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1.
Science ; 273(5273): 370-3, 1996 Jul 19.
Artigo em Inglês | MEDLINE | ID: mdl-8662527
2.
Plant Cell ; 8(12): 2277-2294, 1996 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-12239378

RESUMO

Resistance to cowpea mosaic virus (CPMV) in transgenic Nicotiana benthamiana plants is RNA mediated. In resistant CPMV movement protein (MP) gene-transformed lines, transgene steady state mRNA levels were low, whereas nuclear transcription rates were high, implying that a post-transcriptional gene-silencing mechanism is at the base of the resistance. The silencing mechanism can also affect potato virus X (PVX) RNAs when they contain CPMV MP gene sequences. In particular, sequences situated in the 3[prime] part of the transcribed region of the MP transgene direct elimination of recombinant PVX genomes. Remarkably, successive portions of this 3[prime] part, which can be as small as 60 nucleotides, all tag PVX genomes for degradation. These observations suggest that the entire 3[prime] part of the MP transgene mRNA is the initial target of the silencing mechanism. The arrangement of transgenes in the plant genome plays an important role in establishing resistance because the frequency of resistant lines increased from 20 to 60% when transformed with a transgene containing a direct repeat of MP sequences rather than a single MP transgene. Interestingly, we detected strong methylation in all of the plants containing directly repeated MP sequences. In sensitive lines, only the promoter region was found to be heavily methylated, whereas in resistant lines, only the transcribed region was strongly methylated.

3.
Plant Cell ; 8(5): 783-791, 1996 May.
Artigo em Inglês | MEDLINE | ID: mdl-12239400

RESUMO

During Arabidopsis embryogenesis, the zygote divides asymmetrically in the future apical-basal axis; however, a radial axis is initiated only within the eight-celled embryo. Mutations in the GNOM, KNOLLE, and KEULE genes affect these processes: gnom zygotes tend to divide symmetrically; knolle embryos lack oriented cell divisions that initiate protoderm formation; and in keule embryos, an outer cell layer is present that consists of abnormally enlarged cells from early development. Pattern formation along the two axes is reflected by the position-specific expression of the Arabidopsis lipid transfer protein (AtLTP1) gene. In wild-type embryos, the AtLTP1 gene is expressed in the protoderm and initially in all protodermal cells; later, AtLTP1 expression is confined to the cotyledons and the upper end of the hypocotyl. Analysis of AtLTP1 expression in gnom, knolle, and keule embryos showed that gnom embryos also can have no or reversed apical-basal polarity, whereas radial polarity is unaffected. knolle embryos initially lack but eventually form a radial pattern, and keule embryos are affected in protoderm cell morphology rather than in the establishment of the radial pattern.

4.
Plant Cell ; 5(6): 615-620, 1993 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-12271077

RESUMO

At a nonpermissive temperature, somatic embryos of the temperature-sensitive (ts) carrot cell mutant ts11 only proceed beyond the globular embryo stage in the presence of medium conditioned by wild-type embryos. The causative component in the conditioned medium has previously been identified as a 32-kD acidic endochitinase. In search of a function for this enzyme in plant embryogenesis, several compounds that contain oligomers of N-acetylglucosamine were tested for their ability to promote ts11 embryo formation. Of these compounds, only the Rhizobium lipooligosaccharides or nodulation (Nod) factors were found to be effective in rescuing the formation of ts11 embryos. These results suggest that N-acetylglucosamine-containing lipooligosaccharides from bacterial origin can mimic the effect of the carrot endochitinase. This endochitinase may therefore be involved in the generation of plant analogs of the Rhizobium Nod factors.

