Replication of Maize Streak Virus Mutants in Maize Protoplasts: Evidence for a Movement Protein

157

146

We have cloned, sequenced and analysed an additional five circular ssDNA components of banana bunchy top virus (BBTV) which we have called components 2, 3, 4, 5 and 6. These components were present in all BBTV infections tested. Four of these components (components 3, 4, 5 and 6) had one large open reading frame (ORF) in the virion sense located 3' of a stem-loop structure. Each ORF had a potential TATA box and one or two potential polyadenylation signals associated with it and each polyadenylation signal had an associated GC-rich region containing the trinucleotide sequence TTG. A number of ORFs were identified in component 2 but none of these had appropriately located potential TATA boxes and polyadenylation signals associated with them. None of the ORF amino acid sequences nor the full DNA sequences of any of the components had significant sequence identity with any known protein or nucleic acid sequences. However, the ORF of component 4 encoded a 30 residue hydrophobic domain which may indicate that this ORF encoded a transmembrane protein. Further, the ORFs of components 3 and 5 potentially encoded proteins of about 20 kDa, the size of the BBTV coat protein. There were two regions of sequence identity between the five components described here and the previously described component 1. Each component contained a conserved stem-loop structure and a nonanucleotide potential TATA box which was 5' of the large virion-sense ORF in five of the components. The stem-loop structures were incorporated in a common region (CR-SL) of 69 nucleotides which was 62 % identical between components. All six BBTV components also contained a major common region (CR-M) which was located 5' of the CR-SL in each component, in the non-coding region and was 76 % identical over 92 nucleotides. Each CR-M contained a near-complete 16 nucleotide direct repeat and a GC-box which was similar to the rightward promoter element found in wheat dwarf geminivirus. From these results, BBTV appears to belong to an undescribed plant virus group which could also include subterranean clover stunt virus, coconut foliar decay virus, faba bean necrotic yellows virus and milk vetch dwarf virus.

Section: Discussionsupporting

confidence: 56%

Section: Sequence Comparisons and Analysismentioning

confidence: 98%

The genome organization of banana bunchy top virus: analysis of six ssDNA components

Burns¹,

Harding

Dale³

1995

157

146

“…The functions of the genes encoded by these two components have not been definitively determined. However, the major translational product of BBTV DNA-4 contains a β-sheet of 30 hydrophobic residues toward CDAI the N terminus (Burns et al, 1995), which is similar to a transmembrane domain identified in the V1 proteins of the cerealinfecting geminiviruses (Boulton et al, 1993), suggesting this protein may be involved with cell-to-cell movement. BBTV DNA-5 is the most efficiently primed of all six BBTV components (Hafner et al, 1997 a).…”

Section: Discussionmentioning

confidence: 89%

Promoter activity associated with the intergenic regions of banana bunchy top virus DNA-1 to -6 in transgenic tobacco and banana cells.

Dugdale

Beetham

Becker

et al. 1998

Promoter regions associated with each of the six ssDNA components of banana bunchy top virus (BBTV) have been characterized. DNA segments incorporating the intergenic regions of BBTV DNA-1 to -6 were isolated and fused to the uidA (β-glucuronidase) reporter gene to assess promoter activity. In tobacco cell suspensions, the BBTV DNA-2 and -6 promoters generated levels of GUS expression 2-fold greater and similar to the 800 bp CaMV 35S promoter, respectively. Deletion analysis of the BBTV DNA-6 promoter suggested all the necessary promoter elements required for strong expression were located within 239 nucleotides upstream of the translational start codon. In transgenic tobacco plants, the BBTV-derived promoters generally provided a weak, tissue-specific GUS

“…Conservation of putative gene products between subgroup I members (Table 1) suggests possible functions for the BeYDV genes. The product of maize streak virus (MSV) ORF V1 is required for virus movement (Boulton et al, 1993). Of note, the hydrophobic domain identified in MSV protein V1 and considered to be membrane-associated (Boulton et al, 1993) is conserved in BeYDV.…”

mentioning

confidence: 99%

“…The product of maize streak virus (MSV) ORF V1 is required for virus movement (Boulton et al, 1993). Of note, the hydrophobic domain identified in MSV protein V1 and considered to be membrane-associated (Boulton et al, 1993) is conserved in BeYDV. MSV ORF V2 encodes the coat protein (Morris-Krsinich et al, 1985).…”

mentioning

confidence: 99%

Molecular characterization of a subgroup I geminivirus from a legume in South Africa.

Liu

Tonder²,

Pietersen

et al. 1997

A South African geminivirus for which we propose the name bean yellow dwarf virus (BeYDV) has been isolated from French bean (Phaseolus vulgaris cv. Bonus) showing stunting, chlorosis and leaf curl symptoms. A full-length cloned copy of the viral genome produced characteristic symptoms of the disease when reintroduced into French bean by agroinoculation, and was systemically infectious in Nicotiana benthamiana, N. tabacum, Lycopersicon esculentum, Datura stramonium and Arabidopsis thaliana. BeYDV resembles subgroup I geminiviruses which infect monocotyledonous plants in having a single DNA component, two non-overlapping virion-sense (V1 and V2) and two overlapping complementary-sense (C1 and C2) coding regions, and an intron within the complementarysense coding regions that is excised to produce a C1C2 fusion protein. It is most closely related to tobacco yellow dwarf virus from Australia, the only subgroup I geminivirus previously known to infect dicotyledonous plants, although it is sufficiently dissimilar (65 % nucleotide sequence identity) to be considered a distinct virus.A disease occurring on French beans (Phaseolus vulgaris) has recently been responsible for severe yield losses in South Africa. The highest incidence of the disease occurred in the Northern Province and Mpumalanga districts, where it has been estimated to cause 85-92 % reduction in bean yield in French bean (cv. Bonus). Symptoms of the disease are brittle and leathery primary leaves, thickened and shortened internodes and downward curling of young leaves. Preliminary