Molecular characterization of tomato-infecting begomoviruses in Thailand

Bipartite geminiviruses infecting tomatoes in Thailand were detected by polymerase chain reaction (PCR) using CPA5/CPA2 primers. Products derived from PCR-amplified full-length DNA-A and DNA-B of TYLCV collected from Chiang Mai, Nong Khai, and Sakon Nakhon were cloned and sequenced. DNA-A from Chiang Mai was 2747 nts long; Nong Khai, 2744 nts; and Sakon Nakhon, 2747 nts, and those of DNA-B from Chiang Mai were 2750 nts long; Nong Khai, 2749 nts; and Sakon Nakhon, 2749 nts. The genomes of these virus isolates were organized like those of other begomoviruses. The DNA-A had two ORFs in the virion sense and four ORFs in the complementary sense. The DNA-B had two ORFs in the virion sense and one ORF in the complementary sense. Nucleotide sequences of DNA-A of TYLCV from Chiang Mai, Nong Khai, and Sakon Nakhon were closely related to those of Tomato yellow leaf curl Thailand virus (TYLCTHV) and Tomato yellow leaf curl Thailand virus-[Myanmar] (TYLCTHV-[MM]) with nucleotide sequence identity ranging from 89% to 95%. Based on sequence comparisons and phylogenetic analyses, these three virus isolates studied were identified as new strains of TYLCTHV and named Tomato yellow leaf curl Thailand virus-Chiang Mai (TYLCTHV-[CM]The GenBank accession codes for DNA-A of TYLCTHV-[CM], -[NK], and -[SK] are , and , respectively. The GenBank accession codes for DNA-B of TYLCTHV-[CM], -[NK], and -[SK] are , , and , respectively.), Nong Khai (TYLCTHV-[NK] and Sakon Nakhon (TYLCTHV-[SK]).     

Application of Phi29 DNA polymerase in identification and full-length clone inoculation of tomato yellow leaf curl Thailand virus and tobacco leaf curl Thailand virus

Summary. Tomato plants grown in greenhouses in Thailand developed typical symptoms of a tomato yellow leaf curl Thailand virus (TYLCTHV) infection. After confirmation by ELISA, a Phi29 DNA polymerase approach was chosen for further molecular analysis of TYLCTHV. Total DNA purified from infected tomato leaves was subjected to rolling-circle amplification (RCA) of DNA-A and DNA-B of TYLCVTHV. In addition, a new monopartite geminivirus with a putative recombinant background was identified by RCA and tentatively named tobacco leaf curl Thailand virus (TbLCTHV). To confirm the composition of both geminiviruses, full-length clones were established and used for inoculation of Nicotiana benthamiana by particle bombardment or agroinfection. When TYLCTHV DNA-A and DNA-B were applied together by particle bombardment or agroinfection, severe stunting, yellowing, and leaf curling were observed. Whereas TYLCTHV DNA-A and TbLCTHV revealed no infection after'particle bombardment, similar symptoms in N. benthamiana, like leaf upward curling and yellowing were observed following agroinfection. DNA components of TYLCTHV DNA-A and DNA-B were excised from their respective plasmids, ligated, and amplified by Phi29 DNA polymerase. The ability of viral concatamere inoculation was evaluated in particle co-bombardment experiments on N. benthamiana. Thus, particle bombardment of RCA-derived multimeric products proved to be at least as effective as inoculation with a partial repeat construct and tenfold as effective as inoculation with excised unit-lengths of DNA-A and DNA-B of TYLCVTHV when using each DNA component in an amount of 5 ng.     

Characterization and distribution of tomato yellow margin leaf curl virus, a begomovirus from Venezuela