5.
Biochim Biophys Acta ; 414(2): 206-16, 1975 Dec 04.
Artigo em Inglês | MEDLINE | ID: mdl-172157

RESUMO

1. Bacteroids of Rhizobium leguminosarum (strain PRE) purified from root nodules of Pisum sativum (var. 'Rondo') by the standard procedure of differential centrifugation contained considerable contamination of mitochondrial material. This could be removed by incubation of the bacteroid preparation with 1 M KCl/1% deoxycholate. 2. The DNA content of bacteroid cells of R. leguminosarum was found to have increased about three fold in comparison with the DNA content of free living R. leguminosarum bacteria. 3. No significant difference in DNA composition of free living R. leguminosarum bacteria and bacteroids could be detected by CsCl equilibrium centrifugation, RNA - DNA hybridization and DNA - DNA reassociation studies.


Assuntos
DNA Bacteriano/análise , Rhizobium/análise , Simbiose , Formas Bacterianas Atípicas/análise , DNA Bacteriano/metabolismo , Complexo IV da Cadeia de Transporte de Elétrons/metabolismo , Hibridização de Ácido Nucleico , Renaturação de Ácido Nucleico , Plantas/análise , Rhizobium/metabolismo
6.
Biochim Biophys Acta ; 539(1): 1-11, 1978 Feb 13.
Artigo em Inglês | MEDLINE | ID: mdl-623788

RESUMO

The effects of NH4NO3 on the development of root nodules of Pisum sativum after infection with Rhizobium leguminosarum (strain PRE) and on the nitrogenase activity of the bacteroids in the nodule tissue were studied. The addition of NH4NO3 decreased the nitrogenase activity measured on intact nodules. This reduction of nitrogen fixation did not result from a reduced number of bacteroids or a decreased amount of bacteroid proteins per gram of nodule. The synthesis of nitrogenase, measured as the relative amount of incorporation of [35S]sulfate into the components I and II of nitrogenase was similarly not affected. The addition of NH4NO3 decreased the amount of leghemoglobin in the nodules and there was a quantitative correlation between the leghemoglobin content and the nitrogen-fixing capacity of the nodules. The conclusion is that the decrease of nitrogen-fixing capacity is caused by a decrease of the leghemoglobin content of the root nodules and not by repression of the nitrogenase synthesis.


Assuntos
Fabaceae/metabolismo , Hemeproteínas/metabolismo , Leghemoglobina/metabolismo , Nitratos/farmacologia , Nitrogenase/biossíntese , Plantas Medicinais , Compostos de Amônio Quaternário/farmacologia , Rhizobium/metabolismo , Precursores Enzimáticos/biossíntese , Fixação de Nitrogênio/efeitos dos fármacos , Simbiose
7.
Biochim Biophys Acta ; 562(3): 515-26, 1979 May 24.
Artigo em Inglês | MEDLINE | ID: mdl-454614

RESUMO

Some aspects of root nodule development of Pisum sativum inoculated with Rhizobium leguminosarum were examined. 1. Nitrogenase activity (measured as acetylene reduction) appears to be preceded by leghemoglobin synthesis (measured immunologically). 2. Syntheses of component I and component II of nitrogenase are not strictly coordinated. Synthesis of component I starts before component II. 3. Plant and bacteroid protein synthesis (measured by [35S]sulfate labeling) in root nodules declines rapidly during nodule development. Corresponding with this decline is a decrease in quantity and quality of rRNA.


Assuntos
Fabaceae/microbiologia , Hemeproteínas/biossíntese , Leghemoglobina/biossíntese , Fixação de Nitrogênio , Nitrogenase/biossíntese , Plantas Medicinais , Rhizobium/fisiologia , RNA/metabolismo , RNA Ribossômico/metabolismo , Fatores de Tempo
8.
Plant Physiol ; 117(1): 43-53, 1998 May.
Artigo em Inglês | MEDLINE | ID: mdl-9576773

RESUMO

Carrot (Daucus carota) extracellular protein 3 (EP3) class IV endochitinases were previously identified based on their ability to rescue somatic embryos of the temperature-sensitive cell line ts11. Whole-mount in situ hybridization revealed that a subset of the morphologically distinguishable cell types in embryogenic and nonembryogenic suspension cultures, including ts11, express EP3 genes. No expression was found in somatic embryos. In carrot plants EP3 genes are expressed in the inner integumentary cells of young fruits and in a specific subset of cells located in the middle of the endosperm of mature seeds. No expression was found in zygotic embryos. These results support the hypothesis that the EP3 endochitinase has a "nursing" function during zygotic embryogenesis and that this function can be mimicked by suspension cells during somatic embryogenesis.

