The FRD3 citrate effluxer promotes iron nutrition between symplastically disconnected tissues throughout Arabidopsis development

We present data supporting a general role for FERRIC REDICTASE DEFECTIVE3 (FRD3), an efflux transporter of the efficient iron chelator citrate, in maintaining iron homeostasis throughout plant development. In addition to its well-known expression in root, we show that FRD3 is strongly expressed in Arabidopsis thaliana seed and flower. Consistently, frd3 loss-of-function mutants are defective in early germination and are almost completely sterile, both defects being rescued by iron and/or citrate supply. The frd3 fertility defect is caused by pollen abortion and is associated with the male gametophytic expression of FRD3. Iron imaging shows the presence of important deposits of iron on the surface of aborted pollen grains. This points to a role for FRD3 and citrate in proper iron nutrition of embryo and pollen. Based on the findings that iron acquisition in embryo, leaf, and pollen depends on FRD3, we propose that FRD3 mediated-citrate release in the apoplastic space represents an important process by which efficient iron nutrition is achieved between adjacent tissues lacking symplastic connections. These results reveal a physiological role for citrate in the apoplastic transport of iron throughout development, and provide a general model for multicellular organisms in the cell-to-cell transport of iron involving extracellular circulation.     

What do we need to know about speciation?

Speciation has been a major focus of evolutionary biology research in recent years, with many important advances. However, some of the traditional organising principles of the subject area no longer provide a satisfactory framework, such as the classification of speciation mechanisms by geographical context into allopatric, parapatric and sympatry classes. Therefore, we have asked where speciation research should be directed in the coming years. Here, we present a distillation of questions about the mechanisms of speciation, the genetic basis of speciation and the relationship between speciation and diversity. Our list of topics is not exhaustive; rather we aim to promote discussion on research priorities and on the common themes that underlie disparate speciation processes.     

<Emphasis Type="Italic">Arabidopsis</Emphasis> IRT2 cooperates with the high-affinity iron uptake system to maintain iron homeostasis in root epidermal cells

Iron is an essential nutrient for all organisms but toxic when present in excess. Consequently, plants carefully regulate their iron uptake, dependent on the FRO2 ferric reductase and the IRT1 transporter, to control its homeostasis. Arabidopsis IRT2 gene, whose expression is induced in root epidermis upon iron deprivation, was shown to encode a functional iron/zinc transporter in yeast, and proposed to function in iron acquisition from the soil. In this study, we demonstrate that, unlike its close homolog IRT1, IRT2 is not involved in iron absorption from the soil since overexpression of IRT2 does not rescue the iron uptake defect of irt1-1 mutant and since a null irt2 mutant shows no chlorosis in low iron. Consistently, an IRT2-green fluorescent fusion protein, transiently expressed in culture cells, localizes to intracellular vesicles. However, IRT2 appears strictly co-regulated with FRO2 and IRT1, supporting the view that IRT2 is an integral component of the root response to iron deficiency in root epidermal cells. We propose a model where IRT2 likely prevents toxicity from IRT1-dependent iron fluxes in epidermal cells, through compartmentalization.     

Establishment and characterization of endothelial cell lines from the aorta of miniature pig for the study of xenotransplantation

Pig endothelial cells are the first cells to interact with human immune components after organ xenotransplantation, which is a procedure currently considered to be the best treatment option for end-stage organ failure. It is, therefore, essential to study the mechanisms of molecular interaction between pig endothelial cells and human immune components, in order to overcome xenograft rejection. The aim of this study was to establish immortalized pig aortic endothelial cell lines, in order to facilitate future in vitro studies of human anti-pig immune responses. Endothelial cell lines were established following the transfection of primary endothelial cells isolated from the aortas of the Minnesota miniature pig with plasmid pRNS-1 carrying genes for neomycin resistance and the SV40 large T antigen. The immortalized cell lines showed a relatively rapid doubling time (17.6h) and the endothelial cell phenotype, as indicated by the formation of typical cobblestone monolayers and by the constitutive expression of PECAM-1 and the von Willebrand factor. Flow cytometric analysis demonstrated the constitutive expression of SLA class I and CD86, whereas the expression of E-selectin and SLA class II was only induced after stimulation with human TNF-alpha and pig IFN-gamma, respectively. On the other hand, no CD80 expression was detected in the primary cells or cell lines in the presence or absence of either human TNF-alpha or pig IFN-gamma. A vigorous human T cell proliferation against these cell lines was observed in the mixed lymphocyte-endothelial cell culture. These results suggest that pig endothelial cells, immortalized by the introduction of SV40 T, retain their original characteristics, except for the acquired property of immortalization, and that they may be useful for future in vitro studies of xenogeneic human anti-pig immune responses.     

Correlations between pregnancy pathology, study of the placenta, antenatal echography and examination of the product of conception in a series of 175 congenital malformations

In order to verify the hypothesis that during pregnancy in a woman without peculiar history, signs could be discovered when the fetus is malformed we have reviewed the files of 175 women who had a malformed child and of 300 controls. All of these women had at least one clinical examination and one ultrasonographic examination during pregnancy. Two clinical symptoms were more often discovered in the mother of the malformed fetus (p less than 0.001): decrease of fetal movements and small for date fetus. The placenta is never abnormal in the mother with normal fetus. Placenta is abnormal in 31% of the mother with malformed fetus but the abnormalities are not specific. Ultrasonographic examinations allowed more often the discovery of a malformation when hydramnios (p less than 0.001) or fetal hypotrophy (p less than 0.01) or an anomaly of the morphology of the fetus is discovered. Accuracy of prenatal diagnostic is considered for the different categories of congenital malformations.