Nucleotide sequence of DNA from an altered-virulence isolate D/H of the cauliflower mosaic virus

Detection in vivo of a new gene product (gene III) of cauliflower mosaic virus

Cauliflower mosaic virus DNA contains six major open reading frames (ORFs). As only the mRNA corresponding to the transcription of gene VI and its translation product have been isolated, the identification in infected plants of products corresponding to the five other putative genes remains to be established. The present paper reports the detection of an ORF III product by means of antibodies raised against an NH(2)-terminal synthetic peptide of 19 amino acids corresponding to a sequence predicted from the nucleotide sequence of ORF III. The detection of this gene product raises the question of the mechanism of its expression.

The spherically averaged structure of a DNA isometric plant virus: cauliflower mosaic virus

The organization of cauliflower mosaic virus was reinvestigated by neutron small-angle scattering in buffers containing various amounts of D2O. The molecular weight of the virions and their DNA content were determined and found to agree well with the known primary structure of the nucleic acid. The capsid probably possesses a T = 7 icosahedral organization. The exceptionally low packing density of the outer protein shell may account for some of the unusual properties of these very stable virions.

Third position codon composition suggests two classes of genes within the Cauliflower mosaic virus genome

The translation of viral mRNAs by host ribosomes is essential for infection. Hence, codon usage of virus genes may influence efficiency of infection. In addition, composition of nucleotides in the third position within codons of genes can reflect evolutionary relationships. In this study, third position codon composition was examined for the seven genes of eight Cauliflower mosaic virus isolates. Genes IV-VII had similar codon composition values and were termed Class 1 genes. Genes I-III possessed corresponding codon composition values and were termed Class 2 genes. The codon composition values of Class 1 and genes differed significantly. Neither Class 1 nor Class 2 genes had codon composition values identical to that of the host plant, Arabidopsis thaliana. However, Class 1 genes possessed codon composition values closer to those of the host than Class 2 genes. Examination of the genomes of three Rous sarcoma virus isolates indicated that codon composition values were similar for the gag, pol, and env genes but these genes differed significantly from the src genes. Since codon composition values for Rous sarcoma virus distinguished a "foreign" gene from the rest of the viral genome, it is possible that the Cauliflower mosaic virus genome is composed of genes from two different sources. Others have suggested that Cauliflower mosaic virus evolved in this manner and our data provide support for this hypothesis.

The 5' Third of Cauliflower mosaic virus Gene VI Conditions Resistance Breakage in Arabidopsis Ecotype Tsu-0

ABSTRACT Arabidopsis thaliana ecotypes vary in their responses to viruses. In this study, we analyzed the variation in response of A. thaliana ecotype Tsu-0 to Cauliflower mosaic virus (CaMV). This ecotype was previously reported to be resistant to two CaMV isolates (CM1841 and CM4-184), but susceptible to W260. In this study, we show that Tsu-0 is resistant to four additional CaMV isolates. CaMV propagated within the rosette leaves of Tsu-0 plants, but did not appear to spread systemically into the inflorescence. However, virus viability in rosette leaves of Tsu-0 plants apparently was not compromised because infectious CaMV could be recovered from these organs. W260 overcomes Tsu-0 resistance by a passive mechanism (i.e., this virus avoids activating plant defenses). The portion of the viral genome responsible for W260 resistance breakage was mapped to the 5' third of gene VI, which we have termed RBR-1. This region is also responsible for controlling the ability of CaMV to infect different types of solanaceous plants. Hence, the pathways by which plants of different families interact with CaMV may be conserved through evolution.

Cauliflower mosaic virus ORF III product forms a tetramer in planta: its implication in viral DNA folding during encapsidation

Cauliflower mosaic virus (CaMV) open reading frame (ORF) III encodes a 15 kDa protein; the function of which is as yet unknown. This protein has non-sequence-specific DNA binding activity and is associated with viral particles, suggesting that the ORF III product (P3) is involved in the folding of CaMV DNA during encapsidation. In this study, we demonstrated that P3 forms a tetramer in CaMV-infected plants. A P3-related protein with an apparent molecular weight of 60 kDa was detected by Western blotting analysis using anti-P3 antiserum under non-reducing conditions, while only 15 kDa P3 was detected under reducing conditions. Analysis of P3 using viable mutants with a 27-bp insertion in either ORF III or IV revealed that the 60 kDa protein was a tetramer of P3. The P3 tetramer co-sedimented with viral coat protein in multiple fractions on sucrose gradient centrifugation, suggesting that P3 tetramer binds to mature and immature virions. These results strongly suggested that CaMV P3 forms a tetramer in planta and that disulfide bonds are involved in its formation and/or stabilization. The finding of P3 tetramer in planta suggested that viral DNA would be folded compactly by the interaction with multiple P3 molecules, which would form tetramers, while being packaged into the capsid shell.