A begomovirus causing mottling and leaf deformation in tomato from the State of Mérida was cloned and sequenced. The virus has a bipartite genome comprised of a DNA-A (2,572 nucleotides) and a DNA-B (2,543 nucleotides) with a genome organization typical of New World begomoviruses. Both components share a common region of 115 nucleotides with 98 % sequence identity. Phylogenetic analysis indicated that while no virus sequences were closely related, the A component was distantly related to those of two other tomato-infecting viruses, tomato leaf deformation virus and Merremia mosaic virus; and the DNA-B, to those of pepper huasteco yellow vein virus and Rhynchosia golden mosaic Yucatan virus. The DNA-A and DNA-B sequences were submitted to GenBank (accession no. AY508993 and AY508994, respectively) and later accepted by the International Committee on Taxonomy of Viruses as the genome of a member of a unique virus species with the name Tomato yellow margin leaf curl virus (TYMLCV). Tomato (Solanum lycopersicum L. ‘Fl. Lanai’) plants inoculated with cloned TYMLCV DNA-A and DNA-B became systemically infected and showed chlorotic margins and leaf curling. The distribution of TYMLCV in tomato-producing states in Venezuela was determined by nucleic acid spot hybridization analysis of 334 tomato leaf samples collected from ten states using a TYMLCV-specific probe and confirmed by PCR and sequencing of the PCR fragment. TYMLCV was detected in samples from the states of Aragua, Guárico, and Mérida, suggesting that TYMLCV is widely distributed in Venezuela.     

Tomato yellow leaf curl Thailand virus-[Y72] from Yunnan is a monopartite begomovirus associated with DNAβ

Previous studies have shown that isolates of tomato yellow leaf curl Thailand virus (TYLCTHV) originated from Thailand are bipartite begomoviruses, while all the seven TYLCTHV isolates found in China are associated with DNAβ molecules. In this study, infectious clones of TYLCTHV isolate Y72 (TYLCTHV-[Y72]) and its DNAβ were constructed to verify the bipartite or monopartite nature of TYLCTHV. Agroinoculation showed that TYLCTHV-[Y72] alone was able to induce significant symptoms in Nicotiana benthamiana, Nicotiana glutinosa, and Solanum lycopersicum plants, but co-inoculation with its associated satellite DNAβ produced more severe symptoms, which is similar to tobacco curly shoot virus. Southern blot results showed that TYLCTHV DNAβ could increase the virus accumulation in systemically infected tissues. Thus, TYLCTHV-[Y72] is a monopartite begomovirus, which may represent an evolutionary intermediate between the begomoviruses requiring DNAβ and begomoviruses dispensable of DNAβ. Wei Guo and Xiuling Yang contributed equally to this paper.     

Strains of a new bipartite begomovirus, pepper yellow leaf curl Indonesia virus, in leaf-curl-diseased tomato and yellow-vein-diseased ageratum in Indonesia

The complete nucleotide sequences of begomoviruses from pepper with leaf curl and yellowing symptoms, tomato with leaf curl symptoms, and ageratum with yellow vein in Indonesia were determined. On the basis of genome organization and sequence homology, they were proposed to belong to a new species, Pepper yellow leaf curl Indonesia virus (PepYLCIV), which includes the new strains PepYLCIV-Tomato and PepYLCIV-Ageratum. These viruses had bipartite genomes. Pepper virus DNAs from Indonesia (PepYLCIV, PepYLCIV-Tomato and PepYLCIV-Ageratum DNA-As) were noticeably distinct, forming a separate branch from the viruses infecting pepper. Considerable divergence was observed in the common region (CR) of the genomic components of PepYLCIV (77%), PepYLCIV-Tomato (82%) and PeYLCIV-Ageratum (75%). A stem-loop-forming region and a Rep-binding motif were identical in the CR of the three viruses. The CRs of PepYLCIV-Ageratum DNA-A was approximately 10 nucleotides longer than that of PepYLCIV DNA-A and PepYLCIV-Tomato DNA-A. A similar insertion was also found in the CR of PepYLCIV-Ageratum DNA-B. PepYLCIV DNA-A alone was infectious in pepper and Nicotiana benthamiana plants, and association with DNA-B increased symptom severity.     

Pathogenicity and stability of a truncated DNAbeta associated with Tomato yellow leaf curl China virus

DNAbeta molecules are single-stranded satellite DNA associated with monopartite begomoviruses (family Geminiviridae). DNAbeta possesses a C1 gene on the complementary strand, which has a conserved position and size. To better understand the function of C1 gene in virus infection, a C1 deletion DNAbeta associated with a Tomato yellow leaf curl China virus (TYLCCNV) isolate was constructed. Co-agroinoculation with TYLCCNV showed the truncated DNAbeta was infectious in Nicotiana benthamiana and N. glutinosa plants but not in N. tabacum Samsun, N. tabacum and Lycopersicon esculentum plants. The wild-type TYLCCNV DNAbeta co-agroinoculated with TYLCCNV caused systemic infection in all the above hosts. Results of Southern blot analysis indicate that C1 gene is not required for TYLCCNV and DNAbeta replication. However, the presence of C1 gene in DNAbeta can increase both TYLCCNV and DNAbeta accumulation in infected plants. The truncated TYLCCNV DNAbeta was stable in N. benthamiana and N. glutinosa plants.     