9.
Plant Physiol ; 105(3): 787-797, 1994 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-12232242

RESUMO

We used a semiquantitative root hair deformation assay for Vicia sativa (vetch) to study the activity of Rhizobium leguminosarum bv viciae nodulation (Nod) factors. Five to 10 min of Nod factor-root interaction appears to be sufficient to induce root hair deformation. The first deformation is visible within 1 h, and after 3 h about 80% of the root hairs in a small susceptible zone of the root are deformed. This zone encompasses root hairs that have almost reached their maximal size. The Nod factor accumulates preferentially to epidermal cells of the young part of the root, but is not restricted to the susceptible zone. In the interaction with roots, the glucosamine backbone of Nod factors is shortened, presumably by chitinases. NodRlv-IV(C18:4,Ac) is more stable than NodRlv-V(C18:4,Ac). No correlation was found between Nod factor degradation and susceptibility. Degradation occurs both in the susceptible zone and in the mature zone. Moreover, degradation is not affected by NH4NO3 and is similar in vetch and in the nonhost alfalfa (Medicago sativa).

10.
Plant Physiol ; 115(2): 351-359, 1997 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-12223813

RESUMO

In pea (Pisum sativum) up to 50 nodulation mutants are known, several of which are affected in the early steps of the symbiotic interaction with Rhizobium sp. bacteria. Here we describe the role of the sym2 gene in nodulation (Nod) factor perception. Our experiments show that the sym2A allele from the wild pea variety Afghanistan confers an arrest in infection-thread growth if the Rhizobium leguminosarum bv viciae strain does not produce Nod factors with a NodX-mediated acetylation at their reducing end. Since the induction of the early nodulin gene ENOD12 in the epidermis and the formation of a nodule primordium in the inner cortex were not affected, we conclude that more than one Nod factor-perception mechanism is active. Furthermore, we show that sym2A-mediated control of infection-thread growth was affected by the bacterial nodulation gene nodO.

11.
Mol Plant Microbe Interact ; 10(2): 215-20, 1997 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-9057327

RESUMO

Nod factors secreted by Rhizobium leguminosarum by, viciae induce root hair deformation, the formation of nodule primordia, and the expression of early nodulin genes in Vicia sativa (vetch). Root hair deformation is induced within 3 h in a small, susceptible zone (+/-2 mm) of the root. NH4NO3, known to be a potent blocker of nodule formation, inhibits root hair deformation, initial cortical cell divisions, and infection thread formation. To test whether NH4NO3 affects the formation of a component of the Nod factor perception-transduction system, we studied Nod factor-induced gene expression. The differential display technique was used to search for marker genes, which are induced within 1 to 3 h after Nod factor application. Surprisingly, one of the isolated cDNA clones was identified as a leghemoglobin gene (VsLb1), which is induced in vetch roots within 1 h after Nod factor application. By using the drug brefeldin A, it was then shown that VsLb1 activation does not require root hair deformation. The pVsLb1 clone was used as a marker to show that in vetch plants grown in the presence of NH4NO3, Nod factor perception and transduction leading to gene expression are unaffected.


Assuntos
Fabaceae/genética , Fabaceae/microbiologia , Leghemoglobina/genética , Lipopolissacarídeos/farmacologia , Proteínas de Membrana , Plantas Medicinais , Sequência de Bases , DNA de Plantas/genética , Fabaceae/efeitos dos fármacos , Expressão Gênica/efeitos dos fármacos , Genes de Plantas/efeitos dos fármacos , Marcadores Genéticos , Dados de Sequência Molecular , Nitratos/farmacologia , Proteínas de Plantas/genética , Rhizobium leguminosarum/fisiologia
12.
Mol Plant Microbe Interact ; 2(2): 53-63, 1989.
Artigo em Inglês | MEDLINE | ID: mdl-2520161

