Over-expressing the C(3) photosynthesis cycle enzyme Sedoheptulose-1-7 Bisphosphatase improves photosynthetic carbon gain and yield under fully open air CO(2) fumigation (FACE)

Deciphering the biological processes underlying tomato biomass production and composition

The huge amounts of biomass residues, remaining in the field after tomato fruits harvesting, can be utilized to produce bioenergy. A multiple level approach aimed to characterize two Solanum pennellii introgression lines (ILs), with contrasting phenotypes for plant architecture and biomass was carried out. The study of gene expression dynamics, microscopy cell traits and qualitative and quantitative cell wall chemical compounds variation enabled the discovery of key genes and cell processes involved biomass accumulation and composition. Enhanced biomass production observed in IL2-6 line is due to a more effective coordination of chloroplasts and mitochondria energy fluxes. Microscopy analysis revealed a higher number of cells and chloroplasts in leaf epidermis in the high biomass line whilst chemical measurements on the two lines pointed out striking differences in the cell wall composition and organization. Taken together, our findings shed light on the mechanisms underlying the tomato biomass production and processability.

Discovery of the canonical Calvin-Benson cycle

It has been 65 years since the Calvin-Benson cycle was first formulated. In this paper, the development of the concepts that are critical to the cycle is traced and the contributions of Calvin, Benson, and Bassham are discussed. Some simplified views often found in text books such as ascending paper chromatography and the use of the "lollipop" for short labeling are discussed and further details given. Key discoveries that underpinned elucidation of the cycle such as the importance of sedoheptulose phosphate and ribulose 1,5-bisphosphate are described. The interchange of ideas between other researchers working on what is now called the pentose phosphate pathway and the development of the ideas of Calvin and Benson are explored while the gluconeogenic aspects of the cycle are emphasized. Concerns raised about anomalies of label distribution in glucose are considered. Other carbon metabolism pathways associated with the Calvin-Benson cycle are also described. Finally, there is a section describing the rift between Calvin and Benson.

Synthetic biology approaches for improving photosynthesis

The phenomenal increase in agricultural yields that we have witnessed in the last century has slowed down as we approach the limits of selective breeding and optimization of cultivation techniques. To support the yield increase required to feed an ever-growing population, we will have to identify new ways to boost the efficiency with which plants convert light into biomass. This challenge could potentially be tackled using state-of-the-art synthetic biology techniques to rewrite plant carbon fixation. In this review, we use recent studies to discuss and demonstrate different approaches for enhancing carbon fixation, including engineering Rubisco for higher activity, specificity, and activation; changing the expression level of enzymes within the Calvin cycle to avoid kinetic bottlenecks; introducing carbon-concentrating mechanisms such as inorganic carbon transporters, carboxysomes, and C4 metabolism; and rewiring photorespiration towards more energetically efficient routes or pathways that do not release CO2. We conclude by noting the importance of prioritizing and combining different approaches towards continuous and sustainable increase of plant productivities.

Slower development of PSI activity limits photosynthesis during Euonymus japonicus leaf development

This study primarily explored the limiting factor for photosynthesis during the development of Euonymus japonicus leaves. The analysis of the chlorophyll fluorescence transient, pulse-modulated fluorescence, 820-nm reflection, and expression of core proteins for photosystems demonstrated that photosystem II (PSII) activity developed more rapidly than did photosystem I (PSI) activity. The slower development of the PSI activity restricted linear and cyclic electron transport and thus inhibited the production of ATP and NADPH, which inhibits the activation of Rubisco, resulting in low activity of carboxylation efficiency. The application of exogenous NADPH (50 μM) and ATP (100 μM) to leaves remarkably increased the P_n and CE in the youngest leaf but not in the fully expanded leaf, which indicated that an inadequate supply of the assimilatory power significantly inhibited CE and P_n. We concluded that the slower development of the PSI activity was one of the most important limiting factors for photosynthesis during the development of E. japonicus leaves.

Feeding the world: improving photosynthetic efficiency for sustainable crop production

A number of recent studies have provided strong support demonstrating that improving the photosynthetic processes through genetic engineering can provide an avenue to improve yield potential. The major focus of this review is on improvement of the Calvin-Benson cycle and electron transport. Consideration is also given to how altering regulatory process may provide an additional route to increase photosynthetic efficiency. Here we summarize some of the recent successes that have been observed through genetic manipulation of photosynthesis, showing that, in both the glasshouse and the field, yield can be increased by >40%. These results provide a clear demonstration of the potential for increasing yield through improvements in photosynthesis. In the final section, we consider the need to stack improvement in photosynthetic traits with traits that target the yield gap in order to provide robust germplasm for different crops across the globe.

Functional nanomaterials to augment photosynthesis: evidence and considerations for their responsible use in agricultural applications

At the current population growth rate, we will soon be unable to meet increasing food demands. As a consequence of this potential problem, considerable efforts have been made to enhance crop productivity by breeding, genetics and improving agricultural practices. While these techniques have traditionally been successful, their efficacy since the 'green revolution' has begun to significantly plateau. This stagnation of gains combined with the negative effects of climate change on crop yields has prompted researchers to develop novel and radical methods to increase crop productivity. Recent work has begun exploring the use of nanomaterials as synthetic probes to augment how plants use light. Photosynthesis in crops is often limited by their ability to absorb and exploit solar energy for photochemistry. The capacity to interact with and optimize how plants use light has the potential to increase the productivity of crops and enable the tailoring of crops for different environments and to compensate for predicted climate changes. Advances in the synthesis and surface modification of nanomaterials have overcome previous drawbacks and renewed their potential use as synthetic probes to enhance crop yields. Here, we review the current applications of functional nanomaterials in plants and will make an argument for the continued development of promising new nanomaterials and future applications in agriculture. This will highlight that functional nanomaterials have the clear potential to provide a much-needed route to enhanced future food security. In addition, we will discuss the often-ignored current evidence of nanoparticles present in the environment as well as inform and encourage caution on the regulation of nanomaterials in agriculture.

Systems models, phenomics and genomics: three pillars for developing high-yielding photosynthetically efficient crops

Recent years witnessed a stagnation in yield enhancement in major staple crops, which leads plant biologists and breeders to focus on an urgent challenge to dramatically increase crop yield to meet the growing food demand. Systems models have started to show their capacity in guiding crops improvement for greater biomass and grain yield production. Here we argue that systems models, phenomics and genomics combined are three pillars for the future breeding for high-yielding photosynthetically efficient crops (HYPEC). Briefly, systems models can be used to guide identification of breeding targets for a particular cultivar and define optimal physiological and architectural parameters for a particular crop to achieve high yield under defined environments. Phenomics can support collection of architectural, physiological, biochemical and molecular parameters in a high-throughput manner, which can be used to support both model validation and model parameterization. Genomic techniques can be used to accelerate crop breeding by enabling more efficient mapping between genotypic and phenotypic variation, and guide genome engineering or editing for model-designed traits. In this paper, we elaborate on these roles and how they can work synergistically to support future HYPEC breeding.

