Characterization of CoRoT Target Fields with the Berlin Exoplanet Search Telescope: Identification of Periodic Variable Stars in the LRa1 Field

In this paper, we report on observations of the CoRoT LRa1 field with the Berlin Exoplanet Search Telescope (BEST). The current paper is part of a series of papers describing the results of our stellar variability survey. The BEST is a small aperture telescope with a wide field of view (FOV). It is dedicated to searching for stellar variability within the target fields of the CoRoT space mission to aid in minimizing false-alarm rates and identify potential targets for additional science. The LRa1 field is CoRoT's second long run field located in the galactic anticenter direction. We observed the LRa1 stellar field on 23 nights between November and March 2005/2006. From 6099 stars marked as variable, 39 were classified as periodic variable stars and 27 of them are within the CoRoT FOV. We also confirmed the variability for four stars listed in the General Catalogue of Variable Stars (GCVS)

Why Bothering to Measure Stellar Rotation with CoRoT?

One important goal of the CoRoT experiment is to obtain information about the internal rotation of stars, in particular the ratio of central to surface rotation rates. This will provide constraints on the modelling of transport mechanisms of angular momentum acting in radiative (rotationally induced turbulent) and convective zones (plumes, extension beyond convectively instable regions). Relations between the surface rotation period and age, magnetic activity, mass loss and other stellar characteristics can also be studied with a statistically significant set of data as will be provided by Corot. We present various theoretical efforts performed over the past years in order to develope the theoretical tools which will enable us to study rotation with Corot

Repeated evolution of self-compatibility for reproductive assurance

Sexual reproduction in eukaryotes requires the fusion of two compatible gametes of opposite sexes or mating types. To meet the challenge of finding a mating partner with compatible gametes evolutionary mechanisms such as hermaphroditism and self-fertilisation have repeatedly evolved. Combining insight from comparative genomics, computer simulations and experimental evolution in fission yeast, we shed light on the conditions promoting separate mating types or self-compatibility by mating-type switching. Analogous to multiple independent transitions between switchers and non-switchers in natural populations mediated by structural genomic changes, novel switching genotypes were readily evolving under selection in experimental populations. Detailed fitness measurements accompanied by computer simulations show the benefits and costs of switching during sexual and asexual reproduction governing the occurrence of both strategies in nature. Our findings illuminate the trade-off between the benefits of reproductive assurance and its fitness costs under benign conditions governing the evolution of self-compatibility

A Plant-Specific Transcription Factor IIB-Related Protein, pBRP2, Is Involved in Endosperm Growth Control

General transcription factor IIB (TFIIB) and TFIIB-related factor (BRF), are conserved RNA polymerase II/III (RNAPII/III) selectivity factors that are involved in polymerase recruitment and transcription initiation in eukaryotes. Recent findings have shown that plants have evolved a third type of B-factor, plant-specific TFIIB-related protein 1 (pBRP1), which seems to be involved in RNAPI transcription. Here, we extend the repertoire of B-factors in plants by reporting the characterization of a novel TFIIB-related protein, plant-specific TFIIB-related protein 2 (pBRP2), which is found to date only in the Brassicacea family. Unlike other B-factors that are ubiquitously expressed, PBRP2 expression is restricted to reproductive organs and seeds as shown by RT-PCR, immunofluorescence labelling and GUS staining experiments. Interestingly, pbrp2 loss-of-function specifically affects the development of the syncytial endosperm, with both parental contributions required for wild-type development. pBRP2, is the first B-factor to exhibit cell-specific expression and regulation in eukaryotes, and might play a role in enforcing bi-parental reproduction in angiosperms

DRB2 Is Required for MicroRNA Biogenesis in Arabidopsis thaliana

Background The Arabidopsis thaliana (Arabidopsis) DOUBLE-STRANDED RNA BINDING (DRB) protein family consists of five members, DRB1 to DRB5. The biogenesis of two developmentally important small RNA (sRNA) species, the microRNAs (miRNAs) and trans-acting small interfering RNAs (tasiRNAs) by DICER-LIKE (DCL) endonucleases requires the assistance of DRB1 and DRB4 respectively. The importance of miRNA-directed target gene expression in plant development is exemplified by the phenotypic consequence of loss of DRB1 activity (drb1 plants). Principal Findings Here we report that the developmental phenotype of the drb235 triple mutant plant is the result of deregulated miRNA biogenesis in the shoot apical meristem (SAM) region. The expression of DRB2, DRB3 and DRB5 in wild-type seedlings is restricted to the SAM region. Small RNA sequencing of the corresponding tissue of drb235 plants revealed altered miRNA accumulation. Approximately half of the miRNAs detected remained at levels equivalent to those of wild-type plants. However, the accumulation of the remaining miRNAs was either elevated or reduced in the triple mutant. Examination of different single and multiple drb mutants revealed a clear association between the loss of DRB2 activity and altered accumulation for both the elevated and reduced miRNA classes. Furthermore, we show that the constitutive over-expression of DRB2 outside of its wild-type expression domain can compensate for the loss of DRB1 activity in drb1 plants. Conclusions/Significance Our results suggest that in the SAM region, DRB2 is both antagonistic and synergistic to the role of DRB1 in miRNA biogenesis, adding an additional layer of gene regulatory complexity in this developmentally important tissue

Imprinting of the Polycomb Group Gene MEDEA Serves as a Ploidy Sensor in Arabidopsis

