Installation of C4 photosynthetic pathway enzymes in rice using a single construct

Introduction of a C4 photosynthetic mechanism into C3 crops offers an opportunity to improve photosynthetic efficiency, biomass and yield in addition to potentially improving nitrogen and water use efficiency. To create a two-cell metabolic prototype for an NADP-malic enzyme type C4 rice, we transformed Oryza sativa spp. japonica cultivar Kitaake with a single construct containing the coding regions of carbonic anhydrase, phosphoenolpyruvate (PEP) carboxylase, NADP-malate dehydrogenase, pyruvate orthophosphate dikinase and NADP-malic enzyme from Zea mays, driven by cell-preferential promoters. Gene expression, protein accumulation and enzyme activity were confirmed for all five transgenes, and intercellular localization of proteins was analysed. 13CO2 labelling demonstrated a 10-fold increase in flux though PEP carboxylase, exceeding the increase in measured in vitro enzyme activity, and estimated to be about 2% of the maize photosynthetic flux. Flux from malate via pyruvate to PEP remained low, commensurate with the low NADP-malic enzyme activity observed in the transgenic lines. Physiological perturbations were minor and RNA sequencing revealed no substantive effects of transgene expression on other endogenous rice transcripts associated with photosynthesis. These results provide promise that, with enhanced levels of the C4 proteins introduced thus far, a functional C4 pathway is achievable in rice.This work was funded by a C4 Rice Project grant from Bill & Melinda Gates Foundation to the University of Oxford (2015– 2019; OPP1129902), Max Planck Society (SA, HI, RF, MG, JEL, MS) and Australian Research Council (DP150101037 to ML, JEL, MS and CE140100015). Work in the SK laboratory was supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement number 637765; SK is a Royal Society University Research Fello

Glycine decarboxylase controls photosynthesis and plant growth

AbstractPhotorespiration makes oxygenic photosynthesis possible by scavenging 2-phosphoglycolate. Hence, compromising photorespiration impairs photosynthesis. We examined whether facilitating photorespiratory carbon flow in turn accelerates photosynthesis and found that overexpression of the H-protein of glycine decarboxylase indeed considerably enhanced net-photosynthesis and growth of Arabidopsis thaliana. At the molecular level, lower glycine levels confirmed elevated GDC activity in vivo, and lower levels of the CO2 acceptor ribulose 1,5-bisphosphate indicated higher drain from CO2 fixation. Thus, the photorespiratory enzyme glycine decarboxylase appears as an important feed-back signaller that contributes to the control of the Calvin–Benson cycle and hence carbon flow through both photosynthesis and photorespiration

Metabolic and Transcriptional Analysis of Durum Wheat Responses to Elevated CO2 at Low and High Nitrate Supply

31 páginas, 3 tablas, 5 figuras. -- This is a pre-copyedited, author-produced PDF of an article accepted for publication in Plant and Cell Physiology following peer review. The version of record [Vicente, R., Pérez, P., Martínez-Carrasco, R., Feil, R., Lunn, J. E., Watanabe, M., Arrivault, S., Stitt, M., Hoefgen, R. & Morcuende, R. (2016) Metabolic and Transcriptional Analysis of Durum Wheat Responses to Elevated CO2 at Low and High Nitrate Supply, Plant and Cell Physiology. 57, 2133-2146.] is available online at: http://pcp.oxfordjournals.org/content/57/10/2133.Elevated CO2 (eCO2) can lead to photosynthetic acclimation and this is often intensified by low N. Despite intensive studies of plant responses to eCO2, the regulation mechanism of primary metabolism at the whole plant level in interaction with NO3− supply remains unclear. We examined the metabolic and transcriptional responses triggered by eCO2 in association with physiological-biochemical traits in flag leaves and roots of durum wheat grown hydroponically in ambient and elevated [CO2] with low (LN) and high (HN) NO3− supply. Multivariate analysis revealed a strong interaction between eCO2 and NO3− supply. Photosynthetic acclimation induced by eCO2 in LN-plants was accompanied by an increase in biomass and carbohydrates, and decreases of leaf organic N per unit area, organic acids, inorganic ions, Calvin–Benson cycle intermediates, Rubisco, nitrate reductase activity, amino acids and transcripts for N metabolism, particularly in leaves, whereas NO3− uptake was unaffected. In HN-plants, eCO2 did not decrease photosynthetic capacity or leaf organic N per unit area, but induced transcripts for N metabolism, especially in roots. In conclusion, the photosynthetic acclimation in LN-plants was associated with an inhibition of leaf NO3− assimilation, whereas up-regulation of N metabolism in roots could have mitigated the acclimatory effect of eCO2 in HN-plants.This work was supported by the Spanish National R&D&I Plan of the Ministry of Economy and Competitiveness (grants AGL2009-11987, AGL2013-41363-R (FEDER), BES-2010-031029 to R.V.) and by the Max Planck Society.Peer reviewe

Leaf starch turnover occurs in long days and in falling light at the end of the day

We investigated whether starch degradation occurs at the same time as starch synthesis in Arabidopsis (Arabidopsis thaliana) leaves in the light. Starch accumulated in a linear fashion for about 12 h after dawn, then accumulation slowed and content plateaued. Following decreases in light intensity, the rate of accumulation of starch declined in proportion to the decline in photosynthesis if the decrease occurred 14 h after dawn and in response to decreases in light intensity that occurred >10 h after dawn. Starch measurements in circadian clock mutants suggested that the clock influences the timing of onset of degradation. We conclude that the propensity for leaf starch to be degraded increases with time after dawn. The importance of this phenomenon for efficient use of carbon for growth in long days and for prevention of starvation during twilight is discussed.This work was supported by the European Commission FP7 Collaborative Project TiMet (contract 245143 to O.F., V.M., and A.F.), by BBSRC Institute Strategic Programme Grant BB/J004561/1 to the John Innes Centre (O.F., A.M.S.), by the Max-Planck Society, Germany (H.I., D.S., S.A., R.F., J.E.L., M.S.), by ETH (Zurich), and by SystemsX (Switzerland) grant “Plant Growth in a Changing Environment” (G.M.G., S.C.Z.)

Tomato Fruit Photosynthesis Is Seemingly Unimportant in Primary Metabolism and Ripening But Plays a Considerable Role in Seed Development1[W][OA]

Fruit of tomato (Solanum lycopersicum), like those from many species, have been characterized to undergo a shift from partially photosynthetic to truly heterotrophic metabolism. While there is plentiful evidence for functional photosynthesis in young tomato fruit, the rates of carbon assimilation rarely exceed those of carbon dioxide release, raising the question of its role in this tissue. Here, we describe the generation and characterization of lines exhibiting a fruit-specific reduction in the expression of glutamate 1-semialdehyde aminotransferase (GSA). Despite the fact that these plants contained less GSA protein and lowered chlorophyll levels and photosynthetic activity, they were characterized by few other differences. Indeed, they displayed almost no differences in fruit size, weight, or ripening capacity and furthermore displayed few alterations in other primary or intermediary metabolites. Although GSA antisense lines were characterized by significant alterations in the expression of genes associated with photosynthesis, as well as with cell wall and amino acid metabolism, these changes were not manifested at the phenotypic level. One striking feature of the antisense plants was their seed phenotype: the transformants displayed a reduced seed set and altered morphology and metabolism at early stages of fruit development, although these differences did not affect the final seed number or fecundity. Taken together, these results suggest that fruit photosynthesis is, at least under ambient conditions, not necessary for fruit energy metabolism or development but is essential for properly timed seed development and therefore may confer an advantage under conditions of stress