Knockout of SlSBPASE Suppresses Carbon Assimilation and Alters Nitrogen Metabolism in Tomato Plants

Sedoheptulose-1,7-bisphosphatase (SBPase) is an enzyme in the Calvin⁻Benson cycle and has been documented to be important in carbon assimilation, growth and stress tolerance in plants. However, information on the impact of SBPase on carbon assimilation and nitrogen metabolism in tomato plants (Solanum lycopersicum) is rather limited. In the present study, we investigated the role of SBPase in carbon assimilation and nitrogen metabolism in tomato plants by knocking out SBPase gene SlSBPASE using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) gene editing technology. Compared with wild-type plants, slsbpase mutant plants displayed severe growth retardation. Further analyses showed that knockout of SlSBPASE led to a substantial reduction in SBPase activity and as a consequence, ribulose-1,5-bisphosphate (RuBP) regeneration and carbon assimilation rate were dramatically inhibited in slsbpase mutant plants. It was further observed that much lower levels of sucrose and starch were accumulated in slsbpase mutant plants than their wild-type counterparts during the photoperiod. Intriguingly, mutation in SlSBPASE altered nitrogen metabolism as demonstrated by changes in levels of protein and amino acids and activities of nitrogen metabolic enzymes. Collectively, our data suggest that SlSBPASE is required for optimal growth, carbon assimilation and nitrogen metabolism in tomato plants.

Introgression of UfCyt c6, a thylakoid lumen protein from a green seaweed Ulva fasciata Delile enhanced photosynthesis and growth in tobacco

Cytochromes are important components of photosynthetic electron transport chain. Here we report on genetic transformation of Cytochrome c6 (UfCyt c6) gene from Ulva fasciata Delile in tobacco for enhanced photosynthesis and growth. UfCyt c6 cDNA had an open reading frame of 330 bp encoding a polypeptide of 109 amino acids with a predicted molecular mass of 11.65 kDa and an isoelectric point of 5.21. UfCyt c6 gene along with a tobacco petE transit peptide sequence under control of CaMV35S promoter was transformed in tobacco through Agrobacterium mediated genetic transformation. Transgenic tobacco grew normal and exhibited enhanced growth as compared to wild type (WT) and vector control (VC) tobacco. Transgenic tobacco had higher contents of photosynthetic pigments and better ratios of photosynthetic pigments. The tobacco expressing UfCyt c6 gene exhibited higher photosynthetic rate and improved water use efficiency. Further activity of the water-splitting complex, photosystem II quantum yield, photochemical quenching, electron transfer rate, and photosynthetic yield were found comparatively higher in transgenic tobacco as compared to WT and VC tobacco. Alternatively basal quantum yield of non-photochemical processes in PSII and non-photochemical quenching were estimated lower in tobacco expressing UfCyt c6 gene. As a result of improved photosynthetic performance the transgenic tobacco had higher contents of sugar and starch, and exhibited comparatively better growth. To the best of our knowledge this is the first report on expression of UfCyt c6 gene from U. fasciata for improved photosynthesis and growth in tobacco.

Introgression of UfCyt c6, a thylakoid lumen protein from a green seaweed Ulva fasciata Delile enhanced photosynthesis and growth in tobacco

Cytochromes are important components of photosynthetic electron transport chain. Here we report on genetic transformation of Cytochrome c₆ (UfCyt c₆) gene from Ulva fasciata Delile in tobacco for enhanced photosynthesis and growth. UfCyt c₆ cDNA had an open reading frame of 330 bp encoding a polypeptide of 109 amino acids with a predicted molecular mass of 11.65 kDa and an isoelectric point of 5.21. UfCyt c₆ gene along with a tobacco petE transit peptide sequence under control of CaMV35S promoter was transformed in tobacco through Agrobacterium mediated genetic transformation. Transgenic tobacco grew normal and exhibited enhanced growth as compared to wild type (WT) and vector control (VC) tobacco. Transgenic tobacco had higher contents of photosynthetic pigments and better ratios of photosynthetic pigments. The tobacco expressing UfCyt c₆ gene exhibited higher photosynthetic rate and improved water use efficiency. Further activity of the water-splitting complex, photosystem II quantum yield, photochemical quenching, electron transfer rate, and photosynthetic yield were found comparatively higher in transgenic tobacco as compared to WT and VC tobacco. Alternatively basal quantum yield of non-photochemical processes in PSII and non-photochemical quenching were estimated lower in tobacco expressing UfCyt c₆ gene. As a result of improved photosynthetic performance the transgenic tobacco had higher contents of sugar and starch, and exhibited comparatively better growth. To the best of our knowledge this is the first report on expression of UfCyt c₆ gene from U. fasciata for improved photosynthesis and growth in tobacco.

Chlorophyll fluorescence imaging reveals genetic variation and loci for a photosynthetic trait in diploid potato

Physiology and genetics are tightly interrelated. Understanding the genetic basis of a physiological trait such as the quantum yield of the photosystem II, or photosynthetic responses to environmental changes will benefit the understanding of these processes. By means of chlorophyll fluorescence (CF) imaging, the quantum yield of photosystem II can be determined rapidly, precisely and non-invasively. In this article, the genetic control and variation in the steady-state quantum yield of PSII (Φ_PSII ) is analyzed for diploid potato plants. Current progress in potato research and breeding is slow due to high levels of heterozygosity and complexity of tetraploid genetics. Diploid potatoes offer the possibility of overcoming this problem and advance research for one of the globally most important staple foods. With the help of a diploid genetic mapping population two genetic loci that were strongly associated with differences in Φ_PSII were identified. This is a proof of principle that genetic analysis for Φ_PSII can be done on potato. The effects of three different stress conditions that are important in potato cultivation were also tested: salt stress, low temperature and deficiency in the macronutrient phosphate. For the last two stresses, significant decreases in photosynthetic activity could be shown, revealing potential for stress detection with CF based tools. In general, our findings show the potential of high-throughput phenotyping for physiological research and breeding in potato.

Comparative proteomic analysis of key proteins during abscisic acid-hydrogen peroxide-induced adventitious rooting in cucumber (Cucumis sativus L.) under drought stress

Previous results have shown that hydrogen peroxide (H₂O₂) is involved in abscisic acid (ABA)-induced adventitious root development under drought stress. In this study, a comparative proteomic analysis was conducted to explore the key proteins during ABA-H₂O₂-induced adventitious rooting in cucumber (Cucumis sativus L.) under drought stress. The results revealed that 48 of 56 detected proteins spots were confidently matched to NCBI database entries. Among them, 10 protein spots were up-regulated while 4 protein spots were down-regulated under drought stress; 22 protein spots were up-regulated by ABA under drought stress; treatment with ABA plus H₂O₂ scavenger catalase (CAT) up-regulated 6 protein spots and down-regulated 6 protein spots under drought stress. The identified proteins were divided into three categories: biological process, molecular function, and cellular component. According to their functions, the 48 identified proteins were grouped into 10 categories, including photosynthesis, stress response, protein folding, modification, and degradation, etc. According to subcellular localization, about 24 proteins (half of the total) were predicted to be localized in chloroplasts. ABA significantly up-regulated the expression of photosynthesis-related proteins (SBPase, OEE1), stress-defense-related proteins (2-Cys-Prx, HBP2), and folding-, modification-, and degradation-related proteins (TPal) under drought stress. However, the effects of ABA were inhibited by CAT. The proteins were further analyzed at the transcription level, and the expression of four of five genes (except 2-Cys-Prx) was in accordance with the corresponding protein expression. The protein abundance changes of OEE1 and SBPase were also supported by western blot analysis. Therefore, H₂O₂ may be involved in ABA-induced adventitious root development under drought stress by regulating photosynthesis-related proteins, stress defense-related proteins, and folding-, modification-, and degradation-related proteins.

