Functional Analysis of the Pathogenesis-Related Protein 1 (CaPR1) Gene in the Pepper Response to Chilli veinal mottle virus (ChiVMV) Infection

<i>Chilli veinal mottle virus</i> (ChiVMV) causes severe yield losses in pepper across Asia. It is very urgent to study the host plant resistance to control this viral disease. As a type of defense response gene, pathogenesis-related protein 1 (PR1) is a well-established defense marker against fungal/bacterial pathogens, and its role in virus resistance remains unclear. Here, we cloned <i>CaPR1</i> from the ChiVMV-highly resistant pepper variety 'Perennial'. The 477 bp ORF encodes a 17.65 kDa basic protein containing a conserved CAP-PR1 domain. The subcellular localization of <i>CaPR1</i> revealed that it was located in the plasma membrane, endoplasmic reticulum (ER), and nucleus. RT-qPCR revealed leaf-predominant expression, with earlier and stronger induction in the highly resistant than the highly susceptible variety after ChiVMV inoculation (6.4-fold at 2 days post-inoculation). The overexpression of <i>CaPR1</i> in tobacco significantly increased resistance, reducing disease index by 25% and viral coat protein accumulation. Our findings identified <i>CaPR1</i> as a positive regulator of ChiVMV resistance, providing a molecular target for pepper breeding. In addition, exogenous SA treatment increased the resistance of the highly susceptible cultivar 'Guijiao 12' to ChiVMV, and 0.25 mM had a greater effect.