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Chloroplast phosphoglycerate kinase, a gluconeogenetic enzyme, is required for efficient accumulation of Bamboo mosaic virus.

The tertiary structure in the 3'-untranslated region (3'-UTR) of Bamboo mosaic virus (BaMV) RNA is known to be involved in minus-strand RNA synthesis. Proteins found in the RNA-dependent RNA polymerase (RdRp) fraction of BaMV-infected leaves interact with the radio labeled 3'-UTR probe in electrophoretic mobility shift assays (EMSA). Results derived from the ultraviolet (UV) cross-linking competition assays suggested that two cellular factors, p43 and p51, interact specifically with the 3'-UTR of BaMV RNA. p43 and p51 associate with the poly(A) tail and the pseudoknot of the BaMV 3'-UTR, respectively. p51-containing extracts specifically down-regulated minus-strand RNA synthesis when added to in vitro RdRp assays. LC/MS/MS sequencing indicates that p43 is a chloroplast phosphoglycerate kinase (PGK). When the chloroplast PKG levels were knocked down in plants, using virus-induced gene silencing system, the accumulation level of BaMV coat protein was also reduced.

3' Untranslated Regions↗

The rice mutant dwarf bamboo shoot 1: a leaky mutant of the NACK-type kinesin-like gene can initiate organ primordia but not organ development.

That plant dwarfism is caused by hormonal defects related to gibberellin and brassinosteroid has been well documented. Other contributing elements, however, have not been elucidated. Here, we report on one of the most severe dwarf mutants of rice, dwarf bamboo shoot 1 (dbs1). Most mutant plants died within 1 month after sowing, but a few (5.2%) survived and grew. Vacuolation enlarged cells in the leaf primordia and seminal root before abortion, which disrupted the organized cell files in these organs. Relative to the severe defects in shoot and root growth, the overall structure of the dbs1 embryo was almost normal. Similarly, initiation and organogenesis of the leaf primordia at the shoot apical meristem and those of the lateral root primordia at the root elongation zone occurred normally. These observations suggest that DBS1 is involved in the growth and development of organs but not in organ initiation or organogenesis. Positional cloning of DBS1 revealed that it encoded a NACK-type kinesin-like protein (OsNACK), homologous to the essential components of a mitogen-activated protein kinase cascade during plant cytokinesis. A BLAST search indicated that DBS1 was the only gene encoding the OsNACK-type protein in the rice genome, and the dbs1 mutant produced only small amounts of the translatable DBS1 mRNA. Thus, we conclude that the dbs1 mutation causes a severe defect in DBS1 function but does not completely shut it down. We discuss the leaky phenotype of dbs1 under the restricted functioning of OsNACK.

Cell Division↗

Floral biology and breeding behavior in the bamboo Dendrocalamus strictus Nees.

Floral biology and breeding behavior were studied in the bamboo Dendrocalamus strictus Nees. The inflorescence in this species is a large branching panicle. Fertile florets are intermixed with smaller sterile ones. There are six stamens. The ovary is stipitate and turbinate. The style is long and the stigma is bifid and plumose. Dendrocalamus strictus is typically dichogamous and protogynous. The gynoecium matures 3-4 days before the androecium, effectively preventing self pollination. Flower bloom, which took place over a period of 2 to 3 h, was dependent on air temperature and only occurred between 0600 and 1300 h. Dendrocalamus strictus is anemophilous. Flowers in the male phase were visited by insects. These insects completely neglected the flowers at the female phase. The insects fed on the pollen and were not pollen vectors. When wind was excluded by enclosing the inflorescences in bags there was no seed set, indicating that cross pollination by wind is necessary for fertilization and that parthenocarpy and apomixis are not occurring in this species. Pollen fertility was about 98% as indicated by staining fresh pollen at the time of anther dehiscence and pollen release with Alexander's stain (Alexander 1969). When placed on a modified Brewbaker-Kwak medium containing 1% glucose, the pollen grains germinated well, and the pollen tubes grew to 15-20 times the diameter of mature pollen grains. Although profound protogyny has its disadvantages in times of sporadic flowering, it can be useful in breeding programs because it eliminates the need for emasculation.

