Molecular Pathogens, 2025, Vol.16, No.5, 207-216 http://microbescipublisher.com/index.php/mp 209 receptors like bacteria and fungi, studies have found that plants still have some PRRs involved in antiviral defense. Typical signaling events after PTI triggering include: reactive oxygen species (ROS) burst, calcium ion influx, initiation of MAP kinase cascade, rapid transcription of defense-related genes, etc. (Figure 1) (Necira et al., 2024). Although these responses cannot completely prevent virus replication and spread like specific resistance, they can slow down virus invasion in plants at an early stage. For example, the initial stage of PVY infection in potatoes will induce the production of peroxidase and lignin deposition in local tissues, forming physical and chemical barriers to slow down the movement of the virus (Samarskaya et al., 2022). Figure 1 Systemic response of Nicotiana benthamiana plants to inoculation with mixtures of PVX-GFP combined with dsPVY, dsGFP or control (Ctr) extract. (A) Representative plants were photographed under UV light at 7 days post-inoculation (dpi). (B) Northern blot analysis of total RNA extracted from upper leaf tissues at 7 dpi. (C) qRT-PCR was used to analyze the accumulation of PVX-GFP genomic RNA levels in the systemic leaves at 7 dpi (Adopted from Necira et al., 2024) 3.2 Specific resistance response (ETI) mechanism When a virus successfully breaks through the plant's primary defense line and enters the cell interior, the plant initiates a stronger specific resistance, known as effector-triggered immunity (ETI). ETI is usually triggered by direct or indirect recognition of pathogenic effector proteins by plant disease resistance gene products. For viruses, most resistance genes belong to the NLR immune receptor family. These NLR proteins are distributed in the cytoplasm or nucleus and contain a conserved nucleotide-binding domain and a C-terminal LRR domain, which can act as a "molecular switch": they are usually bound to ADP to maintain a dormant state. Once they recognize virus-specific effectors, they switch to ATP and undergo conformational changes, and assemble into oligomeric complexes to initiate downstream immune responses (Martin et al., 2020).
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