Photosynthetic organisms are frequently exposed to excess light conditions and hence to photo-oxidative stress. To counteract photo-oxidative damage, land plants and most algae make use of non- photochemical quenching (NPQ) of excess light energy, in particular the rapidly inducible and relaxing qE-mechanism. In vascular plants, the constitutively active PsbS protein is the key regulator of qE. In the green algae C. reinhardtii, however, qE activation is only possible after initial high-light (HL) acclimation for several hours and requires the synthesis of LHCSR proteins which act as qE regulators. The precise function of PsbS, which is transiently expressed during HL acclimation in C. reinhardtii, is still unclear. Here, we investigated the impact of different PsbS amounts on HL acclimation characteristics of C. reinhardtii cells. We demonstrate that lower PsbS amounts negatively affect HL acclimation at different levels, including NPQ capacity, electron transport characteristics, antenna organization and morphological changes, resulting in an overall increased HL sensitivity and lower vitality of cells. Contrarily, higher PsbS amounts do not result in a higher NPQ capacity, but nevertheless provide higher fitness and tolerance towards HL stress. Strikingly, constitutively expressed PsbS protein was found to be degraded during HL acclimation. We propose that PsbS is transiently required during HL acclimation for the reorganization of thylakoid membranes and/or antenna proteins along with the activation of NPQ and adjustment of electron transfer characteristics, and that degradation of PsbS is essential in the fully HL acclimated state.

The circadian clock regulates plant tissue hydraulics to synchronize water supply with environmental cycles and thereby optimize growth. The circadian fluctuations in aquaporin transcript abundance suggest that aquaporin water channels play a role in these processes. Here, we show that hydraulic conductivity (K-ros) of Arabidopsis (Arabidopsis thaliana) rosettes displays a genuine circadian rhythmicity with a peak around midday. Combined immunological and proteomic approaches revealed that phosphorylation at two C-terminal sites (Ser280, Ser283) of PLASMA MEMBRANE INTRINSIC PROTEIN 2;1 (AtPIP2;1), a major plasma membrane aquaporin in rosettes, shows circadian oscillations and is correlated with K-ros. Transgenic expression of phosphodeficient and phosphomimetic forms of this aquaporin indicated that AtPIP2;1 phosphorylation is necessary but not sufficient for K-ros regulation. We investigated the supporting role of 14-3-3 proteins, which are known to interact with and regulate phosphorylated proteins. Individual knockout plants for five 14-3-3 protein isoforms expressed in rosettes lacked circadian activation of K-ros. Two of these [GRF4 (14-3-3Phi); GRF10 (14-3-3Epsilon)] showed direct interactions with AtPIP2;1 in the plant and upon coexpression in Xenopus laevis oocytes and activated AtPIP2;1, preferentially when the latter was phosphorylated at its two C-terminal sites. We propose that this regulatory mechanism assists in the activation of phosphorylated AtPIP2;1 during circadian regulation of K-ros.

To promote photomorphogenesis, including plastid development and metabolism, the phytochrome (phy) and the cryptochrome (cry) photoreceptors orchestrate genome-wide changes in gene expression in response to Red (R)- and Blue (B)-light cues. While phys and crys have a clear role in modulating photosynthesis, their role in the coordination of the nuclear genome and the plastome, essential for functional chloroplasts, remains underexplored. Using publicly available genome datasets for WT andphyABCDEorcry1cry2Arabidopsis seedlings, grown, respectively, under R- or B-light, we bioinformatically analyzed the influence of light inputs and photoreceptors in the control of nuclear genes with a function in the chloroplast, and evaluated the role of phyB in the modulation of plastome-encoded genes. We show gene co-induction by R-phys and B-crys for genes with a chloroplastic function, and also apparent photoreceptor-driven preferential responses. Evidence from phyB in Arabidopsis together with published evidence from CRY2 in tomato also supports the participation of both photoreceptor families in the global modulation of the plastome genes. To begin addressing how these light-sensors orchestrate changes in an organellar genome, we evaluated their effect over genes with potential functions in plastid gene-expression regulation based on their TAIR annotation. Results indicate that both crys and phys modulate 'plastome-regulatory genes' with enrichment in the contribution of crys to all processes and of phys to post-transcription and transcription. Furthermore, we identified a new role for HY5 as a relevant light-signaling component in photoreceptor-based anterograde signaling leading to plastome gene regulation.

Plant morphogenesis requires differential and often asymmetric growth. A key role in controlling anisotropic expansion of individual cells is played by the cortical microtubule array. Although highly organized, the array can nevertheless rapidly change in response to internal and external cues. Experiments have identified the microtubule-severing enzyme katanin as a central player in controlling the organizational state of the array. Katanin action is required both for normal alignment and the adaptation of array orientation to mechanical, environmental, and developmental stimuli. How katanin fulfills its controlling role, however, remains poorly understood. On the one hand, from a theoretical perspective, array ordering depends on the "weeding out" of discordant microtubules through frequent catastrophe-inducing collisions among microtubules. Severing would reduce average microtubule length and lifetime, and consequently weaken the driving force for alignment. On the other hand, it has been suggested that selective severing at microtubule crossovers could facilitate the removal of discordant microtubules. Here we show that this apparent conflict can be resolved by systematically dissecting the role of all of the relevant interactions in silico. This procedure allows the identification of the sufficient and necessary conditions for katanin to promote array alignment, stresses the critical importance of the experimentally observed selective severing of the "crossing" microtubule at crossovers, and reveals a hitherto not appreciated role for microtubule bundling. We show how understanding the underlying mechanism can aid with interpreting experimental results and designing future experiments.

