Structural insights into PYR/PYL/RCAR ABA receptors and PP2Cs

[EN] Abscisic acid (ABA) plays an essential function in plant physiology since it is required for biotic and abiotic stress responses as well as control of plant growth and development. A new family of soluble ABA receptors, named PYR/PYL/RCAR, has emerged as ABA sensors able to inhibit the activity of specific protein phosphatases type-2C (PP2Cs) in an ABA-dependent manner. The structural and functional mechanism by which ABA is perceived by these receptors and consequently leads to inhibition of the PP2Cs has been recently elucidated. The module PYR/PYL/RCAR-ABA-PP2C offers an elegant and unprecedented mechanism to control phosphorylation signaling cascades in a ligand-dependent manner. The knowledge of their three-dimensional structures paves the way to the design of ABA agonists able to modulate the plant stress response. (C) 2010 Elsevier Ireland Ltd. All rights reserved.We are grateful to the European Synchrotron Radiation Facility (ESRF) and the EMBL for access to macromolecular crystallography beam lines. Work in the laboratory of Dr Rodriguez is supported by grant BIO2008-00221 from Ministerio de Educación y Ciencia and Fondo Europeo de Desarrollo Regional and Consejo Superior de Investigaciones Científicas (fellowships to JS, RA and LR; Juan de la Cierva contract to MGG). Access to the high Throughput Crystallization facility of the Partnership for Structural Biology in Grenoble (PSB) (https://htxlab.embl.fr) was supported by the European Community – Research InfrastructureAction PCUBE under the FP7 “Capacities” specific program.Santiago Cuéllar, J.; Dupeux, F.; Betz, K.; Antoni-Alandes, R.; González Guzmán, M.; Rodriguez, L.; Márquez, JA.... (2012). Structural insights into PYR/PYL/RCAR ABA receptors and PP2Cs. Plant Science. 182:3-11. https://doi.org/10.1016/j.plantsci.2010.11.014S31118

The Cys-Arg/N-end rule pathway is a general sensor of abiotic stress in flowering plants

Abiotic stresses impact negatively on plant growth, profoundly affecting yield and quality of crops. Although much is known about plant responses, very little is understood at the molecular level about the initial sensing of environmental stress. In plants, hypoxia (low oxygen, which occurs during flooding) is directly sensed by the Cys-Arg/N-end rule pathway of ubiquitin-mediated proteolysis, through oxygen-dependent degradation of group VII Ethylene Response Factor transcription factors (ERFVIIs) via amino-terminal (Nt-) cysteine [1, 2]. Using Arabidopsis (Arabidopsis thaliana) and barley (Hordeum vulgare), we show that the pathway regulates plant responses to multiple abiotic stresses. In Arabidopsis, genetic analyses revealed that response to these stresses is controlled by N-end rule regulation of ERFVII function. Oxygen sensing via the Cys-Arg/N-end rule in higher eukaryotes is linked through a single mechanism to nitric oxide (NO) sensing [3, 4]. In plants, the major mechanism of NO synthesis is via NITRATE REDUCTASE (NR), an enzyme of nitrogen assimilation [5]. Here, we identify a negative relationship between NR activity and NO levels and stabilization of an artificial Nt-Cys substrate and ERFVII function in response to environmental changes. Furthermore, we show that ERFVIIs enhance abiotic stress responses via physical and genetic interactions with the chromatin-remodeling ATPase BRAHMA. We propose that plants sense multiple abiotic stresses through the Cys-Arg/N-end rule pathway either directly (via oxygen sensing) or indirectly (via NO sensing downstream of NR activity). This single mechanism can therefore integrate environment and response to enhance plant survival

Depletion of abscisic acid levels in roots of flooded Carrizo citrange (Poncirus trifoliata L. Raf. x Citrus sinensis L. Osb.) plants is a stress-specific response associated to the differential expression of PYR/PYL/RCAR receptors

