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Leaf CO2 uptake (A) in C4 photosynthesis is limited by the maximum apparent rate of PEPc carboxylation (Vpmax) at low intercellular [CO2] (ci) with a sharp transition to a ci‐saturated rate (Vmax) due to co‐limitation by ribulose‐1:5‐bisphosphate carboxylase/oxygenase (Rubisco) and regeneration of PEP. The response of A to ci has been widely used to determine these two parameters. Vmax and Vpmax depend on different enzymes but draw on a shared pool of leaf resources, such that resource distribution is optimized, and A maximized, when Vmax and Vpmax are co‐limiting. We collected published A/ci curves in 49 C4 species and assessed variation in photosynthetic traits between phylogenetic groups, and as a function of atmospheric [CO2]. The balance of Vmax‐Vpmax varied among evolutionary lineages and C4 subtypes. Operating A was strongly Vmax‐limited, such that re‐allocation of resources from Vpmax towards Vmax was predicted to improve A by 12% in C4 crops. This would not require additional inputs but rather altered partitioning of existing leaf nutrients, resulting in increased water and nutrient‐use efficiency. Optimal partitioning was achieved only in plants grown at pre‐industrial atmospheric [CO2], suggesting C4 crops have not adjusted to the rapid increase in atmospheric [CO2] of the past few decades. This study presents a data set of photosynthetic traits derived from published A‐ci curves measured in 49 C4 species. We determined that leaf photosynthetic resource allocation remains adapted to pre‐industrial atmospheric conditions and is not optimized for today's high [CO2] atmosphere. [ABSTRACT FROM AUTHOR]

Leaf CO2 uptake (A) in C4 photosynthesis is limited by the maximum apparent rate of PEPc carboxylation (Vpmax) at low intercellular [CO2] (ci) with a sharp transition to a ci‐saturated rate (Vmax) due to co‐limitation by ribulose‐1:5‐bisphosphate carboxylase/oxygenase (Rubisco) and regeneration of PEP. The response of A to ci has been widely used to determine these two parameters. Vmax and Vpmax depend on different enzymes but draw on a shared pool of leaf resources, such that resource distribution is optimized, and A maximized, when Vmax and Vpmax are co‐limiting. We collected published A/ci curves in 49 C4 species and assessed variation in photosynthetic traits between phylogenetic groups, and as a function of atmospheric [CO2]. The balance of Vmax‐Vpmax varied among evolutionary lineages and C4 subtypes. Operating A was strongly Vmax‐limited, such that re‐allocation of resources from Vpmax towards Vmax was predicted to improve A by 12% in C4 crops. This would not require additional inputs but rather altered partitioning of existing leaf nutrients, resulting in increased water and nutrient‐use efficiency. Optimal partitioning was achieved only in plants grown at pre‐industrial atmospheric [CO2], suggesting C4 crops have not adjusted to the rapid increase in atmospheric [CO2] of the past few decades. This study presents a data set of photosynthetic traits derived from published A‐ci curves measured in 49 C4 species. We determined that leaf photosynthetic resource allocation remains adapted to pre‐industrial atmospheric conditions and is not optimized for today's high [CO2] atmosphere. [ABSTRACT FROM AUTHOR]

The folding and assembly of Rubisco large and small subunits into L8S8 holoenzyme in chloroplasts involves many auxiliary factors, including the chaperone BSD2. Here we identify apparent intermediary Rubisco‐BSD2 assembly complexes in the model C3 plant tobacco. We show BSD2 and Rubisco content decrease in tandem with leaf age with approximately half of the BSD2 in young leaves (~70 nmol BSD2 protomer.m2) stably integrated in putative intermediary Rubisco complexes that account for <0.2% of the L8S8 pool. RNAi‐silencing BSD2 production in transplastomic tobacco producing bacterial L2 Rubisco had no effect on leaf photosynthesis, cell ultrastructure, or plant growth. Genetic crossing the same RNAi‐bsd2 alleles into wild‐type tobacco however impaired L8S8 Rubisco production and plant growth, indicating the only critical function of BSD2 is in Rubisco biogenesis. Agrobacterium mediated transient expression of tobacco, Arabidopsis, or maize BSD2 reinstated Rubisco biogenesis in BSD2‐silenced tobacco. Overexpressing BSD2 in tobacco chloroplasts however did not alter Rubisco content, activation status, leaf photosynthesis rate, or plant growth in the field or in the glasshouse at 20°C or 35°C. Our findings indicate BSD2 functions exclusively in Rubisco biogenesis, can efficiently facilitate heterologous plant Rubisco assembly, and is produced in amounts nonlimiting to tobacco growth. The required sequence complementarity by plant Rubisco for components of its complex biogenesis interactome poses a significant obstacle to improving catalysis. Here we detail evidence that the Rubisco chaperone BSD2 forms stable intermediary complexes with Rubisco in tobacco and that BSD2 availability does not limit Rubisco biogenesis, photosynthesis, or plant growth in this model C3 plant. We show that the only critical role of BSD2 in tobacco is in Rubisco biogenesis and that BSD2 is not species‐specific and can effectively assemble Rubisco from differing plant species. This work provides a significant advance in engineering photosynthesis and in understanding the folding machinery of chloroplasts and Rubisco. [ABSTRACT FROM AUTHOR]

