Huanglongbing (HLB), considered to be the most serious insect-vectored bacterial disease of citrus, is transmitted in nature by the Asian citrus psyllid Diaphorina citri and the African citrus psyllid Trioza erytreae. D. citri was discovered in southern Florida in 1998 and the HLB disease in 2005. Both have become established throughout citrus-producing areas of Florida. Murraya species are widely grown in southern Florida as ornamental hedges and are readily colonized by D. citri vectors. Colonies of D. citri, isolates of ‘Candidatus Liberibacter asiaticus’ from Taiwan and Florida, and the Murraya species were established in the BSL-3 biosecurity facility at Fort Detrick. In controlled inoculation experiments, D. citri transmitted ‘Ca. L. asiaticus’ into M. paniculata (34/36 plants) and M. exotica (22/23 plants), but not into Bergera (Murraya) koenigii. Disease symptoms rarely developed in Murraya plants; however, positive infections were determined by conventional and real-time polymerase chain reaction (PCR). Back-inoculations of ‘Ca. L. asiaticus’ from M. paniculata to Madam Vinous sweet orange resulted in disease development in 25% of the inoculated plants. Considerable variability was observed in infection rates, titer, and persistence of ‘Ca. L. asiaticus’ in infected Murraya.
Ribosome recoding is used by RNA viruses for translational readthrough or frameshifting past termination codons for the synthesis of extension products. Recoding sites, along with downstream recoding stimulatory elements (RSEs), have long been studied in reporter constructs, because these fragments alone mediate customary levels of recoding and are thus assumed to contain complete instructions for establishment of the proper ratio of termination to recoding. RSEs from the Tombusviridae and Luteoviridae are thought to be exceptions, since they contain a long-distance RNA-RNA connection with the 3= end. This interaction has been suggested to substitute for pseudoknots, thought to be missing in tombusvirid RSEs. We provide evidence that the phylogenetically conserved RSE of the carmovirus Turnip crinkle virus (TCV) adopts an alternative, smaller structure that extends an upstream conserved hairpin and that this alternative structure is the predominant form of the RSE within nascent viral RNA in plant cells and when RNA is synthesized in vitro. The TCV RSE also contains an internal pseudoknot along with the long-distance interaction, and the pseudoknot is not compatible with the phylogenetically conserved structure. Conserved residues just past the recoding site are important for recoding, and these residues are also conserved in the RSEs of gammaretroviruses. Our data demonstrate the dynamic nature of the TCV RSE and suggest that studies using reporter constructs may not be effectively recapitulating RSE-mediated recoding within viral genomes. IMPORTANCERibosome recoding is used by RNA viruses to enable ribosomes to extend translation past termination codons for the synthesis of longer products. Recoding sites and a downstream recoding stimulatory element (RSE) mediate expected levels of recoding when excised and placed in reporter constructs and thus are assumed to contain complete instructions for the establishment of the proper ratio of termination to recoding. We provide evidence that most of the TCV RSE adopts an alternative structure that extends an upstream conserved hairpin and that this alternative structure, and not the phylogenetically conserved structure, is the predominant form of the RSE in RNA synthesized in vitro and in plant cells. The TCV RSE also contains an internal pseudoknot that is not compatible with the phylogenetically conserved structure and an RNA bridge to the 3= end. These data suggest that the TCV RSE is structurally dynamic and that multiple conformations are likely required to regulate ribosomal readthrough. P ositive-sense RNA viruses employ a variety of gene expression strategies for the diversification of their proteomes (1, 2). Two noncanonical mechanisms, Ϫ1 programmed ribosomal frameshifting (Ϫ1PRF) and programmed ribosomal readthrough (PRT), circumvent stop codons for the expression of carboxyterminal extension products, effectively economizing on the limited genome size of most RNA viruses (3, 4). In Ϫ1PRF, the elongating ribosome shifts back 1 residue at a 7-residue...