Journal Article↗

Nucleotide sequence of the genomic RNA of bamboo mosaic potexvirus.

The complete nucleotide sequence of the genomic RNA of bamboo mosaic virus (BaMV) was determined by sequencing a set of overlapping cDNA clones and by direct sequencing of the viral RNA. The RNA genome of BaMV is 6366 nucleotides long [excluding 3'poly(A) tail] and contains six open reading frames (ORFs 1 to 6) coding for polypeptides with M(r) values of 155K, 28K, 13K, 6K, 25K and 14K, respectively. The genome organization and sizes of the encoded proteins are very similar to those of other potexviruses which have been sequenced except that ORF 6 lies completely within ORF 1. The first five putative proteins of the BaMV genome show identities ranging between 44 to 59%, 26 to 49%, 30 to 53%, 15 to 35% and 20 to 30%, respectively, to the corresponding ORFs of other members of the potexvirus group. However the putative product ORF 6 shows no significant similarity to those of other potexvirus ORF products.

Amino Acid Sequence↗

Subcellular localization of the 28 kDa protein of the triple-gene-block of bamboo mosaic potexvirus.

Open reading frame 2 of the bamboo mosaic potexvirus (BaMV) genome encodes a 28 kDa protein, the first of the "triple-gene-block' of BaMV which is believed to play a role in cell-to-cell movement of the virus in host plants. The 28 kDa protein was expressed in Escherichia coli and polyclonal antiserum was raised in a rabbit. Western blot analyses showed that the 28 kDa protein was associated mainly with components in the cell wall and 30000 g pellet fractions of a BaMV-infected leaf homogenate. Immunogold electron microscopy of infected leaf tissues revealed that the 28 kDa protein was associated with electron-dense crystal-line bodies (EDCBs) in the cytoplasm and nuclei. Nuclear EDCBs were found closely associated with nucleoli. Gold-labelled EDCB-like structures were also detected in the cytoplasm, but not within nuclei, in protoplasts up to 48 h post-inoculation. No specific labelling of the 28 kDa protein was found within any cytoplasmic structures or within cell walls.

Animals↗

Subgenomic RNAs of bamboo mosaic potexvirus-V isolate are packaged into virions.

Purified virions of bamboo mosaic potexvirus-V isolate (BaMV-V) were found to contain three major RNA species, the 6.4 kb genomic RNA and two RNAs of 2.0 and 1.0 kb, in addition to associated satellite RNA (0.85 kb). Results of Northern blot hybridization, primer extension analysis and cDNA sequencing showed that the packaged 2.0 and 1.0 kb RNAs of BaMV-V were subgenomic RNAs. In contrast, in the BaMV-O isolate, only genomic RNA was packaged and encapsidated subgenomic RNAs were not detectable. The transcription initiation sites for the 2.0 and 1.0 kb subgenomic RNAs of BaMV-V were located 1 1 and 16 nt upstream of the initiation codon of open reading frames (ORFs) 2 and 5, respectively. The 2.0 and 1.0 kb subgenomic RNAs functioned as messengers for the ORF2 protein and capsid protein, respectively. Packaging of the 1.0 kb subgenomic RNAs resulted in the formation of rod-shaped particles about 70 nm in length. Our results indicate that BaMV isolates have evolved distinctly for packaging of subgenomic RNAs.

Capsid↗

Identification of the RNA-binding sites of the triple gene block protein 1 of bamboo mosaic potexvirus.

