Biomedical subjects

D Tepfer

Publications and source records attributed to D Tepfer.

12 recordsLinked to original sources

PubMed2000

The stachydrine catabolism region in Sinorhizobium meliloti encodes a multi-enzyme complex similar to the xenobiotic degrading systems in other bacteria.

Stachydrine (proline betaine) can be used by Sinorhizobium meliloti as a source of carbon and nitrogen. Catabolism depends on an initial N-demethylation, after which the resultant N-methyl proline enters general metabolism. Deletion and insertion mutagenesis demonstrated that the information necessary for catabolism is carried on the symbiotic plasmid (pSym) distal to nodD2 and the nod-nif cluster. Sequencing of an 8.5kb fragment spanning this region revealed four open reading frames with functional homology to known proteins, including a putative monooxygenase and a putative NADPH-FMN-reductase, which were shown by insertional and frame-shift mutagenesis to be necessary for stachydrine catabolism. Other open reading frames, encoding a putative flavoprotein and a repressor, were judged not to be required for stachydrine catabolism, since they were not included in a fragment capable of complementing a deletion of the entire stc region. Sequence and mutagenesis data suggest that stachydrine is demethylated by an iron-sulfur monooxygenase of the Rieske type with a requirement for a specific reductase. The stc catabolic cluster, therefore, resembles xenobiotic degradation in other bacteria and recalls rhizopine catabolism in S. meliloti. Stachydrine appears to have multiple roles in osmoprotection, nutrition and nodulation. Genes involved in stachydrine catabolism are also necessary for carnitine degradation; thus, they could be important in the catabolism of a variety of root exudates and mediate other relationships.

Amino Acid Sequence↗

PubMed1998

Natural genetic transformation by agrobacterium rhizogenes . Annual flowering in two biennials, belgian endive and carrot

Genetic transformation of Belgian endive (Cichorium intybus) and carrot (Daucus carota) by Agrobacterium rhizogenes resulted in a transformed phenotype, including annual flowering. Back-crossing of transformed (R1) endive plants produced a line that retained annual flowering in the absence of the other traits associated with A. rhizogenes transformation. Annualism was correlated with the segregation of a truncated transferred DNA (T-DNA) insertion. During vegetative growth, carbohydrate reserves accumulated normally in these annuals, and they were properly mobilized prior to anthesis. The effects of individual root-inducing left-hand T-DNA genes on flowering were tested in carrot, in which rolC (root locus) was the primary promoter of annualism and rolD caused extreme dwarfism. We discuss the possible adaptive significance of this attenuation of the phenotypic effects of root-inducing left-hand T-DNA.

Journal Article↗

PubMed1996

Biological activities of the nortropane alkaloid, calystegine B2, and analogs: structure-function relationships.

Calystegines, polyhydroxy nortropane alkaloids, are a recently discovered group of plant secondary metabolites believed to influence rhizosphere ecology as nutritional sources for soil microorganisms and as glycosidase inhibitors. Evidence is presented that calystegines mediate nutritional relationships under natural conditions and that their biological activities are closely correlated with their chemical structures and stereochemistry. Assays using synthetic (+)- and (-)-enantiomers of calystegine B2 established that catabolism by Rhizobium meliloti, glycosidase inhibition, and allelopathic activities were uniquely associated with the natural, (+)-enantiomer. Furthermore, the N-methyl derivative of calystegine B2 was not catabolized by R. meliloti, and it inhibited alpha-galactosidase, but not beta-glucosidase, whereas the parent alkaloid inhibits both enzymes. This N-methyl analog therefore could serve to construct a cellular or animal model for Fabry's disease, which is caused by a lack of alpha-galactosidase activity.

Bacteria↗

PubMed1995

Chemical synthesis, expression and mutagenesis of a gene encoding beta-cryptogein, an elicitin produced by Phytophthora cryptogea.

