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1.
AhGLK1 affects chlorophyll biosynthesis and photosynthesis in peanut leaves during recovery from drought.
Liu, X, Li, L, Li, M, Su, L, Lian, S, Zhang, B, Li, X, Ge, K, Li, L
Scientific reports. 2018;(1):2250
Abstract
Peanut is an important edible oil crop plant whose quality and yield are greatly affected by drought. The process and molecular mechanisms of recovery from drought are also critical to its productivity, but are currently poorly characterized. Here, we investigate the involvement of peanut AhGLK1 in recovery from drought, and in particular its relationship with AhPORA, which encodes a key enzyme in chlorophyll biosynthesis. We found that chlorophyll content, chlorophyll fluorescence, AhPORA protein level and genes related to chlorophyll biosynthesis and photosynthesis declined markedly under drought conditions, but all increased during recovery. Consistent with this, AhGLK1 expression decreased during water stress and increased when the stress was removed. When AhGLK1 was transformed into Arabidopsis glk1glk2 mutant, it increased the survival rate of the mutant during recovery from drought and fully rescued the mutant's pale-green phenotype. In addition, chlorophyll content and fluorescence, and the expression of genes related to chlorophyll biosynthesis and photosynthesis, were all increased. Bioinformatics analysis and experimental evidence suggested that AhGLK1 augments the expression of AhPORA by binding to its promoter. Our findings confirm that AhGLK1 plays a role as a transcription factor that upregulates expression of AhPORA during post-drought recovery, thereby stimulating chlorophyll biosynthesis and photosynthesis.
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2.
Rerouting of Metabolism into Desired Cellular Products by Nutrient Stress: Fluxes Reveal the Selected Pathways in Cyanobacterial Photosynthesis.
Qian, X, Zhang, Y, Lun, DS, Dismukes, GC
ACS synthetic biology. 2018;(5):1465-1476
Abstract
Boosting cellular growth rates while redirecting metabolism to make desired products are the preeminent goals of gene engineering of photoautotrophs, yet so far these goals have been hardly achieved owing to lack of understanding of the functional pathways and their choke points. Here we apply a 13C mass isotopic method (INST-MFA) to quantify instantaneous fluxes of metabolites during photoautotrophic growth. INST-MFA determines the globally most accurate set of absolute fluxes for each metabolite from a finite set of measured 13C-isotopomer fluxes by minimizing the sum of squared residuals between experimental and predicted mass isotopomers. We show that the widely observed shift in biomass composition in cyanobacteria, demonstrated here with Synechococcus sp. PCC 7002, favoring glycogen synthesis during nitrogen starvation is caused by (1) increased flux through a bottleneck step in gluconeogenesis (3PG → GAP/DHAP), and (2) flux overflow through a previously unrecognized hybrid gluconeogenesis-pentose phosphate (hGPP) pathway. Our data suggest the slower growth rate and biomass accumulation under N starvation is due to a reduced carbon fixation rate and a reduced flux of carbon into amino acid precursors. Additionally, 13C flux from α-ketoglutarate to succinate is demonstrated to occur via succinic semialdehyde, an alternative to the conventional TCA cycle, in Synechococcus 7002 under photoautotrophic conditions. We found that pyruvate and oxaloacetate are synthesized mainly by malate dehydrogenase with minimal flux into acetyl coenzyme-A via pyruvate dehydrogenase. Nutrient stress induces major shifts in fluxes into new pathways that deviate from historical metabolic pathways derived from model bacteria.
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3.
Evaluating the kinetic basis of plant growth from organs to ecosystems.
