Milieux et théories rchitecturales et urbaines japonaises

Yann Nussaume, architecte Compte rendu non communiqué

Milieux et théories rchitecturales et urbaines japonaises

Yann Nussaume, architecte Compte rendu non communiqué

« MaT(i)erre(s) » : vers une architecture ?

Confrontés aux évolutions environnementales et à une rupture des relations entre les architectures et les lieux, de nombreux architectes se tournent vers le redéveloppement des « MaT(i)erre(s) ». En recoupant les trajectoires de six architectes actifs sur ce sujet et en comparant leurs processus de conception, cet article s’interroge sur l’émergence d’un « mouvement environnemental » architectural et tente d’en définir les caractéristiques. Pour ce faire, il aborde les différents parcours de ces architectes et les questionnements qui les ont menés à cet intérêt pour les « MaT(i)erre(s) » et discute certaines de leurs orientations communes : repenser le rôle du matériau comme catalyseur de la conception ; réévaluer la coupure architecte/artisan ; favoriser expérimentation et recherche… Reflet des attentes des milieux, le mouvement environnemental des « MaT(i)erre(s) » fait souffler un « esprit nouveau ».Faced with environmental changes and a breakdown in the relationship between architecture and place, many architects are turning to the redevelopment of “MaT(i)erre(s)”. By intersecting the trajectories of six architects active on this subject and by comparing their design processes, this article questions the emergence of an architectural "environmental movement" and attempts to define its characteristics. To do this, it considers the various pathways and questionings of these architects which led them to their interest in “MaT(i)erre(s)”, and discusses some of their common orientations: rethinking the role of material as a catalyst for design; reassessing the architect/craftsman's estrangement; and promoting experimentation and research. Reflecting upon the milieux, the “MaT(i)erre(s)' Environmental Movement” unleashes an “Esprit Nouveau”

Phosphate Import in Plants: Focus on the PHT1 Transporters

The main source of phosphorus for plants is inorganic phosphate (Pi), which is characterized by its poor availability and low mobility. Uptake of this element from the soil relies heavily upon the PHT1 transporters, a specific family of plant plasma membrane proteins that were identified by homology with the yeast PHO84 Pi transporter. Since the discovery of PHT1 transporters in 1996, various studies have revealed that their function is controlled by a highly complex network of regulation. This review will summarize the current state of research on plant PHT1 multigenic families, including physiological, biochemical, molecular, cellular, and genetics studies

A Novel fry1 Allele Reveals the Existence of a Mutant Phenotype Unrelated to 5′->3′ Exoribonuclease (XRN) Activities in Arabidopsis thaliana Roots

BACKGROUND Mutations in the FRY1/SAL1 Arabidopsis locus are highly pleiotropic, affecting drought tolerance, leaf shape and root growth. FRY1 encodes a nucleotide phosphatase that in vitro has inositol polyphosphate 1-phosphatase and 3',(2'),5'-bisphosphate nucleotide phosphatase activities. It is not clear which activity mediates each of the diverse biological functions of FRY1 in planta. PRINCIPAL FINDINGS A fry1 mutant was identified in a genetic screen for Arabidopsis mutants deregulated in the expression of Pi High affinity Transporter 1;4 (PHT1;4). Histological analysis revealed that, in roots, FRY1 expression was restricted to the stele and meristems. The fry1 mutant displayed an altered root architecture phenotype and an increased drought tolerance. All of the phenotypes analyzed were complemented with the AHL gene encoding a protein that converts 3'-polyadenosine 5'-phosphate (PAP) into AMP and Pi. PAP is known to inhibit exoribonucleases (XRN) in vitro. Accordingly, an xrn triple mutant with mutations in all three XRNs shared the fry1 drought tolerance and root architecture phenotypes. Interestingly these two traits were also complemented by grafting, revealing that drought tolerance was primarily conferred by the rosette and that the root architecture can be complemented by long-distance regulation derived from leaves. By contrast, PHT1 expression was not altered in xrn mutants or in grafting experiments. Thus, PHT1 up-regulation probably resulted from a local depletion of Pi in the fry1 stele. This hypothesis is supported by the identification of other genes modulated by Pi deficiency in the stele, which are found induced in a fry1 background. CONCLUSIONS/SIGNIFICANCE Our results indicate that the 3',(2'),5'-bisphosphate nucleotide phosphatase activity of FRY1 is involved in long-distance as well as local regulatory activities in roots. The local up-regulation of PHT1 genes transcription in roots likely results from local depletion of Pi and is independent of the XRNs.This work was supported by an ANR-GENOPLANT grant (RIBOROOT-ANR06 GPLA 011) and the CEA agency. Array hybridizations have been partly supported by RNG (Réseau National des Génopoles, Evry, France). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. No additional external funding received for this study

A novel role for the root cap in phosphate uptake and homeostasis

The root cap has a fundamental role in sensing environmental cues as well as regulating root growth via altered meristem activity. Despite this well-established role in the control of developmental processes in roots, the root cap's function in nutrition remains obscure. Here, we uncover its role in phosphate nutrition by targeted cellular inactivation or phosphate transport complementation in Arabidopsis, using a transactivation strategy with an innovative high-resolution real-time P-33 imaging technique. Remarkably, the diminutive size of the root cap cells at the root-to-soil exchange surface accounts for a significant amount of the total seedling phosphate uptake (approximately 20%). This level of Pi absorption is sufficient for shoot biomass production (up to a 180% gain in soil), as well as repression of Pi starvation-induced genes. These results extend our understanding of this important tissue from its previously described roles in environmental perception to novel functions in mineral nutrition and homeostasis control

Stress induced gene expression drives transient DNA methylation changes at adjacent repetitive elements

Cytosine DNA methylation (mC) is a genome modification that can regulate the expression of coding and non-coding genetic elements. However, little is known about the involvement of mC in response to environmental cues. Using whole genome bisulfite sequencing to assess the spatio-temporal dynamics of mC in rice grown under phosphate starvation and recovery conditions, we identified widespread phosphate starvation-induced changes in mC, preferentially localized in transposable elements (TEs) close to highly induced genes. These changes in mC occurred after changes in nearby gene transcription, were mostly DCL3a-independent, and could partially be propagated through mitosis, however no evidence of meiotic transmission was observed. Similar analyses performed in Arabidopsis revealed a very limited effect of phosphate starvation on mC, suggesting a species-specific mechanism. Overall, this suggests that TEs in proximity to environmentally induced genes are silenced via hypermethylation, and establishes the temporal hierarchy of transcriptional and epigenomic changes in response to stress.David Secco, Chuang Wang, Huixia Shou, Matthew D Schultz, Serge Chiarenza, Laurent Nussaume, Joseph R Ecker, James Whelan, Ryan Liste