Movement Proteins (BC1 and BV1) of Abutilon Mosaic Geminivirus Are Cotransported in and between Cells of Sink but Not of Source Leaves as Detected by Green Fluorescent Protein Tagging

Abstract

Two movement proteins (BV1 and BC1) facilitate the intra- and intercellular transport of begomoviruses in plants. In contrast to other geminiviruses the movement protein BC1 of Abutilon mosaic virus (AbMV) remained in the supernatant after centrifuging plant extracts at 20,000 g. To test whether this unusual behavior results from a distinct intracellular distribution of the protein, the BC1 gene has been fused to the gene of green fluorescent protein (GFP). The resulting plasmids were delivered into nonhost plants (Allium cepa) as well as into mature and immature cells of host plants (Nicotiana tabacum, N. benthamiana) by biolistic bombardment for transient expression in planta. BC1 directed GFP to two different cellular sites. In the majority of nonhost cells as well as in mature cells of host leaves, BC1 was mainly localized in small punctate flecks at the cell periphery or, to a lesser extent, around the nucleus. In sink leaves of host plants, GFP:BC1 additionally developed disc-like structures in the cell periphery. Cobombardment of GFP:BC1 with its cognate infectious DNA A and B did not change their subcellular distribution patterns in source leaves but led to the formation of peculiar needle-like structures in sink leaves. The nuclear shuttle protein (BV1) of AbMV accumulated mainly inside the nuclei as shown by immunohistochemical staining and GFP tagging. In sink cells of host plants it was mobilized to the plasma membrane and to the nucleus of the neighboring cell by coexpressed BC1, GFP:BC1, BC1:GFP, or after cobombardment with the cognate viral DNA. Only under these conditions were GFP:BC1 and BC1:GFP also found in the recipient cell.

AtCSLD2 is an integral Golgi membrane protein with its N-terminus facing the cytosol

“…Plasmid nD2tmd-GFPc-cD2tmd and ST-DsRed (gift from Dr. Federica Brandizzi, Michigan State University), or plasmid GFPc plus ST-DsRed were introduced into onion epidermal cells using biolistic bombardment according to Zhang et al (2001). After being kept in the dark for 16-20 h, the onion peels were observed by means of an upright laser-scanning confocal microscope (Zeiss LsM510 META; Zeiss) according to Hanton et al (2007).…”

Interaction of DNA with the Movement Proteins of Geminiviruses Revisited

“…Wild-type SLCV MP redirected NSP from the nucleus to the cell periphery in protoplasts (38)(39)(40), whereas specific point mutations in MP (39) or NSP (38) prevented this migration. Similarly, in plant tissues, AbMV MP redirected NSP to the cell periphery and into the next cell's nucleus (55). Further neighbor cells received NSP only if the NSP-reporter construct was coinoculated with fully infectious viral DNA.…”

“…More detailed information is available for the MP of Abutilon mosaic virus (AbMV). Cellular imaging of AbMV MP translationally fused to green fluorescent protein or glutathione-S-transferase as reporter proteins showed that MP is tar-geted to the cell periphery in plants (55) or to microsomes and the plasma membranes in fission yeast cells (1), respectively. Sequence analysis of AbMV MP revealed no plausible domain which may function as a transmembrane helix.…”

“…It has been proposed that MP serves as a membrane anchor at the protoplasmic face of microsomes and plasma membranes, thus facilitating the movement of the transport complex along these membranes (54). Moreover, MP can shuttle between the nuclear envelope and the cellular periphery in order to fulfill its task, because green fluorescent protein-MP was also observed in the vicinity of nuclei in some cells (55).…”

Mutational Analysis of Effectors Encoded by Monopartite Begomoviruses and Their Satellites

“…Monopartite begomovirus capsids are composed of a single CP, encoded by the V1 gene or (also known as AV1), depending on the geminivirus [107]. For monopartite geminiviruses, CP is essential for systemic spread through the plant [12].…”