[EN] Soil flooding reduces root abscisic acid (ABA) levels in citrus, conversely to what happens under drought. Despite this reduction, microarray analyses suggested the existence of a residual ABA signaling in roots of flooded Carrizo citrange seedlings. The comparison of ABA metabolism and signaling in roots of flooded and water stressed plants of Carrizo citrange revealed that the hormone depletion was linked to the upregulation of CsAOG, involved in ABA glycosyl ester (ABAGE) synthesis, and to a moderate induction of catabolism (CsCYP707A, an ABA 8'-hydroxylase) and buildup of dehydrophaseic acid (DPA). Drought strongly induced both ABA biosynthesis and catabolism (CsNCED1, 9-cis-neoxanthin epoxycarotenoid dioxygenase 1, and CsCYP707A) rendering a significant hormone accumulation. In roots of flooded plants, restoration of control ABA levels after stress release was associated to the upregulation of CsBGLU18 (an ABA beta-glycosidase) that cleaves ABAGE. Transcriptional profile of ABA receptor genes revealed a different induction in response to soil flooding (CsPYL5) or drought (CsPYL8). These two receptor genes along with CsPYL1 were cloned and expressed in a heterologous system. Recombinant CsPYL5 inhibited Delta NHAB1 activity in vitro at lower ABA concentrations than CsPYL8 or CsPYL1, suggesting its better performance under soil flooding conditions. Both stress conditions induced ABA-responsive genes CsABI5 and CsDREB2A similarly, suggesting the occurrence of ABA signaling in roots of flooded citrus seedlings. The impact of reduced ABA levels in flooded roots on CsPYL5 expression along with its higher hormone affinity reinforce the role of this ABA receptor under soil-flooding conditions and explain the expression of certain ABA-responsive genes.This work was supported by Ministerio de Economia y Competitividad (MINECO), Fondo Europeo de Desarrollo Regional (FEDER) and Universitat Jaume I through grants No. AGL201676574-R, UJI-B2016-23/UJI-B2016-24 to A.G-C. and V.A. and MINECO, FEDER and Consejo Superior de Investigaciones Cientificas (CSIC) through grant BIO2014-52537-R to P.L.R. S.I.Z. and M.M. were supported by predoctoral grants from Universitat Jaume I and Generalitat Valenciana, respectively. M.G.G. was recipient of a "JAE-DOC" contract from the CSIC. Mass spectrometry analyses were performed at the central facilities (Servei Central d'Instrumentacio Cientifica, SCIC) of Universitat Jaume I.Arbona, V.; Zandalinas, SI.; Manzi, M.; González Guzmán, M.; Rodríguez Egea, PL.; Gómez-Cadenas, A. (2017). Depletion of abscisic acid levels in roots of flooded Carrizo citrange (Poncirus trifoliata L. Raf. x Citrus sinensis L. Osb.) plants is a stress-specific response associated to the differential expression of PYR/PYL/RCAR receptors. Plant Molecular Biology. 93(6):623-640. https://doi.org/10.1007/s11103-017-0587-7S623640936Agarwal PK, Jha B (2010) Transcription factors in plants and ABA dependent and independent abiotic stress signalling. Biol Plant 54:201–212Agustí J, Merelo P, Cercós M, Tadeo FR, Talón M (2008) Ethylene-induced differential gene expression during abscission of citrus leaves. 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Coupling the Leidenfrost effect and elastic deformations to power sustained bouncing

The Leidenfrost effect occurs when an object near a hot surface vaporizes rapidly enough to lift itself up and hover. Although well-understood for liquids and stiff sublimable solids, nothing is known about the effect with materials whose stiffness lies between these extremes. Here we introduce a new phenomenon that occurs with vaporizable soft solids: the elastic Leidenfrost effect. By dropping hydrogel spheres onto hot surfaces we find that, rather than hovering, they energetically bounce several times their diameter for minutes at a time. With high-speed video during a single impact, we uncover high-frequency microscopic gap dynamics at the sphere-substrate interface. We show how these otherwise-hidden agitations constitute work cycles that harvest mechanical energy from the vapour and sustain the bouncing. Our findings unleash a powerful and widely applicable strategy for injecting mechanical energy into soft materials, with relevance to fields ranging from soft robotics and metamaterials to microfluidics and active matter

Influence of long term exposure to molten lead on the microstructure and mechanical behaviour of T91 steel

Specimens of T91 9%Cr martensitic steel were exposed to molten lead at 525°C under controlled oxygen partial pressure, for durations ranging from 6 hours to one month. At low oxygen concentration, a thin chromium oxide layer is formed; under higher concentration, the oxide layer becomes thicker and complex. Under all conditions in liquid lead, numerous porosities appear after a few days of exposure to lead in the sub-surface regions of the samples. From the residual deflection of bent samples, the stress relaxation is much faster in liquid lead than under gaseous atmosphere. However, the tensile properties remain unchanged after one month ageing in lead

Resistance to corrosion an embrittlement of T91 steel in stagnant Pb-Bi of eutectic composition

The resistance to corrosion and embrittlement of T91 steel in stagnant Pb-Bi eutectic was studied in the temperature interval 150-650°C. The degradation of the corrosion resistance manifested itself above 350°C, with Pb-Bi sticking at surface inclusions at 600°C and with localized corrosion effects visible at 650°C. Nevertheless, the specimens aged in Pb-Bi did not exhibit any degradation of mechanical properties during ex situ testing in air at room temperature. On the contrary, a liquid metal embrittlement (LME) effect was observed, when the tensile tests were camed out in situ in Pb-Bi in the temperature interval 300-400°C. The LME effect depends on temperature, strain rate, existence of stress concentrators and especially on the chemical composition of the cover gas. This effect was observed in Pb-Bi under He-4% H$_2$ cover gas, whereas almost no LME effect was detected in Ph-Bi under vacuum. A maximum reduction in energy to rupture (around 30%) was found for notched specimens tested in Pb-Bi under He-4% H$_2$ cover gas at a crosshead displacement rate of 6x10$^{-4}$ mm/s at 350°C