Plastid terminal oxidase (PTOX) accepts electrons from plastoquinol to reduce molecular oxygen to water. We introduced the gene encoding Chlamydomonas reinhardtii (Cr)PTOX2 into the Arabidopsis (Arabidopsis thaliana) wild-type (WT) and proton gradient regulation5 (pgr5) mutant defective in cyclic electron transport around photosystem I (PSI). The accumulation of CrPTOX2 only mildly affected photosynthetic electron transport in the WT background during steady-state photosynthesis but partly complemented the induction of nonphotochemical quenching (NPQ) in the pgr5 background. During the induction of photosynthesis by actinic light (AL) of 130 mu mol photons m(-2) s(-1), the high level of PSII yield (Y(II)) was induced immediately after the onset of AL in WT plants accumulating CrPTOX2. NPQ was more rapidly induced in the transgenic plants than in WT plants. P700 was also oxidized immediately after the onset of AL. Although CrPTOX2 does not directly induce a proton concentration gradient (Delta pH) across the thylakoid membrane, the coupled reaction of PSII generated Delta pH to induce NPQ and the downregulation of the cytochrome b(6)f complex. Rapid induction of Y(II) and NPQ was also observed in the pgr5 plants accumulating CrPTOX2. In contrast to the WT background, P700 was not oxidized in the pgr5 background. Although the thylakoid lumen was acidified by CrPTOX2, PGR5 was essential for oxidizing P700. In addition to acidification of the thylakoid lumen to downregulate the cytochrome b(6)f complex (donor-side regulation), PGR5 may be required for draining electrons from PSI by transferring them to the plastoquinone pool. We propose a reevaluation of the contribution of this acceptor-side regulation by PGR5 in the photoprotection of PSI.

High temperature increases meiotic instability in newly generated autotetraploid Arabidopsis thaliana by interfering with chromosome pairing.

Continuous directed evolution of enzymes and other proteins in microbial hosts is capable of outperforming classical directed evolution by executing hypermutation and selection concurrently in vivo, at scale, with minimal manual input. Provided that a target enzyme's activity can be coupled to growth of the host cells, the activity can be improved simply by selecting for growth. Like all directed evolution, the continuous version requires no prior mechanistic knowledge of the target. Continuous directed evolution is thus a powerful way to modify plant or non-plant enzymes for use in plant metabolic research and engineering. Here, we first describe the basic features of the yeast (Saccharomyces cerevisiae) OrthoRep system for continuous directed evolution and compare it briefly with other systems. We then give a step-by-step account of three ways in which OrthoRep can be deployed to evolve primary metabolic enzymes, using a THI4 thiazole synthase as an example and illustrating the mutational outcomes obtained. We close by outlining applications of OrthoRep that serve growing demands (i) to change the characteristics of plant enzymes destined for return to plants, and (ii) to adapt ("plantize") enzymes from prokaryotes-especially exotic prokaryotes-to function well in mild, plant-like conditions.

A proton-coupled potassium transporter regulates root hair development and root gravitropism in a cell-file-specific manner by facilitating polar auxin transport in Arabidopsis root tips.

Iron meteorites are windows into the formation and evolution of planetesimal cores. The trace element compositions of IVA iron meteorites are enigmatic; specifically, to explain the fractionations of different elements requires various sulfur contents of the parent liquid. Here, we propose a possible solution to this problem. IVA irons are thought to sample an exposed core that underwent inward solidification. In an inward solidifying core, sulfur-rich liquids expelled by crystallization are buoyant and stably stratified in the interstices of the mushy solidification front, until they eventually solidify at the eutectic point. Solidification proceeds through in-situ dendritic crystallization of mushy parcels of identical compositions, with the absence of chemical fractionation. In order for fractionation to take place, "pristine"liquids must flow into the mushy front and react with solids, which would be possible if circulation is driven by external forcing, for example, collisions. In this picture, the fluid exchange (which enables fractionation) is driven by occasional events, and each incremental solid can react with only a limited amount of liquid during solidification. We develop a simple model to describe the fractionation associated with this limited solid-liquid equilibration. With this model, we can explain the concentrations of different elements satisfactorily with a single sulfur content (similar to 5 wt%) of the IVA iron parent liquid. Assuming that the stirring is caused by collisions to the solidifying body, we combine the new model for element fractionation with a model for solidification (as a Stefan problem) to suggest a frequency on the order of once per few thousand years for collisions that are large enough to cause the required stirring.