Photosynthetic and Stress Responsive Proteins Are Altered More Effectively in Nicotiana benthamiana Infected with Plum pox virus Aggressive PPV-CR versus Mild PPV-C Cherry-Adapted Isolates

Plum pox virus (PPV, family Potyviridae) is one of the most important viral pathogens of Prunus spp. causing considerable damage to stone-fruit industry worldwide. Among the PPV strains identified so far, only PPV-C, PPV-CR, and PPV-CV are able to infect cherries under natural conditions. Herein, we evaluated the pathogenic potential of two viral isolates in herbaceous host Nicotiana benthamiana. Significantly higher accumulation of PPV capsid protein in tobacco leaves infected with PPV-CR (RU-30sc isolate) was detected in contrast to PPV-C (BY-101 isolate). This result correlated well with the symptoms observed in the infected plants. To further explore the host response upon viral infection at the molecular level, a comprehensive proteomic profiling was performed. Using reverse-phase ultra-high-performance liquid chromatography followed by label-free mass spectrometry quantification, we identified 38 unique plant proteins as significantly altered due to the infection. Notably, the abundances of photosynthesis-related proteins, mainly from the Calvin-Benson cycle, were found more aggressively affected in plants infected with PPV-CR isolate than those of PPV-C. This observation was accompanied by a significant reduction in the amount of photosynthetic pigments extracted from the leaves of PPV-CR infected plants. Shifts in the abundance of proteins that are involved in stimulation of photosynthetic capacity, modification of amino acid, and carbohydrate metabolism may affect plant growth and initiate energy formation via gluconeogenesis in PPV infected N. benthamiana. Furthermore, we suggest that the higher accumulation of H2O2 in PPV-CR infected leaves plays a crucial role in plant defense and development by activating the glutathione synthesis.

Molecular improvement of alfalfa for enhanced productivity and adaptability in a changing environment

Due to an expanding world population and increased buying power, the demand for ruminant products such as meat and milk is expected to grow substantially in coming years, and high levels of forage crop production will therefore be a necessity. Unfortunately, urbanization of agricultural land, intensive agricultural practices, and climate change are all predicted to limit crop production in the future, which means that the development of forage cultivars with improved productivity and adaptability will be essential. Because alfalfa (Medicago sativa L.) is one of the most widely cultivated perennial forage crops, it has been the target of much research in this field. In this review, we discuss progress that has been made towards the improvement of productivity, abiotic stress tolerance, and nutrient-use efficiency, as well as disease and pest resistance, in alfalfa using biotechnological techniques. Furthermore, we consider possible future priorities and avenues for attaining further enhancements in this crop as a means of contributing to the realization of food security in a changing environment.

Daring metabolic designs for enhanced plant carbon fixation

Increasing agricultural productivity is one of the major challenges our society faces. While multiple strategies to enhance plant carbon fixation have been suggested, and partially implemented, most of them are restricted to relatively simple modifications of endogenous metabolism, i.e., "low hanging fruit". Here, I portray the next generation of metabolic solutions to increase carbon fixation rate and yield. These strategies involve major rewiring of central metabolism, including dividing Rubisco's catalysis between several enzymes, replacing Rubisco with a different carboxylation reaction, substituting the Calvin Cycle with alternative carbon fixation pathways, and engineering photorespiration bypass routes that do not release carbon. While the barriers for implementing these elaborated metabolic architectures are quite significant, if we truly want to revolutionize carbon fixation, only daring engineering efforts will lead the way.

Overexpression of bifunctional fructose-1,6-bisphosphatase/sedoheptulose-1,7-bisphosphatase leads to enhanced photosynthesis and global reprogramming of carbon metabolism in Synechococcus sp. PCC 7002

Cyanobacteria fix atmospheric CO₂ to biomass and through metabolic engineering can also act as photosynthetic factories for sustainable productions of fuels and chemicals. The Calvin Benson cycle is the primary pathway for CO₂ fixation in cyanobacteria, algae and C₃ plants. Previous studies have overexpressed the Calvin Benson cycle enzymes, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and bifunctional sedoheptulose-1,7-bisphosphatase/fructose-1,6-bisphosphatase (hereafter BiBPase), in both plants and algae, although their impacts on cyanobacteria have not yet been rigorously studied. Here, we show that overexpression of BiBPase and RuBisCO have distinct impacts on carbon metabolism in the cyanobacterium Synechococcus sp. PCC 7002 through physiological, biochemical, and proteomic analyses. The former enhanced growth, cell size, and photosynthetic O₂ evolution, and coordinately upregulated enzymes in the Calvin Benson cycle including RuBisCO and fructose-1,6-bisphosphate aldolase. At the same time it downregulated enzymes in respiratory carbon metabolism (glycolysis and the oxidative pentose phosphate pathway) including glucose-6-phosphate dehydrogenase (G6PDH). The content of glycogen was also significantly reduced while the soluble carbohydrate content increased. These results indicate that overexpression of BiBPase leads to global reprogramming of carbon metabolism in Synechococcus sp. PCC 7002, promoting photosynthetic carbon fixation and carbon partitioning towards non-storage carbohydrates. In contrast, whilst overexpression of RuBisCO had no measurable impact on growth and photosynthetic O₂ evolution, it led to coordinated increase in the abundance of proteins involved in pyruvate metabolism and fatty acid biosynthesis. Our results underpin that singular genetic modifications in the Calvin Benson cycle can have far broader cellular impact than previously expected. These features could be exploited to more efficiently direct carbons towards desired bioproducts.

Prescreening in large populations as a tool for identifying elevated CO2-responsive genotypes in plants

Elevated atmospheric CO2 concentration (e[CO2]) can stimulate the photosynthesis and productivity of C3 species including food and forest crops. Intraspecific variation in responsiveness to e[CO2] can be exploited to increase productivity under e[CO2]. However, active selection of genotypes to increase productivity under e[CO2] is rarely performed across a wide range of germplasm, because of constraints of space and the cost of CO2 fumigation facilities. If we are to capitalise on recent advances in whole genome sequencing, approaches are required to help overcome these issues of space and cost. Here, we discuss the advantage of applying prescreening as a tool in large genome×e[CO2] experiments, where a surrogate for e[CO2] was used to select cultivars for more detailed analysis under e[CO2] conditions. We discuss why phenotypic prescreening in population-wide screening for e[CO2] responsiveness is necessary, what approaches could be used for prescreening for e[CO2] responsiveness, and how the data can be used to improve genetic selection of high-performing cultivars. We do this within the framework of understanding the strengths and limitations of genotype-phenotype mapping.