The triple gene block protein 1 (TGBp1) encoded by open reading frame 2 of bamboo mosaic potexvirus (BaMV) was overexpressed in Escherichia coli and purified in order to test its RNA-binding activity. UV crosslinking assays revealed that the RNA-binding activity was present mainly in the soluble fraction of the refolded TGBp1. The binding activity was nonspecific and salt concentration-dependent: activity was present at 0-50 mM NaCl but was almost abolished at 200 mM. The RNA-binding domain was located by deletion mutagenesis to the N-terminal 3-24 amino acids of TGBp1. Sequence alignment analysis of the N-terminal 25 amino acids of the TGBp1 homologues of potexviruses identified three arginine residues. Arg-to-Ala substitution at any one of the three arginines eliminated most of the RNA-binding activity, indicating that they were all critical to the RNA-binding activity of the TGBp1 of BaMV.

Amino Acid Sequence↗

Arg-16 and Arg-21 in the N-terminal region of the triple-gene-block protein 1 of Bamboo mosaic virus are essential for virus movement.

The protein encoded by the first gene of the triple gene block (TGBp1) of potexviruses is required for movement of the viruses. It has been reported that single Arg-->Ala substitutions at position 11, 16 or 21 of TGBp1 of Bamboo mosaic virus (BaMV) eliminate its RNA-binding activity, while substitutions at position 16 or 21 only affect its NTPase activity (Liou et al., Virology 277, 336-344, 2000). However, it remains unclear whether these Arg-->Ala substitutions also affect the movement of BaMV in plants. To address this question, six mutants of BaMV, each containing either a single- or a double-alanine substitution at Arg-11, Arg-16 and Arg-21 of TGBp1, were constructed and used to infect Chenopodium quinoa and Nicotiana benthamiana. We found that all of the BaMV mutants were able to replicate in protoplasts of N. benthamiana. However, only the mutant with an Arg-11-->Ala substitution in TGBp1 remained capable of movement from cell to cell in plants. Mutants with Arg-16, Arg-21 or both Arg-16 and Arg-21 of TGBp1 replaced with alanine were defective in virus movement. This defect was suppressed when a wild-type TGBp1 allele was co-introduced into the cells using a novel satellite replicon. The ability to trans-complement the movement defect by the wild-type TGBp1 strongly suggests that the Arg-->Ala substitution at position 16 or 21 of TGBp1, which diminishes the RNA-binding and NTPase activities of TGBp1, also eliminates the capability of BaMV to move from cell to cell in host plants.

Alanine↗

Movement of potexviruses requires species-specific interactions among the cognate triple gene block proteins, as revealed by a trans-complementation assay based on the bamboo mosaic virus satellite RNA-mediated expression system.

The intra- and intercellular transport of potexviruses require interactions among viral RNA, coat protein and elements of the triple gene block proteins (TGBps). In this study, the requirement of bamboo mosaic virus (BaMV) TGBps for movement functions and the compatibilities with those of two potexviruses, Potato virus X (PVX) and Foxtail mosaic virus (FoMV), were examined using a satellite RNA-mediated trans-complementation assay system. Single or multiple TGBps of BaMV, PVX and FoMV were expressed from BaMV satellite RNA (satBaMV RNA) vectors to complement the functions of green fluorescent protein-tagged, movement-defective BaMV with mutation(s) in the matching gene(s). It was found that individual BaMV TGBps expressed from the satellite vector could function normally in trans, whereas bi-gene BaMV TGBp constructs in which the expression of TGBp3 might be impaired and individual TGBp genes from PVX or FoMV could not complement the movement functions of the defective helper viruses. Furthermore, alterations of the ratio among TGBps by ectopic expression of individual components of TGBps from satBaMV RNA vectors did not affect the cell-to-cell movement capabilities of wild-type BaMV significantly. The results indicate that species-specific interactions among movement proteins are obligatory for the cell-to-cell movement of BaMV and possibly other potexviruses.

Genetic Techniques↗

Purification and Characterization of Sucrose Synthetase from the Shoot of Bamboo Leleba oldhami.

