The C2 protein of tomato leaf curl Taiwan virus is a pathogenicity determinant that interferes with expression of host genes encoding chromomethylases

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 (β-glucuronidase) promoter activity. C2 protein is an important pathogenicity determinant of ToLCTWV and interferes with host components involved in DNA methylation.

Combinatorial interactions between viral proteins expand the potential functional landscape of the tomato yellow leaf curl virus proteome

“…Although full functionality of C2-GFP or GFP-C2 during the viral infection has not been demonstrated, C-terminal GFP fusions have been used in functional studies with other geminiviral C2 proteins (e.g. [ 42 – 45 ]). Local infection assays with two TYLCV mutant viruses unable to express CP, TYLCV-CPmut1 and TYLCV-CPmut2, in which early stop codons are introduced and alternative transcriptional initiation sites have been removed (for details, see Materials and Methods ), demonstrate that the presence of CP is not only sufficient, but also required for the re-localization of C2-GFP into the nucleolus in infected cells ( Fig 3D ).…”

A virus-encoded protein suppresses methylation of the viral genome through its interaction with AGO4 in the Cajal body

“…Notably, the geminiviral genome forms minichromosomes and is subjected to epigenetic modifications, including cytosine DNA methylation and histone modifications ( Ceniceros-Ojeda et al, 2016 ; Deuschle et al, 2016 ; Jackel et al, 2016 ; Kushwaha et al, 2017 ; Raja et al, 2008 ; Wang et al, 2018 ). The findings that methylation of viral DNA negatively impacts viral replication ( Brough et al, 1992 ; Ermak et al, 1993 ), that different geminivirus-encoded proteins have evolved to suppress DNA methylation ( Buchmann et al, 2009 ; Ismayil et al, 2018 ; Raja et al, 2008 ; Rodríguez-Negrete et al, 2013 ; Tu et al, 2017 ; Wang et al, 2018 ; Yang et al, 2013 ; Yang et al, 2011 ; Zhang et al, 2011 ), and that methylation of the viral genome correlates with host resistance or recovery ( Butterbach et al, 2014 ; Ceniceros-Ojeda et al, 2016 ; Raja et al, 2008 ; Torchetti et al, 2016 ; Yadav and Chattopadhyay, 2011 ) strongly support the idea that the plant-mediated methylation of the viral DNA acts as an antiviral defence mechanism, underscoring DNA methylation as an active battlefield in the interaction between plants and geminiviruses.…”

Molecular Characterization and Genomic Function of Grapevine Geminivirus A

“… Li et al (2018) found that S-acylation of C4 was essential for beet severe curly top virus symptom determination. The C2 protein of tomato leaf curl Taiwan virus was shown to be an important pathogenicity determinant, which interferes with host DNA methylation ( Tu et al, 2017 ). To counteract RNA silencing defenses in plant, many geminivirus V2 proteins have been shown to serve as RNA silencing suppressors ( Yang et al, 2018 ).…”