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Seed quality and carbon primary metabolism.
Domergue, JB, Abadie, C, Limami, A, Way, D, Tcherkez, G
Plant, cell & environment. 2019;(10):2776-2788
Abstract
Improving seed quality is amongst the most important challenges of contemporary agriculture. In fact, using plant varieties with better germination rates that are more tolerant to stress during seedling establishment may improve crop yield considerably. Therefore, intense efforts are currently being devoted to improve seed quality in many species, mostly using genomics tools. However, despite its considerable importance during seed imbibition and germination processes, primary carbon metabolism in seeds is less studied. Our knowledge of the physiology of seed respiration and energy generation and the impact of these processes on seed performance have made limited progress over the past three decades. In particular, (isotope-assisted) metabolomics of seeds has only been assessed occasionally, and there is limited information on possible quantitative relationships between metabolic fluxes and seed quality. Here, we review the recent literature and provide an overview of potential links between metabolic efficiency, metabolic biomarkers, and seed quality and discuss implications for future research, including a climate change context.
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Getting closer: vein density in C4 leaves.
Kumar, D, Kellogg, EA
The New phytologist. 2019;(3):1260-1267
Abstract
Contents Summary 1260 I. Introduction 1260 II. Molecular and genetic mechanisms of C4 leaf venation 1262 III. Conclusions and future perspectives 1266 Acknowledgements 1266 References 1266 SUMMARY C4 grasses are major contributors to the world's food supply. Their highly efficient method of carbon fixation is a unique adaptation that combines close vein spacing and distinct photosynthetic cell types. Despite its importance, the molecular genetic basis of C4 leaf development is still poorly understood. Here we summarize current knowledge of leaf venation and review recent progress in understanding molecular and genetic regulation of vascular patterning events in C4 plants. Evidence points to the interplay of auxin, brassinosteroids, SHORTROOT/SCARECROW and INDETERMINATE DOMAIN transcription factors. Identification and functional characterization of candidate regulators acting early in vascular development will be essential for further progress in understanding the precise regulation of these processes.
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Integration of sulfate assimilation with carbon and nitrogen metabolism in transition from C3 to C4 photosynthesis.
Jobe, TO, Zenzen, I, Rahimzadeh Karvansara, P, Kopriva, S
Journal of experimental botany. 2019;(16):4211-4221
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Abstract
The first product of sulfate assimilation in plants, cysteine, is a proteinogenic amino acid and a source of reduced sulfur for plant metabolism. Cysteine synthesis is the convergence point of the three major pathways of primary metabolism: carbon, nitrate, and sulfate assimilation. Despite the importance of metabolic and genetic coordination of these three pathways for nutrient balance in plants, the molecular mechanisms underlying this coordination, and the sensors and signals, are far from being understood. This is even more apparent in C4 plants, where coordination of these pathways for cysteine synthesis includes the additional challenge of differential spatial localization. Here we review the coordination of sulfate, nitrate, and carbon assimilation, and show how they are altered in C4 plants. We then summarize current knowledge of the mechanisms of coordination of these pathways. Finally, we identify urgent questions to be addressed in order to understand the integration of sulfate assimilation with carbon and nitrogen metabolism particularly in C4 plants. We consider answering these questions to be a prerequisite for successful engineering of C4 photosynthesis into C3 crops to increase their efficiency.
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Embracing 3D Complexity in Leaf Carbon-Water Exchange.
Earles, JM, Buckley, TN, Brodersen, CR, Busch, FA, Cano, FJ, Choat, B, Evans, JR, Farquhar, GD, Harwood, R, Huynh, M, et al
Trends in plant science. 2019;(1):15-24
Abstract
Leaves are a nexus for the exchange of water, carbon, and energy between terrestrial plants and the atmosphere. Research in recent decades has highlighted the critical importance of the underlying biophysical and anatomical determinants of CO2 and H2O transport, but a quantitative understanding of how detailed 3D leaf anatomy mediates within-leaf transport has been hindered by the lack of a consensus framework for analyzing or simulating transport and its spatial and temporal dynamics realistically, and by the difficulty of measuring within-leaf transport at the appropriate scales. We discuss how recent technological advancements now make a spatially explicit 3D leaf analysis possible, through new imaging and modeling tools that will allow us to address long-standing questions related to plant carbon-water exchange.
