543 research outputs found
CLONING OF AN AZORHIZOBIUM-CAULINODANS ENDOGLUCANASE GENE AND ANALYSIS OF ITS ROLE IN SYMBIOSIS
IDENTIFICATION AND CHARACTERIZATION OF A FUNCTIONAL NODD GENE IN AZORHIZOBIUM-CAULINODANS ORS571
Rapport concernant l'influence des endiguements à Saaftinge sur le régime des marées de l'Escaut Maritime
7,4'-Dihydroxyflavanone is the major Azorhizobium nod gene-inducing factor present in Sesbania rostrata seedling exudate
Exudate from Sesbania rostrata seedlings contains signaling compounds that induce the common nodABC operon of the bacterial symbiont Azorhizobium caulinodans ORS571. An Azorhizobium strain harboring a nodA::lacZ reporter fusion was used to monitor the nod-inducing activity of crude exudate fractions that were separated by reversed-phase chromatography. The major inducer was shown, by spectroscopic analysis and by comparison with chemically synthesized compounds, to be 7,4'-dihydroxyflavanone (liquiritigenin). Newly synthesized analogues, 7,3'-dihydroxyflavanone and 7,2'-dihydroxyflavanone, have only poor inducing activity
AN AZORHIZOBIUM-CAULINODANS ORS571 LOCUS INVOLVED IN LIPOPOLYSACCHARIDE PRODUCTION AND NODULE FORMATION ON SESBANIA-ROSTRATA STEMS AND ROOTS
Azorhizobium caulinodans ORS571 is able to nodulate roots and stems of the tropical legume Sesbania rostrata. An ORS571 Tn5 insertion mutant, strain ORS571-X15, had a rough colony morphology, was nonmotile, and showed clumping behavior on various media. When this pleiotropic mutant was inoculated on roots or stems of the host, no nodules developed (Nod-). Compared with the wild type, strain ORS571-X15 produced lipopolysaccharides (LPS) with an altered ladder pattern on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels, suggestive of a different O-antigen structure with a lower degree of polymerization. A cosmid clone, pRG20, that fully complemented all phenotypes of ORS571-X15 was isolated. With a 6-kb EcoRI subfragment of pRG20, clumping was relieved and nodulation was almost completely restored, but the strain was still nonmotile. LPS preparations from these complemented strains resembled the wild-type LPS, although minor quantitative and qualitative differences were evident. The sequence of the locus hit by the Tn5 in ORS571-X15 (the oac locus) revealed a striking homology with the rfb locus of Salmonella typhimurium, which is involved in O-antigen biosynthesis. The Tn5 insertion position was mapped to the oac3 gene, homologous to rfbA, encoding dTDP-D-glucose synthase. Biochemical assaying showed that ORS571-X15 is indeed defective in dTDP-D-glucose synthase activity, essential for the production of particular deoxyhexoses. Therefore, it was proposed that the O antigen of the mutant strain is devoid of such sugars
MtNRLK1, a CLAVATA1-like leucine-rich repeat receptor-like kinase upregulated during nodulation in Medicago truncatula
Peptides are signaling molecules regulating various aspects of plant development, including the balance between cell division and differentiation in different meristems. Among those, CLAVATA3/Embryo Surrounding Region-related (CLE-ESR) peptide activity depends on leucine-rich-repeat receptor-like-kinases (LRR-RLK) belonging to the subclass XI. In legume plants, such as the Medicago truncatula model, specific CLE peptides were shown to regulate root symbiotic nodulation depending on the LRR-RLK SUNN (Super Numeric Nodules). Amongst the ten M. truncatula LRR-RLK most closely related to SUNN, only one showed a nodule-induced expression, and was so-called MtNRLK1 (Nodule-induced Receptor-Like Kinase 1). MtNRLK1 expression is associated to root and nodule vasculature as well as to the proximal meristem and rhizobial infection zone in the nodule apex. Except for the root vasculature, the MtNRLK1 symbiotic expression pattern is different than the one of MtSUNN. Functional analyses either based on RNA interference, insertional mutagenesis, and overexpression of MtNRLK1 however failed to identify a significant nodulation phenotype, either regarding the number, size, organization or nitrogen fixation capacity of the symbiotic organs formed
Consumer sensory analysis of high flavonoid transgenic tomatoes
Tomatoes have ameliorative effects on cardiovascular disease and cancer (Agarwal and Rao 2000; Rao 2002). In this study, metabolic engineering of flavonoids was utilized to improve the nutritional value of tomatoes by increasing flavonol and anthocyanin content. Total flavonol content was significantly increased in both the peel and flesh using the onion chalcone isomerase (CHI) gene. The Delila (Del) and Rosea1 (Ros1) genes from the snapdragon Antirrhinum majus were concomitantly expressed to produce an anthocyaninârich tomato which was purple in color. Sensory evaluation by a panel of 81 untrained consumers revealed no significant difference in liking of color or texture between CHI, Del/Ros1, and wildâtype tomatoes. Consumers reported marginal but significantly higher preference for the flavor and overall liking of CHI tomatoes over Del/Ros1 and wildâtype tomatoes. This study is the first to report the results of sensory tests of transgenic tomatoes by a consumer panel representing the general consuming public
An analysis of the boundaries of the octopine TL-DNA in tumors induced by Agrobacterium tumefaciens
The genome of the versatile nitrogen fixer Azorhizobium caulinodans ORS571
<p>Abstract</p> <p>Background</p> <p>Biological nitrogen fixation is a prokaryotic process that plays an essential role in the global nitrogen cycle. <it>Azorhizobium caulinodans </it>ORS571 has the dual capacity to fix nitrogen both as free-living organism and in a symbiotic interaction with <it>Sesbania rostrata</it>. The host is a fast-growing, submergence-tolerant tropical legume on which <it>A. caulinodans </it>can efficiently induce nodule formation on the root system and on adventitious rootlets located on the stem.</p> <p>Results</p> <p>The 5.37-Mb genome consists of a single circular chromosome with an overall average GC of 67% and numerous islands with varying GC contents. Most nodulation functions as well as a putative type-IV secretion system are found in a distinct symbiosis region. The genome contains a plethora of regulatory and transporter genes and many functions possibly involved in contacting a host. It potentially encodes 4717 proteins of which 96.3% have homologs and 3.7% are unique for <it>A. caulinodans</it>. Phylogenetic analyses show that the diazotroph <it>Xanthobacter autotrophicus </it>is the closest relative among the sequenced genomes, but the synteny between both genomes is very poor.</p> <p>Conclusion</p> <p>The genome analysis reveals that <it>A. caulinodans </it>is a diazotroph that acquired the capacity to nodulate most probably through horizontal gene transfer of a complex symbiosis island. The genome contains numerous genes that reflect a strong adaptive and metabolic potential. These combined features and the availability of the annotated genome make <it>A. caulinodans </it>an attractive organism to explore symbiotic biological nitrogen fixation beyond leguminous plants.</p
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