First plasma of the A-PHOENIX electron cyclotron resonance ion source

International audienceA-PHOENIX is a new compact hybrid electron cyclotron resonance ion source (ECRIS) using a large permanent magnet hexapole (1.92 Tesla at the magnet surface) and High Temperature Superconducting Solenoids (3 Tesla) to make min-|B| structure suitable for 28 GHz CW operation. The final assembly of the source was achieved at the end of june 2007. The first plasma of A-PHOENIX at 18 GHz was done on August the 16th 2007. The technological specificities of A-PHOENIX are presented. The large hexapole builded is presented and experimental magnetic measurements show that it is nominal with respect to simulation. A fake plasma chamber prototype including thin iron inserts showed that the predicted radial magnetic confinement can be fulfilled up to 2.15 Tesla at the plasma chamber wall. Planning of experiments scheduled until end 2008 is presented

The MYST histone acetyltransferases are essential for gametophyte development in Arabidopsis

<p>Abstract</p> <p>Background</p> <p>Histone acetyltransferases (HATs) play critical roles in the regulation of chromatin structure and gene expression. Arabidopsis genome contains 12 HAT genes, but the biological functions of many of them are still unknown. In this work, we studied the evolutionary relationship and cellular functions of the two Arabidopsis HAT genes homologous to the MYST family members.</p> <p>Results</p> <p>An extensive phylogenetic analysis of 105 MYST proteins revealed that they can be divided into 5 classes, each of which contains a specific combination of protein modules. The two Arabidopsis MYST proteins, HAM1 and HAM2, belong to a "green clade", clearly separated from other families of HATs. Using a reverse genetic approach, we show that <it>HAM1 </it>and <it>HAM2 </it>are a functionally redundant pair of genes, as single Arabidopsis <it>ham1 </it>and <it>ham2 </it>mutants displayed a wild-type phenotype, while no double mutant seedling could be recovered. Genetic analysis and cytological study revealed that <it>ham1ham2 </it>double mutation induced severe defects in the formation of male and female gametophyte, resulting in an arrest of mitotic cell cycle at early stages of gametogenesis. RT-PCR experiments and the analysis of transgenic plants expressing the <it>GUS </it>reporter gene under the <it>HAM1 </it>or the <it>HAM2 </it>promoter showed that both genes displayed an overlapping expression pattern, mainly in growing organs such as shoots and flower buds.</p> <p>Conclusion</p> <p>The work presented here reveals novel properties for MYST HATs in Arabidopsis. In addition to providing an evolutionary relationship of this large protein family, we show the evidence of a link between MYST and gamete formation as previously suggested in mammalian cells. A possible function of the Arabidopsis MYST protein-mediated histone acetylation during cell division is suggested.</p

Experimental and theoretical investigation of the Preglow in ECRIS

International audienceA careful study of pulsed mode operation of the PHOENIX ECR ion source has clearly demonstrated the reality of an unexpected transient current peak occurring at the very beginning of the gas breakdown. This regime was named the Preglow, as an explicit reference to the classical Afterglow occurring at the microwave pulse end. After the transient Preglow peak, the plasma regime relaxes to the classical steady state one. Argon Preglow experiments performed at LPSC are presented. A theoretical 0-dimension model of ECR gas breakdown in a magnetic trap, developed at IAP RAS, is presented in detail. Results of the simulation are compared with the experimental Preglow peaks and discussed

Immunity onset alters plant chromatin and utilizes EDA16 to regulate oxidative homeostasis

Perception of microbes by plants leads to dynamic reprogramming of the transcriptome, which is essential for plant health. The appropriate amplitude of this transcriptional response can be regulated at multiple levels, including chromatin. However, the mechanisms underlying the interplay between chromatin remodeling and transcription dynamics upon activation of plant immunity remain poorly understood. Here, we present evidence that activation of plant immunity by bacteria leads to nucleosome repositioning, which correlates with altered transcription. Nucleosome remodeling follows distinct patterns of nucleosome repositioning at different loci. Using a reverse genetic screen, we identify multiple chromatin remodeling ATPases with previously undescribed roles in immunity, including EMBRYO SAC DEVELOPMENT ARREST 16, EDA16. Functional characterization of the immune-inducible chromatin remodeling ATPase EDA16 revealed a mechanism to negatively regulate immunity activation and limit changes in redox homeostasis. Our transcriptomic data combined with MNase-seq data for EDA16 functional knock-out and over-expressor mutants show that EDA16 selectively regulates a defined subset of genes involved in redox signaling through nucleosome repositioning. Thus, collectively, chromatin remodeling ATPases fine-tune immune responses and provide a previously uncharacterized mechanism of immune regulation