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Carbon assimilation in crops at high temperatures.
Slattery, RA, Ort, DR
Plant, cell & environment. 2019;(10):2750-2758
Abstract
Global temperatures are rising, and higher rates of temperature increase are projected over land areas that encompass the globe's major agricultural regions. In addition to increased growing season temperatures, heat waves are predicted to become more common and severe. High temperatures can inhibit photosynthetic carbon gain of crop plants and thus threaten productivity, the effects of which may interact with other aspects of climate change. Here, we review the current literature assessing temperature effects on photosynthesis in key crops with special attention to field studies using crop canopy heating technology and in combination with other climate variables. We also discuss the biochemical reactions related to carbon fixation that may limit crop photosynthesis under warming temperatures and the current strategies for adaptation. Important progress has been made on several adaptation strategies demonstrating proof-of-concept for translating improved photosynthesis into higher yields. These are now poised to test in important food crops.
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Engineering Strategies to Boost Crop Productivity by Cutting Respiratory Carbon Loss.
Amthor, JS, Bar-Even, A, Hanson, AD, Millar, AH, Stitt, M, Sweetlove, LJ, Tyerman, SD
The Plant cell. 2019;(2):297-314
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Abstract
Roughly half the carbon that crop plants fix by photosynthesis is subsequently lost by respiration. Nonessential respiratory activity leading to unnecessary CO2 release is unlikely to have been minimized by natural selection or crop breeding, and cutting this large loss could complement and reinforce the currently dominant yield-enhancement strategy of increasing carbon fixation. Until now, however, respiratory carbon losses have generally been overlooked by metabolic engineers and synthetic biologists because specific target genes have been elusive. We argue that recent advances are at last pinpointing individual enzyme and transporter genes that can be engineered to (1) slow unnecessary protein turnover, (2) replace, relocate, or reschedule metabolic activities, (3) suppress futile cycles, and (4) make ion transport more efficient, all of which can reduce respiratory costs. We identify a set of engineering strategies to reduce respiratory carbon loss that are now feasible and model how implementing these strategies singly or in tandem could lead to substantial gains in crop productivity.
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Photocatalytic Difluoromethylation Reactions of Aromatic Compounds and Aliphatic Multiple C-C Bonds.
Barata-Vallejo, S, Postigo, A
Molecules (Basel, Switzerland). 2019;(24)
Abstract
Among the realm of visible light photocatalytic transformations, late-stage difluoromethylation reactions (introduction of difluoromethyl groups in the last stages of synthetic protocols) have played relevant roles as the CF2X group substitutions exert positive impacts on the physical properties of organic compounds including solubility, metabolic stability, and lipophilicity, which are tenets of considerable importance in pharmaceutical, agrochemical, and materials science. Visible-light-photocatalyzed difluoromethylation reactions are shown to be accomplished on (hetero)aromatic and carbon-carbon unsaturated aliphatic substrates under mild and environmentally benign conditions.
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Plant carbon metabolism and climate change: elevated CO2 and temperature impacts on photosynthesis, photorespiration and respiration.
