Subcellular Targeting of the Coat Protein of African Cassava Mosaic Geminivirus

Abstract

The coat protein (CP) of geminiviruses is involved in a number of processes during the life cycle of the virus. The predominant function is encapsidation of single-stranded DNA and formation of the virus particle to protect viral DNA during transmission. The CP of monopartite geminiviruses is absolutely essential for virus movement, whereas CP mutants of bipartite geminiviruses are able to infect some host plants systemically, indicating an involvement of the CP in host specificity. During the life cycle of geminiviruses, the viral DNA enters the nucleus of the infected cell where virus replication, transcription, and encapsidation occur. For systemic infection, the virus moves cell-to-cell from the site of inoculation to vascular tissue and via phloem to other plant tissues. To move, viral DNA has to shuttle in and out of the nucleus and through plasmodesmata. Parts of the bipartite African cassava mosaic virus (ACMV) CP were fused with green fluorescent protein (GFP) or beta-glucuronidase (GUS). CP domains were identified that mediate both nuclear import and export, as well as targeting of CP-fusion proteins to the cell periphery. These results indicate that domains of the CP facilitate several aspects of geminivirus movement, including nuclear import and export and transport of the viral genome to the cell periphery.

Molecular characterization of begomoviruses and DNA satellites from Vietnam: additional evidence that the New World geminiviruses were present in the Old World prior to continental separation

“…The basic domains in the CP N-terminal region form an essential part of the NLS in Old World viruses and their C. Ha and others role in nuclear targeting has been demonstrated for TYLCV (Kunik et al, 1998), ACMV (Unseld et al, 2001) and MYMV (Guerra-Peraza et al, 2005). The reason for the absence of these domains in New World viruses is unclear.…”

“…3. DBasic domains of the nuclear-localization signals (Guerra-Peraza et al, 2005;Kunik et al, 1998;Unseld et al, 2001) are shown in bold. The 7-PWRsMaGT motifs (Harrison et al, 2002) are underlined.…”

Disassembly of African cassava mosaic virus

“…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. Deletions within these regions, which may overlap with DNA binding and multimerization regions, inhibited the formation of virus particles .…”

“…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.…”

Interaction of DNA with the Movement Proteins of Geminiviruses Revisited

“…Both CP and NSP are targeted to the nucleus, and at least NSP, hence its name, is able to shuttle between the nucleus and the cytoplasm (19,24,33,38,46,47,50). Protein domains responsible for DNA binding and intracellular localization have been analyzed for several geminiviruses.…”