Michaletz, ST
The New phytologist. 2018;(1):37-44
Abstract
Contents Summary 37 I. Introduction 37 II. Predictions for metabolic kinetics 38 III. Kinetics of net photosynthesis 38 IV. Kinetics of plant growth 40 V. Hypotheses for higher-level kinetic decoupling 41 VI. Conclusions 42 Acknowledgements 42 References 42 SUMMARY Understanding how temperature influences the scaling of physiological rates through levels of biological organization is critical for predicting plant responses to climate. Metabolic theory predicts that many rates increase exponentially with temperature following an activation energy (E) of 0.32 eV for photosynthesis. Here, I evaluate this prediction for net photosynthesis and organ, individual, and ecosystem growth. Observed E for photosynthesis varied widely but was not statistically different from predictions, while E for organs was greater than predicted, and E for individuals and ecosystems only weakly characterized temperature responses. I review several hypotheses that may underlie these results. Understanding how multiple rate-limiting processes coalesce into a single E that characterizes metabolic responses to temperature, and how to best estimate E from unimodal data, remain important challenges.
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4.
Comparative phytotoxicity of usnic acid, salicylic acid, cinnamic acid and benzoic acid on photosynthetic apparatus of Chlamydomonas reinhardtii.
Gao, Y, Liu, W, Wang, X, Yang, L, Han, S, Chen, S, Strasser, RJ, Valverde, BE, Qiang, S
Plant physiology and biochemistry : PPB. 2018;:1-12
Abstract
The effects of four phytotoxins usnic acid (UA), salicylic acid (SA), cinnamic acid (CA) and benzoic acid (BA) on photosynthesis of Chlamydomonas reinhardtii were studied in vivo to identify and localise their initial action sites on two photosystems. Our experimental evidence shows that the four phytotoxins have multiple targets in chloroplasts, which mainly lie in photosystem II (PSII), not photosystem I (PSI). They share an original action site by blocking electron transport beyond QA (primary plastoquinone acceptor) at PSII acceptor side since a fast increase of the J-step level is the greatest change in chlorophyll a fluorescence induction kinetics OJIP in C. reinhardtii cells treated with the phytotoxins. UA decreases photosynthetic activity by reducing O2 evolution rate, interrupting PSII electron transport at both the donor and acceptor sides, inactivating the PSII reaction centers (RCs), reducing the content of chlorophylls and carotenoids, destroying the conformation of antenna pigment assemblies, and casuing the degradation of D1/D2 proteins. SA damage to photosynthetic machinery is mainly attributed to inhibition of PSII electron transport beyond QA at the acceptor side, inactivation of the PSII RCs, reduction of chlorophyll content, digestion of thylakoid ploypeptides and destabilization of thylakoid membranes. Both CA and BA affect the photosynthetic process by decreasing PSII electron transport efficiency at the acceptor side and the amount of active PSII RCs. Besides, the initial cause of BA-inhibiting photosynthesis is also assocaited with the O2 evolution rate and the disconnection of some antenna molecules from PSII RCs.
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5.
Effect of UV-B radiation on the content of UV-B absorbing compounds and photosynthetic parameters in Parmotrema austrosinense from two contrasting habitats.
Barták, M, Pláteníková, E, Carreras, H, Hájek, J, Morkusová, J, Mateos, AC, Marečková, M
Plant biology (Stuttgart, Germany). 2018;(5):808-816
Abstract
We studied the resistance of Parmotrema austrosinense to UV-B stress. We focused on the effects of a high dose UV-B radiation on the content of chlorophylls, carotenoids and UV-B screening compounds. Photosynthetic parameters were measured by chlorophyll fluorescence (potential and effective quantum yields, photochemical and non-photochemical quenching) and evaluated in control and UV-B-treated lichens. Lichens from two different locations in Cordoba, Argentina, were selected: (i) high altitude and dry plots at (Los Gigantes) and (ii) lowland high salinity plots (Salinas Grandes). UV-B treatment led to a decrease in the content of photosynthetic pigments and UV-B screens (absorbance decrease in 220-350 nm) in the samples from Salinas Grandes, while in Los Gigantes samples, an increase in UV-B screen content was observed. Chlorophyll fluorescence parameters showed a UV-B-induced decline in FV /FM , ΦPSII and qP indicating limitation of primary photosynthetic processes in photosystem II (PSII) of symbiotic alga, more pronounced in Salinas Grandes samples. Protective mechanism of PSII were activated by the UV-B treatment to a higher extent in samples from Salinas Grandes (NPQ 0.48) than in Los Gigantes samples (NPQ 0.26). We concluded that site-related characteristics, and in particular different UV-B radiation regimen, had a strong effect on resistance of the photosynthetic apparatus of P. austrosinense to UV-B radiation.
