Biomedical subjects

A van Kammen

Publications and source records attributed to A van Kammen.

At least 19 recordsLinked to original sources

PubMed2003

Studies on the C-terminus of the Cowpea mosaic virus movement protein.

Cowpea mosaic virus (CPMV) spreads from cell-to-cell as virus particles through tubular structures in modified plasmodesmata which are composed of viral movement protein (MP). Mutational analysis of the MP has revealed that the N-terminal and central regions of the MP are involved in tubule formation and that the C-terminal domain probably has a role in the interactions with virus particles. By constructing C-terminal deletion mutants and comoviral hybrid MPs, it was possible to delineate the C-terminal border of the tubule-forming domain to a small region between amino acids 292 and 298. Experiments with tripartite viruses in protoplasts indicated that the C-terminus of the MP is involved in the incorporation of virus particles in the tubule and that for efficient incorporation of virus particles all MP molecules incorporated in a tubule need to contain a functional C-terminus. A mutant virus coding for a MP in which the last 10 C-terminal amino acids were replaced by the green fluorescent protein (GFP) was able to form tubules in protoplasts. These tubules did not contain virus particles, probably because the GFP interferes with the incorporation of virions into the tubule. These results suggest a model for the structure of the tubule in which the C-terminus of the MP is located inside the tubular structure, where it is able to interact with virus particles.

Amino Acid Sequence↗

PubMed2001

N-acetylglucosamine and glucosamine-containing arabinogalactan proteins control somatic embryogenesis.

In plants, complete embryos can develop not only from the zygote, but also from somatic cells in tissue culture. How somatic cells undergo the change in fate to become embryogenic is largely unknown. Proteins, secreted into the culture medium such as endochitinases and arabinogalactan proteins (AGPs) are required for somatic embryogenesis. Here we show that carrot (Daucus carota) AGPs can contain glucosamine and N-acetyl-D-glucosaminyl and are sensitive to endochitinase cleavage. To determine the relevance of this observation for embryogenesis, an assay was developed based on the enzymatic removal of the cell wall from cultured cells. The resulting protoplasts had a reduced capacity for somatic embryogenesis, which could be partially restored by adding endochitinases to the protoplasts. AGPs from culture medium or from immature seeds could fully restore or even increase embryogenesis. AGPs pretreated with chitinases were more active than untreated molecules and required an intact carbohydrate constituent for activity. AGPs were only capable of promoting embryogenesis from protoplasts in a short period preceding cell wall reformation. Apart from the increase in embryogenesis, AGPs can reinitiate cell division in a subpopulation of otherwise non-dividing protoplasts. These results show that chitinase-modified AGPs are extracellular matrix molecules able to control or maintain plant cell fate.

Acetylglucosamine↗

PubMed2000

Mutational analysis of the cowpea mosaic virus movement protein.

Cowpea mosaic virus moves from cell-to-cell in a virion form through tubular structures that are assembled in modified plasmodesmata. Similar tubular structures are formed on the surface of protoplasts inoculated with cowpea mosaic virus. The RNA 2-encoded movement protein (MP) is responsible for the induction and formation of these structures. To define functional domains of the MP, an alanine-substitution mutagenesis was performed on eight positions in the MP, including two conserved sequence motifs, the LPL and D motifs. Results show that these two conserved motifs as well as the central region of the MP are essential for cell-to-cell movement. Several viruses carrying mutations in the N- or C-terminal parts of their MP retained infectivity on cowpea plants. Coexpression studies revealed that mutant MPs did not interfere with the activity of wild-type MP and could not mutually complement their defects.

Alanine↗

PubMed2000

Engineering cowpea mosaic virus RNA-2 into a vector to express heterologous proteins in plants.

A series of new cowpea mosaic virus (CPMV) RNA-2-based expression vectors were designed. The jellyfish green fluorescent protein (GFP) was introduced between the movement protein (MP) and the large (L) coat protein or downstream of the small (S) coat protein. Release of the GFP inserted between the MP and L proteins was achieved by creating artificial processing sites each side of the insert, either by duplicating the MP-L cleavage site or by introducing a sequence encoding the foot-and-mouth disease virus (FMDV) 2A catalytic peptide. Eight amino acids derived from the C-terminus of the MP and 14-19 amino acids from the N-terminus of the L coat protein were necessary for efficient processing of the artificial Gln/Met sites. Insertion of the FMDV 2A sequence at the C-terminus of the GFP resulted in a genetically stable construct, which produced particles containing about 10 GFP-2A-L fusion proteins. Immunocapture experiments indicated that some of the GFP is present on the virion surface. Direct fusion of GFP to the C-terminus of the S coat protein resulted in a virus which was barely viable. However, when the sequence of GFP was linked to the C-terminus by an active FMDV 2A sequence, a highly infectious construct was obtained.