Windows Intuitive Model of Vegetation response to Atmosphere and Climate Change (WIMOVAC) has been used widely as a generic modular mechanistically rich model of plant production. It can predict the responses of leaf and canopy carbon balance, as well as production in different environmental conditions, in particular those relevant to global change. Here, we introduce an open source Java user-friendly version of WIMOVAC. This software is platform independent and can be easily downloaded to a laptop and used without any prior programming skills. In this article, we describe the structure, equations and user guide and illustrate some potential applications of WIMOVAC. [ABSTRACT FROM AUTHOR]

A paradigm shift is needed and timely in moving plant modelling from largely isolated efforts to a connected community endeavour that can take full advantage of advances in computer science and in mechanistic understanding of plant processes. Plants in silico (Ps i) envisions a digital representation of layered dynamic modules, linking from gene networks and metabolic pathways through to cellular organization, tissue, organ and whole plant development, together with resource capture and use efficiency in dynamic competitive environments, ultimately allowing a mechanistically rich simulation of the plant or of a community of plants in silico. The concept is to integrate models or modules from different layers of organization spanning from genome to phenome to ecosystem in a modular framework allowing the use of modules of varying mechanistic detail representing the same biological process. Developments in high-performance computing, functional knowledge of plants, the internet and open-source version controlled software make achieving the concept realistic. Open source will enhance collaboration and move towards testing and consensus on quantitative theoretical frameworks. Importantly, Ps i provides a quantitative knowledge framework where the implications of a discovery at one level, for example, single gene function or developmental response, can be examined at the whole plant or even crop and natural ecosystem levels. [ABSTRACT FROM AUTHOR]

High-performance computing has facilitated development of biomass production models that capture the key mechanisms underlying production at high spatial and temporal resolution. Direct responses to increasing [ CO2] and temperature are important to long-lived emerging woody bioenergy crops. Fast-growing willow ( S alix spp.) within short rotation coppice ( SRC) has considerable potential as a renewable biomass source, but performance over wider environmental conditions and under climate change is uncertain. We extended the bioenergy crop modeling platform, Bio Cro, to SRC willow by adding coppicing and C3 photosynthesis subroutines, and modifying subroutines for perennation, allocation, morphology, phenology and development. Parameterization with measurements of leaf photosynthesis, allocation and phenology gave agreement of modeled with measured yield across 23 sites in Europe and North America. Predictions for the continental USA suggest yields of ≥17 Mg ha−1 year−1 in a 4 year rotation. Rising temperature decreased predicted yields, an effect partially ameliorated by rising [ CO2]. This model, based on over 100 equations describing the physiological and biophysical mechanisms underlying production, provides a new framework for utilizing mechanism of plant responses to the environment, including future climates. As an open-source tool, it is made available here as a community resource for further application, improvement and adaptation. [ABSTRACT FROM AUTHOR]

Rising atmospheric [ CO2] is a uniform, global change that increases C3 photosynthesis and could offset some of the negative effects of global climate change on crop yields. Genetic variation in yield responsiveness to rising [ CO2] would provide an opportunity to breed more responsive crop genotypes. A multi-year study of 18 soybean ( G lycine max Merr.) genotypes was carried out to identify variation in responsiveness to season-long elevated [ CO2] (550 ppm) under fully open-air replicated field conditions. On average across 18 genotypes, elevated [ CO2] stimulated total above-ground biomass by 22%, but seed yield by only 9%, in part because most genotypes showed a reduction in partitioning of energy to seeds. Over four years of study, there was consistency from year to year in the genotypes that were most and least responsive to elevated [ CO2], suggesting heritability of CO2 response. Further analysis of six genotypes did not reveal a photosynthetic basis for the variation in yield response. Although partitioning to seed was decreased, cultivars with the highest partitioning coefficient in current [ CO2] also had the highest partitioning coefficient in elevated [ CO2]. The results show the existence of genetic variation in soybean response to elevated [ CO2], which is needed to breed soybean to the future atmospheric environment. [ABSTRACT FROM AUTHOR]