Are GM Crops for Yield and Resilience Possible?

Crop yield improvements need to accelerate to avoid future food insecurity. Outside Europe, genetically modified (GM) crops for herbicide- and insect-resistance have been transformative in agriculture; other traits have also come to market. However, GM of yield potential and stress resilience has yet to impact on food security. Genes have been identified for yield such as grain number, size, leaf growth, resource allocation, and signaling for drought tolerance, but there is only one commercialized drought-tolerant GM variety. For GM and genome editing to impact on yield and resilience there is a need to understand yield-determining processes in a cell and developmental context combined with evaluation in the grower environment. We highlight a sugar signaling mechanism as a paradigm for this approach.

The impact of modifying photosystem antenna size on canopy photosynthetic efficiency-Development of a new canopy photosynthesis model scaling from metabolism to canopy level processes

Canopy photosynthesis (Ac ) describes photosynthesis of an entire crop field and the daily and seasonal integrals of Ac positively correlate with daily and seasonal biomass production. Much effort in crop breeding has focused on improving canopy architecture and hence light distribution inside the canopy. Here, we develop a new integrated canopy photosynthesis model including canopy architecture, a ray tracing algorithm, and C3 photosynthetic metabolism to explore the option of manipulating leaf chlorophyll concentration ([Chl]) for greater Ac and nitrogen use efficiency (NUE). Model simulation results show that (a) efficiency of photosystem II increased when [Chl] was decreased by decreasing antenna size and (b) the light received by leaves at the bottom layers increased when [Chl] throughout the canopy was decreased. Furthermore, the modelling revealed a modest ~3% increase in Ac and an ~14% in NUE was accompanied when [Chl] reduced by 60%. However, if the leaf nitrogen conserved by this decrease in leaf [Chl] were to be optimally allocated to other components of photosynthesis, both Ac and NUE can be increased by over 30%. Optimizing [Chl] coupled with strategic reinvestment of conserved nitrogen is shown to have the potential to support substantial increases in Ac , biomass production, and crop yields.

Engineering photosynthesis: progress and perspectives

Photosynthesis is the basis of primary productivity on the planet. Crop breeding has sustained steady improvements in yield to keep pace with population growth increases. Yet these advances have not resulted from improving the photosynthetic process per se but rather of altering the way carbon is partitioned within the plant. Mounting evidence suggests that the rate at which crop yields can be boosted by traditional plant breeding approaches is wavering, and they may reach a “yield ceiling” in the foreseeable future. Further increases in yield will likely depend on the targeted manipulation of plant metabolism. Improving photosynthesis poses one such route, with simulations indicating it could have a significant transformative influence on enhancing crop productivity. Here, we summarize recent advances of alternative approaches for the manipulation and enhancement of photosynthesis and their possible application for crop improvement.

Increased SBPase activity improves photosynthesis and grain yield in wheat grown in greenhouse conditions

To meet the growing demand for food, substantial improvements in yields are needed. This is particularly the case for wheat, where global yield has stagnated in recent years. Increasing photosynthesis has been identified as a primary target to achieve yield improvements. To increase leaf photosynthesis in wheat, the level of the Calvin-Benson cycle enzyme sedoheptulose-1,7-biphosphatase (SBPase) has been increased through transformation and expression of a Brachypodium distachyon SBPase gene construct. Transgenic lines with increased SBPase protein levels and activity were grown under greenhouse conditions and showed enhanced leaf photosynthesis and increased total biomass and dry seed yield. This showed the potential of improving yield potential by increasing leaf photosynthesis in a crop species such as wheat. The results are discussed with regard to future strategies for further improvement of photosynthesis in wheat.This article is part of the themed issue 'Enhancing photosynthesis in crop plants: targets for improvement'.

Metabolic Pathways Involved in Carbon Dioxide Enhanced Heat Tolerance in Bermudagrass

Global climate changes involve elevated temperature and CO2 concentration, imposing significant impact on plant growth of various plant species. Elevated temperature exacerbates heat damages, but elevated CO2 has positive effects on promoting plant growth and heat tolerance. The objective of this study was to identify metabolic pathways affected by elevated CO2 conferring the improvement of heat tolerance in a C4 perennial grass species, bermudagrass (Cynodon dactylon Pers.). Plants were planted under either ambient CO2 concentration (400 μmol⋅mol-1) or elevated CO2 concentration (800 μmol⋅mol-1) and subjected to ambient temperature (30/25°C, day/night) or heat stress (45/40°C, day/night). Elevated CO2 concentration suppressed heat-induced damages and improved heat tolerance in bermudagrass. The enhanced heat tolerance under elevated CO2 was attributed to some important metabolic pathways during which proteins and metabolites were up-regulated, including light reaction (ATP synthase subunit and photosystem I reaction center subunit) and carbon fixation [(glyceraldehyde-3-phosphate dehydrogenase, GAPDH), fructose-bisphosphate aldolase, phosphoglycerate kinase, sedoheptulose-1,7-bisphosphatase and sugars) of photosynthesis, glycolysis (GAPDH, glucose, fructose, and galactose) and TCA cycle (pyruvic acid, malic acid and malate dehydrogenase) of respiration, amino acid metabolism (aspartic acid, methionine, threonine, isoleucine, lysine, valine, alanine, and isoleucine) as well as the GABA shunt (GABA, glutamic acid, alanine, proline and 5-oxoproline). The up-regulation of those metabolic processes by elevated CO2 could at least partially contribute to the improvement of heat tolerance in perennial grass species.

Enhanced photosynthetic capacity increases nitrogen metabolism through the coordinated regulation of carbon and nitrogen assimilation in Arabidopsis thaliana

Plant growth and productivity depend on interactions between the metabolism of carbon and nitrogen. The sensing ability of internal carbon and nitrogen metabolites (the C/N balance) enables plants to regulate metabolism and development. In order to investigate the effects of an enhanced photosynthetic capacity on the metabolism of carbon and nitrogen in photosynthetically active tissus (source leaves), we herein generated transgenic Arabidopsis thaliana plants (ApFS) that expressed cyanobacterial fructose-1,6-/sedoheptulose-1,7-bisphosphatase in their chloroplasts. The phenotype of ApFS plants was indistinguishable from that of wild-type plants at the immature stage. However, as plants matured, the growth of ApFS plants was superior to that of wild-type plants. Starch levels were higher in ApFS plants than in wild-type plants at 2 and 5 weeks. Sucrose levels were also higher in ApFS plants than in wild-type plants, but only at 5 weeks. On the other hand, the contents of various free amino acids were lower in ApFS plants than in wild-type plants at 2 weeks, but were similar at 5 weeks. The total C/N ratio was the same in ApFS plants and wild-type plants, whereas nitrite levels increased in parallel with elevations in nitrate reductase activity at 5 weeks in ApFS plants. These results suggest that increases in the contents of photosynthetic intermediates at the early growth stage caused a temporary imbalance in the free-C/free-N ratio and, thus, the feedback inhibition of the expression of genes involved in the Calvin cycle and induction of the expression of those involved in nitrogen metabolism due to supply deficient free amino acids for maintenance of the C/N balance in source leaves of ApFS plants.