Requirement of cauliflower mosaic virus open reading frame VI product for viral gene expression and multiplication in turnip protoplasts

Cauliflower mosaic virus (CaMV) open reading frame (ORF) VI product (P6) has been shown to be the major constituent of viral inclusion body, to function as a post-transcriptional transactivator, and to be essential for infectivity on whole plants. Although these findings suggest that P6 has an important role in viral multiplication, it is unknown whether P6 is required for viral multiplication in a single cell. To address this question, we transfected turnip protoplasts with an ORF VI frame-shift (4 bp deletion) mutant (pCaFS6) of an infectious CaMV DNA clone (pCa122). The mutant was uninfectious. Co-transfection of plasmids expressing P6 complemented the mutant. Overexpression of P6 elevated the infection rate in co-transfection experiments with either pCa122 or pCaFS6. This would have been achieved by elevating the level of pregenomic 35S RNA, a putative polycistronic mRNA for ORFs I, II, III, IV and V, and by enhancing the accumulation of these five viral gene products. When CaMV ORFs I, II, III, IV and V were expressed from monocistronic constructs in which each of the ORFs was placed just downstream of the 35S promoter, the accumulation of ORF III, IV and V products depended on the co-expression of P6. The accumulation of ORF I and II products was not detected, even in the presence of P6. These results suggest that P6 is involved in the stabilization of other viral gene products as well as in the activation of viral gene expression, and thus, is a prerequisite for CaMV multiplication.

Variability in Coat Protein Sequence Homology Among American and European Sources of Strawberry Vein Banding Virus

Strawberry vein banding virus (SVBV) isolates from North America, Czech Republic, Norway, and Germany were collected and their variability was determined by dot blot hybridization and confirmed by sequencing of a 431-nucleotide fragment from the middle part of the coat protein gene. Two different substitutions were found between the American and two Czech SVBV isolates, but the other isolates were identical in the compared region to the American isolate. Digoxigenin-labeled probes were prepared from these isolates and used for hybridization with polymerase chain reaction-amplified fragments of 26 Czech SVBV field isolates. No significant differences in the hybridization signal were found with any combination of samples and probes. These results show that the European isolates probably originate from a common ancestor and may have been introduced to Europe from America with planting or breeding material.

Cauliflower Mosaic Virus Isolate NY8153 Breaks Resistance in Arabidopsis Ecotype En-2

ABSTRACT Arabidopsis thaliana ecotype En-2 was previously shown to be resistant to cauliflower mosaic caulimovirus (CaMV) isolate CM4-184. In this study, En-2 plants were screened with eight other isolates of CaMV to identify viruses capable of overcoming resistance and to determine if the mechanism of resistance was the same for each virus. En-2 resistance to most CaMV isolates was mediated by the same mechanism, i.e., preventing virus long-distance movement. One CaMV isolate, NY8153, was found that produced a severe systemic infection on En-2 plants. In addition, the CM1841 isolate was able to spread systemically through En-2 plants, to a limited extent, without producing visible symptoms. These data indicate that the resistance shown by En-2 plants is not an all-or-none phenomenon. En-2 plants were susceptible to turnip mosaic potyvirus, suggesting that resistance is specific to CaMV.

Sequence of a cauliflower mosaic virus strain infecting solanaceous plants

The complete nucleotide sequence (8031 bp) of the DNA of cauliflower mosaic virus (CaMV) strain B29 is reported. This strain is unusual, since it infects both cruciferous and solanaceous plants. So far, from data of sequence comparisons between B29 and other CaMV strains there is no evidence for any obvious correlation between host range and distinct sequence features.

