Study maps host hopping in begomoviruses

Begomovirus complex viruses expand or lose hosts through small alterations in the genome. A study identified a 63-nucleotide fragment in the C-terminal region of the TrAP/REn proteins as responsible for the ability of Tomato leaf curl New Delhi virus (ToLCNDV) to infect tomatoes.

Researchers analyzed three variants: one that infects only cucumber (ToLCNDV-C), another that infects tomato and cucumber (ToLCNDV-T&C), and a third restricted to tomato (ToLCKV-T). Agroinoculation assays showed that the exchange of the TrAP/REn region between the variants altered the host range.

The ToLCNDV-C variant, originally unable to infect tomatoes, began infecting the crop after receiving the TrAP/REn region from the ToLCNDV-T&C variant. The infection rate reached 6 positive plants out of 17 inoculated. The reverse switch reduced infection efficiency in tomatoes and cucumbers.

The analysis detailed that the determinant for host gain is concentrated in a specific 63-nucleotide fragment at the C-terminal of TrAP/REn. Isolated point mutations prevented infection in tomatoes. Only the replacement of the complete fragment restored the ability to infect.

Protein interaction

The authors also evaluated the interaction of these viral proteins with plant factors using a yeast two-hybrid assay. Results indicated differences in the interaction with host proteins such as PCNA and AGO1. The tomato-adapted variant showed a distinct interaction pattern compared to the cucumber-restricted variant.

Further experiments indicated that the TrAP/REn protein, in conjunction with the B-DNA genomic component, promotes infection in non-habitual hosts. The ToLCKV-T variant, typical of tomatoes, infected cucumbers to a limited extent when it received TrAP/REn from ToLCNDV-T&C and the corresponding B-DNA. However, viral accumulation remained low and no visible symptoms were observed.

Host jump

The results indicate that host jumping does not depend on a single isolated gene. Adaptation involves complex interactions between viral proteins and plant cellular factors. The study reinforces that small recombinations or mutations can alter the range of infection and favor the emergence of new variants with an impact on crops such as tomatoes and cucurbits.

The study used isolates collected in India in 2022 and combined infectious cloning, inoculation via AgrobacteriumTransmission via whitefly and quantification by real-time PCR were performed. The clone sequences were deposited in GenBank.

Further information can be found at doi.org/10.1111/mpp.70202