The making of a chloroplast

Since its endosymbiotic beginning, the chloroplast has become fully integrated into the biology of the host eukaryotic cell. The exchange of genetic information from the chloroplast to the nucleus has resulted in considerable co-ordination in the activities of these two organelles during all stages of plant development. Here, we give an overview of the mechanisms of light perception and the subsequent regulation of nuclear gene expression in the model plant Arabidopsis thaliana, and we cover the main events that take place when proplastids differentiate into chloroplasts. We also consider recent findings regarding signalling networks between the chloroplast and the nucleus during seedling development, and how these signals are modulated by light. In addition, we discuss the mechanisms through which chloroplasts develop in different cell types, namely cotyledons and the dimorphic chloroplasts of the C4 plant maize. Finally, we discuss recent data that suggest the specific regulation of the light-dependent phases of photosynthesis, providing a means to optimize photosynthesis to varying light regimes

Conservation of ciliary proteins in plants with no cilia

<p>Abstract</p> <p>Background</p> <p>Eukaryotic cilia are complex, highly conserved microtubule-based organelles with a broad phylogenetic distribution. Cilia were present in the last eukaryotic common ancestor and many proteins involved in cilia function have been conserved through eukaryotic diversification. However, cilia have also been lost multiple times in different lineages, with at least two losses occurring within the land plants. Whereas all non-seed plants produce cilia for motility of male gametes, some gymnosperms and all angiosperms lack cilia. During these evolutionary losses, proteins with ancestral ciliary functions may be lost or co-opted into different functions.</p> <p>Results</p> <p>Here we identify a core set of proteins with an inferred ciliary function that are conserved in ciliated eukaryotic species. We interrogate this genomic dataset to identify proteins with a predicted ancestral ciliary role that have been maintained in non-ciliated land plants. In support of our prediction, we demonstrate that several of these proteins have a flagellar localisation in protozoan trypanosomes. The phylogenetic distribution of these genes within the land plants indicates evolutionary scenarios of either sub- or neo-functionalisation and expression data analysis shows that these genes are highly expressed in <it>Arabidopsis thaliana </it>pollen cells.</p> <p>Conclusions</p> <p>A large number of proteins possess a phylogenetic ciliary profile indicative of ciliary function. Remarkably, many genes with an ancestral ciliary role are maintained in non-ciliated land plants. These proteins have been co-opted to perform novel functions, most likely before the loss of cilia, some of which appear related to the formation of the male gametes.</p

Local cues and asymmetric cell divisions underpin body plan transitions in the moss Physcomitrella patens

Background: Land plants evolved from aquatic algae more than 450 million years ago. Algal sisters of land plants grow through the activity of apical initial cells that cleave either in one plane to generate filaments or in two planes to generate mats. Acquisition of the capacity for cell cleavage in three planes facilitated the formation of upright bushy body plans and enabled the invasion of land. Evolutionary transitions between filamentous, planar, and bushy growth are mimicked within moss life cycles. Results: We have developed lineage analysis techniques to assess how transitions between growth forms occur in the moss Physcomitrella patens. We show that initial cells giving rise either to new filaments or bushy shoots are frequently juxtaposed on a single parent filament, suggesting a role for short-range cues in specifying differences in cell fate. Shoot initials cleave four times to establish a tetrahedral shape and subsequently cleave in three planes, generating bushy growth. Asymmetric and self-replacing divisions from the tetrahedral initial generate leaf initials that divide asymmetrically to self-replace and to produce daughter cells with restricted fate. The cessation of division in the leaf is distributed unevenly and contributes to final leaf shape. Conclusions: In contrast to flowering plants, changes in body plan in P. patens are regulated by cues acting at the level of single cells and are mediated through asymmetric divisions. Genetic mechanisms regulating shoot and leaf development in P. patens are therefore likely to differ substantially from mechanisms operating in plants with more recent evolutionary origins

Flip-Flap: A Simple Dual-View Imaging Method for 3D Reconstruction of Thick Plant Samples

Plant development is a complex process that relies on molecular and cellular events being co-ordinated in space and time. Microscopy is one of the most powerful tools available to investigate this spatiotemporal complexity. One step towards a better understanding of complexity in plants would be the acquisition of 3D images of entire organs. However, 3D imaging of intact plant samples is not always simple and often requires expensive and/or non-trivial approaches. In particular, the inner tissues of thick samples are challenging to image. Here, we present the Flip-Flap method, a simple imaging protocol to produce 3D images of cleared plant samples at the organ scale. This method allows full 3D reconstruction of plant organs suitable for 3D segmentation and further related analysis and can be easily handled by relatively inexperienced microscopists