Interaction between the aphid transmission factor and virus particles is a part of the molecular mechanism of cauliflower mosaic virus aphid transmission

Cauliflower mosaic virus (CaMV) aphid transmission factor (ATF or P18) is presumed to interact with both virus particles and vector mouthparts, thereby mediating virus aphid transmission. We developed a protein-protein binding assay and our results clearly show that virus particles bind strongly and specifically to P18 whether P18 was obtained from plants, a baculovirus expression system, or the pGEX-3X Escherichia coli expression system. We overproduced, using the pGEX-3X expression system, various fragments of P18 and thereby demonstrated that the C-terminal 31 amino acid residues are responsible for the interaction. Using PCR-based mutagenesis, 2 amino acid residues essential for interaction were identified. Point substitutions (amino acids 157 from Ile to Asn or 159 from Gly to Ser) were sufficient to abolish the interaction, whereas another mutation (amino acid 158 from Ile to Ser) had no effect on P18 virus binding. We evaluated whether there was a correlation between the ability of P18 to interact with CaMV particles and its biological activity. Aphid transmission assays were carried out and we demonstrated that the loss of the virus binding capacity had a dramatic effect on the ability of P18 to mediate aphid transmission. Thus, our results suggest that binding between P18 and virus particles is likely to be one of the molecular mechanisms involved in CaMV aphid transmission.

Patterns of nucleotide sequence variation among cauliflower mosaic virus isolates

A consensus nucleotide sequence of the DNA of nine isolates of cauliflower mosaic virus (CaMV) was used to examine variation of nucleotide sequence in CaMV. Variability in coding regions was lowest in open reading frames (ORFs) 1, 2, 3 and 5 and higher in ORFs 4 and 6. Silent substitutions were not uniformly distributed among the ORFs. The large intergenic region was also variable, particularly in loops and bulges of a predicted secondary structure for this region of the 35S RNA transcript. A profile of frequencies of the substitution of consensus nucleotides with other nucleotides revealed a deficit of A to G transitions and an excess of transversions involving A. Most insertions/deletions could be accounted for by template misalignment during replication. The results suggest that the major source of variation in CaMV DNA sequences is associated with replication by reverse transcription.

Somatic homologous recombination in planta: the recombination frequency is dependent on the allelic state of recombining sequences and may be influenced by genomic position effects

We have previously described a non-selective method for scoring somatic recombination in the genome of whole plants. The recombination substrate consists of a defective partial dimer of Cauliflower Mosaic Virus (CaMV) sequences, which can code for production of viable virus only upon homologous recombination; this leads to disease symptoms on leaves. Brassica napus plants (rapeseed) harbouring the recombination substrate as a transgene were used to examine the time in plant development at which recombination takes place. The analysis of three transgene loci revealed recombination frequencies specific for each locus. Recombination frequencies were increased if more than one transgene locus was present per genome, either in allelic (homozygosity of the transgene locus) or in non-allelic positions. In both cases, the overall recombination frequency was found to be elevated to approximately the sum of the frequencies for the individual transgene loci or slightly higher, suggesting that the respective transgene loci behave largely independently of each other. For all plants tested (single locus, two or multiple loci) maximal recombination frequencies were of the order of 10(-6) events per cell division.

The complete nucleotide sequence of cauliflower mosaic virus isolate BBC

We report the complete nucleotide sequence of BBC, a new and unique isolate of cauliflower mosaic virus (CaMV). The organization of the BBC genome agrees with that of previously sequenced CaMV isolates.

Expression of a downstream gene from a bicistronic transcription unit in transgenic tobacco plants

We have constructed a set of plasmids carrying an artificial compact stop-start codon sequence, TGATGTAACATGA, between an upstream open reading frame, terminating at one of the stop codons, and a downstream kanamycin-resistance (KmR)-encoding gene (nptII) initiating at the second ATG. These plasmids were introduced into tobacco protoplasts by direct gene transfer. The efficiency of expression of the downstream nptII gene was measured by scoring the number of KmR transformants. With a closer distance between the functional stop and start codons, a tendency to less efficient expression of nptII was found. The integration and expression of both genes as a bicistronic transcription unit were verified by Southern- and Northern-blot analyses. A possible application of the compact stop-start codon sequence for insertional mutagenesis is discussed.

Detection of cauliflower mosaic virus (CaMV) in single aphids by the polymerase chain reaction (PCR)

The detection for the first time of a plant virus in a single aphid by the high sensitivity polymerase chain reaction (PCR) technology is reported. The application of PCR for the detection of viruses in their vectors will aid the understanding of the complex virus-vector relationship and therefore allow the development of new approaches for control of spread of plant virus diseases.

Agroinfection of transgenic plants leads to viable cauliflower mosaic virus by intermolecular recombination

Intermolecular reconstitution of a plant virus has been detected in whole plants in a system using a defective cauliflower mosaic virus genome and transgenic host plants containing the missing viral gene. The information for the gene VI protein of the virus was integrated into the chromosome of host Brassica napus plants and leaves of these plants were inoculated with Agrobacterium tumefaciens containing the complementing viral sequences. In several cases, upper leaves contained replicating viral DNA which was able to incite CaMV symptoms on turnip plants. The sequence of the resultant recombinant viral molecules suggested that both DNA and RNA recombination events may have been involved in the production of functional virus, one event being gene targeting of the T-DNA.