Predominance of tomato leaf curl Gujarat virus as a monopartite begomovirus: association with tomato yellow leaf curl Thailand betasatellite

Tomato leaf curl is a serious malady in the state of Maharashtra, India, causing nearly 100 % yield loss. An extensive survey was done in the affected fields of tomato in the year 2008, and members of three species of begomoviruses were identified as causing the disease. More than 60 % of the samples from diseased plants were infected with tomato leaf curl Gujarat virus (ToLCGuV). Isolates collected from these fields differed from the Varanasi isolate of ToLCGuV in not having a DNA B component. Instead, they were like typical Old World monopartite begomoviruses in that they were associated with only one betasatellite, tomato yellow leaf curl Thailand betasatellite (TYLCTHB). ToLCGuV alone is readily infectious, expressing systemic symptoms in Nicotiana benthamiana and tomato. Co-inoculation of ToLCGuV with TYLCTHB, increased symptom severity and reduced the incubation time required for symptom expression. ToLCGuV successfully interacted with heterologous DNA B component of ToLCNDV [IN:Pun:JID:08], and co-inoculation of these two resulted in yellow mottling symptoms that were typical of DNA B.     

Tomato yellow leaf curl China virus: monopartite genome organization and agroinfection of plants.

The complete DNA sequence (2734 nucleotides) of the monopartite genome of tomato yellow leaf curl China virus (TYLCCNV), a begomovirus transmitted by the whitefly Bemisia tabaci, was determined. The circular genomic DNA contains six open reading frames (ORFs) encoding proteins of molecular weights >10 kDa, of which two (V1 and V2) are located on the virion-sense strand and four (C1, C2, C3 and C4) on the complementary-sense strand. The ORFs are comparable to those of other whitefly-transmitted begomoviruses with a monopartite genome and to those encoded by DNA-A of bipartite begomoviruses. Sequence comparisons with other geminiviruses showed that TYLCCNV belongs to Begomovirus from the Old World. No putative DNA-B genome was found. Nicotiana species and tomato plants agroinoculated with the TYLCCNV monopartite genome developed typical yellowing and leaf-curling symptoms. The cloned molecule carried all the information needed for virus replication and systemic infection of plants.     

Molecular analysis of new isolates of Tomato leaf curl Philippines virus and an associated betasatellite occurring in the Philippines

Three new begomovirus isolates and one betasatellite were obtained from a tomato plant exhibiting leaf curl symptom in Laguna, the Philippines. Typical begomovirus DNA components representing the three isolates (PH01, PH02 and PH03) were cloned, and their full-length sequences were determined to be 2754 to 2746 nucleotides. The genome organizations of these isolates were similar to those of other Old World monopartite begomoviruses. The sequence data indicated that PH01 and PH02 were variants of strain B of the species Tomato leaf curl Philippines virus, while PH03 was a variant of strain A of the species Tomato leaf curl Philippines virus. These isolates were designated ToLCPV-B[PH:Lag1:06], ToLCPV-B[PH:Lag2:06], and ToLCPV-A[PH:Lag3:06], respectively. Phylogenetic analysis revealed that the present isolates form a separate monophyletic cluster with indigenous begomoviruses reported earlier in the Philippines. A betasatellite isolated from same sample belongs to the betasatellite species Tomato leaf curl Philippines betasatellite and designated Tomato leaf curl Philippines betasatellite-[Philippines:Laguna1:2006], ToLCPHB-[PH:Lag1:06]. When co-inoculated with this betasatellite, tomato leaf curl Philippines virus induced severe symptoms in N. benthamiana and Solanum lycopersicum plants. Using a PVX-mediated transient assay, we found that the C4 and C2 proteins of tomato leaf curl Philippines virus and the βC1 protein of ToLCPHB-[PH:Lag1:06] function as a suppressor of RNA silencing.     