RESUMO

The role of the Rhizobium nod genes in the induction of nodulin gene expression was examined by analyzing nodules formed on vetch roots by bacterial strains containing only the nod region. Introduction of an 11-kb cloned nod region of the R. leguminosarum sym plasmid pRL1JI into sym plasmid-cured rhizobia conferred on the recipient strains the ability to induce nodules in which all nodulin genes were expressed. This proves that from the sym plasmid only the nod region is involved in the induction of nodulin gene expression. A transconjugant of Agrobacterium carrying the same nod region induces nodules in which only early nodulin gene expression is detected. Thus, the nod region is essential for the induction of early nodulin gene expression. In this case, nodule cytology may indicate that a defense response of the plant interferes with the induction of late nodulin gene expression. Indirect evidence is presented that indeed the Rhizobium nod genes are also in some way involved in the induction of the expression of late noduling genes. The combination between histological data and pattern of nodulin gene expression furthermore reveals a correlation between nodule structure and nodulin gene expression. This correlation may aid in speculations about the functions of nodulins.


Assuntos
Fabaceae/microbiologia , Proteínas de Membrana , Proteínas de Plantas/genética , Plantas Medicinais , Rhizobium/genética , Western Blotting , Cromossomos Bacterianos/fisiologia , Fabaceae/anatomia & histologia , Fabaceae/crescimento & desenvolvimento , Regulação da Expressão Gênica , Imuno-Histoquímica , Fixação de Nitrogênio/genética , Proteínas de Plantas/metabolismo , Plasmídeos , Mapeamento por Restrição
13.
Gene ; 78(1): 135-46, 1989 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-2548928

RESUMO

An expression system for the production of polymerase proteins of cowpea mosaic virus (CPMV) in Escherichia coli cells is described. High-level synthesis of proteins containing protease and polymerase moieties (110-kDa protein) and polymerase alone (87-kDa protein) were obtained from cells containing different plasmid constructions. Precursor and processed forms of CPMV proteins were detected by immunoblotting with antisera directed against 170-kDa precursor polyprotein and 24-kDa viral protease. Crude lysates and supernatant fractions of the lysates from E. coli cells harboring the various plasmid constructions were analysed for poly(A)-oligo(U) polymerase activity and found to be negative for CPMV activity under conditions where similar expression systems for the production of poliovirus RNA polymerase activity were positive. Thus, conditions for CPMV RNA replication may indeed be different from those for poliovirus even though the genomic organization of these viruses is similar.


Assuntos
RNA Polimerases Dirigidas por DNA/biossíntese , Escherichia coli/genética , Vírus do Mosaico/genética , Peptídeo Hidrolases/biossíntese , DNA Recombinante , RNA Polimerases Dirigidas por DNA/análise , RNA Polimerases Dirigidas por DNA/metabolismo , Immunoblotting , Vírus do Mosaico/enzimologia , Peptídeo Hidrolases/análise , Peptídeo Hidrolases/metabolismo , Plasmídeos , Poliovirus/genética , Solubilidade
14.
Gene ; 87(1): 31-6, 1990 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-2185138

RESUMO

The nucleotide (nt) sequence of the Rhizobium leguminosarum nifH promoter region contains a consensus promoter, a consensus upstream activator sequence (UAS), a pseudo (psi) promoter and a psi UAS. We mapped the transcription start point for the consensus promoter sequence by primer extension. This promoter differs from the consensus in one of the four supposedly invariant nt and can be activated by the Klebsiella pneumoniae nifA product in Escherichia coli. Under these conditions the psi promoter and psi UAS do not function. A low-copy-number plasmid construct containing the psi UAS as well as the consensus UAS delayed the onset of symbiotic nitrogen fixation in nodules induced on Pisum sativum. Studies of high-copy-number nifH promoter constructs showed that partial deletion of the consensus UAS does not alter the ability to inhibit nitrogen fixation by titration of NifA suggesting that NifA can also complex with RNA polymerase containing the alternative sigma-factor RpoN.