Cauliflower mosaic virus: a 420 subunit (T = 7), multilayer structure

The structures of the Cabb-B and CM1841 strains of cauliflower mosaic virus (CaMV) have been solved to about 3 nm resolution from unstained, frozen-hydrated samples that were examined with low-irradiation cryo-electron microscopy and three-dimensional image reconstruction procedures. CaMV is highly susceptible to distortions. Spherical particles, with a maximum diameter of 53.8 nm, are composed of three concentric layers (I-III) of solvent-excluded density that surround a large, solvent-filled cavity (approximately 27 nm dia). The outermost layer (I) contains 72 capsomeric morphological units, with 12 pentavalent pentamers and 60 hexavalent hexamers for a total of 420 subunits (37-42 kDa each) arranged with T = 7 icosahedral symmetry. CaMV is the first example of a T = 7 virus that obeys the rules of stoichiometry proposed for isometric viruses by Caspar and Klug (1962, Cold Spring Harb. Symp. Quant. Biol. 27, 1-24), although the hexameric capsomers exhibit marked departure from the regular sixfold symmetry expected for a structure in which the capsid protein subunits are quasi-equivalently related. The double-stranded DNA genome is distributed in layers II and III along with a portion of the viral protein. The CaMV reconstructions are consistent with the model based on neutron diffraction studies (Kruse et al., 1987, Virology 159, 166-168) and, together, these structural models are discussed in relation to a replication-assembly model (Hull et al., 1987, J. Cell Sci. (Suppl.) 7, 213-229). Remarkable agreement between the reconstructions of CaMV Cabb-B and CM1841 suggests that other strains of CaMV adopt the same basic structure.

The regions of sequence variation in caulimovirus gene VI

The sequence of gene VI from figwort mosaic virus (FMV) clone x4 was determined and compared with that previously published for FMV clone DxS. Both clones originated from the same virus isolation, but the virus used to clone DxS was propagated extensively in a host of a different family prior to cloning whereas that used to clone x4 was not. Differences in the amino acid sequence inferred from the DNA sequences occurred in two clusters. An N-terminal conserved region preceded two regions of variation separated by a central conserved region. Variation in cauliflower mosaic virus (CaMV) gene VI sequences, all of which were derived from virus isolates from hosts from one host family, was similar to that seen in the FMV comparison, though the extent of variation was less. Alignment of gene VI domains from FMV and CaMV revealed regions of amino acid sequence identical in both viruses within the conserved regions. The similarity in the pattern of conserved and variable domains of these two viruses suggests common host-interactive functions in caulimovirus gene VI homologues, and possibly an analogy between caulimoviruses and certain animal viruses in the influence of the host on sequence variability of viral genes.

Genetic analysis of determinants of disease severity and virus concentration in cauliflower mosaic virus

Cauliflower mosaic virus (CaMV) strains CM1841 and W260 produced markedly different symptoms when inoculated onto turnips (Brassica campestris L. 'Just Right'). The CM1841 strain induced a mild degree of stunting of infected plants while strain W260 caused moderate to severe stunting. Although CM1841 was significantly milder than W260, it accumulated to a significantly higher concentration than W260 in systemically infected leaves. We constructed a series of hybrid viruses in order to map regions of W260 responsible for enhanced disease severity relative to CM1841 and to map regions of CM1841 responsible for higher virus accumulation. We found that the characteristic degree of stunting caused by a CaMV isolate is determined in a complex manner by viral genes that influence viral gene expression and viral genes that disrupt host metabolism. Genes I and VI influenced both virus concentration and stunting severity, suggesting that these regions affected disease severity primarily through their effect on gene expression. In addition, an interaction between genes IV and VI was observed which further indicated that stunting severity was influenced by differential accumulation of virus. In contrast, three regions of W260 influenced the stunting phenotype but had no effect, or a negative effect, on virus concentration. The three regions contained (1) portions of genes II and III, (2) gene IV, independent of gene VI, and (3) the 3' half of gene V and the 19 S promoter. These regions may influence stunting severity primarily by disrupting host metabolism. Additionally, some of the chimeric viruses induced systemic necrosis on leaves, a symptom that is not characteristic of either CM1841 or W260. The necrotic flecking symptom was caused by an interaction between a W260 DNA segment containing gene I and the 5' half of gene II and a CM1841 DNA segment containing the 3' half of gene II, gene III, and gene IV.