Amino Acid Sequence↗

PubMed1999

Beijerinck's contribution to the virus concept--an introduction.

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.

Animals↗

PubMed1998

Paracentromeric sequences on tomato chromosome 6 show homology to human satellite III and to the mammalian CENP-B binding box.

In order to isolate centromeric sequences from tomato (Lycopersicon esculentum) chromosome 6, a large-scale RAPD screen was performed. Among 1500 polymorphic RAPD markers tested, 100 were identified as chromosome 6-specific, using a L. esculentum substitution line carrying chromosome 6 from L. pennellii. Fifty-seven of these markers proved to originate from L. pennellii, and of these, 13 were genetically mapped between the morphological markers yellow virescent (yv) and thiaminless (tl), which flank the centromere. These markers could be assigned to three genetic loci, with 11 of the markers mapping to a single locus. Further resolution of this cluster was achieved using radiation-induced deletions that removed yv or tl but not the centromere. Seven markers were shown to be located outside all of the deletions. These seven markers and three of the other markers of the cluster were cloned and sequenced. Five of the clones are present as single-copy or low-copy-number sequences and five represent middle repetitive sequences. Three sequences show homology to the mammalian CENP-B binding box; clone AG12 contains two of these boxes and also shows homology to human satellite III.

Autoantigens↗

PubMed1998

FISH studies reveal the molecular and chromosomal organization of individual telomere domains in tomato.

The molecular and cytological organization of the telomeric repeat (TR) and the subtelomeric repeat (TGR1) of tomato were investigated by fluorescence in situ hybridization (FISH) techniques. Hybridization signals on extended DNA fibres, visualized as linear fluorescent arrays representing individual telomeres, unequivocally demonstrated the molecular co-linear arrangement of both repeats. The majority of the telomeres consisted of a TR and a TGR1 region separated by a spacer. Microscopic measurements of the TR and TGR1 signals revealed high variation in length of both repeats, with maximum sizes of 223 and 1330 kb, respectively. A total of 27 different combinations of TR and TGR1 was detected, suggesting that all chromosome ends have their own unique telomere organization. The fluorescent tracks on the extended DNA fibres were subdivided into four classes: (i) TR-spacer-TGR1; (ii) TR-TGR1; (iii) only TR; (iv) only TGR1. FISH to pachytene chromosomes enabled some of the TR/TGR1 groups to be assigned to specific chromosome ends and to interstitial regions. These signals also provided evidence for a reversed order of the TR and TGR1 sites at the native chromosome ends, suggesting a backfolding telomere structure with the TGR1 repeats occupying the most terminal position of the chromosomes. The FISH signals on diakinesis chromosomes revealed that distal euchromatin areas and flanking telomeric heterochromatin remained highly decondensed around the chiasmata in the euchromatic chromosome areas. The rationale for the occurrence and distribution of the TR and TGR1 repeats on the tomato chromosomes are discussed.

Base Sequence↗

PubMed1997

AtLTP1 luciferase expression during carrot somatic embryogenesis.

The carrot (Daucus carota L.) EP2 gene encodes a Lipid Transfer Protein (LTP) which is expressed during protoderm formation in developing embryos. To develop a vital reporter system for gene expression during somatic embryo development a 1.1 kB fragment of the Arabidopsis thaliana LTP1 promoter was fused to the firefly luciferase (LUC) coding sequence. The AtLTP1 luciferase expression pattern in transformed carrot suspension cultures was identical to the expression pattern of the endogenous carrot EP2 gene. Cell tracking experiments revealed that all somatic embryos were derived from AtLTP1 luciferase expressing cell clusters. However, not all cell clusters that expressed the AtLTP1 luciferase reporter gene developed into a somatic embryo, suggesting that initiation of an embryogenic pathway in tissue culture does not always lead to development of a somatic embryo.

Antigens, Plant↗

PubMed1997

Nod factor-induced expression of leghemoglobin to study the mechanism of NH4NO3 inhibition on root hair deformation.

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.

Base Sequence↗

PubMed1997

Ethylene provides positional information on cortical cell division but is not involved in Nod factor-induced root hair tip growth in Rhizobium-legume interaction.