Elicitins are 10 kDa holoproteins secreted by Phytophthora fungi, that elicit an incompatible hypersensitive reaction, leading to resistance against fungal and bacterial plant pathogens. Comparison of primary sequences of alpha-elicitins and beta-elicitins indicated several potential necrotic activity-determining residues. All of the highly necrotic beta-elicitins have a hydrophilic residue (usually lysine) at position 13, whereas in the less necrotic alpha-elicitins this residue is replaced by a valine. Here, we report the synthesis and expression of a gene encoding a highly necrotic elicitin, beta-cryptogein, and we show that the substitution of Lys-13 of this recombinant protein by a valine leads to a drastic alteration to the necrotic activity of the recombinant protein.

Algal Proteins↗

PubMed1994

Changing root system architecture through inhibition of putrescine and feruloyl putrescine accumulation.

Plant roots provide anchorage and absorb the water and minerals necessary for photosynthesis in the aerial parts of the plant. Since plants are sessile organisms, their root systems must forage for resources in heterogeneous soils through differential branching and elongation [(1988) Funct. Ecol. 2, 345-351; (1991) Plant Roots: The Hidden Half, pp. 3-25, Marcel Dekker, NY]. Adaptation to drought, for instance, can be facilitated by increased root growth and penetration. Root systems thus develop as a function of environmental variables and the needs of the plant [(1988) Funct. Ecol. 2, 345-351; (1986) Bot. Gaz. 147, 137-147; (1991) Plant Roots: The Hidden Half, pp. 309-330, Marcel Dekker, NY]. We show, in a model system consisting of excised tobacco roots, that both alpha-DL-difluoromethylornithine (an inhibitor of putrescine biosynthesis) and the rolA gene (from the root-inducing transferred DNA of Agrobacterium rhizogenes) stimulate overall root growth and cause a conversion in the pattern of root system formation, producing a dominant or 'tap' root. These morphological changes are correlated with a depression in the accumulation of polyamines and their conjugates.

Coumaric Acids↗

PubMed1989

Use of roots transformed by Agrobacterium rhizogenes in rhizosphere research: applications in studies of cadmium assimilation from sewage sludges.

The use of roots transformed by Agrobacterium rhizogenes in models for the rhizosphere is discussed. A list of species for which transformed root cultures have been obtained is provided and the example of studies of cadmium assimilation from sewage sludges is given to illustrate how transformed root cultures can be used in physiological tests under non-sterile conditions.

Biological Availability↗

PubMed1988

A plasmid of Rhizobium meliloti 41 encodes catabolism of two compounds from root exudate of Calystegium sepium.

Our objectives were to identify substances produced by plant roots that might act as nutritional mediators of specific plant-bacterium relationships and to delineate the bacterial genes responsible for catabolizing these substances. We discovered new compounds, which we call calystegins, that have the characteristics of nutritional mediators. They were detected in only 3 of 105 species of higher plants examined: Calystegia sepium, Convolvulus arvensis (both of the Convolvulaceae family), and Atropa belladonna. Calystegins are abundant in organs in contact with the rhizosphere and are not found, or are observed only in small quantities, in aerial plant parts. Just as the synthesis of calystegins is infrequent in the plant kingdom, their catabolism is rare among rhizosphere bacteria that associate with plants and influence their growth. Of 42 such bacteria tested, only one (Rhizobium meliloti 41) was able to catabolize calystegins and use them as a sole source of carbon and nitrogen. The calystegin catabolism gene(s) (cac) in this strain is located on a self-transmissible plasmid (pRme41a), which is not essential to nitrogen-fixing symbiosis with legumes. We suggest that under natural conditions calystegins provide an exclusive carbon and nitrogen source to rhizosphere bacteria which are able to catabolize these compounds. Calystegins (and the corresponding microbial catabolic genes) might be used to analyze and possibly modify rhizosphere ecology.

Alkaloids↗

PubMed1986

Nucleotide sequence analysis of TL-DNA of Agrobacterium rhizogenes agropine type plasmid. Identification of open reading frames.