Recombination sites in cauliflower mosaic virus DNAs: implications for mechanisms of recombination

Pairs of mutant cauliflower mosaic virus (CaMV) DNAs readily recombine in plants. Five plasmid clones of CaMV DNAs resulting from infection of turnips with pairs of mutant DNAs from DNAs resulting from infection of turnips with pairs of mutant DNAs from different isolates were obtained. Restriction analysis and nucleotide sequencing identified deletions in two cloned recombinants, VR1249 and VR244B. The sequence missing in the former was consistent with its deletion by splicing of an RNA intermediate. These DNAs were not infectious in turnips. VR1243, VR244A, and VR246 induced in turnips disease symptoms that were mixtures of those produced by the parental isolates. Junctions between sequences of the parental isolates were identified by restriction fragment analysis. Three cloned chimeras resulted from multiple recombination events. Nucleotide sequencing identified more precisely the junctions in the five cloned chimeras and in three chimeras previously characterized. Consistent with a model in which reverse transcription plays a major role in generating recombinants, six chimeras had junctions at or near the site for initiation of DNA(-) strand synthesis, three had junctions near the initiation site of 35 S RNA transcription, and one junction was found near the initiation site of 19 S mRNA transcription. Junctions were also found in regions not bearing any obvious relation to DNA (-) strand synthesis by reverse transcription, suggesting that recombination of double-stranded DNAs may also generate CaMV DNA recombinants.

The cauliflower mosaic virus open reading frame VII product can be expressed in Saccharomyces cerevisiae but is not detected in infected plants

Antiserum was prepared against a synthetic peptide corresponding to the N-terminal 20 amino acids of the protein encoded by cauliflower mosaic virus (CaMV) open reading frame VII (ORF VII). This antiserum was used to detect the expression of CaMV ORF VII either in Saccharomyces cerevisiae transformed by an expression vector containing CaMV ORF VII or in CaMV-infected plants. Only in S. cerevisiae has a 14-kilodalton protein been detected.

Characteristics of a strong promoter from figwort mosaic virus: comparison with the analogous 35S promoter from cauliflower mosaic virus and the regulated mannopine synthase promoter

A segment of DNA from the genome of figwort mosaic virus (FMV) strain M3 possesses promoter activity when tested in electroporated protoplasts from, and transgenic plants of, Nicotiana tabacum cv. Xanthi nc. The 1.1 kb DNA segment, designated the '34S' promoter, is derived from a position on the FMV genome comparable to the position on the cauliflower mosaic virus (CaMV) genome containing the 35S promoter. The 34S and 35S promoters show approximately 63% nucleotide homology in the TATA, CCACT, and -18 to +1 domains, but in sequences further upstream the homology drops below 50%. Promoter activities were estimated using beta-glucuronidase and neomycin phosphotransferase II reporter gene systems. The activity of the 34S promoter segment approximates that of the 35S promoter in both protoplast transient expression assays and in stably transformed tobacco plants. Truncation of 5' sequences from the 34S promoter indicates that promoter strength depends upon DNA sequences located several hundred nucleotides upstream from the TATA box. In leaf tissue the 34S promoter is 20-fold more active than the mannopine synthase (MAS) promoter from Agrobacterium tumefaciens T-DNA. The 34S promoter lacks the root-specific and wound-stimulated expression of the MAS promoter, showing relatively uniform root, stem, leaf, and floral activities.

Disease symptoms in transgenic tobacco induced by integrated gene VI of cauliflower mosaic virus

A chimeric vector (pKR 612B1) containing the neomycin phosphotransferase (APH) gene from the Tn5 transposon under the control of the gene VI promoter of cauliflower mosaic virus (CaMV) and the cloned gene VI region (SalI-BstEII) of the same virus were used to cotransform tobacco protoplasts. Using the polyethylene glycol transformation procedure, a large number of protoplasts were transformed and proved to be resistant to kanamycin (Km). Whole Km-resistant plants were regenerated and shown to contain the integrated foreign genes. DNA from transformed clones was analyzed by Southern blot hybridization, showing the presence of the Tn5-derived gene and the viral gene. Transgenic plants containing the viral gene show mild mosaic patterns and fasciation. The expression of the gene VI product was detected by immunoblots.

