VESICLE-INDUCING PROTEIN IN PLASTIDS1 (VIPP1), proposed to play a role in thylakoid biogenesis, is conserved in photosynthetic organisms and is closely related to Phage Shock Protein A (PspA), which is involved in plasma membrane integrity in Escherichia coli. This study showed that chloroplasts/plastids in Arabidopsis thaliana vipp1 knockdown and knockout mutants exhibit a unique morphology, forming balloon-like structures. This altered morphology, as well as lethality of vipp1, was complemented by expression of VIPP1 fused to green fluorescent protein (VIPP1-GFP). Several lines of evidence show that the balloon chloroplasts result from chloroplast swelling related to osmotic stress, implicating VIPP1 in the maintenance of plastid envelopes. In support of this, Arabidopsis VIPP1 rescued defective proton leakage in an E. coli pspA mutant. Microscopy observation of VIPP1-GFP in transgenic Arabidopsis revealed that VIPP1 forms large macrostructures that are integrated into various morphologies along the envelopes. Furthermore, live imaging revealed that VIPP1-GFP is highly mobile when chloroplasts are subjected to osmotic stress. VIPP1-GFP showed dynamic movement in the transparent area of spherical chloroplasts, as the fluorescent molecules formed filament-like structures likely derived from disassembly of the large VIPP1 complex. Collectively, our data demonstrate that VIPP1 is a multifunctional protein in chloroplasts that is critically important for envelope maintenance.

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Stomata are essential for efficient gas and water-vapor exchange between the atmosphere and plants. Stomatal density and movement are controlled by a series of signal molecules including phytohormones and peptides as well as by environmental stimuli. It is known that heterotrimeric G-proteins play an important role in the ABA-inhibited stomatal opening. In this study, the G-protein signaling pathway was also found to regulate stomatal density on the lower epidermis of Arabidopsis cotyledons. The loss-of-function mutation of the G-protein alpha-subunit (GPA1) showed a reduction in stomatal density, while overexpression of the constitutively active form of GPA1(QL) increased stomatal density, indicating a positive role of the active form of GPA1 in stomatal development. In contrast, stomatal density increased in the null mutant of the G-protein beta-subunit (AGB1) but decreased in transgenic lines that overexpressed AGB1. Stomatal analysis of the gpa1 agb1 double mutants displayed an average value of stomatal density compared to the single mutants. Taken together, these results suggest that the stomatal density in Arabidopsis is modulated by GPA1 and AGB1 in an antagonistic manner.

This Letter presents for the first time a scheme to generate intense high-order optical vortices that carry orbital angular momentum in the extreme ultraviolet region based on relativistic harmonics from the surface of a solid target. In the three-dimensional particle-in-cell simulation, the high-order harmonics of the high-order vortex mode is generated in both reflected and transmitted light beams when a linearly polarized Laguerre-Gaussian laser pulse impinges on a solid foil. The azimuthal mode of the harmonics scales with its order. The intensity of the high-order vortex harmonics is close to the relativistic region, with the pulse duration down to attosecond scale. The obtained intense vortex beam possesses the combined properties of fine transversal structure due to the high-order mode and the fine longitudinal structure due to the short wavelength of the high-order harmonics. In addition to the application in high-resolution detection in both spatial and temporal scales, it also presents new opportunities in the intense vortex required fields, such as the inner shell ionization process and high energy twisted photons generation by Thomson scattering of such an intense vortex beam off relativistic electrons. Light beams can exhibit helical wave fronts: the light phase "winds up" around the spatial beam center and forms an optical vortex. The phase wind imprints an orbital angular momentum (OAM) to the beam [1,2]. The characteristic helical phase profiles of optical vortices are described by expðilϕÞ multipliers, where ϕ is the azimuthal coordinate and the integer number l is their topological charge, corresponding to the order of the mode. The total phase accumulated in one full annular loop is 2πl, and an OAM of lℏ is carried by per photon for an l-order linearly polarized optical vortex beam. Based on this, the high-order optical vortex beam provides a powerful tool in optical information to investigate the entanglement state [3] and for studies of cold atoms and enhancing atomic transition [4][5][6][7].In order to provide more quantum information and for other potential applications, high-order vortex beams are required. However, limited by the etching resolution, the common method using forked diffraction grating [8] or the spiral phase plates [1] to generate the optical vortex beams is difficult to be used to obtain them. Many studies have attempted to generate light beams with OAM. For example, a relativistic electron beam can act as a mode converter that interacts with a laser in a helical undulator [9-11] and high-energy photons in MeV-GeV with OAM can be obtained by Compton backscattering of twisted laser photons off relativistic electrons [12], where the mode of the Laguerre-Gaussian (LG) pulse remains unchanged. In addition, in view of the gas high-order harmonics generation (HHG) scheme [13][14][15], because of the confluence of OAM and HHG, this scheme has an extraordinarily promising perspective. The observed harmonics possess a helical wave front in both experimental [16,17] and theoretical...