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6.
Understanding the Genetic Basis of C4 Kranz Anatomy with a View to Engineering C3 Crops.
Sedelnikova, OV, Hughes, TE, Langdale, JA
Annual review of genetics. 2018;:249-270
Abstract
One of the most remarkable examples of convergent evolution is the transition from C3 to C4 photosynthesis, an event that occurred on over 60 independent occasions. The evolution of C4 is particularly noteworthy because of the complexity of the developmental and metabolic changes that took place. In most cases, compartmentalized metabolic reactions were facilitated by the development of a distinct leaf anatomy known as Kranz. C4 Kranz anatomy differs from ancestral C3 anatomy with respect to vein spacing patterns across the leaf, cell-type specification around veins, and cell-specific organelle function. Here we review our current understanding of how Kranz anatomy evolved and how it develops, with a focus on studies that are dissecting the underlying genetic mechanisms. This research field has gained prominence in recent years because understanding the genetic regulation of Kranz may enable the C3-to-C4 transition to be engineered, an endeavor that would significantly enhance crop productivity.
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7.
Is vegetative area, photosynthesis, or grape C uploading involved in the climate change-related grape sugar/anthocyanin decoupling in Tempranillo?
Salazar-Parra, C, Aranjuelo, I, Pascual, I, Aguirreolea, J, Sánchez-Díaz, M, Irigoyen, JJ, Araus, JL, Morales, F
Photosynthesis research. 2018;(1):115-128
Abstract
Foreseen climate change is expected to impact on grape composition, both sugar and pigment content. We tested the hypothesis that interactions between main factors associated with climate change (elevated CO2, elevated temperature, and water deficit) decouple sugars and anthocyanins, and explored the possible involvement of vegetative area, photosynthesis, and grape C uploading on the decoupling. Tempranillo grapevine fruit-bearing cuttings were exposed to CO2 (700 vs. 400 ppm), temperature (ambient vs. + 4 °C), and irrigation levels (partial vs. full) in temperature-gradient greenhouses. In a search for mechanistic insights into the underlying processes, experiments 1 and 2 were designed to maximize photosynthesis and enlarge leaf area range among treatments, whereas plant growth was manipulated in order to deliberately down-regulate photosynthesis and control vegetative area in experiments 3 and 4. Towards this aim, treatments were applied either from fruit set to maturity with free vegetation and fully irrigated or at 5-8% of pot capacity (experiments 1 and 2), or from veraison to maturity with controlled vegetation and fully irrigated or at 40% of pot capacity (experiments 3 and 4). Modification of air 13C isotopic composition under elevated CO2 enabled the further characterization of whole C fixation period and C partitioning to grapes. Increases of the grape sugars-to-anthocyanins ratio were highly and positively correlated with photosynthesis and grape 13C labeling, but not with vegetative area. Evidence is presented for photosynthesis, from fruit set to veraison, and grape C uploading, from veraison to maturity, as key processes involved in the establishment and development, respectively, of the grape sugars to anthocyanins decoupling.
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8.
Metallic nanoparticles influence the structure and function of the photosynthetic apparatus in plants.