The complete sequence of soybean chlorotic mottle virus DNA and the identification of a novel promoter

The complete nucleotide sequence of an infectious clone of soybean chlorotic mottle virus (SoyCMV) DNA was determined and compared with those of three other caulimoviruses, cauliflower mosaic virus (CaMV), carnation etched ring virus and figwort mosaic virus. The double-stranded DNA genome of SoyCMV (8,175 bp) contained nine open reading frames (ORFs) and one large intergenic region. The primer binding sites, gene organization and size of ORFs were similar to those of the other caulimoviruses, except for ORF I, which was split into ORF Ia and Ib. The amino acid sequences deduced from each ORF showed only short, highly homologous regions in several of the corresponding ORFs of the three other caulimoviruses. A promoter fragment of 378 bp in SoyCMV ORF III showed a strong expression activity, comparable to that of the CaMV 35S promoter, in tobacco mesophyll protoplasts as determined by a beta-glucuronidase assay using electrotransfection. The fragment contained CAAT and TATA boxes but no transcriptional enhancer signal as reported for the CaMV 35S promoter. Instead, it had sequences homologous to a part of the translational enhancer signal reported for the 5'-leader sequence of tobacco mosaic virus RNA.

Segregation of cauliflower mosaic virus symptom genetic determinants

We have created a series of hybrid cauliflower mosaic virus (CaMV) genomes between a severe virus strain (Cabb BJI) and a mild strain (Bari 1) to map the virus genetic loci responsible for specific systemic symptom characters produced in infected turnip plants. Recombinants were generated in vivo by recombinational rescue and in vitro by restriction enzyme fragment exchange. On infection, hybrids induced either parental (wild-type) symptoms or segregated parental characters. Some of the engineered hybrid genomes produced novel symptomatic effects not observed in either of the parental strains whilst others reverted to express parental symptom characters following passaging. Determinants defining differences between the two CaMV strains in respect of four specific symptom characters were delimited to separate genome regions. A locus involved in determining the rate of spread of systemic vein clearing symptoms mapped to a region containing part of gene VII and gene I (nts 109-780). This phenomenon is consistent with the putative involvement of the CaMV gene I product in mediating virus movement within infected plants. Determinants influencing the degree of leaf chlorosis were located in a separate genome domain encompassing part of gene VI together with the large intergenic region and part of gene VII (nts 6103-90). Determinants controlling timing of initial systemic symptom appearance were mapped to a region between nts 2150 and 4438 containing part of gene III, gene IV, and part of gene V. Plant stunting was influenced by loci in at least two separate regions, one containing parts of gene I and II, and a second within the reverse transcriptase gene (V). We conclude that symptoms produced by CaMV infection can be subdivided into individual characters, the genetic determinants of which segregate to different virus genetic loci and are not restricted to a single gene product.

Nucleotide sequence analysis of cDNA encoding the coat protein of cucumber mosaic virus: genome organization and molecular features of the protein

The cDNA sequence coding for the coat protein of cucumber mosaic virus (Japanese Y strain) was cloned, and its nucleotide sequence was determined. The sequence contains an open reading frame that encodes the coat protein composed of 218 amino acids. The nucleotide and deduced amino acid sequences of the coat protein of this strain were compared with those of the Q strain; the homologies of the sequences were 78% and 81%, respectively. Further study of the sequences gave an insight into the genome organization and the molecular features of the coat protein. The coding region can be divided into three characteristic regions. The N-terminal region has conserved features in the positively charged structure, the hydropathy pattern and the predicted secondary structure, although the amino acid sequence is varied mainly due to frameshift mutations. It is noteworthy that the positions of arginine residues in this region are highly conserved. Both the nucleotide and amino acid sequences of the central region are well conserved. The amino acid sequence of the C-terminal region is not conserved, because of frameshift mutations, however, the total number of amino acids is conserved. The nucleotide sequence of the 3'-noncoding region is divergent, but it could form a tRNA-like structure similar to those reported for other viruses. Detailed investigation suggests that the Y and Q strains are evolutionarily distant.

The leading sequence of caulimovirus large RNA can be folded into a large stem-loop structure

The 600 nt long sequences preceeding the first large ORFs (ORF VII) of three caulimoviruses, although varying in primary sequence, can be folded into a large stem/loop structure centered around a conserved stretch of 36 nucleotides. Deletions of the conserved sequence delay symptom appearance considerably, but do not affect expression of a reporter gene in plant protoplasts. Another striking similarity between the leaders concerns the number and distribution of small open reading frames (sORF) they carry. Expression of two of these sORFs was tested by fusion of a reporter gene: both were expressed in plant protoplasts.