ABSTRACT Photosynthesis is arguably the most researched of all plant processes. A dynamic model of leaf photosynthesis that includes each discrete process from light capture to carbohydrate synthesis, e-photosynthesis, is described. It was developed by linking and extending our previous models of photosystem II (PSII) energy transfer and photosynthetic C3 carbon metabolism to include electron transfer processes around photosystem I (PSI), ion transfer between the lumen and stroma, ATP synthesis and NADP reduction to provide a complete representation. Different regulatory processes linking the light and dark reactions are also included: Rubisco activation via Rubisco activase, pH and xanthophyll cycle-dependent non-photochemical quenching mechanisms, as well as the regulation of enzyme activities via the ferredoxin-theoredoxin system. Although many further feedback and feedforward controls undoubtedly exist, it is shown that e-photosynthesis effectively mimics the typical kinetics of leaf CO2 uptake, O2 evolution, chlorophyll fluorescence emission, lumen and stromal pH, and membrane potential following perturbations in light, [CO2] and [O2] observed in intact C3 leaves. The model provides a framework for guiding engineering of improved photosynthetic efficiency, for evaluating multiple non-invasive measures used in emerging phenomics facilities, and for quantitative assessment of strengths and weaknesses within the understanding of photosynthesis as an integrated process. [ABSTRACT FROM AUTHOR]

ABSTRACT Soybean ( Glycine max Merr.) is the world's most widely grown legume and provides an important source of protein and oil. Global soybean production and yield per hectare increased steadily over the past century with improved agronomy and development of cultivars suited to a wide range of latitudes. In order to meet the needs of a growing world population without unsustainable expansion of the land area devoted to this crop, yield must increase at a faster rate than at present. Here, the historical basis for the yield gains realized in the past 90 years are examined together with potential metabolic targets for achieving further improvements in yield potential. These targets include improving photosynthetic efficiency, optimizing delivery and utilization of carbon, more efficient nitrogen fixation and altering flower initiation and abortion. Optimization of investment in photosynthetic enzymes, bypassing photorespiratory metabolism, engineering the electron transport chain and engineering a faster recovery from the photoprotected state are different strategies to improve photosynthesis in soybean. These potential improvements in photosynthetic carbon gain will need to be matched by increased carbon and nitrogen transport to developing soybean pods and seeds in order to maximize the benefit. Better understanding of control of carbon and nitrogen transport along with improved knowledge of the regulation of flower initiation and abortion will be needed to optimize sink capacity in soybean. Although few single targets are likely to deliver a quantum leap in yields, biotechnological advances in molecular breeding techniques that allow for alteration of the soybean genome and transcriptome promise significant yield gains. [ABSTRACT FROM AUTHOR]

A rising global population and demand for protein-rich diets are increasing pressure to maximize agricultural productivity. Rising atmospheric [CO2] is altering global temperature and precipitation patterns, which challenges agricultural productivity. While rising [CO2] provides a unique opportunity to increase the productivity of C3 crops, average yield stimulation observed to date is well below potential gains. Thus, there is room for improving productivity. However, only a fraction of available germplasm of crops has been tested for CO2 responsiveness. Yield is a complex phenotypic trait determined by the interactions of a genotype with the environment. Selection of promising genotypes and characterization of response mechanisms will only be effective if crop improvement and systems biology approaches are closely linked to production environments, that is, on the farm within major growing regions. Free air CO2 enrichment (FACE) experiments can provide the platform upon which to conduct genetic screening and elucidate the inheritance and mechanisms that underlie genotypic differences in productivity under elevated [CO2]. We propose a new generation of large-scale, low-cost per unit area FACE experiments to identify the most CO2-responsive genotypes and provide starting lines for future breeding programmes. This is necessary if we are to realize the potential for yield gains in the future. [ABSTRACT FROM AUTHOR]