Overexpression of the RieskeFeS Protein Increases Electron Transport Rates and Biomass Yield

In this study, we generated transgenic Arabidopsis (Arabidopsis thaliana) plants overexpressing the Rieske FeS protein (PetC), a component of the cytochrome b₆f (cyt b₆f) complex. Increasing the levels of this protein resulted in concomitant increases in the levels of cyt f (PetA) and cyt b₆ (PetB), core proteins of the cyt b₆f complex. Interestingly, an increase in the levels of proteins in both the photosystem I (PSI) and PSII complexes also was seen in the Rieske FeS overexpression plants. Although the mechanisms leading to these changes remain to be identified, the transgenic plants presented here provide novel tools to explore this. Importantly, overexpression of the Rieske FeS protein resulted in substantial and significant impacts on the quantum efficiency of PSI and PSII, electron transport, biomass, and seed yield in Arabidopsis plants. These results demonstrate the potential for manipulating electron transport processes to increase crop productivity.

Overexpression of the RieskeFeS Protein Increases Electron Transport Rates and Biomass Yield

In this study, we generated transgenic Arabidopsis (Arabidopsis thaliana) plants overexpressing the Rieske FeS protein (PetC), a component of the cytochrome b6f (cyt b6f) complex. Increasing the levels of this protein resulted in concomitant increases in the levels of cyt f (PetA) and cyt b6 (PetB), core proteins of the cyt b6f complex. Interestingly, an increase in the levels of proteins in both the photosystem I (PSI) and PSII complexes also was seen in the Rieske FeS overexpression plants. Although the mechanisms leading to these changes remain to be identified, the transgenic plants presented here provide novel tools to explore this. Importantly, overexpression of the Rieske FeS protein resulted in substantial and significant impacts on the quantum efficiency of PSI and PSII, electron transport, biomass, and seed yield in Arabidopsis plants. These results demonstrate the potential for manipulating electron transport processes to increase crop productivity.

Leaf Photosynthetic Parameters Related to Biomass Accumulation in a Global Rice Diversity Survey

Mining natural variations is a major approach to identify new options to improve crop light use efficiency. So far, successes in identifying photosynthetic parameters positively related to crop biomass accumulation through this approach are scarce, possibly due to the earlier emphasis on properties related to leaf instead of canopy photosynthetic efficiency. This study aims to uncover rice (Oryza sativa) natural variations to identify leaf physiological parameters that are highly correlated with biomass accumulation, a surrogate of canopy photosynthesis. To do this, we systematically investigated 14 photosynthetic parameters and four morphological traits in a rice population, which consists of 204 U.S. Department of Agriculture-curated minicore accessions collected globally and 11 elite Chinese rice cultivars in both Beijing and Shanghai. To identify key components responsible for the variance of biomass accumulation, we applied a stepwise feature-selection approach based on linear regression models. Although there are large variations in photosynthetic parameters measured in different environments, we observed that photosynthetic rate under low light (Alow) was highly related to biomass accumulation and also exhibited high genomic inheritability in both environments, suggesting its great potential to be used as a target for future rice breeding programs. Large variations in Alow among modern rice cultivars further suggest the great potential of using this parameter in contemporary rice breeding for the improvement of biomass and, hence, yield potential.

Increasing crop yield and resilience with trehalose 6-phosphate: targeting a feast-famine mechanism in cereals for better source-sink optimization

Food security is a pressing global issue. New approaches are required to break through a yield ceiling that has developed in recent years for the major crops. As important as increasing yield potential is the protection of yield from abiotic stresses in an increasingly variable and unpredictable climate. Current strategies to improve yield include conventional breeding, marker-assisted breeding, quantitative trait loci (QTLs), mutagenesis, creation of hybrids, genetic modification (GM), emerging genome-editing technologies, and chemical approaches. A regulatory mechanism amenable to three of these approaches has great promise for large yield improvements. Trehalose 6-phosphate (T6P) synthesized in the low-flux trehalose biosynthetic pathway signals the availability of sucrose in plant cells as part of a whole-plant sucrose homeostatic mechanism. Modifying T6P content by GM, marker-assisted selection, and novel chemistry has improved yield in three major cereals under a range of water availabilities from severe drought through to flooding. Yield improvements have been achieved by altering carbon allocation and how carbon is used. Targeting T6P both temporally and spatially offers great promise for large yield improvements in productive (up to 20%) and marginal environments (up to 120%). This opinion paper highlights this important breakthrough in fundamental science for crop improvement.

Simultaneous stimulation of sedoheptulose 1,7-bisphosphatase, fructose 1,6-bisphophate aldolase and the photorespiratory glycine decarboxylase-H protein increases CO2 assimilation, vegetative biomass and seed yield in Arabidopsis

In this article, we have altered the levels of three different enzymes involved in the Calvin-Benson cycle and photorespiratory pathway. We have generated transgenic Arabidopsis plants with altered combinations of sedoheptulose 1,7-bisphosphatase (SBPase), fructose 1,6-bisphophate aldolase (FBPA) and the glycine decarboxylase-H protein (GDC-H) gene identified as targets to improve photosynthesis based on previous studies. Here, we show that increasing the levels of the three corresponding proteins, either independently or in combination, significantly increases the quantum efficiency of PSII. Furthermore, photosynthetic measurements demonstrated an increase in the maximum efficiency of CO₂ fixation in lines over-expressing SBPase and FBPA. Moreover, the co-expression of GDC-H with SBPase and FBPA resulted in a cumulative positive impact on leaf area and biomass. Finally, further analysis of transgenic lines revealed a cumulative increase of seed yield in SFH lines grown in high light. These results demonstrate the potential of multigene stacking for improving the productivity of food and energy crops.

Real-time iTRAQ-based proteome profiling revealed the central metabolism involved in nitrogen starvation induced lipid accumulation in microalgae

To understand the post-transcriptional molecular mechanisms attributing to oleaginousness in microalgae challenged with nitrogen starvation (N-starvation), the longitudinal proteome dynamics of Chlorella sp. FC2 IITG was investigated using multipronged quantitative proteomics and multiple reaction monitoring assays. Physiological data suggested a remarkably enhanced lipid accumulation with concomitant reduction in carbon flux towards carbohydrate, protein and chlorophyll biosynthesis. The proteomics-based investigations identified the down-regulation of enzymes involved in chlorophyll biosynthesis (porphobilinogen deaminase) and photosynthetic carbon fixation (sedoheptulose-1,7 bisphosphate and phosphoribulokinase). Profound up-regulation of hydroxyacyl-ACP dehydrogenase and enoyl-ACP reductase ascertained lipid accumulation. The carbon skeletons to be integrated into lipid precursors were regenerated by glycolysis, β-oxidation and TCA cycle. The enhanced expression of glycolysis and pentose phosphate pathway enzymes indicates heightened energy needs of FC2 cells for the sustenance of N-starvation. FC2 cells strategically reserved nitrogen by incorporating it into the TCA-cycle intermediates to form amino acids; particularly the enzymes involved in the biosynthesis of glutamate, aspartate and arginine were up-regulated. Regulation of arginine, superoxide dismutase, thioredoxin-peroxiredoxin, lipocalin, serine-hydroxymethyltransferase, cysteine synthase, and octanoyltransferase play a critical role in maintaining cellular homeostasis during N-starvation. These findings may provide a rationale for genetic engineering of microalgae, which may enable synchronized biomass and lipid synthesis.