Interaction of tomato yellow leaf curl virus with diverse betasatellites enhances symptom severity

The complete nucleotide sequence was determined for a begomovirus isolated from tomato exhibiting leaf curling and yellowing symptoms in Tochigi Prefecture in Japan. The genome organization of this virus was similar to those of other Old World monopartite begomoviruses. Neither a DNA betasatellite nor a DNA-B component was detected. It had the highest total nucleotide sequence identity (99%) with tomato yellow leaf curl virus-Israel[Japan:Tosa:2005] (TYLCV-IL[JR:Tos:05]) and TYLCV-Israel[Japan:Haruno:2005] (TYLCV-IL[JR:Han:05]). Its coat protein V1 also showed an identical amino acid sequence with those of TYLCV-IL[JR:Tos:05] and TYLCV-IL[JR:Han:05]. Thus, the begomovirus was determined to be an isolate of TYLCV-IL designated as TYLCV-Israel[Japan:Tochigi:2007] (TYLCV-IL[JR:Toc:07]). We investigated the interaction of TYLCV-IL[JR:Toc:07] with two known satellites associated with tomato yellow dwarf disease in Japan, tobacco leaf curl Japan betasatellite [Japan:Ibaraki:2006] and honeysuckle yellow vein mosaic betasatellite [Japan:Nara:2006], as well as with tomato leaf curl Philippines betasatellite [Philippines:Laguna1:2008], in tomato and Nicotiana benthamiana plants. TYLCV-IL[JR:Toc:07] trans-replicated these betasatellites, inducing more severe tomato yellow leaf curl disease-related symptoms than TYLCV-IL[JR:Toc:07] alone.     

Molecular characterization of Tobacco leaf curl Pusa virus, a new monopartite Begomovirus associated with tobacco leaf curl disease in India

Leaf curl disease of tobacco (TbLCD) is endemic in India. A monopartite Begomovirus, a betasatellite and an alphasatellite were found associated with the disease in Pusa, Bihar. The DNA-A of the Begomovirus associated with TbLCD in Pusa, Bihar was found to comprise of 2707 nt with a typical Old World begomovirus-like genome organization. The full-length sequence of DNA-A [HQ180391] showed that the Pusa isolate is a newly described member of the genus Begomovirus, as it had <89% sequence homology with DNA-A of all the known begomoviruses. The isolate is tentatively named as Tobacco leaf curl Pusa virus [India:Pusa:2010]. The betasatellite (HQ180395) associated with TbLCD in Pusa was identified as a variant of Tomato leaf curl Bangladesh betasatellite [IN:Raj:03], with which it shared 90.4% sequence identity. The alphasatellite (HQ180392) associated with the disease had highest 87% nucleotide sequence identity with Tomato leaf curl alphasatellite. The Begomovirus, betasatellite, and alphasatellite associated with TbLCD in Pusa, Bihar, India were found to be recombinants of extant begomoviruses, betasatellites and alphasatellites spreading in the Indian sub-continent and South-East Asia.     

Molecular characterization of squash leaf curl Yunnan virus,a new begomovirus and evidence for recombination

Summary. Virus isolate Y23V, obtained from squash showing leaf curl symptoms in Yunnan, China, was readily differentiated from four studied Chinese begomovirus isolates in reactions with a set of monoclonal antibodies raised against begomoviruses. The complete nucleotide sequence (2714nts) of the DNA-A-like molecule of Y23V was determined. The DNA-A of Y23V is most closely related to that of tomato yellow leaf curl Thailand virus-[1] (TYLCTHV-[1]) (84% sequence identity). However, the AC1 and AC4 gene of Y23V DNA-A resembled to Pepper leaf curl virus from Bangladesh (PepLCBDV). The DNA-A of Y23V has three distinct regions: the region from 74-2071nts is 95% identical to TYLCTHV-[1] excluding a 27nt deletion; the following 386nts are 91% identical to PepLCBDV and the rest of the DNA-A is not closely related to any reported begomovirus. Y23V, therefore, is considered to have arisen by recombination. The 84% sequence identity of Y23V with TYLCTHV-[1] allows Y23V to be considered as a distinct begomovirus species, for which the name squash leaf curl Yunnan virus (SLCYNV) is proposed.Received August 5, 2003; accepted May 14, 2003     

Sequence characterization of Tomato leaf curl Sinaloa virus and <Emphasis Type="Italic">Tomato severe leaf curl virus</Emphasis>: Phylogeny of New World begomoviruses and detection of recombination

