Developmental and pathogen-induced activation of an msr gene, str246C, from tobacco involves multiple regulatory elements

A family of genes, the so-called msr genes (multiple stimulus response), has recently been identified on the basis of sequence homology in various plant species. Members of this gene family are thought to be regulated by a number of environmental or developmental stimuli, although it is not known whether any one member responds more specifically to one stimulus, or whether each gene member responds to various environmental stimuli. In this report, we address this question by studying the tobacco msr gene str246C. Using transgenic tobacco plants containing 2.1 kb of 5 flanking DNA sequence from the str246C gene fused to the -glucuronidase (GUS) coding region, the complex expression pattern of the str246C promoter has been characterized. Expression of the str246C promoter is strongly and rapidly induced by bacterial, fungal and viral infection and this induction is systemic. Elicitor preparations from phytopathogenic bacteria and fungi activate the str246C promoter to high levels, as do wounding, the application of auxin, auxin and cytokinin, salicylic acid or copper sulfate, indicating the absence of gene specialization within the msr gene family, at least for str246C. In addition, GUS activity was visualized. histochemically in root meristematic tissues of tobacco seedlings and is restricted to roots and sepals of mature plants. Finally, analysis of a series of 5 deletions of the str246C promoter-GUS gene fusion in transgenic tobacco plants confirms the involvement of multiple regulatory elements. A region of 83 by was found to be necessary for induction of promoter activity in response to Pseudomonas solanacearum, while auxin inducibility and root expression are apparently not controlled by this element, since its removal does not abolish either response. An element of the promoter with a negative effect on promoter activation by P. solanacearum was also identified.Joint first authors     

Mass transfer analysis for immobilized cells of Lactococcus lactis sp. using both simulations and in-situ pH measurements

Mathematical modeling and in-situ pH measurements were used to characterize the effects of the microenvironment on alginate gel beads immobilized cells of Lactococcus lactis. Mass transfer limitations led to a progressive pH acidification within gel beads which determined both the cell distribution and the cellular activity of entrapped cells. The dynamics of the system is discussed in relation to the overall activity of the immobilized cell reactor.     

Production of concentrated freeze-dried cultures of Bifidobacterium longumin k-carrageenan-locust bean gum gel

Bifidobacterium longum was immobilized in k-carrageenan/locust bean gum gel beads, and cultured in a medium containing Lactobacillus MRS broth and whey-permeate. The same beads were incubated for 5 successive batch fermentations and freeze-dried following mixing with a protective solution. Viable population in the beads increased from 8 3 10 7 to 4.7 3 10 10 cfu/g after three batch fermentations, but no further increase in viable cell population could be achieved in the last two fermentations. The freeze-dried culture contained 3 3 10 10 cfu/g with a survival rate of approximately 10%. Survival to freeze-drying of immobilized cells was as good as that of classical free-cell cultures. Stability of freeze-dried cultures during storage at minus 17, 4 and 20°C was not influenced by immobilization.     

Distinct response of Medicago suspension cultures and roots to Nod factors and chitin oligomers in the elicitation of defense-related responses

The induction of plant defense-related responses by chitin oligomers and the Rhizobium meliloti lipo-chito-oligosaccharide nodulation signals (Nod factors) in Medicago cell cultures and roots was investigated by following the expression of genes encoding enzymes of the isoflavonoid biosynthetic pathway, such as chalcone synthase, chalcone reductase, isoflavone reductase, as well as genes encoding a pathogenesis-related protein and a peroxidase. In suspension-cultured cells, all genes except the peroxidase gene were induced by both the R. meliloti Nod factor NodRm-IV(C16:2,S) and chitin oligomers with a minimum of three sugar residues. However, activation of these genes was not elicited by the symbiotically inactive, desulfated NodRm-IV(C16:2). Moreover, the cells were more sensitive to the chitin oligosaccharides than to the Nod factor. Analysis of flavonoids in Medicago microcallus cultures revealed differences between cells treated with N -acetyl-chitotetraose and those treated with Nod factor and demonstrated increased production of the phytoalexin medicarpin in the presence of Nod factor. In Medicago roots, none of the tested genes was activated by the N -acetylchitotetraose, whereas the Nod factor at micro-molar concentration enhanced transient expression of the isoflavonoid biosynthetic genes. The differential responses to Nod factors and chitin oligomers suggest that Medicago cells possess distinct perception systems for these related molecules.     

Retroviral Oligonucleotide Distributions Correlate with Biased Nucleotide Compositions of Retrovirus Sequences,Suggesting a Duplicative Stepwise Molecular Evolution

A computer-assisted analysis was made of 24 complete nucleotide sequences selected from the vertebrate retroviruses to represent the ten viral groups. The conclusions of this analysis extend and strengthen the previously made hypothesis on the Moloney murine leukemia virus: The evolution of the nucleotide sequence appears to have occurred mainly through at least three overlapping levels of duplication: (1) The distributions of overrepresented (3–6)-mers are consistent with the universal rule of a trend toward TG/CT excess and with the persistence of a certain degree of symmetry between the two strands of DNA. This suggests one or several original tandemly repeated sequences and some inverted duplications. (2) The existence of two general core consensuses at the level of these (3–6)-mers supports the hypothesis of a common evolutionary origin of vertebrate retroviruses. Consensuses more specific to certain sequences are compatible with phylogenetic trees established independently. The consensuses could correspond to intermediary evolutionary stages. (3) Most of the (3–6)-mers with a significantly higher than average frequency appear to be internally repeated (with monomeric or oligomeric internal iterations) and seem to be at least partly the cause of the bias observed by other researchers at the level of retroviral nucleotide composition. They suggest a third evolutionary stage by slippage-like stepwise local duplications. Received: 3 January 1996 / Accepted: 27 March 1996     

Genetic and molecular analysis of the tRNA-tufB operon of the myxobacterium Stigmatella aurantiaca.

The tufB gene, encoding elongation factor Tu (EF-Tu), from the myxobacterium Stigmatella aurantiaca was cloned and sequenced. It is preceded by four tRNA genes, the first ever described in myxobacteria. The tRNA synthesized from these genes and the general organization of the locus seem identical to that of Escherichia coli, but differences of potential importance were found in the tRNA sequences and in the intergenic regions. The primary structure of EF-Tu was deduced from the tufB DNA sequence. The factor is composed of 396 amino acids, with a predicted molecular mass of 43.4 kDa, which was confirmed by expression of tufB in maxicells. Sequence comparisons between S.aurantiaca EF-Tu and other bacterial homologues from E.coli, Salmonella typhimurium and Thermus thermophilus displayed extensive homologies (75.9%). Among the variable positions, two Cys residues probably involved in the temperature sensitivity of E.coli and S.typhimurium EF-Tu are replaced in T.thermophilus and S.aurantiaca EF-Tu. Since two or even three tuf genes have been described in other bacterial species, the presence of multiple tuf genes was sought for. Southern and Northern analysis are consistent with two tuf genes in the genome of S.aurantiaca. Primer extension experiments indicate that the four tRNA genes and tufB are organized in a single operon.     

Molecular basis and PCR-DNA typing of the Fya/fyb blood group polymorphism

Spondyloepiphyseal dysplasia tarda (SEDL) is an X-linked recessive disorder characterized in affected males by short stature resulting from a growth defect of the vertebral bodies. We have extended our earlier studies by analyzing 15 families with newly identified microsatellite DNA markers; analysis of recombination events with these markers indicates that the gene responsible for SEDL is located in Xp22 between DXS 16 and DXS 987 on an interval spanning approximately 2 Mb.