A 108-fold purification of the sucrose synthetase from the extract of the shoot of bamboo Lelaba oldhami was achieved by ammonium sulfate fractionation, calcium phosphate gel adsorption, and chromatographic separations on Sephadex G-100 and diethylaminoethyl-cellulose columns. Some properties of this enzyme, namely thermal and pH stabilities, stabilization by aqueous glycerol, pH optimum, substrate specificities, effects of metallic ions, effects of sulfhydryl reagents, molecular weight, sedimentation constants, isoelectric point, and substrate saturation kinetics had been investigated.The substrate saturation kinetics indicated that the enzyme could be an allosteric enzyme with the saccharide substrates (sucrose and fructose) serving as the homotropic allosteric effectors in regulating the biosynthesis and degradation of sucrose.

Journal Article↗

Half-sib family structure of Fagus crenata saplings in an old-growth beech-dwarf bamboo forest.

Half-sib family structure of Fagus crenata saplings was examined in an old-growth beech-dwarf bamboo (Sasa spp.) forest using microsatellite genotypes in parentage analysis to identify the half-sib families in two 50 x 50 m plots: one with 36 adults, 641 saplings and no Sasa cover, the other with 21 adults, 61 saplings and Sasa cover. For large proportions of the saplings (44.6% and 75.4%, respectively) both of their parents were found within the same plot, indicating that pollination events frequently involved short-range pollen dispersal, probably because of the high density of adults in the study population. Although almost all of the adults had half-sib families, the number of offspring in the families was highly variable. In the plot with no Sasa cover, the variation in the number of offspring was significantly explained by the size of parents, i.e. the reproductive success is higher for large adults than for small adults. The half-sibs were aggregately distributed around their parents and the distribution overlapped among different half-sib families, which may be due to the limited seed dispersal and overlapping seed shadows of this species. As expected, there was weak genetic structure in the plot. By contrast, in the plot with Sasa cover, the half-sibs were distributed sparsely with a low density, and the degree of genetic structure was very weak. The difference in the half-sib family structure and genetic structure among saplings presumably reflects the difference in density that should be affected by regeneration dynamics associated with environmental conditions.

Demography↗

Bamboo-joint-like appearance of the stomach: a histopathological study.

A bamboo joint-like (BJL) appearance is an endoscopic finding characterized by swollen longitudinal folds transversed by erosive fissures or linear furrows, and it seems to be associated with Crohn's disease (CD). We performed gastroduodenoscopy in 1781 patients, and found BJL lesions in 15 (65.2%) of 23 CD patients and 20 (1.1%) of 1758 non-CD patients. Histological examination of the biopsy specimens showed sharp, fissure-like erosion or mucosal cleft in 7 (50%) out of 14 CD patients and one (20%) out of 5 non-CD patients. All cases with fissure-like erosion or, mucosal cleft revealed lymphoid aggregates, eosinophilic infiltration and edema in the superficial portion of the surrounding lamina propria. Epithelioid granuloma was seen at the base of the fissure-like erosion in two cases with CD. Our results indicated that fissure-like erosion or mucosal cleft in gastric biopsy specimens reflects the BJL appearance, and that such findings may provide a diagnostic clue to CD.

Adult↗

Endosymbiotic microbiota of the bamboo pseudococcid Antonina crawii (Insecta, Homoptera).