Expression of CaMV ORF IV in Escherichia coli

A CaMV DNA fragment corresponding to nucleotides 2200-3992 and including the coding sequence (2200-3670) of open reading frame IV was inserted in the pTG908 prokaryotic expression vector. In the recombinant pTG-IV plasmid, ORF IV, which codes for the coat protein precursor, was fused to the N-terminal coding sequence of the lambda CII gene, which is under transcriptional control of the lambda PL promoter. The expected fusion protein CII-ORF IV had a calculated molecular weight of 58.4 Kd. Nevertheless, temperature induction of the PL promoter resulted in synthesis of a major 76-Kd fusion protein: the coat protein precursor migrated abnormally on SDS polyacrylamide gel.

Relative strengths of the 35S cauliflower mosaic virus, 1', 2', and nopaline synthase promoters in transformed tobacco sugarbeet and oilseed rape callus tissue

The 35S promoter of cauliflower mosaic virus and promoters from the nopaline synthase, 1' and 2' genes of Agrobacterium tumefaciens T-DNA were fused to the bacterial octopine synthase and chitinase gene coding regions. These chimaeric gene constructions were introduced into tobacco, sugarbeet and oilseed rape cells and their relative levels of expression measured by primer extension analysis of RNA isolated from pooled populations of stably transformed calli. In tobacco callus, the 35S promoter provided the highest levels of gene expression, followed by the 2', 1' and nopaline synthase promoters. While the ranking of these promoters is conserved in sugarbeet and oilseed rape callus, there is between-species variation in the relative strength of these promoters. In all three species, transcription initiation is conserved for each of the chimaeric gene constructions. Additional constructions in which the 5' untranslated leader of a petunia chlorophyll a/b binding protein gene is substituted for DNA downstream of the 35S transcription start site demonstrates that heterologous 5' leader sequences can be utilized to augment steady-state levels of reporter gene expression.

Host range control of cauliflower mosaic virus

Studies with recombinant genomes of cauliflower mosaic virus (CaMV) strains D4, CM1841, and Cabb-B have shown that a host range determinant of CaMV is encoded within the first half of region VI, a gene which codes for P62, an inclusion body protein. In order to further study the host specificity of CaMV, a fourth CaMV strain, W260, was chosen that has a host range that is intermediate between D4 and CM1841. To determine which portion of the W260 genome controls systemic spread, recombinant viruses made between this strain and CM1841 and D4 were tested for their ability to systemically infect several solanaceous plants (Datura stramonium, Nicotiana edwardsonii, and Nicotiana bigelovii). The first half of gene VI specified the type of local lesions and systemic spread of recombinant strains in D. stramonium. In N. edwardsonii, it was found that the first half of gene VI controlled the type of local lesion formed but systemic spread was dependent on the whole of gene VI. In N. bigelovii the number of genes that determined systemic spread of CaMV varied with the strain of CaMV. Systemic spread of D4 in N. bigelovii was dependent on the first half of gene VI. In contrast, systemic spread of W260 in the same host was dependent on the whole of gene VI and another locus which mapped within genes I-V. Consequently, it appears that other viral proteins may interact with P62 or that P62 may function well in some hosts only in compatible forms of other viral proteins.

Sequence of figwort mosaic virus DNA (caulimovirus group)

The nucleotide sequence of an infectious clone of figwort mosaic virus (FMV) was determined using the dideoxynucleotide chain termination method. The double-stranded DNA genome (7743 base pairs) contained eight open reading frames (ORFs), seven of which corresponded approximately in size and location to the ORFs found in the genome of cauliflower mosaic virus (CaMV) and carnation etched ring virus (CERV). ORFs I and V of FMV demonstrated the highest degrees of nucleotide and amino acid sequence homology with the equivalent coding regions of CaMV and CERV. Regions II, III and IV showed somewhat less homology with the analogous regions of CaMV and CERV, and ORF VI showed homology with the corresponding gene of CaMV and CERV in only a short segment near the middle of the putative gene product. A 16 nucleotide sequence, complementary to the 3' terminus of methionine initiator tRNA (tRNAimet) and presumed to be the primer binding site for initiation of reverse transcription to produce minus strand DNA, was found in the FMV genome near the discontinuity in the minus strand. Sequences near the three interruptions in the plus strand of FMV DNA bear strong resemblance to similarly located sequences of 3 other caulimoviruses and are inferred to be initiation sites for second strand DNA synthesis. Additional conserved sequences in the small and large intergenic regions are pointed out including a highly conserved 35 bp sequence that occurs in the latter region.