Assuntos
Proteínas de Bactérias/genética , Genes Bacterianos , Fixação de Nitrogênio/genética , Regiões Promotoras Genéticas , Rhizobium/genética , Fatores de Transcrição , Sequência de Bases , Deleção Cromossômica , Clonagem Molecular , Escherichia coli/genética , Regulação Bacteriana da Expressão Gênica , Dados de Sequência Molecular , Mapeamento por Restrição
15.
Biochimie ; 75(8): 741-7, 1993.
Artigo em Inglês | MEDLINE | ID: mdl-8286445

RESUMO

The involvement of the AUG codons at positions 115, 161, 512 and 524 in translation and infectivity of cowpea mosaic virus M RNA was studied. Mutations were introduced in each of these codons in a full length cDNA clone of M RNA and the effect of the mutations was examined by translation from in vitro transcripts of these mutant cDNAs in rabbit reticulocyte lysates and by checking the replication of these transcripts in the presence of B RNA in cowpea protoplasts and plants. It was found that AUG115, at the beginning of an open reading frame (ORF) for a putative 2-kDa protein, can be used in vitro to initiate translation, but mutation of this AUG codon in the M RNA does not affect the ability of the virus to infect cowpea plants. AUG161, located at the beginning of the large ORF, was shown to be essential for expression of the large 105-kDa polyprotein and for replication of M RNA. Translation of the second 95-kDa polyprotein was found to start at AUG512. Upon mutation of this AUG codon efficient initiation of translation occurred at AUG524. Results with M RNAs that lack AUG512 and/or 524 indicate that an intact 95-kDa polyprotein is not required for replication of M RNA but that this protein has an essential function in cell-to-cell movement of the virus.


Assuntos
Códon , Comovirus/genética , RNA Viral/genética , Sequência de Aminoácidos , Sequência de Bases , Comovirus/patogenicidade , Análise Mutacional de DNA , DNA Complementar , Dados de Sequência Molecular , Doenças das Plantas/microbiologia , Biossíntese de Proteínas , Protoplastos/microbiologia
16.
Arch Virol Suppl ; 15: 1-8, 1999.
Artigo em Inglês | MEDLINE | ID: mdl-10470266

RESUMO

The existence of viruses was first recognized when certain pathogens were found to pass through filters that otherwise stop bacteria. Pasteur made such observations in 1887 with the pathogen of rabies, but he thought that the pathogen was a very subtle microbe. In 1886 Adolf Mayer studied the mosaic disease of tobacco plants. He was unable to observe the least trace of a microbe, but still assumed that the pathogen was a bacterium. In 1892 Iwanovsky demonstrated that tobacco mosaic was caused by an agent that passed through bacteria-proof filters but he insisted till the end of his life that the tobacco mosaic virus was a small bacterium. Similar observations were made by Loeffler and Frosch in 1898 on foot-and-mouth disease of cattle. Beijcrinck confirmed the filterability of tobacco mosaic virus but confirmed its properties in more detail and then, in 1898, firmly concluded that tobacco mosaic virus is not a microbe but a contagium vivum fluidum. His idea that a pathogen can be a soluble molecule that proliferates when it is part of the protoplasm of a living cell was revolutionary and new. This new concept has laid the foundation of virus research and directed further studies on the nature of viruses.


Assuntos
Vírus do Mosaico do Tabaco , Virologia/história , Animais , Bovinos , História do Século XIX , História do Século XX , Países Baixos , Doenças das Plantas/virologia , Plantas Tóxicas , Nicotiana/virologia , Vírus do Mosaico do Tabaco/isolamento & purificação , Vírus do Mosaico do Tabaco/fisiologia , Vírus do Mosaico do Tabaco/ultraestrutura
17.
Arch Virol Suppl ; 9: 381-92, 1994.
Artigo em Inglês | MEDLINE | ID: mdl-8032269

