Movement of tomato yellow leaf curl geminivirus (TYLCV): involvement of the protein encoded by ORF C4.

Tomato yellow leaf curl virus (TYLCV) is a whitefly-transmitted geminivirus with a monopartite genome. We have investigated the ability of a TYLCV DNA mutant containing a disrupted ORF C4 to infect Nicotiana benthamiana and tomato plants. The mutant retained the capability of autonomous replication in protoplast-derived cells of tomato and was able to infect N. benthamiana plants systemically although DNA levels were reduced and symptom development was attenuated. However, when tomato plants were inoculated, the virus was unable to move systemically unless a second site mutation or a reversion in planta restored the integrity of ORF C4. The infected plants remained asymptomatic or showed very mild symptoms. The results strongly suggest that the ORF C4 encodes a protein involved in virus movement, a novel finding for whitefly-transmitted geminiviruses. The involvement of a C4 protein in symptom determination is discussed.