Nod factors secreted by Rhizobium leguminosarum bv. viciae induce root hair deformation, involving a reinitiation of tip growth, and the formation of nodule primordia in Vicia sativa (vetch). Ethylene is a potent inhibitor of cortical cell division, an effect that can be counteracted by applying silver ions (Ag+) or aminoethoxy-vinylglycine (AVG). In contrast to the inhibitory effect on cortical cell division, ethylene promotes the formation of root hairs (which involves tip growth) in the root epidermis of Arabidopsis. We investigate the possible paradox concerning the action of ethylene, putatively promoting Nod factor induced tip growth whilst, at the same time, inhibiting cortical cell division. We show, by using the ethylene inhibitors AVG and Ag+, that ethylene has no role in the reinitiation of root hair tip growth induced by Nod factors (root hair deformation) in vetch. However, root hair formation is controlled, at least in part, by ethylene. Furthermore, we show that ACC oxidase, which catalizes the last step in ethylene biosynthesis, is expressed in the cell layers opposite the phloem in that part of the root where nodule primordia are induced upon inoculation with Rhizobium. Therefore, we test whether endogenously produced ethylene provides positional information controlling the site where nodule primordia are formed by determining the position of nodules formed on pea roots grown in the presence of AVG or Ag+.

Amino Acid Oxidoreductases↗

PubMed1996

Modification of phytohormone response by a peptide encoded by ENOD40 of legumes and a nonlegume.

The gene ENOD40 is expressed during early stages of legume nodule development. A homolog was isolated from tobacco, which, as does ENOD40 from legumes, encodes an oligopeptide of about 10 amino acids. In tobacco protoplasts, these peptides change the response to auxin at concentrations as low as 10(-12) to 10(-16)M. The peptides encoded by ENOD40 appear to act as plant growth regulators.

Amino Acid Sequence↗

PubMed1996

The pea early nodulin gene PsENOD7 maps in the region of linkage group I containing sym2 and leghaemoglobin.

The early nodulin gene, PsENOD7, is expressed in pea root nodules induced by Rhizobium leguminosarum bv. viciae, but not in other plant organs. In situ hybridization showed that this gene is transcribed during nodule maturation in the infected cells of the proximal part of the prefixation zone II. At the transition of zone II into interzone II-III, the level of PsENOD7 mRNA drops markedly. PsENOD7 has no significant homology to other genes. RFLP mapping studies have shown that PsENOD7 is located in linkage group I between the leghaemoglobin genes and sym2.

Amino Acid Sequence↗

PubMed1996

Nitrogen metabolism in actinorhizal nodules of Alnus glutinosa: expression of glutamine synthetase and acetylornithine transaminase.

Two nodule cDNA clones representing genes involved in Alnus glutinosa nitrogen metabolism were analysed. ag11 encoded glutamine synthetase (GS), the enzyme responsible for ammonium assimilation, while ag118 encoded acetylornithine transaminase (AOTA), an enzyme involved in the biosynthesis of citrulline, the nitrogen transport form in Alnus. GS mRNA was found at highest levels in root nodules, where it was present in the infected cells as well as in the cells of the pericycle of the vascular system. AOTA transcripts were found at high levels in nodules, confined to the infected cells, suggesting that in nodules of A. glutinosa, citrulline biosynthesis takes place mainly in the infected cells.

Actinomycetales↗

PubMed1996

An improved method of partially digesting plant megabase DNA suitable for YAC cloning: application to the construction of a 5.5 genome equivalent YAC library of tomato.

An improved method for preparing partially digested tomato DNA has been developed, that is suitable for YAC cloning. It involves (i) isolation of high molecular-weight DNA from agarose-embedded leaf protoplasts, (ii) controlled partial digestion in situ using EcoRl endonuclease in the presence of EcoRI methylase (M. EcoRl), and (iii) fractionation of the partial digest on a Clamped Homogeneous Electric Fields (CHEF) gel. Unlike methods commonly used for generating partial digests, the present method allows one to produce digests in which the bulk of restriction fragments are of the desired size. Use of these partial digests in constructing YAC libraries of the tomato lines Moneymaker-Cf4 and VFNT Cherry resulted in libraries (total 21,060 clones, 5.5 genome equivalents) in which 80% of the YACs have inserts between 200 and 600 kb. Both libraries have been screened with selected RFLP markers linked to the Cladosporium fulvum Cf4 locus on chromosome 1, using a three-dimensional PCR-based screening technique. To this end, the RFLP markers have been sequenced to allow for the synthesis of specific primers. Thus, for each marker tested several YAC clones have been isolated, including a family of clones that carry leucine-rich repeat sequences located around the Cf4/Cf9 locus.