When a relativistic laser pulse with a high photon density interacts with a specially tailored thin foil target, a strong torque is exerted on the resulting spiral-shaped foil plasma, or "light fan." Because of its structure, the latter can gain significant orbital angular momentum (OAM), and the opposite OAM is imparted to the reflected light, creating a twisted relativistic light pulse. Such an interaction scenario is demonstrated by particle-in-cell simulation as well as analytical modeling, and should be easily verifiable in the laboratory. As an important characteristic, the twisted relativistic light pulse has a strong torque and ultrahigh OAM density. DOI: 10.1103/PhysRevLett.112.235001 PACS numbers: 52.38.-r, 03.50.De, 42.50.Tx, 52.59.-f Prompted by the fast development of laser techniques [1], light-matter interaction has entered the regime of a relativistic laser-plasma interaction. Over the past few decades, a number of novel mechanisms and schemes have been proposed. Among these mechanisms and schemes, the most promising application is for use in laser-driven plasma accelerator science, such as laser wakefield acceleration of electrons [2] and a laser driving foil to accelerate protons [3]. Laser-plasma interaction can also be an efficient source of high-order harmonic generation (HHG) [4], x rays [5], and even gamma rays [6,7]. One of the key issues in the above mechanisms is how to make use of the laser ponderomotive force efficiently to pump a strong charge separation field in plasma, which is the origin of particle acceleration. Hence, it is the force (the accelerating force, the confining force, etc.) that people care about most in relativistic laser plasma physics. The effect of another important dynamical quantity, the torque, although as important as force, has not been revealed for a relativistic laser pulse. How to observe the orbital angular momentum (OAM) in laser-plasma interaction and how the appearance of OAM would essentially affect the process are of special interest. Circularly polarized light carries a spin angular momentum of AEℏ per photon; however, the total OAM of a normal Gaussian pulse, commonly found in the current chirped pulse amplification technology, is zero. Therefore, observation of the torque and OAM in relativistic laserplasma interaction is rare.OAM has been discussed extensively for weak light [8-13] and extreme ultraviolet light [14][15][16]. Since Allen et al. first showed that a Laguerre-Gaussian (LG) laser pulse has finite OAM [8], many applications using twisted light have been found [9][10][11]. The OAM of a twisted light can be transferred to matter. More interestingly, several phenomena observed in astrophysics, like pulsars, are related to the OAM of light and plasma [17,18]. Thus, simulating and investigating such an immense process in a laboratory on the Earth would be of great convenience. Recently, Mendonca et al. have derived the solutions of plasma wave with OAM [19,20]. They also created a donut plasma wakefield using an intense laser with OAM f...

Large-scale analysis of the GC-content distribution at the gene level reveals both common features and basic differences in genomes of different groups of species. Sharp changes in GC content are detected at the transcription boundaries for all species analyzed, including human, mouse, rat, chicken, fruit fly, and worm. However, two substantially distinct groups of GC-content profiles can be recognized: warm-blooded vertebrates including human, mouse, rat, and chicken, and invertebrates including fruit fly and worm. In vertebrates, sharp positive and negative spikes of GC content are observed at the transcription start and stop sites, respectively, and there is also a progressive decrease in GC content from the 5 untranslated region to the 3 untranslated region along the gene. In invertebrates, the positive and negative GC-content spikes at the transcription start and stop sites are preceded by spikes of opposite value, and the highest GC content is found in the coding regions of the genes. Cross-correlation analysis indicates high frequencies of GC-content spikes at transcription start and stop sites. The strong conservation of this genomic feature seen in comparisons of the human͞mouse and human͞rat orthologs, and the clustering of genes with GC-content spikes on chromosomes imply a biological function. The GC-content spikes at transcription boundaries may reflect a general principle of genomic punctuation. Our analysis also provides means for identifying these GC-content spikes in individual genomic sequences.gene clustering ͉ gene ontology ͉ transcription start site ͉ transcription stop site

Integrity of biomembranes is vital to living organisms. In bacteria, PspA is considered to act as repairing damaged membrane by forming large supercomplexes in Arabidopsis (Arabidopsis thaliana). Vulnerable to oxidative stress, photosynthetic organisms also contain a PspA ortholog called VIPP1, which has an additional C-terminal tail (Vc). In this study, Vc was shown to coincide with an intrinsically disordered region, and the role of VIPP1 in membrane protection against stress was investigated. We visualized VIPP1 by fusing it to GFP (VIPP1-GFP that fully complemented lethal vipp1 mutations), and investigated its behavior in vivo with live imaging. The intrinsically disordered nature of Vc enabled VIPP1 to form what appeared to be functional particles along envelopes, whereas the deletion of Vc caused excessive association of the VIPP1 particles, preventing their active movement for membrane protection. Expression of VIPP1 lacking Vc complemented vipp1 mutation, but exhibited sensitivity to heat shock stress. Conversely, transgenic plants over-expressing VIPP1 showed enhanced tolerance against heat shock, suggesting that Vc negatively regulates VIPP1 particle association and acts in maintaining membrane integrity. Our data thus indicate that VIPP1 is involved in the maintenance of photosynthetic membranes. During evolution, chloroplasts have acquired enhanced tolerance against membrane stress by incorporating a disordered C-terminal tail into VIPP1.

SUMMARYHeterotrimeric G protein knock-out mutants have no phenotypic defect in chloroplast development, and the connection between the G protein signaling pathway and chloroplast development has only been inferred from pharmaceutical evidence. Thus, whether G protein signaling plays a role in chloroplast development remains an open question. Here, we present genetic evidence, using the leaf-variegated mutant thylakoid formation 1 (thf1), indicating that inactivation or activation of the endogenous G protein a-subunit (GPA1) affects chloroplast development, as does the ectopic expression of the constitutively active Ga-subunit (cGPA1). Molecular biological and genetic analyses showed that FtsH complexes, which are composed of type-A (FtsH1/FtsH5) and type-B (FtsH2/FtsH8) subunits, are required for cGPA1-promoted chloroplast development in thf1. Furthermore, the ectopic expression of cGPA1 rescues the leaf variegation of ftsh2. Consistent with this finding, microarray analysis shows that ectopic expression of cGPA1 partially corrects mis-regulated gene expression in thf1. This overlooked function of G proteins provides new insight into our understanding of the integrative signaling network, which dynamically regulates chloroplast development and function in response to both intracellular and extracellular signals.