Intracellular and Intercellular Movement of Maize Streak Geminivirus V1 and V2 Proteins Transiently Expressed as Green Fluorescent Protein Fusions

Abstract

Transient expression of the maize streak geminivirus virion-sense proteins V1 and V2 (movement protein, MP, and coat protein, CP, respectively) in maize leaves allowed investigation of their roles in inter- and intracellular movement. Bombardment of a construct directing expression of a V1:green fluorescent protein (GFP) fusion product resulted in significantly increased spread of fluorescence from the bombarded cell to adjacent cells compared to that obtained following expression of free GFP. A mutant V1:GFP fusion product exhibited markedly less movement than the V1:GFP protein. Thus, the MSV V1 protein moves from cell to cell in the absence of other viral proteins. However, V1:GFP did not localize to plasmodesmata in maize or tobacco leaves although a tobacco mosaic virus MP:GFP fusion protein was shown to do so in tobacco. The CP:GFP fusion product targeted exclusively to the nucleus and did not move from cell to cell or exit the nucleus when expressed alone. When coexpressed with V1, some CP:GFP fluorescence was seen at the cell periphery in a proportion of cells, but in no case was cell-to-cell movement of CP:GFP detected. The likely roles of V1 and CP in MSV movement are discussed.

Virion Stability Is Important for the Circulative Transmission of Tomato Yellow Leaf Curl Sardinia Virus by Bemisia tabaci , but Virion Access to Salivary Glands Does Not Guarantee Transmissibility

“…After passing the hemolymph/salivary gland (SG) barrier, virions enter the SGs from which they are inoculated back into plants. Beside encapsidating the genome and transporting it in and out of the nucleus (44,45,49,67,68), the capsid protein (CP) of geminiviruses is the only viral protein mediating transmission (6,11). The CP of the begomovirus Tomato yellow leaf curl Sardinia virus (TYLCSV), which has a monopartite genome (42), is also essential for systemic plant infection (71).…”

Disassembly of African cassava mosaic virus

“…The single CP possesses a molecular mass of 30.1 kDa and a calculated pI of 10.0. Each geminate particle encapsidates one circular DNA molecule so that two virions are needed for infection in case of bipartite geminiviruses.Encapsidating the viral genome, the geminivirus CP is important for insect transmission (Briddon et al, 1990; Höfer et al, 1997; Höhnle et al, 2001;Kheyr-Pour et al, 2000; Noris et al, 1998) and transport of the viral DNA in and out of the nucleus (Kotlizky et al, 2000;Kunik et al, 1998Kunik et al, , 1999 Liu et al, 1999;Unseld et al, 2001Unseld et al, , 2004. For the ACMV CP, three regions have been determined that mediate nuclear import (Unseld et al, 2001), whereby the central region is not only important for nuclear import but also for export.…”

In vivo expression and binding activity of scFv-RWAV, which recognizes the coat protein of tomato leaf curl New Delhi virus (family Geminiviridae)

“…Such retargeting was not achieved by the MSV coat protein, and the GFP fusion remained permanently restricted to the nucleus [10]. In contrast, nuclear export was achieved by the central domain of the ACMV coat protein (residues 100-127), and three key leucine residues at positions 102, 118 and 123 are thought to be required [13].…”

“…AV1-DsRed has a molecular weight of 55.4 kDa, which exceeds the size required for efficient passive nuclear diffusion (20-40 kDa) [8][9][10][11]. The localization is consistent with the presence of an NLS in the coat proteins of geminiviruses [10,[12][13][14][15][16], which resulted in the exclusive nuclear localization of both maize streak virus (MSV) and African cassava mosaic virus (ACMV) coat protein GFP fusions [10,13]. In our experiments, free DsRed (25.8 kDa) expressed using a control vector was localized in both the cytoplasm and the nucleus, suggesting passive nuclear diffusion.…”