Integration of phot1, phot2, and PhyB signalling in light-induced chloroplast movements

Abstract In Arabidopsis thaliana, chloroplasts move towards the periclinal cell walls upon exposure to low blue light intensities and to anticlinal walls under high light. The regulation of these chloroplast movements involves members of both the phototropin and phytochrome families of photoreceptors. Examination of fluence-rate response dependencies in phot1 and phot2 mutants revealed that although both photoreceptors are capable of inducing chloroplast accumulation under low-light conditions, the signals from these photoreceptors appear to be antagonistic. Chloroplast movements in wild-type plants were intermediate between those of the single phot mutants, consistent with each operating through separate signalling cascades. Mutants in phot2 showed transient chloroplast avoidance responses upon exposure to intense blue light, and slow but sustained chloroplast avoidance under intense white light, indicating that in the absence of phot2, phot1 is capable of generating both a low and a high-light response signal. Mutations in phytochrome B (phyB) caused an enhanced avoidance response at intermediate and high light intensities. Examination of phyB, phot1phyB, and phot2phyB mutants indicated that this enhancement is caused by PhyB inhibition of the high-light avoidance response in wild-type plants. In addition, our results suggest that the inhibition by PhyB is not exclusive to either of the phot1 or phot2 signalling pathways

The Arabidopsis PHYTOCHROME KINASE SUBSTRATE2 protein is a phototropin signaling element that regulates leaf flattening and leaf positioning.

In Arabidopsis (Arabidopsis thaliana), the blue light photoreceptor phototropins (phot1 and phot2) fine-tune the photosynthetic status of the plant by controlling several important adaptive processes in response to environmental light variations. These processes include stem and petiole phototropism (leaf positioning), leaf flattening, stomatal opening, and chloroplast movements. The PHYTOCHROME KINASE SUBSTRATE (PKS) protein family comprises four members in Arabidopsis (PKS1-PKS4). PKS1 is a novel phot1 signaling element during phototropism, as it interacts with phot1 and the important signaling element NONPHOTOTROPIC HYPOCOTYL3 (NPH3) and is required for normal phot1-mediated phototropism. In this study, we have analyzed more globally the role of three PKS members (PKS1, PKS2, and PKS4). Systematic analysis of mutants reveals that PKS2 (and to a lesser extent PKS1) act in the same subset of phototropin-controlled responses as NPH3, namely leaf flattening and positioning. PKS1, PKS2, and NPH3 coimmunoprecipitate with both phot1-green fluorescent protein and phot2-green fluorescent protein in leaf extracts. Genetic experiments position PKS2 within phot1 and phot2 pathways controlling leaf positioning and leaf flattening, respectively. NPH3 can act in both phot1 and phot2 pathways, and synergistic interactions observed between pks2 and nph3 mutants suggest complementary roles of PKS2 and NPH3 during phototropin signaling. Finally, several observations further suggest that PKS2 may regulate leaf flattening and positioning by controlling auxin homeostasis. Together with previous findings, our results indicate that the PKS proteins represent an important family of phototropin signaling proteins

Hox-controlled reorganisation of intrasegmental patterning cues underlies Drosophila posterior spiracle organogenesis

10 páginas, 8 figuras. Material complementario del artículo esta disponible en http://dev.biologists.org/cgi/content/full/132/13/3093/DC1Hox proteins provide axial positional information and control segment morphology in development and evolution. Yet how they specify morphological traits that confer segment identity and how axial positional information interferes with intrasegmental patterning cues during organogenesis remain poorly understood. We have investigated the control of Drosophila posterior spiracle morphogenesis, a segment-specific structure that forms under Abdominal-B (AbdB) Hox control in the eighth abdominal segment (A8). We show that the Hedgehog (Hh), Wingless (Wg) and Epidermal Growth Factor Receptor (Egfr) pathways provide specific inputs for posterior spiracle morphogenesis and act in a genetic network made of multiple and rapidly evolving Hox/signalling interplays. A major function of AbdB during posterior spiracle organogenesis is to reset A8 intrasegmental patterning cues, first by reshaping wg and rhomboid expression patterns, then by reallocating the Hh signal and later by initiating de novo expression of the posterior compartment gene engrailed in anterior compartment cells. These changes in expression patterns confer axial specificity to otherwise reiteratively used segmental patterning cues, linking intrasegmental polarity and acquisition of segment identity.This work was supported by the `Centre National de la Recherche Scientifique' (CNRS), grants from `la Ligue Nationale Contre Le Cancer (équipe labellisée La Ligue)', `l'Association pour la Recherche contre le Cancer' (ARC), The Royal Society, The Welcome Trust, the `Minesterio de education y ciencia (BFU 2004 0 96) and ARC and EMBO long term fellowships to S. Merabet.Peer reviewe