It has been suggested that a class of chemically peculiar metal-poor stars called iron-rich metal-poor (IRMP) stars formed from molecular cores with metal contents dominated by thermonuclear supernova nucleosynthesis. If this interpretation is accurate, then IRMP stars should be more common in environments where thermonuclear supernovae were important contributors to chemical evolution. Conversely, IRMP stars should be less common in environments where thermonuclear supernovae were not important contributors to chemical evolution. At constant [Fe/H] less than or similar to -1, the Milky Way's satellite classical dwarf spheroidal (dSph) galaxies and the Magellanic Clouds have lower [alpha/Fe] than the Milky Way field and globular cluster populations. This difference is thought to demonstrate the importance of thermonuclear supernova nucleosynthesis for the chemical evolution of the Milky Way's satellite classical dSph galaxies and the Magellanic Clouds. We use data from the Sloan Digital Sky Survey Apache Point Observatory Galactic Evolution Experiment and Gaia to infer the occurrence of IRMP stars in the Milky Way's satellite classical dSph galaxies eta( dSph) and the Magellanic Clouds eta (Mag), as well as in the Milky Way field eta (MWF) and globular cluster populations eta (MWGC). In order of decreasing occurrence, we find eta(dSph)=0.07(-0.02)(+0.02) , eta(Mag)=0.037(-0.006)(+0.007) , eta(MWF)=0.0013(-0.0005)(+0.0006) , and a 1 sigma upper limit eta (MWGC) < 0.00057. These occurrences support the inference that IRMP stars formed in environments dominated by thermonuclear supernova nucleosynthesis and that the time lag between the formation of the first and second stellar generations in globular clusters was longer than the thermonuclear supernova delay time.

The progenitor systems and explosion mechanisms responsible for the thermonuclear events observationally classified as Type Ia supernovae are uncertain and difficult to uniquely constrain using traditional observations of Type Ia supernova host galaxies, progenitors, light curves, and remnants. For the subset of thermonuclear events that are prolific producers of iron, we use published theoretical nucleosynthetic yields to identify a set of elemental abundance ratios infrequently observed in metal-poor stars but shared across a range of progenitor systems and explosion mechanisms: [Na, Mg, Co/Fe] < 0. We label stars with this abundance signature "iron-rich metal-poor," or IRMP stars. We suggest that IRMP stars formed in environments dominated by thermonuclear nucleosynthesis and consequently that their elemental abundances can be used to constrain both the progenitor systems and explosion mechanisms responsible for thermonuclear explosions. We identify three IRMP stars in the literature and homogeneously infer their elemental abundances. We find that the elemental abundances of BD +80 245, HE 0533-5340, and SMSS J034249.53-284216.0 are best explained by the (double) detonations of sub-Chandrasekhar-mass CO white dwarfs. If our interpretation of IRMP stars is accurate, then they should be very rare in globular clusters and more common in the Magellanic Clouds and dwarf spheroidal galaxies than in the Milky Way's halo. We propose that future studies of IRMP stars will quantify the relative occurrences of different thermonuclear event progenitor systems and explosion mechanisms.