Summary. Diseases caused by begomoviruses (family Geminiviridae, genus Begomovirus) constitute a serious constraint to tomato production in Nicaragua. In this study, the complete nucleotide (nt) sequences of the DNA-A and DNA-B components were determined for the first time for Tomato leaf curl Sinaloa virus (ToLCSinV). In addition, the complete nt sequence was determined for the DNA-A component of two isolates of Tomato severe leaf curl virus (ToSLCV). The genome organization of ToLCSinV and ToSLCV was identical to the bipartite genomes of other begomoviruses described from the Americas. A phylogenetic analysis of DNA-A including 45 begomovirus species showed that the indigenous begomoviruses of the New World can be divided into three major clades and an intermediate group: AbMV clade, SLCV clade, “Brazil clade”, and BGYMV group. Phylogenetic analyses of the DNA-A and DNA-B components and their open reading frames indicated that ToLCSinV and ToSLCV belong to different clades: ToLCSinV to the AbMV clade, and ToSLCV to the SLCV clade. The two Nicaraguan isolates of ToSLCV showed a close relationship with ToSLCV from Guatemala (ToSLCV-[GT96-1]) and Tomato chino La Paz virus (ToChLPV), but differed significantly in the AV1 and AC1 regions, respectively. Computer-based predictions indicated that recombination with another begomovirus had taken place within AV1 of ToSLCV dividing this species into two strains. A high probability was also found that ToChLPV is involved in the evolution of ToSLCV.     

Tomato leaf curl Joydebpur virus: a monopartite begomovirus causing severe leaf curl in tomato in West Bengal

A begomovirus was isolated from tomato plants showing leaf curl and stunting symptoms in farmers’ fields near the district of Kalyani, West Bengal, India. Viral genomic components amplified by rolling-circle amplification were cloned and sequenced. The genome organization of this virus was found to be similar to those of Old World monopartite begomovirus, with DNA A and a betasatellite component. Neither alphasatellite nor DNA B component was detected. The begomovirus showed highest sequence identity of 93.6% to tomato leaf curl Joydebpur virus (ToLCJoV-[IN:Kal:Chi:06]) and was thus identified to be an isolate of ToLCJoV. The betasatellite isolated from these samples was identified as tomato leaf curl Joydebpur betasatellite. ToLCJoV-[IN:Kal:Tom:08] alone induced severe symptoms in Solanum lycopersicum, N. benthamiana and N. glutinosa plants, and its severity was enhanced when co-inoculated with the cognate betasatellite. ToLCJoV-[IN:Kal:Tom:08] trans-replicated four more non-cognate betasatellites and induced severe symptoms in N. benthamiana and tomato. Since DNA A replicated efficiently and caused systemic symptom expression, it is hypothesized that ToLCJoV is essentially a monopartite virus, which could have acquired a betasatellite from an unknown source.     

Differential pathogenicity among Tomato leaf curl Gujarat virus isolates from India

Tomato leaf curl Gujarat virus (ToLCGV) has been identified as one of the most destructive pathogens causing tomato leaf curl disease (ToLCD) in India. In the tomato growing regions of Dhanbad and Ramgarh, plants bearing severe symptoms of ToLCD such as leaf curling, leaf crinkling, yellowing and leaf rolling was observed in the farmer fields. The association of begomovirus in these samples was confirmed by PCR and the causal viruses were identified as the isolates of ToLCGV. However, association of cognate DNA B component could not be ascertained from these samples. Indeed, like other Old World begomoviruses, the present ToLCGV isolates were found to be associated with a particular betasatellite, Tomato yellow leaf curl Thailand betasatellite (TYLCTHB). Although DNA A of both ToLCGV isolates could alone infect tomato inducing systemic symptoms, the difference in virulence was observed. Co-inoculation of TYLCTHB reduced the incubation period without influencing the accumulation of helper virus DNA and hence, differential pathogenesis among ToLCGV isolates was governed by the helper component rather than betasatellite. ToLCGV infection with DNA B increases the accumulation of DNA A component of Dhanbad isolate but not of Ramgarh isolate. Results indicated that the begomovirus identified from Ramgarh sample was a mild strain of ToLCGV.     

