictions. There are various mechanisms by which high temperature affects resistance: On the one hand, high temperature can inhibit ETI signals. Studies have found that the synthesis and signaling of SA in Arabidopsis are inhibited at 28 °C~30 °C, causing plants that were originally resistant to TMV to become susceptible. On the other hand, high temperature may directly affect the structural stability of NLR proteins, making them difficult to activate. Some rust-resistant NLRs in wheat are more effective at high temperatures, while the opposite is true for tobacco N genes. This is because different NLRs have different temperature sensitivities. The wheat stripe rust resistance gene Xa7 ismore resistant under high temperature conditions, suggesting that some resistance mechanisms are strengthened under high temperatures (Tatineni et al., 2016). Photoperiod and light intensity are also factors. Generally, sufficient light is beneficial for plants to accumulate resistance substances and trigger defense responses. For example, ultraviolet light can induce certain antiviral secondary metabolites (Ogneva et al., 2021; Xiong et al., 2021). Under low light conditions, there is insufficient carbohydrates in the plant, the immune response is also weakened, and the virus is more likely to expand. Water and nutrients also affect resistance indirectly by affecting plant vigor and metabolism. Drought stress is often accompanied by an increase in ABA, which may weaken the SA pathway and increase virus susceptibility. 7.2 Influence of host genetic background In addition to the environment, the plant's own genetic background, that is, the composition of other genes in the genome besides the main resistance genes, will also significantly affect the antiviral phenotype. Even if different varieties or strains carry the same primary resistance gene, their resistance expression intensity may be different, which is attributed to differences in secondary genes or regulatory elements in the background. Although all potato varieties carry the Ry gene, some varieties still show mild symptoms or low-level infection under high PVY conditions in the field. This may be because their background lacks certain cofactors that enhance resistance. Further analysis revealed that this was related to combinations of other loci in these families, and that some backgrounds may harbor potential suppressors such that resistance genes are underexpressed. Therefore, methods
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