Robotics and Automated Systems for Environmental Sustainability: Monitoring Terrestrial Biodiversity

It is critical to protect Earth’s biodiversity, not just for its own intrinsic value, but also for the ecosystem services it underpins. Yet biodiversity is in crisis, with up to 1 million animal and plant species at risk of extinction, many within decades. This dire projection has captured world attention and triggered major mitigation efforts, but we are faced with problems in assessing global trends in biodiversity – which species, taxa, habitats and ecosystems are suffering the greatest declines? Are current mitigation measures having any positive impact? To answer key questions such as these, ecologists are seeking the help of robotics and automated systems (RAS) experts in the monumental task of attempting to monitor the state of biodiversity.In this White Paper, we have surveyed recent literature and consulted more than 120 international expert ecologists and engineers working in the fields of biodiversity and robotics. We have done this to evaluate the potential for developing robotic and autonomous systems that could massively extend the scope of terrestrial biodiversity monitoring across habitats globally. The complexities of biodiversity itself, and the many barriers and challenges that must be overcome in monitoring it, are formidable. We assess each of these barriers in turn, highlighting currently available RAS solutions, as well as nascent technologies that may be relevant to future RAS for biodiversity (RAS-BD) monitoring. Using this information, we have drawn up a roadmap of actions needed to address the barriers that should be easiest to overcome. Encouragingly, we find that a variety of existing RAS capabilities may be transferable to a biodiversity monitoring context. Beyond these are the harder barriers, where promising novel ideas being researched at UK universities and research institutes may, in time, become integral parts of future RAS-BD monitoring technology. We believe that RAS-BD technology has great potential to complement and considerably extend the field survey work undertaken by expert human observers. In the UK, we are fortunate in having particular strengths in both biodiversity and robotics research; as a nation we are in an ideal position to integrate them and become a leading force in the development and application of RAS-BD monitoring. To this end, we propose these recommendations that we hope will guide future government strategy in an area that is vital to the future of humanity:● The creation and funding of an integrated multidisciplinary task force, including academics and industry specialists with expertise in RAS and biodiversity, to support technological research and development.● Future UK funding and focus should be prioritised to utilise existing RAS capabilities to develop first generation RAS-BD technology for monitoring biodiversity.● Relevant nascent technologies being researched by numerous UK academic teams need increased and accelerated research and development funding to turn pioneering concepts into enhanced RAS-BD technology suited to overcoming the hardest monitoring barriers that ecologists encounter.● Education strategies should be developed to foster links between aspiring engineers, biologists andcomputer technologists, both in the curriculum of schools, and at later stages in universities and research facilities

Searching for gravitational waves from known pulsars

We present upper limits on the amplitude of gravitational waves from 28 isolated pulsars using data from the second science run of LIGO. The results are also expressed as a constraint on the pulsars' equatorial ellipticities. We discuss a new way of presenting such ellipticity upper limits that takes account of the uncertainties of the pulsar moment of inertia. We also extend our previous method to search for known pulsars in binary systems, of which there are about 80 in the sensitive frequency range of LIGO and GEO 600.Comment: Accepted by CQG for the proceeding of GWDAW9, 7 pages, 2 figure

Re-creation of a Key Step in the Evolutionary Switch from C3 to C4 Leaf Anatomy

The C4 photosynthetic pathway accounts for ∼25% of primary productivity on the planet despite being used by only 3% of species. Because C4 plants are higher yielding than C3 plants, efforts are underway to introduce the C4 pathway into the C3 crop rice. This is an ambitious endeavor; however, the C4 pathway evolved from C3 on multiple independent occasions over the last 30 million years, and steps along the trajectory are evident in extant species. One approach toward engineering C4 rice is to recapitulate this trajectory, one of the first steps of which was a change in leaf anatomy. The transition from C3 to so-called “proto-Kranz” anatomy requires an increase in organelle volume in sheath cells surrounding leaf veins. Here we induced chloroplast and mitochondrial development in rice vascular sheath cells through constitutive expression of maize GOLDEN2-LIKE genes. Increased organelle volume was accompanied by the accumulation of photosynthetic enzymes and by increased intercellular connections. This suite of traits reflects that seen in “proto-Kranz” species, and, as such, a key step toward engineering C4 rice has been achieved.Research was funded by a C4 Rice Project grant from The Bill & Melinda Gates Foundation to IRRI (2012–2015; OPPGD1394) and the University of Oxford (2015–2019; OPP1129902)