Tighe-Neira, R, Carmora, E, Recio, G, Nunes-Nesi, A, Reyes-Diaz, M, Alberdi, M, Rengel, Z, Inostroza-Blancheteau, C
Plant physiology and biochemistry : PPB. 2018;:408-417
Abstract
The applications of nanoparticles continue to expand into areas as diverse as medicine, bioremediation, cosmetics, pharmacology and various industries, including agri-food production. The widespread use of nanoparticles has generated concerns given the impact these nanoparticles - mostly metal-based such as CuO, Ag, Au, CeO2, TiO2, ZnO, Co, and Pt - could be having on plants. Some of the most studied variables are plant growth, development, production of biomass, and ultimately oxidative stress and photosynthesis. A systematic appraisal of information about the impact of nanoparticles on these processes is needed to enhance our understanding of the effects of metallic nanoparticles and oxides on the structure and function on the plant photosynthetic apparatus. Most nanoparticles studied, especially CuO and Ag, had a detrimental impact on the structure and function of the photosynthetic apparatus. Nanoparticles led to a decrease in concentration of photosynthetic pigments, especially chlorophyll, and disruption of grana and other malformations in chloroplasts. Regarding the functions of the photosynthetic apparatus, nanoparticles were associated with a decrease in the photosynthetic efficiency of photosystem II and decreased net photosynthesis. However, CeO2 and TiO2 nanoparticles may have a positive effect on photosynthetic efficiency, mainly due to an increase in electron flow between the photosystems II and I in the Hill reaction, as well as an increase in Rubisco activity in the Calvin and Benson cycle. Nevertheless, the underlying mechanisms are poorly understood. The future mechanistic work needs to be aimed at characterizing the enhancing effect of nanoparticles on the active generation of ATP and NADPH, carbon fixation and its incorporation into primary molecules such as photo-assimilates.
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9.
Reduced vacuolar β-1,3-glucan synthesis affects carbohydrate metabolism as well as plastid homeostasis and structure in Phaeodactylum tricornutum.
Huang, W, Haferkamp, I, Lepetit, B, Molchanova, M, Hou, S, Jeblick, W, Río Bártulos, C, Kroth, PG
Proceedings of the National Academy of Sciences of the United States of America. 2018;(18):4791-4796
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Abstract
The β-1,3-glucan chrysolaminarin is the main storage polysaccharide of diatoms. In contrast to plants and green algae, diatoms and most other algal groups do not accumulate storage polysaccharides in their plastids. The diatom Phaeodactylum tricornutum possesses only a single gene encoding a putative β-1,3-glucan synthase (PtBGS). Here, we characterize this enzyme by expressing GFP fusion proteins in P. tricornutum and by creating and investigating corresponding gene silencing mutants. We demonstrate that PtBGS is a vacuolar protein located in the tonoplast. Metabolite analyses of two mutant strains with reduced amounts of PtBGS reveal a reduction in their chrysolaminarin content and an increase of soluble sugars and lipids. This indicates that carbohydrates are shunted into alternative pathways when chrysolaminarin production is impaired. The mutant strains show reduced growth and lower photosynthetic capacities, while possessing higher photoprotective abilities than WT cells. Interestingly, a strong reduction in PtBGS expression also results in aberrations of the usually very regular thylakoid membrane patterns, including increased thylakoid thickness, reduced numbers of thylakoids per plastid, and increased numbers of lamellae per thylakoid stack. Our data demonstrate the complex intertwinement of carbohydrate storage in the vacuoles with carbohydrate metabolism, photosynthetic homeostasis, and plastid morphology.
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10.
Hormonal and environmental signals guiding stomatal development.
Qi, X, Torii, KU
BMC biology. 2018;(1):21
Abstract
Stomata are pores on plant epidermis that facilitate gas exchange and water evaporation between plants and the environment. Given the central role of stomata in photosynthesis and water-use efficiency, two vital events for plant growth, stomatal development is tightly controlled by a diverse range of signals. A family of peptide hormones regulates stomatal patterning and differentiation. In addition, plant hormones as well as numerous environmental cues influence the decision of whether to make stomata or not in distinct and complex manners. In this review, we summarize recent findings that reveal the mechanism of these three groups of signals in controlling stomatal formation, and discuss how these signals are integrated into the core stomatal development pathway.