We characterized the intracellular symbiotic microbiota of the bamboo pseudococcid Antonina crawii by performing a molecular phylogenetic analysis in combination with in situ hybridization. Almost the entire length of the bacterial 16S rRNA gene was amplified and cloned from A. crawii whole DNA. Restriction fragment length polymorphism analysis revealed that the clones obtained included three distinct types of sequences. Nucleotide sequences of the three types were determined and subjected to a molecular phylogenetic analysis. The first sequence was a member of the gamma subdivision of the division Proteobacteria (gamma-Proteobacteria) to which no sequences in the database were closely related, although the sequences of endosymbionts of other homopterans, such as psyllids and aphids, were distantly related. The second sequence was a beta-Proteobacteria sequence and formed a monophyletic group with the sequences of endosymbionts from other pseudococcids. The third sequence exhibited a high level of similarity to sequences of Spiroplasma spp. from ladybird beetles and a tick. Localization of the endosymbionts was determined by using tissue sections of A. crawii and in situ hybridization with specific oligonucleotide probes. The gamma- and beta-Proteobacteria symbionts were packed in the cytoplasm of the same mycetocytes (or bacteriocytes) and formed a large mycetome (or bacteriome) in the abdomen. The spiroplasma symbionts were also present intracellularly in various tissues at a low density. We observed that the anterior poles of developing eggs in the ovaries were infected by the gamma- and beta-Proteobacteria symbionts in a systematic way, which ensured vertical transmission. Five representative pseudococcids were examined by performing diagnostic PCR experiments with specific primers; the beta-Proteobacteria symbiont was detected in all five pseudococcids, the gamma-Proteobacteria symbiont was found in three, and the spiroplasma symbiont was detected only in A. crawii.

Animals↗

Identification and characterization of the Escherichia coli-expressed RNA-dependent RNA polymerase of bamboo mosaic virus.

Bamboo mosaic virus (BaMV), a member of the potexvirus group, infects primarily members of the Bambusoideae. The open reading frame 1 (ORF1) of BaMV encodes a 155-kDa polypeptide that was postulated to be involved in the replication and the formation of cap structure at the 5' end of the viral genome. To characterize the activities associated with the 155-kDa viral protein, it was expressed in Escherichia coli BL21(DE3) cells with thioredoxin, hexahistidine, and S. Tag fused consecutively at its amino terminus, and the fusion protein was purified by metal affinity chromatography. Several RNA fragments, prepared by in vitro transcription, were tested as substrates for the RNA-dependent RNA polymerase (RdRp) activity. Among them, the expressed fusion enzyme was able to generate a 32P-labeled RNA product when 3'-end RNA fragments of the positive strand or negative strand of BaMV were included in the assay mixture. Dot hybridization assay revealed that the reaction products are complementary to their RNA substrates. Taken together, the evidence suggests that the 155-kDa protein encoded by ORF1 of BaMV has an RdRp activity and should be involved in the replication of BaMV. Mutational analyses demonstrate the importance of the GDD motif in the polymerase activity, and deletion studies suggest that the polymerase activity resides in the carboxyl terminus of the 155-kDa viral protein.

Base Sequence↗

Sufficient length of a poly(A) tail for the formation of a potential pseudoknot is required for efficient replication of bamboo mosaic potexvirus RNA.

RNAs transcribed from a full-length infectious cDNA clone of the bamboo mosaic potexvirus (strain O) genome, pBaMV-O, were infectious to Nicotiana benthamiana plants. Mutant genomes in which the poly(A) tail is absent or replaced by a 3' tRNA-like structure from turnip yellow mosaic virus RNA failed to amplify detectably in N. benthamiana protoplasts. No amplification was detected in protoplasts inoculated with transcripts containing 4, 7, or 10 adenylate residues at the 3' end, whereas transcript inocula with 15 adenylate residues resulted in coat protein accumulation to a level 26% of that resulting from inoculation with transcripts with 25 adenylate residues (designated as wild type). Coat protein accumulation levels of 69 and 98% relative to wild type were observed after inoculation of protoplasts with transcripts bearing poly(A) tails 18 and 22 nucleotides long, respectively. The presence of a putative 3' pseudoknot structure including at least 13 adenylate residues of the 3'-terminal poly(A) tail was supported by enzymatic and chemical structural analysis. The functional relevance of this putative pseudoknot was tested by mutations that affected basepairing within the pseudoknot. These results support the existence of functional 3' pseudoknot that includes part of the 3' poly(A) tail.

Base Sequence↗

Bamboo mosaic potexvirus satellite RNA (satBaMV RNA)-encoded P20 protein preferentially binds to satBaMV RNA.