Evidence of local evolution of tomato-infecting begomovirus species in West Africa: characterization of tomato leaf curl Mali virus and tomato yellow leaf crumple virus from Mali

Tomato yellow leaf curl (TYLC) and tomato leaf curl (ToLC) diseases are serious constraints to tomato production in Mali and other countries in West Africa. In 2003 and 2004, samples of tomato showing virus-like symptoms were collected during a survey of tomato virus diseases in Mali. Three predominant symptom phenotypes were observed: (1) TYLC/ToLC (stunted upright growth and upcurled leaves with interveinal yellowing and vein purpling), (2) yellow leaf crumple and (3) broccoli or bonsai (severe stunting and distorted growth). Squash blot (SB) hybridization with a general begomovirus probe and/or SB/PCR analyses revealed begomovirus infection in plants with each of these symptom phenotypes and no evidence of phytoplasma infection. Sequence analysis of PCR-amplified begomovirus fragments revealed two putative new begomovirus species associated with the TYLC/ToLC and yellow leaf crumple symptom phenotypes, respectively. Full-length clones of these begomoviruses were obtained using PCR and overlapping primers. When introduced into N. benthamiana and tomato plants, these clones induced upward leaf curling and crumpling (the TYLC/ToLC-associated begomovirus) or downward leaf curl/yellow mottle (yellow leaf crumple-associated begomovirus) symptoms. Thus, these begomoviruses were named tomato leaf curl Mali virus (ToLCMLV) and tomato yellow leaf crumple virus (ToYLCrV). The genome organization of both viruses was similar to those of other monopartite begomoviruses. ToLCMLV and ToYLCrV were most closely related to each other and to tobacco leaf curl Zimbabwe virus (TbLCZV-[ZW]) and tomato curly stunt virus from South Africa (ToCSV-ZA). Thus, these likely represent tomato-infecting begomoviruses that evolved from indigenous begomoviruses on the African continent. Mixed infections of ToLCMLV and ToYLCrV in N. benthamiana and tomato plants resulted in more severe symptoms than in plants infected with either virus alone, suggesting a synergistic interaction. Agroinoculation experiments indicated that both viruses induced symptomatic infections in tomato and tobacco, whereas neither virus induced disease symptoms in pepper, common bean, small sugar pumpkin, African eggplant, or Arabidopsis. Virus-specific PCR primers were developed for detection of ToLCMLV and ToYLCrV and will be used to further investigate the distribution and host range of these viruses.     

Development of a real-time PCR for Tomato yellow leaf curl Sardinia virus

Recently, tomato yellow leaf curl disease has become important for the tomato grown both in greenhouse and field conditions in Tunisia. Here, we describe a rapid, specific, reliable, and sensitive real-time PCR, based on TaqMan chemistry, for Tomato yellow leaf curl Sardinia virus (TYLCSV). This method proved suitable for the detection and quantification of this virus in tomato, pepper and bean plants. It detected the virus even in the samples that were negative by conventional assays.     

Functional analysis of the naturally recombinant DNA-A of the bipartite begomovirus Tomato chlorotic mottle virus

All geminiviruses found in Brazil belong to the Begomovirus genus with a bipartite genome that is split between two genomic components, DNA-A and DNA-B. The DNA-A of the bipartite begomovirus ToCMoV-[MG-Bt] (Tomato chlorotic mottle virus), however, possesses as a peculiar characteristic the capacity to systemically infect Nicotiana benthamiana. Here we further characterize this variant DNA-A and show that it also infects Solanum lycopersicum and other host plants, in the absence of DNA-B. The ToCMoV-[MG-Bt]-DNA-A encodes an additional ORF, designated AC5, but otherwise its genome organization is similar to other DNA-A from Western Hemisphere begomoviruses. We showed that this AC5 putative ORF is not essential for infection, as disruption of its coding capacity caused no effect on ToCMoV-[MG-Bt]-DNA-A-mediated infection process. Likewise, the ToCMoV-[MG-Bt]-DNA-A ac4 mutant was indistinguishable from its wild type counterpart in all hosts tested. In contrast, an av1 (coat protein) mutant was unable to infect systemically N. benthamiana and Chenopodium quinoa in the absence of DNA-B. However, inclusion of DNA-B in the infection assay fully rescued the movement defect of the ToCMoV-[MG-Bt]-DNA-A av1 mutant. These results suggest that at suboptimal conditions for infection the coat protein is required for ToCMoV-[MG-Bt] systemic movement.