Base Sequence↗

PubMed1996

Identification of agthi1, whose product is involved in biosynthesis of the thiamine precursor thiazole, in actinorhizal nodules of Alnus glutinosa.

A cDNA clone, pAgthi1, encoding a homologue of yeast Thi4, which is involved in thiazole biosynthesis, was isolated from a library made from poly(A) RNA from actinorhizal nodules of Alnus glutinosa by differential screening with nodule and root cDNA, respectively. The corresponding gene, agthi1, was shown to be expressed at high levels in nodules and shoot tips of A. glutinosa, while having low expression levels in roots, flowers, and developing fruits. The function of AgThi1 was demonstrated by yeast complementation studies, in which AgThi1 was able to rescue a yeast thi4 mutant when fused to the yeast Thi4 signal peptide. In A. glutinosa nodules, high levels of agthi1 mRNA were detected in the infected cortical cells and in the pericycle of the nodule vascular system. A homologue of this cDNA, ara6/tz, was identified in Arabidopsis thaliana. ara6 maps in a region of chromosome 5 of Arabidopsis containing the tz locus which is consistent with the fact that ara6 transcription is disturbed in two tz mutant lines. ara6/tz is expressed at high levels in chloroplast-containing parenchymatic cells of leaves, inflorescence shoots and flowers of Arabidopsis, and at lower levels in the vascular system.

Arabidopsis↗

PubMed1995

A 200 bp region of the pea ENOD12 promoter is sufficient for nodule-specific and nod factor induced expression.

ENOD12 is one of the first nodulin genes expressed upon inoculation with Rhizobium and also purified Nod factors are able to induce ENOD12 expression. The ENOD12 gene family in pea (Pisum sativum) has two members. A cDNA clone representing PsENOD12A [26] and a PsENOD12B genomic clone [7] have been previously described. The isolation and characterization of a PsENOD12A genomic clone is presented in this paper. By using a Vicia hirsuta-Agrobacterium rhizogenes transformation system it is shown that both genes have a similar expression pattern in transgenic V. hirsuta root nodules. Promoter analyses of both PsENOD12 promoters showed that the 200 bp immediately upstream of the transcription start are sufficient to direct nodule-specific and Nod factor-induced gene expression.

Base Sequence↗

PubMed1995

VsENOD5, VsENOD12 and VsENOD40 expression during Rhizobium-induced nodule formation on Vicia sativa roots.

We isolated ENOD5, ENOD12 and ENOD40 homologues from Vicia sativa and studied their expression pattern during Rhizobium-induced nodule formation. Comparison of the VsENOD40 nucleotide sequence with the pea, soybean and alfalfa ENOD40 sequences showed that the sequences contain two conserved regions, called region I and region II. Comparison of all the potential open reading frames (ORFs) showed that all the five different ENOD40 clones encode a highly conserved small polypeptide of 12 or 13 amino acids encoded by an ORF located in region I. Furthermore we studied with in situ hybridization the expression pattern of VsENOD5, VsENOD12 and VsENOD40 during Rhizobium-induced nodule formation. Although the expression of these genes is largely similar to that of the pea counterparts, differences where found for the expression of VsENOD12 and VsENOD40 in Vicia. VsENOD12 is expressed in the whole prefixation zone II, whereas in pea ENOD12 is only expressed in the distal part of this zone. VsENOD40 is expressed in the uninfected cells of interzone II-III, while in pea ENOD40 is expressed in both the uninfected and infected cells of this zone.

Amino Acid Sequence↗

PubMed1995

Early nodulin gene expression during Nod factor-induced processes in Vicia sativa.

Rhizobium leguminosarum bv. viciae-secreted Nod factors are able to induce root hair deformation, the formation of nodule primordia and the expression of early nodulin genes in Vicia sativa (vetch). To obtain more insight into the mode of action of Nod factors the expression of early nodulin genes was followed during Nod factor-induced root hair deformation and nodule primordium formation. The results of these studies suggested that the expression of VsENOD5 and VsENOD12 is not required for root hair deformation. In the Nod factor-induced primordia both VsENOD12 and VsENOD40 are expressed in a spatially controlled manner similar to that found in Rhizobium-induced nodule primordia. In contrast, VsENOD5 expression has never been observed in Nod factor-induced primordia, showing that the induction of VsENOD5 and VsENOD12 expression are not coupled. VsENOD5 expression is induced in the root epidermis by Nod factors and in Rhizobium-induced nodule primordia only in cells infected by the bacteria, suggesting that the Nod factor does not reach the inner cortical cells.

Base Sequence↗