Histone H3 Interacts and Colocalizes with the Nuclear Shuttle Protein and the Movement Protein of a Geminivirus

Abstract

Geminiviruses are plant-infecting viruses with small circular single-stranded DNA genomes. These viruses utilize nuclear shuttle proteins (NSPs) and movement proteins (MPs) for trafficking of infectious DNA through the nuclear pore complex and plasmodesmata, respectively. Here, a biochemical approach was used to identify host factors interacting with the NSP and MP of the geminivirus Bean dwarf mosaic virus (BDMV). Based on these studies, we identified and characterized a host nucleoprotein, histone H3, which interacts with both the NSP and MP. The specific nature of the interaction of histone H3 with these viral proteins was established by gel overlay and in vitro and in vivo coimmunoprecipitation (co-IP) assays. The NSP and MP interaction domains were mapped to the N-terminal region of histone H3. These experiments also revealed a direct interaction between the BDMV NSP and MP, as well as interactions between histone H3 and the capsid proteins of various geminiviruses. Transient-expression assays revealed the colocalization of histone H3 and NSP in the nucleus and nucleolus and of histone H3 and MP in the cell periphery and plasmodesmata. Finally, using in vivo co-IP assays with a Myc-tagged histone H3, a complex composed of histone H3, NSP, MP, and viral DNA was recovered. Taken together, these findings implicate the host factor histone H3 in the process by which an infectious geminiviral DNA complex forms within the nucleus for export to the cell periphery and cell-to-cell movement through plasmodesmata.Viruses are obligate parasites that utilize host cellular machinery to mediate their replication and infection processes. Plant-infecting viruses encode movement proteins (MPs) that facilitate the cell-to-cell trafficking of their infectious nucleic acids along endogenous pathways, such as plasmodesmata, during the process of systemic infection (11,30,47). Although it is widely recognized that the interactions between virusencoded MPs and host proteins are essential for a viable systemic infection, much remains to be elucidated in terms of the actual pathways involved. Indeed, although a number of host proteins involved in the viral systemic infection process have been identified (47), no consensus pathway has emerged. This likely reflects the diversity of plant viruses and the different cellular pathways utilized.Plant viruses with DNA genomes, such as members of the family Geminiviridae, must utilize cellular components to cross both the nuclear pore and plasmodesmata (PD) for cell-to-cell trafficking of an infectious form of the virus. Geminiviruses possess small circular single-stranded DNA (ssDNA) genomes encapsidated within twinned icosahedral virions, and they replicate in the nucleus via double-stranded DNA (dsDNA) forms (13, 45). To cross nuclear and plasmodesmal boundaries, the bipartite geminiviruses of the genus Begomovirus, such as Bean dwarf mosaic virus (BDMV) (27), encode two proteins from the DNA-B component (35,45,52). The product of the BV1 gene is a nuclear shuttle protein (NSP), whereas t...

The induction of stromule formation by a plant DNA-virus in epidermal leaf tissues suggests a novel intra- and intercellular macromolecular trafficking route

“…The identification of three phosphorylation sites in the AbMV MP, which have an impact on symptom development and/or vDNA accumulation (Kleinow et al, 2009a), indicates a regulation of diverse MP functions by yet unknown host kinases. Currently, three interacting host factors of begomoviral MPs have been identified: a histone H3 (Zhou et al, 2011), a synaptotagmin (SYTA; Lewis and Lazarowitz, 2010), and a chaperone, the heat shock cognate 70 kDa protein cpHSC70-1 (Krenz et al, 2010). Gel overlay assays, and in vitro and in vivo co-immunoprecipitation (Co-IP) experiments showed an interaction of H3 with NSP and MP of BDMV as well as with CPs of different geminiviruses (Zhou et al, 2011).…”

“…Currently, three interacting host factors of begomoviral MPs have been identified: a histone H3 (Zhou et al, 2011), a synaptotagmin (SYTA; Lewis and Lazarowitz, 2010), and a chaperone, the heat shock cognate 70 kDa protein cpHSC70-1 (Krenz et al, 2010). Gel overlay assays, and in vitro and in vivo co-immunoprecipitation (Co-IP) experiments showed an interaction of H3 with NSP and MP of BDMV as well as with CPs of different geminiviruses (Zhou et al, 2011). In Nicotiana tabacum protoplasts and N. benthamiana leaves, transiently expressed H3 co-localized with NSP in the nucleus and the presence of MP redirected H3 to the cell periphery and plasmodesmata.…”

Two Populations of Viral Minichromosomes Are Present in a Geminivirus-Infected Plant Showing Symptom Remission (Recovery)

“…After transmission by the insect vector, the ssDNA genome is released from the capsid and converted to double-stranded DNA (dsDNA) through complementary strand replication (CSR) assisted by host enzymes (5). Viral DNA is further processed into a covalently closed circular conformation (cccDNA), which is wrapped around nucleosomes to form a minichromosome that is the template for replication and transcription and to interact with other cellular proteins (6)(7)(8). In addition, it might associate with viral movement proteins and histone H3 to move from cell to cell (6)(7)(8).…”

“…Viral DNA is further processed into a covalently closed circular conformation (cccDNA), which is wrapped around nucleosomes to form a minichromosome that is the template for replication and transcription and to interact with other cellular proteins (6-8). In addition, it might associate with viral movement proteins and histone H3 to move from cell to cell (6)(7)(8).RNA silencing is a ubiquitous eukaryotic gene regulation mechanism. In plants, it can act posttranscriptionally (posttranscriptional gene silencing [PTGS]) by cleavage or translation arrest of RNA targets in a sequence-specific manner or at the transcriptional level (transcriptional gene silencing [TGS]) by cytosine methylation of DNA and/or posttranslational modifications of histones (i.e., methylation, acetylation, phosphorylation, ubiquitination) located at the DNA targets (9-11).…”

The Nucleolar Fibrillarin Protein Is Required for Helper Virus-Independent Long-Distance Trafficking of a Subviral Satellite RNA in Plants

“…In addition to identifying fibrillarin, we identified other host proteins, such as histone H3, which is crucial for trafficking of a geminivirus DNA through the nuclear pore complex and PD (Zhou et al, 2011), in our co-IP experiments (Table 1). These proteins may also interact with P20, directly or indirectly, to form fibrillarin-based satBaMV RNP complexes.…”