Begomoviral Movement Protein Effects in Human and Plant Cells: Towards New Potential Interaction Partners.

Susanna Krapp,Christina Wege,Tatjana Kleinow,Susanne Bailer,Manfred Marschall,Irina Stephan,Christina Funk,Barbara Alberter,Eva Greiner,Björn Krenz,Christian Schuy

doi:10.3390/v9110334

Abstract

Geminiviral single-stranded circular DNA genomes replicate in nuclei so that the progeny DNA has to cross both the nuclear envelope and the plasmodesmata for systemic spread within plant tissues. For intra- and intercellular transport, two proteins are required: a nuclear shuttle protein (NSP) and a movement protein (MP). New characteristics of ectopically produced Abutilon mosaic virus (AbMV) MP (MPAbMV), either authentically expressed or fused to a yellow fluorescent protein or epitope tags, respectively, were determined by localization studies in mammalian cell lines in comparison to plant cells. Wild-type MPAbMV and the distinct MPAbMV: reporter protein fusions appeared as curled threads throughout mammalian cells. Co-staining with cytoskeleton markers for actin, intermediate filaments, or microtubules identified these threads as re-organized microtubules. These were, however, not stabilized by the viral MP, as demonstrated by nocodazole treatment. The MP of a related bipartite New World begomovirus, Cleome leaf crumple virus (ClLCrV), resulted in the same intensified microtubule bundling, whereas that of a nanovirus did not. The C-terminal section of MPAbMV, i.e., the protein’s oligomerization domain, was dispensable for the effect. However, MP expression in plant cells did not affect the microtubules network. Since plant epidermal cells are quiescent whilst mammalian cells are proliferating, the replication-associated protein RepAbMV protein was then co-expressed with MPAbMV to induce cell progression into S-phase, thereby inducing distinct microtubule bundling without MP recruitment to the newly formed threads. Co-immunoprecipitation of MPAbMV in the presence of RepAbMV, followed by mass spectrometry identified potential novel MPAbMV-host interaction partners: the peptidyl-prolyl cis-trans isomerase NIMA-interacting 4 (Pin4) and stomatal cytokinesis defective 2 (SCD2) proteins. Possible roles of these putative interaction partners in the begomoviral life cycle and cytoskeletal association modes are discussed.

Highlights

Circular single-stranded DNA viruses are the smallest viruses known to infect eukaryotes
MPAbMV :enhanced yellow fluorescent protein (EYFP) signals appeared as curled filamentous threads throughout the cell (Figure 1a), whereas freely expressed EYFP analyzed in parallel
All Bimolecular fluorescence complementation (BiFC) combinations resulted in an yellow fluorescent protein (YFP) signal arising within the nucleus, predominantly in the nucleolus (Figure S5). These results suggest that MPAbMV has the potential to interact with both factors, and, most interestingly, a begomoviral movement protein (MP) was observed to be located within the nucleus for the first time, which raises many questions and must be addressed in the future

Summary

Introduction

Circular single-stranded DNA (ssDNA) viruses are the smallest viruses known to infect eukaryotes. The ssDNA viruses of the family Geminiviridae belong to the most devastating plant viruses causing heavy losses on food and cash crops [1]. Their genomes consist of one (monopartite) or two (bipartite) circular ssDNA molecules, which are packaged separately in twinned icosahedral particles, their name [2]. The small genomes (2.5 to 3.0 kb in size) multiply in the nuclei of host cells by complementary strand replication, rolling circle replication, and recombination-dependent replication [3,4]. Due to its replication in nuclei, geminivirus DNA has to cross two distinct barriers for systemic spread: the nuclear envelope and the plasmodesmata. The majority of begomoviruses within the family Geminiviridae possess a bipartite genome designated DNA A and DNA B, where

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