ABSTRACT
Tomato (Solanum lycopersicum) is one of the most important crops worldwide and is severely affected by geminiviruses. Tomato leaf curl Taiwan virus (ToLCTWV), belonging to the geminiviruses, was isolated in Taiwan and causes tremendous crop loss. The geminivirus-encoded C2 proteins are crucial for a successful interaction between the virus and host plants. However, the exact functions of the viral C2 protein of ToLCTWV have not been investigated. We analyzed the molecular function(s) of the C2 protein by transient or stable expression in tomato cv. Micro-Tom and Nicotiana benthamiana. Severe stunting of tomato and N. benthamiana plants infected with ToLCTWV was observed. Expression of ToLCTWV C2-green fluorescent protein (GFP) fusion protein was predominately located in the nucleus and contributed to activation of a coat protein promoter. Notably, the C2-GFP fluorescence was distributed in nuclear aggregates. Tomato and N. benthamiana plants inoculated with potato virus X (PVX)-C2 displayed chlorotic lesions and stunted growth. PVX-C2 elicited hypersensitive responses accompanied by production of reactive oxygen species in N. benthamiana plants, which suggests that the viral C2 was a potential recognition target to induce host-defense responses. In tomato and N. benthamiana, ToLCTWV C2 was found to interfere with expression of genes encoding chromomethylases. N. benthamiana plants with suppressed NbCMT3-2 expression were more susceptible to ToLCTWV infection. Transgenic N. benthamiana plants expressing the C2 protein showed decreased expression of the NbCMT3-2 gene and pNbCMT3-2::GUS (ß-glucuronidase) promoter activity. C2 protein is an important pathogenicity determinant of ToLCTWV and interferes with host components involved in DNA methylation.
