Circular RNAs (circRNAs) play important roles in plant stress responses, yet their dynamic regulation during stress remains unclear. This study elucidates a molecular mechanism whereby the grapevine U2 snRNP core component VvU2A′ enhances salt tolerance through a circRNA-mediated post-transcriptional network. We found that VvU2A′ expression is induced by salt stress and positively regulates salt tolerance in grapevine. CircRNA sequencing revealed 497 VvU2A′-regulated differentially expressed circRNAs, including downregulated VvcircHMA1. Mechanistic investigation revealed that VvcircHMA1 acts as a competitive endogenous RNA by sequestering VvmiR167b, thereby attenuating its cleavage activity on the target mRNA VvARF6. Functional analyses revealed that both VvcircHMA1 and VvARF6 negatively regulate salt tolerance, while VvmiR167b positively regulates it. Collectively, our study reveals a novel mechanism by which the splicing factor VvU2A′ enhances salt stress response through the VvcircHMA1-VvmiR167b-VvARF6 cascade, providing promising molecular targets for breeding salt-resistant grapevines.

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