An empirical analysis of the Swiss generalized system of preferences

The progressively introduced DFQFMA for LDCs has a positive effect on the size of LDCs preferential exports to Switzerland. Consequently, the DFQFMA has considerably improved market access for the worlds poorest countries. Eliminating tariffs (progressively) causes preferential agro-food and textile exports of LDCs to rise substantially. However, it has to be remarked that the success of the DFQFMA is limited to the agro-food and textile sectors and to a few countries. The descriptive analysis of agro-food exports indicates that trade liberalization is a success story merely for a few LDCs, namely Tanzania, Ethiopia, Côte dIvoire, Mozambique, Malawi, Senegal and Uganda. Those seven countries capture a total share of nearly 80 percent of LDCs agro-food exports to Switzerland. In the textile sector we observe an even higher degree of market concentration concerning LDCs preferential exports. Here, three countries, namely Bangladesh, Cambodia and Nepal, account for 98 percent of LDCs preferential textile exports. It also can be noted that the GSP is a useful supplement to duty-free tariffs (duty-free market access) under the WTO regime. For instance, 100 percent of LDCs agro-food exports from 2002 to 2011 entered Switzerland under reduced or duty-free tariffs. However, the share of preferential exports under the GSP was on average only 36 percent. In this context, the preference margin, which represents the main incentive to export under preferential conditions, compensates the costs of compliance associated with the GSP and yields an additional benefit for the importer has a consistent and positive effect on the level of the utilization rate. In particular, the application of the Heckman´selection model in article no. 1 makes clear that once trade contracts are established and an exporter has overcome bureaucratic obstacles in the form of proof of origin and proof of direct shipment, the preference margin appears as the main incentive to export under preferential conditions granted by the GSP. While the effect of the size of GSP eligible trade has a positive and significant effect in the case of the PPML estimations, the effect turned negative when the sample was restricted to positive values of the utilization rate in the case of the outcome equation of the Heckman selection model. This finding encourages our confidence that the preference margin acts as the main incentive for exporting under preferential conditions. However, to benefit from these preferential tariffs, the institutional quality of a given DC or LDC is of crucial importance. Additionally, we address the question of whether reciprocal trade preferences are more beneficial for DCs compared to non-reciprocal trade preferences. Because trade preferences under the Swiss GSP are offered to the country group of DCs as a whole, non-reciprocal trade preferences are not tailored to the export structure of a particular DC. Consequently, by switching from non-reciprocal to negotiated reciprocal trade preferences, DCs such as Tunisia expect to negotiate terms which are tailored to their export structure and better conditions than competitors from countries which are still beneficiaries of the GSP. The Tunisian case study reveals that the switch from the GSP to an FTA causes no significant advantage in most of the export sectors. This implies that switching from non-reciprocal to reciprocal trade preferences yields advantages in export sectors where Tunisia has comparative cost advantages. This is especially true for the textile sector and partly so for the agro-food sector

Luminosity Measurement in the L3 Detector at LEP

One of the limiting factors in the determination of the electroweak parameters from cross section measurements of e+e- annihilation close to the Z pole is the precision of the luminosity measurement. The luminosity monitor of the L3 detector at LEP and the analysis of its data are described. Using a combination of a BGO calorimeter and a 3-layer silicon tracker, the absolute luminosity has been measured with an experimental precision of 0.08% in 1993 and 0.05% in 1994. The measurement relies on a detailed understanding of small-angle elastic e+e-(Bhabha) scattering from the experimental and theoretical point of view, as well as an excellent knowledge of the detector geometry