A satellite RNA of 836 nucleotides [excluding the poly(A) tail] depends on the bamboo mosaic potexvirus (BaMV) for its replication and encapsidation. The BaMV satellite RNA (satBaMV) contains a single open reading frame encoding a 20-kDa nonstructural protein (P20). The P20 protein with eight histidine residues at the C terminus was overexpressed in Escherichia coli. Experiments of gel retardation, UV cross-linking, and Northwestern hybridization demonstrated that purified P20 was a nucleic-acid-binding protein. The binding of P20 to nucleic acids was strong and highly cooperative. P20 preferred binding to satBaMV- or BaMV-related sequences rather than to nonrelated sequences. By deletion analysis, the P20 binding sites were mainly located at the 5' and 3' untranslated regions of satBaMV RNA, and the RNA-protein interactions could compete with the poly(G) and, less efficiently, with the poly(U) homopolymers. The N-terminal arginine-rich motif of P20 was the RNA binding domain, as shown by in-frame deletion analysis. This is the first report that a plant virus satellite RNA-encoded nonstructural protein preferentially binds with nucleic acids.

Amino Acid Sequence↗

Characterization of the AdoMet-dependent guanylyltransferase activity that is associated with the N terminus of bamboo mosaic virus replicase.

Bamboo mosaic virus (BaMV), a member of the potexvirus group, infects primarily members of the Bambusoideae. Open reading frame 1 (ORF1) of BaMV encodes a 155-kDa polypeptide that has long been postulated to be a replicase involved in the replication and formation of the cap structure at the 5' end of the viral genome. To identify and characterize the enzymatic activities associated with the N-terminal domain of the BaMV ORF1 protein, the intact replicase and two C-terminally truncated proteins were expressed in Saccharomyces cerevisiae. All three versions of BaMV ORF1 proteins could be radiolabeled by [alpha-(32)P]GTP, which is a characteristic of guanylyltransferase activity. The presence of S-adenosylmethionine (AdoMet) was essential for this enzymatic activity. Thin-layer chromatography analysis suggests that the radiolabeled moiety linked to the N-terminal domain of the BaMV ORF1 protein is m(7)GMP. The N-terminal domain also exhibited methyltransferase activity that catalyzes the transfer of the [(3)H]methyl group from AdoMet to GTP or guanylylimidodiphosphate. Therefore, during cap structure formation in BaMV, methylation of GTP may occur prior to transguanylation as for alphaviruses and brome mosaic virus. This study establishes the association of RNA capping activity with the N-terminal domain of the replicase of potexviruses and further supports the idea that the reaction sequence of RNA capping is conserved throughout the alphavirus-like superfamily of RNA viruses.

Amino Acid Sequence↗

Sequences at the 3' untranslated region of bamboo mosaic potexvirus RNA interact with the viral RNA-dependent RNA polymerase.

The 3' untranslated region (UTR) of bamboo mosaic potexvirus (BaMV) genomic RNA was found to fold into a series of stem-loop structures including a pseudoknot structure. These structures were demonstrated to be important for viral RNA replication and were believed to be recognized by the replicase (C.-P. Cheng and C.-H. Tsai, J. Mol. Biol. 288:555-565, 1999). Electrophoretic mobility shift and competition assays have now been used to demonstrate that the Escherichia coli-expressed RNA-dependent RNA polymerase domain (Delta 893) derived from BaMV open reading frame 1 could specifically bind to the 3' UTR of BaMV RNA. No competition was observed when bovine liver tRNAs or poly(I)(C) double-stranded homopolymers were used as competitors, and the cucumber mosaic virus 3' UTR was a less efficient competitor. Competition analysis with different regions of the BaMV 3' UTR showed that Delta 893 binds to at least two independent RNA binding sites, stem-loop D and the poly(A) tail. Footprinting analysis revealed that Delta 893 could protect the sequences at loop D containing the potexviral conserved hexamer motif and part of the stem of domain D from chemical cleavage.

3' Untranslated Regions↗