Multilevel Control of Organelle DNA Sequence Length in Plants

We have compared the length of noncoding organelle DNA spacers in a broad sample of plant species characterized by different life history traits to test hypotheses regarding the nature of the mechanisms driving changes in their size. We first demonstrate that the spacers do not evolve at random in size but have experienced directional evolutionary trends during plant diversification. We then study the relationships between spacer lengths and other molecular features and various species attributes by taking into account population genetic processes acting within cell lineages. Comparative techniques are used to test these relationships while controlling for species phylogenetic relatedness. The results indicate that spacer length depends on mode of organelle transmission, on population genetic structure, on nucleotide content, on rates of molecular evolution, and on life history traits, in conformity with predictions based on a model of intracellular competition among replicating organelle genomes. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Regulation of phospholipase D by phosphorylation-dependent mechanisms

The rapid production of phosphatidic acid following receptor stimulation has been demonstrated in a wide range of mammalian cells. Virtually every cell uses phosphatidylcholine as substrate to produce phosphatidic acid in a controlled reaction catalyzed by specific PLD isoforms. Considerable effort has been directed at studying the regulation of PLD activities and subsequent work has characterized a family of proteins including PLD1 and PLD2. Whereas both PLD enzymes are dependent on phosphatidylinositol 4,5-bisphosphate for activity only the PLD1 isoform was strongly stimulated by the small GTPases ARF and RhoA and by protein kinase Cα as well. A role for tyrosine kinase activities in the membrane recruitment of small GTPases, in the synthesis of phosphatidylinositol 4,5-bisphosphate and tyrosine phosphorylation of PLD1 and PLD2 has been uncovered. However, it still not clear exactly how tyrosine phosphorylation of proteins contributes to PLD activation in cells. Here we review the data linking tyrosine phosphorylation of proteins to the activation of PLD and describe recent finding on the sites and possible mechanisms of action of tyrosine kinases in receptor-mediated PLD activation. Finally, a model illustrating the potential complex interplay linking these signaling events with the activation of PLD is presented.     

Environmental determinants of Great Cormorant (Phalacrocorax carbo) distribution in small man-made waterbodies – a case study of gravel pits in southwest France

In the Midi-Pyrénées region (southwest France), the increasing number of gravel pits has allowed the wintering of numerous species of waterbirds such as Great Cormorants (Phalacrocorax carbo). The debate about cormorant predation on fish stock has been sufficiently strong to have resulted in reductions in cormorant numbers by control shooting. In this context, cormorants were studied during winters 1996/1997 and 1997/1998 at two gravel pit sites in the Garonne floodplain. Human disturbances and fish densities were found to be the main parameters determining the abundance of fishing cormorants. This work will help to prompt further research and the development of a management strategy for this species.     

Rate of differentiation and emergence of nodal maize roots

The timing of root production is one of the parameters required for modelling the root system architecture. The objectives of this study are (1) to describe the rate of appearance of adventitious root primordia of maize and their rate of emergence out of the stem; (2) to test equations for the prediction of the rank of the phytomer on which root emergence occurs, in a wide range of field situations.Maize, cultivar Dea, was grown in controlled conditions and in the field in 1987, 1988, 1989 and 1991. Plants were regularly sampled and the following data were recorded: foliar stage, number of root primordia and number of emerged roots per phytomer. Root primordia were counted in transverse thin sections in the stem.At a single plant level, root primordia differentiation occurred sequentially on the successive phytomers, with no overlapping between two phytomers. The same was true for root emergence. Roots belonging to the same phytomer emerged at approximately the same time.At a plant population level, there was a linear relationship between the rank of the phytomer on which root primordia were differentiated and cumulated degree-days after sowing. A linear relationship was also observed between the rank of the phytomer on which roots were emerging and cumulated degree-days or foliar stage. In the range of field situations tested (several years, sowing dates and planting densities), both equations gave an accurate prediction of the timing of root emergence during the plant cycle.     

Characterization of the cryptic Escherichia lineages: rapid identification and prevalence

Strains phenotypically indistinguishable from Escherichia coli and belonging to at least five distinct cryptic lineages, named Escherichia clades I to V, that are genetically divergent from E. coli yet members of the genus have been recently found using multi-locus sequence typing (MLST). Very few epidemiological data are available on these strains as their detection by MLST is not suitable for large-scale studies. In this work, we developed a rapid PCR method based on aes and chuA allele-specific amplifications that assigns a strain a cryptic lineage membership. By screening more than 3500 strains with this approach, we show that the cryptic lineages of Escherichia are unlikely to be detected in human faecal samples (2-3% frequency) and even less likely to be isolated from extra-intestinal body sites (< 1% frequency). They are more abundant in animal faeces ranging from 3-8% in non-human mammals to 8-28% in birds. Overall, the strains from the clade V are the most abundant and from the clade II very rare. These results suggest that members of the cryptic clades are unlikely to be of significance to human and health but may influence the use of 'E. coli' as an indicator of water quality.     

Natural regulatory T cells control the development of atherosclerosis in mice

Atherosclerosis is an immunoinflammatory disease elicited by accumulation of lipids in the artery wall and leads to myocardial infarction and stroke. Here, we show that naturally arising CD4(+)CD25(+) regulatory T cells, which actively maintain immunological tolerance to self and nonself antigens, are powerful inhibitors of atherosclerosis in several mouse models. These results provide new insights into the immunopathogenesis of atherosclerosis and could lead to new therapeutic approaches that involve immune modulation using regulatory T cells.