A viral protein diverts the endocytic VPS9a-Rab5 pathway to promote virus infection in plants

Endocytosis is central to cellular trafficking and signaling across eukaryotes, yet whether and how plant viruses actively reprogram this pathway remains unclear. Here, we show that the geminiviral betasatellite-encoded βC1 reprograms the host VPS9a-Rab5 endocytic module to promote viral infection. βC1 associates with the Rab5 GTPases ARA6 and ARA7 as well as their guanine nucleotide exchange factor VPS9a, stabilizing the VPS9a-Rab5 complex and enhancing nucleotide exchange. This catalytic potentiation sustains Rab5 activation and drives endosome proliferation, which, in turn, stabilizes βC1 to support efficient viral replication. Genetic disruption of Rab5 or VPS9a compromises endocytosis, reduces βC1 accumulation, and restricts infection by multiple geminiviruses. Together, these findings define the VPS9a-Rab5 module as a central proviral hub linking host membrane dynamics to effector stability and viral DNA amplification, revealing an unanticipated strategy in which a viral effector amplifies a cellular regulatory catalyst to reprogram a fundamental cellular pathway for virus infection.