Axial light emission and Ar metastable densities in a parallel plate dc micro discharge in steady state and transient regimes

Axial emission profiles in a parallel plate dc micro discharge (feedgas: argon; discharge gap d=1mm; pressure p=10Torr) were studied by means of time resolved imaging with a fast ICCD camera. Additionally, volt-ampere (V-A) characteristics were recorded and Ar* metastable densities were measured by tunable diode laser absorption spectroscopy (TDLAS). Axial emission profiles in the steady state regime are similar to corresponding profiles in standard size discharges (d=1cm, p=1Torr). For some discharge conditions relaxation oscillations are present when the micro discharge switches periodically between low current Townsend-like mode and normal glow. At the same time the axial emission profile shows transient behavior, starting with peak distribution at the anode, which gradually moves towards the cathode during the normal glow. The development of argon metastable densities highly correlates with the oscillating discharge current. Gas temperatures in the low current Townsend-like mode (T= 320-400K) and the high current glow mode (T=469-526K) were determined by the broadening of the recorded spectral profiles as a function of the discharge current.Comment: submitted to Plasma Sources Sci. Techno

Involvement of Arabidopsis BIG protein in cell death mediated by Myo- Inositol homeostasis

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Study of pulsed ECRIS plasma near breakdown: the Preglow

International audienceA careful study of pulsed mode operation of the PHOENIX ECR ion source has clearly demonstrated the reality of an unexpected transient current peak, occurring at the very beginning of the plasma breakdown. This regime was named the Preglow, as an explicit reference to the Afterglow occurring at the microwave pulse end. After the transient Preglow peak, the plasma regime relaxes to the classical steady state one. Argon Preglow experiments performed at LPSC are presented. A theoretical model of ECR gas breakdown in a magnetic trap, developed at IAP, showing satisfactory agreement with the experimental results is suggested

Arabidopsis S2Lb links AtCOMPASS-like and SDG2 activity in H3K4me3 independently from histone H2B monoubiquitination.

The functional determinants of H3K4me3, their potential dependency on histone H2B monoubiquitination, and their contribution to defining transcriptional regimes are poorly defined in plant systems. Unlike in Saccharomyces cerevisiae, where a single SET1 protein catalyzes H3K4me3 as part of COMPlex of proteins ASsociated with Set1 (COMPASS), in Arabidopsis thaliana, this activity involves multiple histone methyltransferases. Among these, the plant-specific SET DOMAIN GROUP 2 (SDG2) has a prominent role. We report that SDG2 co-regulates hundreds of genes with SWD2-like b (S2Lb), a plant ortholog of the Swd2 axillary subunit of yeast COMPASS. We show that S2Lb co-purifies with the AtCOMPASS core subunit WDR5, and both S2Lb and SDG2 directly influence H3K4me3 enrichment over highly transcribed genes. S2Lb knockout triggers pleiotropic developmental phenotypes at the vegetative and reproductive stages, including reduced fertility and seed dormancy. However, s2lb seedlings display little transcriptomic defects as compared to the large repertoire of genes targeted by S2Lb, SDG2, or H3K4me3, suggesting that H3K4me3 enrichment is important for optimal gene induction during cellular transitions rather than for determining on/off transcriptional status. Moreover, unlike in budding yeast, most of the S2Lb and H3K4me3 genomic distribution does not rely on a trans-histone crosstalk with histone H2B monoubiquitination. Collectively, this study unveils that the evolutionarily conserved COMPASS-like complex has been co-opted by the plant-specific SDG2 histone methyltransferase and mediates H3K4me3 deposition through an H2B monoubiquitination-independent pathway in Arabidopsis