RESUMO

The genome of cowpea mosaic virus (CPMV) is divided among two positive strand RNA molecules. B-RNA is able to replicate independently from M-RNA in cowpea protoplasts. Replication of mutant B-transcripts could not be supported by co-inoculated wild-type B-RNA, indicating that B-RNA cannot be efficiently replicated in trans. Hence replication of a B-RNA molecule is tightly linked to its translation and/or at least one of the replicative proteins functions in cis only. Remarkably also for efficient replication of M-RNA one of its translation products was found to be required in cis. This 58K protein possibly helps in directing the B-RNA-encoded replication complex to the M-RNA. In order to identify the viral polymerase the CPMV B-RNA-specific proteins have been produced individually in cowpea protoplasts using CaMV 35S promoter based expression vectors. Only protoplasts transfected with a vector containing the 200K coding sequence were able to support replication of co-transfected M-RNA. Despite this, CPMV-specific RNA polymerase activity could not be detected in extracts of these protoplasts using a poly(A)/oligo(U) assay. These results indicate that, in contrast to the poliovirus polymerase, the CPMV polymerase is not able to accept oligo(U) as a primer and in addition support the concept that translation and replication are linked.


Assuntos
Comovirus/crescimento & desenvolvimento , Biossíntese de Proteínas , RNA Viral/biossíntese , Animais , Células Cultivadas , Comovirus/genética , Análise Mutacional de DNA , RNA Polimerases Dirigidas por DNA/biossíntese , RNA Polimerases Dirigidas por DNA/genética , Escherichia coli/genética , Fabaceae/microbiologia , Insetos/citologia , Modelos Genéticos , Plantas Medicinais , Protoplastos/microbiologia , RNA Viral/genética , Replicação Viral
18.
Arch Virol Suppl ; 9: 87-97, 1994.
Artigo em Inglês | MEDLINE | ID: mdl-8032285

RESUMO

The vast majority of positive-strand RNA viruses (more than 500 species) are adapted to infection of plant hosts. Genome sequence comparisons of these plant RNA viruses have revealed that most of them are genetically related to animal cell-infecting counterparts; this led to the concept of "superfamilies". Comparison of genetic maps of representative plant and animal viruses belonging to the same superfamily (e.g. cowpea mosaic virus [CPMV] versus picornaviruses and tobacco mosaic virus versus alphaviruses) have revealed genes in the plant viral genomes that appear to be essential adaptations needed for successful invasion and spread through their plant hosts. The best studied example represents the "movement protein" gene that is actively involved in cell-to-cell spread of plant viruses, thereby playing a key role in virulence and pathogenesis. In this paper the host adaptations of a number of plant viruses will be discussed, with special emphasis on the cell-to-cell movement mechanism of comovirus CPMV.


Assuntos
Vírus de Plantas/fisiologia , Vírus de RNA/fisiologia , Adaptação Fisiológica , Comovirus/fisiologia , Organelas/ultraestrutura , Vírus de Plantas/ultraestrutura , Plantas/microbiologia , Plantas/ultraestrutura , Protoplastos/ultraestrutura , Especificidade da Espécie , Proteínas Virais/biossíntese , Proteínas Virais/genética
20.
Avian Dis ; 25(4): 785-94, 1981.
Artigo em Inglês | MEDLINE | ID: mdl-6279068

RESUMO

An adenovirus isolated from the trachea of a chicken with respiratory disease was compared with an isolate obtained from the trachea of a clinically normal chicken. The isolates caused similar respiratory disease experimentally but differed in plaque morphology and fluorescent-antibody reactions in infected chick embryos.


Assuntos
Infecções por Adenoviridae/veterinária , Adenoviridae/isolamento & purificação , Aviadenovirus/isolamento & purificação , Galinhas , Doenças das Aves Domésticas/microbiologia , Infecções Respiratórias/veterinária , Animais , Aviadenovirus/crescimento & desenvolvimento , Aviadenovirus/imunologia , Linhagem Celular , Embrião de Galinha , Chlorocebus aethiops , Reações Cruzadas , Rim , Testes de Neutralização , Traqueia/microbiologia
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