Dusenge, ME, Duarte, AG, Way, DA
The New phytologist. 2019;(1):32-49
Abstract
Contents Summary 32 I. The importance of plant carbon metabolism for climate change 32 II. Rising atmospheric CO2 and carbon metabolism 33 III. Rising temperatures and carbon metabolism 37 IV. Thermal acclimation responses of carbon metabolic processes can be best understood when studied together 38 V. Will elevated CO2 offset warming-induced changes in carbon metabolism? 40 VI. No plant is an island: water and nutrient limitations define plant responses to climate drivers 41 VII. Conclusions 42 Acknowledgements 42 References 42 Appendix A1 48 SUMMARY Plant carbon metabolism is impacted by rising CO2 concentrations and temperatures, but also feeds back onto the climate system to help determine the trajectory of future climate change. Here we review how photosynthesis, photorespiration and respiration are affected by increasing atmospheric CO2 concentrations and climate warming, both separately and in combination. We also compile data from the literature on plants grown at multiple temperatures, focusing on net CO2 assimilation rates and leaf dark respiration rates measured at the growth temperature (Agrowth and Rgrowth , respectively). Our analyses show that the ratio of Agrowth to Rgrowth is generally homeostatic across a wide range of species and growth temperatures, and that species that have reduced Agrowth at higher growth temperatures also tend to have reduced Rgrowth , while species that show stimulations in Agrowth under warming tend to have higher Rgrowth in the hotter environment. These results highlight the need to study these physiological processes together to better predict how vegetation carbon metabolism will respond to climate change.
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Modelling carbon sources and sinks in terrestrial vegetation.
Fatichi, S, Pappas, C, Zscheischler, J, Leuzinger, S
The New phytologist. 2019;(2):652-668
Abstract
Contents Summary 652 I. Introduction 652 II. Discrepancy in predicting the effects of rising [CO2 ] on the terrestrial C sink 655 III. Carbon and nutrient storage in plants and its modelling 656 IV. Modelling the source and the sink: a plant perspective 657 V. Plant-scale water and Carbon flux models 660 VI. Challenges for the future 662 Acknowledgements 663 Authors contributions 663 References 663 SUMMARY The increase in atmospheric CO2 in the future is one of the most certain projections in environmental sciences. Understanding whether vegetation carbon assimilation, growth, and changes in vegetation carbon stocks are affected by higher atmospheric CO2 and translating this understanding in mechanistic vegetation models is of utmost importance. This is highlighted by inconsistencies between global-scale studies that attribute terrestrial carbon sinks to CO2 stimulation of gross and net primary production on the one hand, and forest inventories, tree-scale studies, and plant physiological evidence showing a much less pronounced CO2 fertilization effect on the other hand. Here, we review how plant carbon sources and sinks are currently described in terrestrial biosphere models. We highlight an uneven representation of complexity between the modelling of photosynthesis and other processes, such as plant respiration, direct carbon sinks, and carbon allocation, largely driven by available observations. Despite a general lack of data on carbon sink dynamics to drive model improvements, ways forward toward a mechanistic representation of plant carbon sinks are discussed, leveraging on results obtained from plant-scale models and on observations geared toward model developments.
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Evolutionary trajectories, accessibility and other metaphors: the case of C4 and CAM photosynthesis.
Edwards, EJ
The New phytologist. 2019;(4):1742-1755
Abstract
Are evolutionary outcomes predictable? Adaptations that show repeated evolutionary convergence across the Tree of Life provide a special opportunity to dissect the context surrounding their origins, and identify any commonalities that may predict why certain traits evolved many times in particular clades and yet never evolved in others. The remarkable convergence of C4 and Crassulacean Acid Metabolism (CAM) photosynthesis in vascular plants makes them exceptional model systems for understanding the repeated evolution of complex phenotypes. This review highlights what we have learned about the recurring assembly of C4 and CAM, focusing on the increasingly predictable stepwise evolutionary integration of anatomy and biochemistry. With the caveat that we currently understand C4 evolution better than we do CAM, I propose a general model that explains and unites C4 and CAM evolutionary trajectories. Available data suggest that anatomical modifications are the 'rate-limiting step' in each trajectory, which in large part determines the evolutionary accessibility of both syndromes. The idea that organismal structure exerts a primary influence on innovation is discussed in the context of other systems. Whether the rate-limiting step occurs early or late in the evolutionary assembly of a new phenotype may have profound implications for its distribution across the Tree of Life.