The virus in action. 
ToLCV severely affects crop yield in a variety of crops like papaya, chilli and tomato and causes the leaf curl disease. Efficient replication will generate more siRNA and consequent gene-silencing. A virus-based vector, which replicates efficiently, will be a robust gene-silencing vector.
The team designed the compact vector based on the ToLCV genome and a self replicating episome (extra-chromosomal DNA) was released when this construct was injected into the plant leaves through agrobacterium.
To their surprise, the ToLCV episome multiplied and accumulated efficiently in a wide variety of plants including rice, tobacco, tomato and Arabidopsis. In all of these plants, the amount of viral episome reached its peak at 12 days of the injection. In the process of replication, the researchers also noticed that viral episome activated the plant RNAi machinery — its defense system that plays a role in controlling foreign DNA invasion into the plant cell.
The episome was engineered to direct this machinery to silence the host cell gene, namely PCNA, essential for the active replication of growing plant cells. The silencing retarded the growth of the plants. "ToLCV based vector system could be used to silence almost any host gene, in principle, in order to address its function in plants," says lead researcher Sunil Mukherjee.The advantage of this novel episome-based selective gene silencing lies in its economy, ease of handling and transient nature compared to the traditional knockout methods, he says.