After conjugation in hypotrichous ciliates, a new macronucleus is produced from a copy of the micronucleus. This transformation involves large-scale reorganization of DNA, with conversion of the chromosomal micronuclear genome into short, gene-sized DNA molecules in the macronucleus. To study directly the changes that occur during this process, techniques were developed for synchronous mating of large populations of the hypotrichous ciliate E. crassus. The micronuclear chromosomes are polytenized during the first 20 h of macronuclear development. The polytene chromosomes lack the band-interband organization observed in othe hypotrichs and in the Diptera. Polytenization is followed by transectioning of the chromosomes. DNA was isolated at various times of macronuclear development and the average MW of the DNA decreases at the time of chromosome transectioning. A small size group of macronuclear DNA molecules (450-550 base pairs) is excised from the chromosomal DNA .apprx. 10 h later in macronuclear development.

Fine particulate matter (PM2.5) is a criteria pollutant. Its sensitivity to meteorology implies its distribution will likely change with climate shifts. Limited availability of global climate models with full chemistry complicates efforts to assess rigorously the uncertainties in the PM2.5 response to a warming climate. We evaluate the potential for PM2.5 distributions in a chemistry-climate model under current-day and warmer climate conditions over the Northeastern United States to be represented by a Synthetic Aerosol tracer (SAt). The SAt implemented into the Geophysical Fluid Dynamics Laboratory chemistry-climate model (AM3) follows the protocol of a recent multimodel community effort (HTAP), with CO emissions, 25-day chemical lifetime, and wet deposition rate of sulfate. Over the Northeastern United States, the summer daily time series of SAt correlates strongly with that of PM2.5, with similar cumulative density functions under both present and future climate conditions. With a linear regression model derived from PM2.5 and SAt in the current-day simulation, we reconstruct both the current-day and future PM2.5 daily time series from the simulated SAt. This reconstruction captures the summer mean PM2.5, the incidence of days above the 24-h mean PM2.5 NAAQS, and PM2.5 responses to climate change. This reconstruction also works over other polluted Northern Hemispheric regions and in spring. Our proof-of-concept study demonstrates that simple tracers can be developed to mimic PM2.5, including its response to climate change, as an easy-to-implement and low-cost addition to physical climate models that should help air quality managers to reap the benefits of climate models that have no chemistry. Citation: Fang, Y., A. M. Fiore, J.-F. Lamarque, L. W. Horowitz, and M. Lin (2013), Using synthetic tracers as a proxy for summertime PM2.5 air quality over the Northeastern United States in physical climate models, Geophys. Res. Lett., 40, 755-760, doi:10.1002/grl.50162.

In addition to its well-established role in plant development, the hormone cytokinin regulates plant responses to biotic and abiotic stresses. It was previously shown that cytokinin signaling acts negatively upon drought and osmotic stress tolerance and that gain-of-function of the cytokinin response regulator ARR1 causes osmotic stress hypersensitivity. Here we show that increased ARR1 action increases tolerance to heat shock and that this is correlated with increased accumulation of the heat shock proteins Hsp17.6 and Hsp70. These results show that the heat shock tolerance of plants can be elevated by increasing the expression of a cytokinin response activator.

Aims. We study the stellar and dust properties of a well-defined sample of local elliptical galaxies to investigate the relationship between host galaxy properties and nuclear activity.

In this work, the microalloying effect on glass-forming ability (GFA) has been investigated from the structural aspect, by performing synchrotron radiation X-ray diffraction and absorption measurements coupled with simulations in the NiNbZr ternary system. By sorting out the preferred Voronoi clusters, we propose a new structural parameter which counts the fraction of the five-connected shell atoms in clusters and find it is strongly associated with the GFA. In particular, this structural parameter has the highest value in a composition where the best GFA is achieved. The present work provides an in-depth understanding of microalloying-induced high GFAs in multicomponent alloys. (C) 2016 Elsevier Ltd. All rights reserved.

Tunable symmetry breaking plays a crucial role for the manipulation of topological phases of quantum matter. Here, through combined high-pressure magnetotransport measurements, Raman spectroscopy, and x-ray diffraction, we demonstrate a pressure-induced topological phase transition in nodal-line semimetal ZrSiS. Symmetry analysis and first-principles calculations suggest that this pressure-induced topological phase transition may be attributed to weak lattice distortions by nonhydrostatic compression, which breaks some crystal symmetries, such as the mirror and inversion symmetries. This finding provides some experimental evidence for crystal symmetry protection for the topological semimetal state, which is at the heart of topological relativistic fermion physics.