The cap-independent translational regulation of NbRabGAP1 in Nicotiana benthamiana during BaMV infection

Abstract While cap-dependent translation is the eukaryotic norm, alternative pathways enable selective protein synthesis during stress. We describe a cap-independent mechanism regulating NbRabGAP1, a host factor essential for bamboo mosaic virus (BaMV) movement in Nicotiana benthamiana. The 5′ untranslated region (5′ UTR, 553-nt) of NbRabGAP1 contains three upstream open reading frames (uORFs) that typically hinder ribosome scanning. Using bicistronic reporter assays, we identified a functional internal ribosome entry site (IRES) within nucleotides 61-150. This IRES features a predicted stable Y-shaped RNA structure and a purine-rich R-motif. We demonstrate that NbPAB8, a poly(A)-binding protein, specifically binds this R-motif to enhance IRES-mediated translation over 2.5-fold. During BaMV infection, NbPAB8 expression is transiently upregulated, coinciding with maintained NbRabGAP1 levels despite potential repression of global cap-dependent translation. This represents a regulatory switch where viral infection triggers a PAB8-dependent IRES mechanism to sustain the vesicle trafficking machinery required for viral movement. Our findings reveal how viral stress rewires host translational control through specific RNA-protein interactions, ensuring the synthesis of critical host factors via IRES-mediated pathways. Highlight During bamboo mosaic virus infection, NbPAB8 binds a purine-rich IRES in the NbRabGAP1 5′ UTR, bypassing global translation repression to maintain vesicle trafficking essential for viral movement. Competing Interest Statement The authors have declared no competing interest. Footnotes Jia-Ling Shih: mermaid8104041004{at}gmail.com, I-Hsuan Chen: eva611{at}gmail.com, Ying-Ping Huang: ypingannie{at}gmail.com, Ying-Wen Huang: ywhuang0101{at}dragon.nchu.edu.tw