The nuclear shuttle protein determines host-range specificity of Tomato leaf curl New Delhi virus strains in tomato and cucurbit plants

Background The bipartite begomovirus Tomato leaf curl New Delhi virus causes major losses in solanaceous and cucurbit crops. Viral strains differ in host range, with some infecting both tomato and cucurbits, whereas others are restricted to cucurbits. The viral determinants responsible for these differences remain unclear. Results To identify viral factors controlling host specificity, we compared agroinfectious clones of the cucurbit-restricted CB strain and the Jessore (Jes) strain, which infects both tomato and cucurbits. CB DNA-A infected tomato only when paired with Jes DNA-B, demonstrating that DNA-B determines host specificity. Transient expression of the Jes DNA-B–encoded Nuclear Shuttle Protein (NSP) enabled CB DNA-A + B to systemically infect tomato, identifying NSP as the key host-range determinant. CB caused stronger symptoms in cucumber, and CB DNA-A enhanced virulence in tomato when combined with Jes DNA-B, indicating DNA-A as a determinant of virulence. Co-inoculation of CB DNA-A + B with two monopartite geminiviruses showed that Tomato yellow leaf curl Sardinia virus (TYLCSV) facilitated proliferation and systemic movement of the CB DNA-B component in tomato, whereas CB DNA-A was not detected. Conclusions Our study identifies the NSP as the key viral factor determining host specificity in the two tested ToLCNDV strains, highlights the contribution of DNA-A to virulence, and demonstrates that co-infection with other viruses can influence host adaptation. These insights are valuable for improved prediction of viral epidemics, disease management strategies, and breeding of resistant cultivars.