Importance of Fluctuations in Light on Plant Photosynthetic Acclimation

The acclimation of plants to light has been studied extensively, yet little is known about the effect of dynamic fluctuations in light on plant phenotype and acclimatory responses. We mimicked natural fluctuations in light over a diurnal period to examine the effect on the photosynthetic processes and growth of Arabidopsis (Arabidopsis thaliana). High and low light intensities, delivered via a realistic dynamic fluctuating or square wave pattern, were used to grow and assess plants. Plants subjected to square wave light had thicker leaves and greater photosynthetic capacity compared with fluctuating light-grown plants. This, together with elevated levels of proteins associated with electron transport, indicates greater investment in leaf structural components and photosynthetic processes. In contrast, plants grown under fluctuating light had thinner leaves, lower leaf light absorption, but maintained similar photosynthetic rates per unit leaf area to square wave-grown plants. Despite high light use efficiency, plants grown under fluctuating light had a slow growth rate early in development, likely due to the fact that plants grown under fluctuating conditions were not able to fully utilize the light energy absorbed for carbon fixation. Diurnal leaf-level measurements revealed a negative feedback control of photosynthesis, resulting in a decrease in total diurnal carbon assimilated of at least 20%. These findings highlight that growing plants under square wave growth conditions ultimately fails to predict plant performance under realistic light regimes and stress the importance of considering fluctuations in incident light in future experiments that aim to infer plant productivity under natural conditions in the field.

Rooting for cassava: insights into photosynthesis and associated physiology as a route to improve yield potential

Contents 50 I. 50 II. 52 III. 54 IV. 55 V. 57 VI. 57 VII. 59 60 References 61 SUMMARY: As a consequence of an increase in world population, food demand is expected to grow by up to 110% in the next 30-35 yr. The population of sub-Saharan Africa is projected to increase by > 120%. In this region, cassava (Manihot esculenta) is the second most important source of calories and contributes c. 30% of the daily calorie requirements per person. Despite its importance, the average yield of cassava in Africa has not increased significantly since 1961. An evaluation of modern cultivars of cassava showed that the interception efficiency (ɛ_i ) of photosynthetically active radiation (PAR) and the efficiency of conversion of that intercepted PAR (ɛ_c ) are major opportunities for genetic improvement of the yield potential. This review examines what is known of the physiological processes underlying productivity in cassava and seeks to provide some strategies and directions toward yield improvement through genetic alterations to physiology to increase ɛ_i and ɛ_c . Possible physiological limitations, as well as environmental constraints, are discussed.

The Role of Sink Strength and Nitrogen Availability in the Down-Regulation of Photosynthetic Capacity in Field-Grown Nicotiana tabacum L. at Elevated CO2 Concentration

Down-regulation of photosynthesis is among the most common responses observed in C₃ plants grown under elevated atmospheric CO₂ concentration ([CO₂]). Down-regulation is often attributed to an insufficient capacity of sink organs to use or store the increased carbohydrate production that results from the stimulation of photosynthesis by elevated [CO₂]. Down-regulation can be accentuated by inadequate nitrogen (N) supply, which may limit sink development. While there is strong evidence for down-regulation of photosynthesis at elevated [CO₂] in enclosure studies most often involving potted plants, there is little evidence for this when [CO₂] is elevated fully under open-air field treatment conditions. To assess the importance of sink strength on the down-regulation of photosynthesis and on the potential of N to mitigate this down-regulation under agriculturally relevant field conditions, two tobacco cultivars (Nicotiana tabacum L. cv. Petit Havana; cv. Mammoth) of strongly contrasting ability to produce the major sink of this crop, leaves, were grown under ambient and elevated [CO₂] and with two different N additions in a free air [CO₂] (FACE) facility. Photosynthetic down-regulation at elevated [CO₂] reached only 9% in cv. Mammoth late in the season likely reflecting sustained sink strength of the rapidly growing plant whereas down-regulation in cv. Petit Havana reached 25%. Increased N supply partially mitigated down-regulation of photosynthesis in cv. Petit Havana and this mitigation was dependent on plant developmental stage. Overall, these field results were consistent with the hypothesis that sustained sink strength, that is the ability to utilize photosynthate, and adequate N supply will allow C₃ crops in the field to maintain enhanced photosynthesis and therefore productivity as [CO₂] continues to rise.

Expression of cyanobacterial FBP/SBPase in soybean prevents yield depression under future climate conditions

Predictions suggest that current crop production needs to double by 2050 to meet global food and energy demands. Based on theory and experimental studies, overexpression of the photosynthetic enzyme sedoheptulose-1,7-bisphosphatase (SBPase) is expected to enhance C3 crop photosynthesis and yields. Here we test how expression of the cyanobacterial, bifunctional fructose-1,6/sedoheptulose-1,7-bisphosphatase (FBP/SBPase) affects carbon assimilation and seed yield (SY) in a major crop (soybean, Glycine max). For three growing seasons, wild-type (WT) and FBP/SBPase-expressing (FS) plants were grown in the field under ambient (400 μmol mol−1) and elevated (600 μmol mol−1) CO2 concentrations [CO2] and under ambient and elevated temperatures (+2.7 °C during daytime, +3.4 °C at night) at the SoyFACE research site. Across treatments, FS plants had significantly higher carbon assimilation (4–14%), Vc,max (5–8%), and Jmax (4–8%). Under ambient [CO2], elevated temperature led to significant reductions of SY of both genotypes by 19–31%. However, under elevated [CO2] and elevated temperature, FS plants maintained SY levels, while the WT showed significant reductions between 11% and 22% compared with plants under elevated [CO2] alone. These results show that the manipulation of the photosynthetic carbon reduction cycle can mitigate the effects of future high CO2 and high temperature environments on soybean yield.

One crop breeding cycle from starvation? How engineering crop photosynthesis for rising CO2 and temperature could be one important route to alleviation

Global climate change is likely to severely impact human food production. This comes at a time when predicted demand for primary foodstuffs by a growing human population and changing global diets is already outpacing a stagnating annual rate of increase in crop productivity. Additionally, the time required by crop breeding and bioengineering to release improved varieties to farmers is substantial, meaning that any crop improvements needed to mitigate food shortages in the 2040s would need to start now. In this perspective, the rationale for improvements in photosynthetic efficiency as a breeding objective for higher yields is outlined. Subsequently, using simple simulation models it is shown how predicted changes in temperature and atmospheric [CO2] affect leaf photosynthetic rates. The chloroplast accounts for the majority of leaf nitrogen in crops. Within the chloroplast about 25% of nitrogen is invested in the carboxylase, Rubisco, which catalyses the first step of CO2 assimilation. Most of the remaining nitrogen is invested in the apparatus to drive carbohydrate synthesis and regenerate ribulose-1:5-bisphosphate (RuBP), the CO2-acceptor molecule at Rubisco. At preindustrial [CO2], investment in these two aspects may have been balanced resulting in co-limitation. At today's [CO2], there appears to be over-investment in Rubisco, and despite the counter-active effects of rising temperature and [CO2], this imbalance is predicted to worsen with global climate change. By breeding or engineering restored optimality under future conditions increased productivity could be achieved in both tropical and temperate environments without additional nitrogen fertilizer. Given the magnitude of the potential shortfall, better storage conditions, improved crop management and better crop varieties will all be needed. With the short time-scale at which food demand is expected to outpace supplies, all available technologies to improve crop varieties, from classical crop breeding to crop genetic engineering should be employed. This will require vastly increased public and private investment to support translation of first discovery in laboratories to replicated field trials, and an urgent re-evaluation of regulation of crop genetic engineering.