Balanced maternal and paternal genome contributions are a requirement for successful seed development. Unbalanced contributions often cause seed abortion, a phenomenon that has been termed “triploid block.” Misregulation of imprinted regulatory genes has been proposed to be the underlying cause for abnormalities in growth and structure of the endosperm in seeds with deviating parental contributions. We identified a mutant forming unreduced pollen that enabled us to investigate direct effects of unbalanced parental genome contributions on seed development and to reveal the underlying molecular mechanism of dosage sensitivity. We provide evidence that parent-of-origin–specific expression of the Polycomb group (PcG) gene MEDEA is causally responsible for seed developmental aberrations in Arabidopsis seeds with increased paternal genome contributions. We propose that imprinted expression of PcG genes is an evolutionary conserved mechanism to balance parental genome contributions in embryo nourishing tissues

H3K27me3 Profiling of the Endosperm Implies Exclusion of Polycomb Group Protein Targeting by DNA Methylation

Polycomb group (PcG) proteins act as evolutionary conserved epigenetic mediators of cell identity because they repress transcriptional programs that are not required at particular developmental stages. Each tissue is likely to have a specific epigenetic profile, which acts as a blueprint for its developmental fate. A hallmark for Polycomb Repressive Complex 2 (PRC2) activity is trimethylated lysine 27 on histone H3 (H3K27me3). In plants, there are distinct PRC2 complexes for vegetative and reproductive development, and it was unknown so far whether these complexes have target gene specificity. The FERTILIZATION INDEPENDENT SEED (FIS) PRC2 complex is specifically expressed in the endosperm and is required for its development; loss of FIS function causes endosperm hyperproliferation and seed abortion. The endosperm nourishes the embryo, similar to the physiological function of the placenta in mammals. We established the endosperm H3K27me3 profile and identified specific target genes of the FIS complex with functional roles in endosperm cellularization and chromatin architecture, implicating that distinct PRC2 complexes have a subset of specific target genes. Importantly, our study revealed that selected transposable elements and protein coding genes are specifically targeted by the FIS PcG complex in the endosperm, whereas these elements and genes are densely marked by DNA methylation in vegetative tissues, suggesting that DNA methylation prevents targeting by PcG proteins in vegetative tissues

Transiting exoplanets from the CoRoT space mission. VIII. CoRoT-7b: the first super-Earth with measured radius

Copyright © The European Southern Observatory (ESO)Aims. We report the discovery of very shallow (ΔF/F ≈ 3.4×10−4), periodic dips in the light curve of an active V = 11.7 G9V star observed by the CoRoT satellite, which we interpret as caused by a transiting companion. We describe the 3-colour CoRoT data and complementary ground-based observations that support the planetary nature of the companion. Methods. We used CoRoT colours information, good angular resolution ground-based photometric observations in- and out- of transit, adaptive optics imaging, near-infrared spectroscopy, and preliminary results from radial velocity measurements, to test the diluted eclipsing binary scenarios. The parameters of the host star were derived from optical spectra, which were then combined with the CoRoT light curve to derive parameters of the companion. Results. We examined all conceivable cases of false positives carefully, and all the tests support the planetary hypothesis. Blends with separation >0.40'' or triple systems are almost excluded with a 8 × 10−4 risk left. We conclude that, inasmuch we have been exhaustive, we have discovered a planetary companion, named CoRoT-7b, for which we derive a period of 0.853 59 ± 3 × 10−5 day and a radius of Rp = 1.68 ± 0.09 REarth. Analysis of preliminary radial velocity data yields an upper limit of 21 MEarth for the companion mass, supporting the finding. Conclusions. CoRoT-7b is very likely the first Super-Earth with a measured radius. This object illustrates what will probably become a common situation with missions such as Kepler, namely the need to establish the planetary origin of transits in the absence of a firm radial velocity detection and mass measurement. The composition of CoRoT-7b remains loosely constrained without a precise mass. A very high surface temperature on its irradiated face, ≈1800–2600 K at the substellar point, and a very low one, ≈50 K, on its dark face assuming no atmosphere, have been derived

Identification of a second major resistance gene to Rice yellow mottle virus, RYMV2, in the African cultivated rice species, O. glaberrima

Rice yellow mottle virus (RYMV) is the most damaging rice-infecting virus in Africa. However, few sources of high resistance and only a single major resistance gene, RYMV1, are known to date. We screened a large representative collection of African cultivated rice (Oryza glaberrima) for RYMV resistance. Whereas high resistance is known to be very rare in Asian cultivated rice (Oryza sativa), we identified 29 (8%) highly resistant accessions in O. glaberrima. The MIF4G domain of RYMV1 was sequenced in these accessions. Some accessions possessed the rymv1-3 or rymv1-4 recessive resistance alleles previously described in O. glaberrima Tog5681 and Tog5672, respectively, and a new allele, rymv1-5, was identified, thereby increasing the number of resistance alleles in O. glaberrima to three. In contrast, only a single allele has been reported in O. sativa. Markers specific to the different alleles of the RYMV1 gene were developed for marker-assisted selection of resistant genotypes for disease management. In addition, the presence of the dominant susceptibility allele (Rymv1-1) in 15 resistant accessions suggests that their resistance is under different genetic control. An allelism test involving one of those accessions revealed a second major resistance gene, i.e., RYMV2. The diversity of resistance genes against RYMV in O. glaberrima species is discussed in relation to the diversification of the virus in Africa