Detection of CaMV gene I and gene VI protein products in vivo using antisera raised to COOH-terminal β-galactosidase fusion proteins

Specific antisera were prepared to the inclusion body protein (gene VI product) and the gene I product of cauliflower mosaic virus (CaMV). Translational fusions between the lacZ gene and gene VI or gene I were constructed by cloning the relevant DNA fragments into the expression vectors pUR290, pUR291 or pUR292. Large amounts of fusion protein were synthesized when the inserted DNA fragment was in frame with the lacZ gene of the expression vector. These fusion proteins were used to raise specific antisera to gene VI and gene I proteins of CaMV. Antiserum to the gene VI product detected a range of proteins in crude extracts and in a subcellular fraction enriched for virus inclusion bodies. This range of proteins was further shown to be related to gene VI by Staphylococcus aureus V8 partial proteolysis. Antiserum to the gene I product detected viral specific proteins of 46, 42 and 38 K in preparations of CaMV replication complexes from infected plants but not in any other subcellular fraction.

Region VI of cauliflower mosaic virus encodes a host range determinant

A domain of cauliflower mosaic virus (CaMV) which controls systemic spread in two solanaceous hosts (Datura stramonium and Nicotiana bigelovii) was mapped to the first half of open reading frame 6. Whereas ordinary strains of CaMV are unable to infect solanaceous species except to replicate locally in inoculated leaves, a new CaMV strain (D4) induces chlorotic local lesions and systemically infects both D. stramonium and N. bigelovii. To determine which portion of the CaMV genome controls systemic spread of the virus in solanaceous hosts, nine recombinant genomes constructed between D4 and two ordinary strains of the virus were tested for their ability to infect solanaceous hosts. A 496-base-pair DNA segment comprising the first half of open reading frame 6 specified the type of local lesions and systemic spread of the virus in solanaceous hosts. Exchange of this segment of the genome between strains of CaMV converted a compatible host reaction to an incompatible (hypersensitive) one in response to infection. This suggests that the gene VI protein interacts with the plant to suppress hypersensitivity, the normal response of solanaceous hosts to CaMV infection.

Region VI of cauliflower mosaic virus encodes a host range determinant

A domain of cauliflower mosaic virus (CaMV) which controls systemic spread in two solanaceous hosts (Datura stramonium and Nicotiana bigelovii) was mapped to the first half of open reading frame 6. Whereas ordinary strains of CaMV are unable to infect solanaceous species except to replicate locally in inoculated leaves, a new CaMV strain (D4) induces chlorotic local lesions and systemically infects both D. stramonium and N. bigelovii. To determine which portion of the CaMV genome controls systemic spread of the virus in solanaceous hosts, nine recombinant genomes constructed between D4 and two ordinary strains of the virus were tested for their ability to infect solanaceous hosts. A 496-base-pair DNA segment comprising the first half of open reading frame 6 specified the type of local lesions and systemic spread of the virus in solanaceous hosts. Exchange of this segment of the genome between strains of CaMV converted a compatible host reaction to an incompatible (hypersensitive) one in response to infection. This suggests that the gene VI protein interacts with the plant to suppress hypersensitivity, the normal response of solanaceous hosts to CaMV infection.

Amino acid sequence homology in gag region of reverse transcribing elements and the coat protein gene of cauliflower mosaic virus

A nucleic acid binding protein (NBP) derived from the gag gene of retroviruses that is thought to interact with genomic RNA in virion cores, contains a highly conserved arrangement of cysteine residues. A search of available nucleic acid and protein sequences has revealed that the motif CysX2CysX4HisX4Cys (NBPcys) is invarient in all replication competent retroviruses, a Syrian hamster intracisternal A-particle gene, the Drosophila retrotransposon copia and in cauliflower mosaic virus (CaMV). In each case, NBPcys is located in that part of the 'gag-pol' region just preceding a conserved protease amino acid sequence. This is of special significance for CaMV as NBPcys is in the coat protein gene (ORF IV) upstream of the putative reverse transcriptase gene (ORF V) and demonstrates that the gag-pol arrangement of reverse transcribing elements is preserved in CaMV. Moreover, CaMV differs from all other known NBPcys-containing elements in that it packages a DNA genome in virions.

Oligonucleotide directed mutagenesis of cauliflower mosaic virus DNA using a repair-resistant nucleoside analogue: identification of an agnogene initiation codon

Mutation of the initiation codon of the dispensible open reading frame, ORF VII, of cauliflower mosaic virus (CaMV) delayed the appearance of disease symptoms, but the mutants reverted with high frequency. This suggests a role of this start codon in viral expression. Oligonucleotide-directed mutagenesis, utilizing a novel, repair-resistant deoxyguanosine analogue, 2'-deoxy-7-deazainosine (dDI), highly improved the yield of mutants.