Synthetic biology for CO2 fixation

Recycling of carbon dioxide (CO₂) into fuels and chemicals is a potential approach to reduce CO₂ emission and fossil-fuel consumption. Autotrophic microbes can utilize energy from light, hydrogen, or sulfur to assimilate atmospheric CO₂ into organic compounds at ambient temperature and pressure. This provides a feasible way for biological production of fuels and chemicals from CO₂ under normal conditions. Recently great progress has been made in this research area, and dozens of CO₂-derived fuels and chemicals have been reported to be synthesized by autotrophic microbes. This is accompanied by investigations into natural CO₂-fixation pathways and the rapid development of new technologies in synthetic biology. This review first summarizes the six natural CO₂-fixation pathways reported to date, followed by an overview of recent progress in the design and engineering of CO₂-fixation pathways as well as energy supply patterns using the concept and tools of synthetic biology. Finally, we will discuss future prospects in biological fixation of CO₂.

Changes in SBPase activity influence photosynthetic capacity, growth, and tolerance to chilling stress in transgenic tomato plants

Sedoheptulose-1, 7-bisphosphatase (SBPase) is an important enzyme involved in photosynthetic carbon fixation in the Calvin cycle. Here, we report the impact of changes in SBPase activity on photosynthesis, growth and development, and chilling tolerance in SBPase antisense and sense transgenic tomato (Solanum lycopersicum) plants. In transgenic plants with increased SBPase activity, photosynthetic rates were increased and in parallel an increase in sucrose and starch accumulation was evident. Total biomass and leaf area were increased in SBPase sense plants, while they were reduced in SBPase antisense plants compared with equivalent wild-type tomato plants. Under chilling stress, when compared with plants with decreased SBPase activity, tomato plants with increased SBPase activity were found to be more chilling tolerant as indicated by reduced electrolyte leakage, increased photosynthetic capacity, and elevated RuBP regeneration rate and quantum efficiency of photosystem II. Collectively, our data suggest that higher level of SBPase activity gives an advantage to photosynthesis, growth and chilling tolerance in tomato plants. This work also provides a case study that an individual enzyme in the Calvin cycle may serve as a useful target for genetic engineering to improve production and stress tolerance in crops.

Comparative Proteomics of Leaves from Phytase-Transgenic Maize and Its Non-transgenic Isogenic Variety

To investigate unintended effects in genetically modified crops (GMCs), a comparative proteomic analysis between the leaves of the phytase-transgenic maize and the non-transgenic plants was performed using two-dimensional gel electrophoresis and mass spectrometry. A total of 57 differentially expressed proteins (DEPs) were successfully identified, which represents 44 unique proteins. Functional classification of the identified proteins showed that these DEPs were predominantly involved in carbohydrate transport and metabolism category, followed by post-translational modification. KEGG pathway analysis revealed that most of the DEPs participated in carbon fixation in photosynthesis. Among them, 15 proteins were found to show protein-protein interactions with each other, and these proteins were mainly participated in glycolysis and carbon fixation. Comparison of the changes in the protein and tanscript levels of the identified proteins showed that most proteins had a similar pattern of changes between proteins and transcripts. Our results suggested that although some significant differences were observed, the proteomic patterns were not substantially different between the leaves of the phytase-transgenic maize and the non-transgenic isogenic type. Moreover, none of the DEPs was identified as a new toxic protein or an allergenic protein. The differences between the leaf proteome might be attributed to both genetic modification and hybrid influence.

The glucose 6-phosphate shunt around the Calvin-Benson cycle

It is just over 60 years since a cycle for the regeneration of the CO2-acceptor used in photosynthesis was proposed. In this opinion paper, we revisit the origins of the Calvin-Benson cycle that occurred at the time that the hexose monophosphate shunt, now called the pentose phosphate pathway, was being worked out. Eventually the pentose phosphate pathway was separated into two branches, an oxidative branch and a non-oxidative branch. It is generally thought that the Calvin-Benson cycle is the reverse of the non-oxidative branch of the pentose phosphate pathway but we describe crucial differences and also propose that some carbon routinely passes through the oxidative branch of the pentose phosphate pathway. This creates a futile cycle but may help to stabilize photosynthesis. If it occurs it could explain a number of enigmas including the lack of complete labelling of the Calvin-Benson cycle intermediates when carbon isotopes are fed to photosynthesizing leaves.

Chloroplast FBPase and SBPase are thioredoxin-linked enzymes with similar architecture but different evolutionary histories

The Calvin-Benson cycle of carbon dioxide fixation in chloroplasts is controlled by light-dependent redox reactions that target specific enzymes. Of the regulatory members of the cycle, our knowledge of sedoheptulose-1,7-bisphosphatase (SBPase) is particularly scanty, despite growing evidence for its importance and link to plant productivity. To help fill this gap, we have purified, crystallized, and characterized the recombinant form of the enzyme together with the better studied fructose-1,6-bisphosphatase (FBPase), in both cases from the moss Physcomitrella patens (Pp). Overall, the moss enzymes resembled their counterparts from seed plants, including oligomeric organization-PpSBPase is a dimer, and PpFBPase is a tetramer. The two phosphatases showed striking structural homology to each other, differing primarily in their solvent-exposed surface areas in a manner accounting for their specificity for seven-carbon (sedoheptulose) and six-carbon (fructose) sugar bisphosphate substrates. The two enzymes had a similar redox potential for their regulatory redox-active disulfides (-310 mV for PpSBPase vs. -290 mV for PpFBPase), requirement for Mg(2+) and thioredoxin (TRX) specificity (TRX f > TRX m). Previously known to differ in the position and sequence of their regulatory cysteines, the enzymes unexpectedly showed unique evolutionary histories. The FBPase gene originated in bacteria in conjunction with the endosymbiotic event giving rise to mitochondria, whereas SBPase arose from an archaeal gene resident in the eukaryotic host. These findings raise the question of how enzymes with such different evolutionary origins achieved structural similarity and adapted to control by the same light-dependent photosynthetic mechanism-namely ferredoxin, ferredoxin-thioredoxin reductase, and thioredoxin.