The Panicum mosaic virus-like translation enhancer (PTE) functions as a cap-independent translation enhancer (3’CITE) in members of several Tombusviridae genera including 7/19 carmoviruses. For nearly all PTE, a kissing-loop connects the element with a hairpin found in several conserved locations in the genomic RNA (5’ terminal hairpin or ~100 nt from the 5’end) and small subgenomic RNA (~63 nt from the 5’end). Moving the interaction closer to the 5’end in reporter mRNAs using Saguaro cactus virus (SCV) sequences had either a minimal or substantial negative effect on translation. Movement of the kissing loop from position 104 to the SCV 5’ terminal hairpin also reduced translation by 4-fold. These results suggest that relocating the PTE kissing loop closer to the 5’end reduces PTE efficiency, in contrast to results for the Barley yellow dwarf BTE and Tomato bushy stunt virus Y-shaped 3’CITEs , suggesting that different 3’CITEs have different bridging requirements.
Damsteegt, V. D., Stone, A. L., Kublmann, M., Gildow, F E., Domier, L. L., Sherman, D. J., Tian, B., and Schneider, W. L. 2011. Acquisition and transmissibility of U.S. Soybean dwarf virus isolates by tbe soybean aphid. Aphis glycines. Plant Dis. 95:945-950.Soybean dwarf virus (SbDV) exists as several distinct strains based on symptomatology, vector specificity, and host range. Originally characterized Japanese isolates of SbDV were specifically transmitted by Aulacorthum solani. More recently, additional Japanese isolates and endemic U.S. isolates bave been shown to be transmitted by several different apbid species. The soybean aphid. Aphis glycines, tbe only aphid that colonizes soybean, has been shown to be a very inefficient vector of some SbDV isolates from Japan and the United States. Transmission experiments have shown that tbe soybean apbid can transmit certain isolates of SbDV from soybean to soybean and clover species and from clover to clover and soybean witb long acquisition and inoculation access periods. Although transmission of SbDV by tbe soybean apbid is very inefficient, tbe large soybean apbid populations that develop on soybean may have epidemiological potential to produce serious SbDV-induced yield losses.Soybean dwarf virus (SbDV) is the causal agent of an economically important disease of soybean (Glycine max (L.) Merr.) in Japan (34-37) and a minor disease of other crops elsewhere (21). The causal virus has been transmitted to more than 50 species of forage legumes, pulse crops, and other broadleaf plants representing three families (1,5,6,18,21).As a member of the Luteoviridae, SbDV is transmitted only by apbids in a circulative, persistent manner. It is pbloem-limited and occurs in low concentration in plants (32). Tbe virus consists of several distinct strains based on symptomatology in soybeans, specificity of transmission by apbid species, physiochemical properties, and nucleotide sequence (5,27-30,37). The originally described Japanese soybean strains (SbDV-DS and SbDV-YS), hereinafter called SbDV-D and SbDV-Y, and a subterranean clover red-leaf virus (SCRLV, now synonymous with SbDV) described in Australia (20) were transmitted almost exclusively by Aulacorthum solani Kaltenbacb. An isolate serologically related to SCRLV found in California (19), and other related isolates found worldwide, were transmitted by Acyrthosiphon pisum (Harris) and other aphid species (7,11,16,22,23), and not by A. solani. More recently, dwarfing and yellowing strains of SbDV (SbDV-DP and SbDV-YP) have been described from Japan tbat were transmitted by Acyrthosiphon pisum (37). Except for one report (15), all earlier attempts to transmit strains of SbDV by tbe soybean aphid Aphis glycines Matsumora have been unsuccessful (11,32,41). The soybean apbid has been reported to transmit several plant vinises (4,11) including tbe Indonesian Soybean dwarf virus (17). Tbe Indonesian SbDV was shown to be serologically distinct from Japanese SbDV isolates, and no further reports about this virus could be found.Corresp...
Soybean dwarf virus (SbDV), first identified as an agricultural problem in Japan, has emerged as a growing problem in the Midwestern United States. The majority of research on SbDV had been limited to four lab maintained strains from Japan. SbDV had been found in clover in the eastern United States, but these isolates rarely emerged into soybeans. These isolates were analyzed by multiplex PCR and sequencing, revealing that some were infections of both Y and D components, including a recombinant subisolate. Phylogenetic analyses for the US isolates revealed a broad diversity of SbDV, with selection pressure greater on the movement protein than the coat protein. The field isolates from the Eastern United States showed differences in symptoms, aphid transmission and host range, demonstrating that a study of field isolates is an important complement to laboratory maintained strains in understanding the biology and evolution of plant viruses.
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