While secondary mass inferences based on single-lined spectroscopic binary (SB1) solutions are subject to sini degeneracies, this degeneracy can be lifted through the observations of eclipses. We combine the subset of Gaia Data Release 3 SB1 solutions consistent with brown dwarf-mass secondaries with the Transiting Exoplanet Survey Satellite (TESS) Object of Interest (TOI) list to identify three candidate transiting brown dwarf systems. Ground-based precision radial velocity follow-up observations confirm that TOI-2533.01 is a transiting brown dwarf with M=72-3+3MJup=0.069-0.003+0.003M circle dot orbiting TYC 2010-124-1 and that TOI-5427.01 is a transiting very low-mass star with M=93-2+2MJup=0.088-0.002+0.002M circle dot orbiting UCAC4 515-012898. We validate TOI-1712.01 as a very low-mass star with M=82-7+7MJup=0.079-0.007+0.007M circle dot transiting the primary in the hierarchical triple system BD+45 1593. Even after accounting for third light, TOI-1712.01 has a radius nearly a factor of 2 larger than predicted for isolated stars with similar properties. We propose that the intense instellation experienced by TOI-1712.01 diminishes the temperature gradient near its surface, suppresses convection, and leads to its inflated radius. Our analyses verify Gaia DR3 SB1 solutions in the low Doppler semiamplitude limit, thereby providing the foundation for future joint analyses of Gaia radial velocities and Kepler, K2, TESS, and PLAnetary Transits and Oscillations light curves for the characterization of transiting massive brown dwarfs and very low-mass stars.

The MSb2 compounds with M = Cr,Fe, Ru, and Os have been investigated under high pressuresby synchrotron powder X-ray diffraction. All compounds, except CrSb2, were found to retain the marcasite structure up to the highestpressures (more than 50 GPa). In contrast, we found that CrSb2 has a structural phase transition around 10 GPa to a metastable,MoP2-type structure with Cr coordinated to seven Sb atoms.In addition, we compared ambient temperature compression with laser-heatingexperiments and found that laser-heating at pressures below and abovethis phase transition results in the known CuAl2-type structure.Density functional theory calculations show that this tetragonal structureis the most stable in the whole pressure interval. However, a crossingof the marcasite's and MoP2-like structure'senthalpies occurs between 5 and 7.5 GPa, which is in good agreementwith the experimental data. The phase transition to the MoP2-type structure observed in this work opens up for discovering othercompounds with this new transition pathway from the marcasite structure.

M & eacute;langes are mixtures of subducted materials and serpentinized mantle rocks that form along the slab-mantle interface in subduction zones. It has been suggested that m & eacute;lange rocks may be able to ascend from the slab-top into the overlying mantle, as solid or partially molten buoyant diapirs, and transfer their compositional signatures to the source regions of arc magmas. However, their ability to buoyantly rise is in part tied to their phase equilibria during melting and residual densities after melt extraction, all of which are poorly constrained. Here, we report a series of piston-cylinder experiments performed at 1.5-2.5 GPa and 500-1050 degrees C on three natural m & eacute;lange rocks that span a range of m & eacute;lange compositions. Using phase equilibria, solidus temperatures, and densities for all experiments, we show that melting of m & eacute;langes is unlikely to occur along the slab-top at pressures <= 2.5 GPa, so that diapirism into the hotter mantle wedge would be required for melting to initiate. For the two metaluminous m & eacute;lange compositions, diapir formation is favored up to pressures of at least 2.5 GPa. For the peraluminous m & eacute;lange composition investigated, diapir buoyancy is possible at 1.5 GPa but limited at 2.5 GPa due to the formation of high-density garnet, primarily at the expense of chlorite. We also evaluate whether thermodynamic modeling (Perple_X) can accurately reproduce the phase equilibria, solidus temperatures, and density evolution of m & eacute;lange compositions. Our analysis shows good agreement between models and experiments in m & eacute;lange compositions with low initial water contents and low-pressure (<= 1.5 GPa) conditions. However, discrepancies between the thermodynamic models and experiments become larger at higher pressures and high-water contents, highlighting the need for an improved thermodynamic database that can model novel bulk compositions beyond the canonical subducting lithologies. This study provides experimental constraints on m & eacute;lange buoyancy that can inform numerical models of m & eacute;lange diapirism and influence the interpretations of both geophysical signals and geochemical characteristics of magmas in subduction zones.(c) 2023 The Author(s). Published by Elsevier B.V.This is an open access article under the CC BY-NC-ND license (http://creativecommons .org /licenses /by-nc -nd /4 .0/).