Differential proteomic analysis of embryogenic lines in oil palm (Elaeis guineensis Jacq)

Oil palm tissue culture is one way to produce superior oil palm planting materials. However, the low rate of embryogenesis is a major hindrance for the adoption of this technology in oil palm tissue culture laboratories. In this study, we use proteomic technologies to compare differential protein profiles in leaves from palms of high and low proliferation rates in tissue culture in order to understand the underlying biological mechanism for the low level of embryogenesis. Two protein extraction methods, namely trichloroacetic acid/acetone precipitation and polyethylene glycol fractionation were used to produce total proteins and fractionated protein extracts respectively, with the aim of improving the resolution of protein species using two-dimensional gel electrophoresis. A total of 40 distinct differential abundant protein spots were selected from leaf samples collected from palms with proven high and low proliferation rates. The variant proteins were subsequently identified using mass spectrometric analysis. Twelve prominent protein spots were then characterised using real-time polymerase chain reaction to compare the mRNA expression and protein abundant profiles. Three proteins, namely triosephosphate isomerase, l-ascorbate peroxidase, and superoxide dismutase were identified to be potential biomarker candidates at both the protein abundant and mRNA expression levels.

BIOLOGICAL SIGNIFICANCE

In this study, proteomic analysis was used to identify abundant proteins from total protein extracts. PEG fractionation was used to reveal lower abundant proteins from both high and low proliferation embryogenic lines of oil palm samples in tissue culture. A total of 40 protein spots were found to be significant in abundance and the mRNA levels of 12 of these were assessed using real time PCR. Three proteins namely, triosephosphate isomerase, l-ascorbate peroxidase and superoxide dismutase were found to be concordant in their mRNA expression and protein abundance. Triosephosphate isomerase is a key enzyme in glycolysis. Both l-ascorbate peroxidase and superoxide dismutase play a role in anti-oxidative scavenging defense systems. These proteins have potential for use as biomarkers to screen for high and low embryogenic oil palm samples.

Functional and transcriptional characterization of a barley mutant with impaired photosynthesis

Chemical mutagenesis induces variations that may assist in the identification of targets for adaptation to growth under atmospheric CO2 enrichment. The aim of this work was to characterize the limitations causing reduced photosynthetic capacity in G132 mutagenized barley (Hordeum vulgare L. cv. Graphic) grown in a glasshouse. Compared to the wild type (WT) G132 showed increased transcript levels for the PSII light harvesting complex, but lower levels of chlorophyll, transcripts for protochlorophyllide oxidoreductase A and psbQ, and PSII quantum efficiency in young leaves. Rubisco limitation had an overriding influence on G132 photosynthesis, and was due to strong and selective decreases in Rubisco protein and activity. These reductions were accompanied by enhanced Rubisco transcripts, but increased levels of a Rubisco degradation product. G132 showed lower levels of carbohydrates, amino acids and corresponding transcripts, and proteins, but not of nitrate. Many of the measured parameters recovered in the mutant as development progressed, or decreased less than in the WT, indicating that senescence was delayed. G132 had a longer growth period than the WT and similar final plant dry matter. The reduced resource investment in Rubisco of G132 may prove useful for studies on barley adaptation to elevated CO2 and climate change.

Enhanced leaf photosynthesis as a target to increase grain yield: insights from transgenic rice lines with variable Rieske FeS protein content in the cytochrome b6 /f complex

Although photosynthesis is the most important source for biomass and grain yield, a lack of correlation between photosynthesis and plant yield among different genotypes of various crop species has been frequently observed. Such observations contribute to the ongoing debate whether enhancing leaf photosynthesis can improve yield potential. Here, transgenic rice plants that contain variable amounts of the Rieske FeS protein in the cytochrome (cyt) b6 /f complex between 10 and 100% of wild-type levels have been used to investigate the effect of reductions of these proteins on photosynthesis, plant growth and yield. Reductions of the cyt b6 /f complex did not affect the electron transport rates through photosystem I but decreased electron transport rates through photosystem II, leading to concomitant decreases in CO2 assimilation rates. There was a strong control of plant growth and grain yield by the rate of leaf photosynthesis, leading to the conclusion that enhancing photosynthesis at the single-leaf level would be a useful target for improving crop productivity and yield both via conventional breeding and biotechnology. The data here also suggest that changing photosynthetic electron transport rates via manipulation of the cyt b6 /f complex could be a potential target for enhancing photosynthetic capacity in higher plants.

Characterization and molecular cloning of a serine hydroxymethyltransferase 1 (OsSHM1) in rice

Serine hydroxymethyltransferase (SHMT) is important for one carbon metabolism and photorespiration in higher plants for its participation in plant growth and development, and resistance to biotic and abiotic stresses. A rice serine hydroxymethyltransferase gene, OsSHM1, an ortholog of Arabidopsis SHM1, was isolated using map-based cloning. The osshm1 mutant had chlorotic lesions and a considerably smaller, lethal phenotype under natural ambient CO2 concentrations, but could be restored to wild type with normal growth under elevated CO2 levels (0.5% CO2 ), showing a typical photorespiratory phenotype. The data from antioxidant enzymes activity measurement suggested that osshm1 was subjected to significant oxidative stress. Also, OsSHM1 was expressed in all organs tested (root, culm, leaf, and young panicle) but predominantly in leaves. OsSHM1 protein is localized to the mitochondria. Our study suggested that molecular function of the OsSHM1 gene is conserved in rice and Arabidopsis.

Multigene manipulation of photosynthetic carbon assimilation increases CO2 fixation and biomass yield in tobacco

Over the next 40 years it has been estimated that a 50% increase in the yield of grain crops such as wheat and rice will be required to meet the food and fuel demands of the increasing world population. Transgenic tobacco plants have been generated with altered combinations of sedoheptulose-1,7-bisphosphatase, fructose-1,6-bisphosphate aldolase, and the cyanobacterial putative-inorganic carbon transporter B, ictB, of which have all been identified as targets to improve photosynthesis based on empirical studies. It is shown here that increasing the levels of the three proteins individually significantly increases the rate of photosynthetic carbon assimilation, leaf area, and biomass yield. Furthermore, the daily integrated measurements of photosynthesis showed that mature plants fixed between 12-19% more CO2 than the equivalent wild-type plants. Further enhancement of photosynthesis and yield was observed when sedoheptulose-1,7-bisphosphatase, fructose-1,6-bisphosphate aldolase, and ictB were over-expressed together in the same plant. These results demonstrate the potential for the manipulation of photosynthesis, using multigene-stacking approaches, to increase crop yields.

Meeting the global food demand of the future by engineering crop photosynthesis and yield potential

Increase in demand for our primary foodstuffs is outstripping increase in yields, an expanding gap that indicates large potential food shortages by mid-century. This comes at a time when yield improvements are slowing or stagnating as the approaches of the Green Revolution reach their biological limits. Photosynthesis, which has been improved little in crops and falls far short of its biological limit, emerges as the key remaining route to increase the genetic yield potential of our major crops. Thus, there is a timely need to accelerate our understanding of the photosynthetic process in crops to allow informed and guided improvements via in-silico-assisted genetic engineering. Potential and emerging approaches to improving crop photosynthetic efficiency are discussed, and the new tools needed to realize these changes are presented.