We have determined the nucleotide sequence of the Ri TL-DNA region from an Agrobacterium rhizogenes agropine-type plasmid using subcloned regions from the essentially identical Ri TL-DNAs from strains A4 and HRI. This sequenced region of 21,126 base pairs (bp) contains the complete TL-DNA region of the Ri plasmid as determined by analysis of TL-DNA borders in the genome of infected, clonal, Convolvulus arvensis plants. The left and right borders of the TL-DNA are flanked by 25-bp sequences which match the 25-bp terminal sequences found near the borders of T-DNA regions of Agrobacterium tumefaciens Ti plasmids. Other DNA sequences similar to these 25-bp terminal sequences are found within the TL region, and some of these sequences appear to be associated with Ri TL-DNA structures found in transformed tobacco plants. The TL-DNA region contains 18 open reading frames, many of which have 5' and 3' regulatory elements similar to those found in eukaryotic genes. In many cases, CCAAT and TATA elements were found upstream from putative transcriptional initiation codons, and poly(A) addition (AATAAA) elements were observed in presumed 3'-noncoding regions. Comparison of Ri TL-DNA coding and noncoding sequence regions with T-DNA sequence regions from octopine type Ti plasmid pTi15955 reveals no extensive sequence homologies.

Base Sequence↗

PubMed1985

Structure and expression of Ri T-DNA from Agrobacterium rhizogenes in Nicotiana tabacum. Organ and phenotypic specificity.

The incorporation of transferred DNA (T-DNA) from the Ri plasmid of Agrobacterium rhizogenes into the chromosomal DNA of higher plants is correlated with the appearance of a complex phenotype. The transformed genotype and phenotype undergo Mendelian inheritance. Through studies of Ri T-DNA content and transcription in Nicotiana tabacum, we have delineated a particular part of this foreign DNA as the likely source of the transformed phenotype. One inducible/repressible aspect of the transformed phenotype is termed T' and is correlated with the presence of a supplementary Ri T-DNA-encoded transcript. This transcript is found specifically in leaves, whereas most of the other T-DNA transcripts are more abundant in roots. The T' phenotype does not appear to be due to structural changes in the Ri T-DNA. It is inherited in a dominant Mendelian fashion. We propose that the T' phenotype is caused by heritable changes in the regulation of Ri T-DNA expression. We comment on the potential of this system as a model for studying eukaryotic gene expression.

DNA Restriction Enzymes↗

PubMed1984

Transformation of several species of higher plants by Agrobacterium rhizogenes: sexual transmission of the transformed genotype and phenotype.

The T-DNA of the Ri plasmid from Agrobacterium rhizogenes is compatible with the regeneration of whole plants from genetically transformed roots and is transmitted through meiosis to the progeny of genetically transformed plants in carrot, tobacco, and morning glory (Convolvulus arvensis). The presence of Ri T-DNA is correlated with a phenotype that in some respects is invariable from species to species and in other respects varies as a function of species, organ clone within species, or individual. The transformed phenotype concerns a variety of morphological and physiological traits, is dominantly inherited in tobacco, but does not in general appear to be deleterious. The Ri T-DNA may provide a molecular starting point for studying a number of basic phenomena in plant morphology and physiology.

Genotype↗

PubMedDate not supplied

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Base Sequence↗

PubMedDate not supplied

Betaine use by rhizosphere bacteria: genes essential for trigonelline, stachydrine, and carnitine catabolism in Rhizobium meliloti are located on pSym in the symbiotic region.

Rhizobium meliloti is known to use betaines synthesized by its host, Medicago sativa, as osmoprotectants and sources of energy. It is shown in the present report that the symbiotic megaplasmid (pSym) of R. meliloti RCR2011 encodes functions essential to the catabolism of three betaines, trigonelline (nicotinic acid N-methylbetaine), stachydrine (proline betaine or dimethylproline), and carnitine (gamma-trimethyl-beta-hydroxybutyrobetaine). Preliminary evidence is presented showing that functions on pSym also influence the catabolism of choline and its oxidative product, glycine betaine. Genes implicated in betaine catabolism are found in the symbiotic region of pSym. Trigonelline catabolism functions lie between two clusters of symbiotic genes, nifKDH and nok/fixVI'. Stachydrine and carnitine functions lie to the right of trigonelline catabolism functions, immediately to the right of fixVI'. Information necessary to choline and glycine betaine catabolism is probably encoded to the right of stachydrine catabolism functions.

Alkaloids↗