It is anticipated that enrichment of the atmosphere with CO2 will increase photosynthetic carbon assimilation in C3 plants. Analysis of controlled environment studies conducted to date indicates that plant growth at concentrations of carbon dioxide ([CO2]) anticipated for 2050 (∼ 550 µmol mol−1) will stimulate leaf photosynthetic carbon assimilation ( A) by 20 to 40%. Simultaneously, concentrations of tropospheric ozone ([O3]) are expected to increase by 2050, and growth in controlled environments at elevated [O3] significantly reduces A. However, the simultaneous effects of both increases on a major crop under open-air conditions have never been tested. Over three consecutive growing seasons > 4700 individual measurements of A, photosynthetic electron transport ( JPSII) and stomatal conductance ( gs) were measured on Glycine max (L.) Merr. (soybean). Experimental treatments used free-air gas concentration enrichment (FACE) technology in a fully replicated, factorial complete block design. The mean A in the control plots was 14.5 µmol m−2 s−1. At elevated [CO2], mean A was 24% higher and the treatment effect was statistically significant on 80% of days. There was a strong positive correlation between daytime maximum temperatures and mean daily integrated A at elevated [CO2], which accounted for much of the variation in CO2 effect among days. The effect of elevated [CO2] on photosynthesis also tended to be greater under water stress conditions. The elevated [O3] treatment had no statistically significant effect on mean A, gs or JPSII on newly expanded leaves. Combined elevation of [CO2] and [O3] resulted in a slightly smaller increase in average A than when [CO2] alone was elevated, and was significantly greater than the control on 67% of days. Thus, the change in atmospheric composition predicted for the middle of this century will, based on the results of a 3 year open-air field experiment, have smaller effects on photosynthesis, gs and whole chain electron transport through photosystem II than predicted by the substantial literature on relevant controlled environment studies on soybean and likely most other C3 plants. [ABSTRACT FROM AUTHOR]

Accurately predicting plant function and global biogeochemical cycles later in this century will be complicated if stomatal conductance ( gs) acclimates to growth at elevated [CO2], in the sense of a long-term alteration of the response of gs to [CO2], humidity ( h) and/or photosynthetic rate ( A). If so, photosynthetic and stomatal models will require parameterization at each growth [CO2] of interest. Photosynthetic acclimation to long-term growth at elevated [CO2] occurs frequently. Acclimation of gs has rarely been examined, even though stomatal density commonly changes with growth [CO2]. Soybean was grown under field conditions at ambient [CO2] (378 µmol mol−1) and elevated [CO2] (552 µmol mol−1) using free-air [CO2] enrichment (FACE). This study tested for stomatal acclimation by parameterizing and validating the widely used Ball et al. model (1987 , Progress in Photosynthesis Research, vol IV, 221–224) with measurements of leaf gas exchange. The dependence of gs on A, h and [CO2] at the leaf surface was unaltered by long-term growth at elevated [CO2]. This suggests that the commonly observed decrease in gs under elevated [CO2] is due entirely to the direct instantaneous effect of [CO2] on gs and that there is no longer-term acclimation of gs independent of photosynthetic acclimation. The model accurately predicted gs for soybean growing under ambient and elevated [CO2] in the field. Model parameters under ambient and elevated [CO2] were indistinguishable, demonstrating that stomatal function under ambient and elevated [CO2] could be modelled without the need for parameterization at each growth [CO2]. [ABSTRACT FROM AUTHOR]

Two C4 plants, Miscanthus × giganteus and Cyperus longus L., were grown at suboptimal growth temperatures and the relationships between the quantum efficiencies of photosynthetic electron transport through photosystem II (PSII) (PSII operating efficiency; Fq′/ Fm′) and CO2 assimilation ( φCO2) in leaves were examined. When M. × giganteus was grown at 10 °C, the ratio of the PSII operating efficiency to φCO2 increased relative to that found in leaves grown at 14 and 25 °C. Similar increases in the Fq′/ Fm′ : φCO2 occurred in the leaves of two C. longus ecotypes when the plants were grown at 17 °C, compared to 25 °C. These elevations of Fq′/ Fm′ : φCO2 at low growth temperatures were not attributable to the development of anthocyanins, as has been suggested for maize, and were indicative of the operation of an alternative sink to CO2 assimilation for photosynthetic reducing equivalents, possibly oxygen reduction via a Mehler reaction, which would act as a mechanism for protection of PSII from photoinactivation and damage. Furthermore, in M. × giganteus grown at 10 °C, further protection of PSII was effected by a 20-fold increase in zeaxanthin content in dark-adapted leaves, which was associated with much higher levels of non-photochemical quenching of excitation energy, compared to that observed in leaves grown at 14 and 25 °C. These differences may explain the long growing season and remarkable productivity of this C4 plant in cool climates, even in comparison to other C4 species such as C. longus, which occur naturally in such climates. [ABSTRACT FROM AUTHOR]

The yield potential ( Yp) of a grain crop is the seed mass per unit ground area obtained under optimum growing conditions without weeds, pests and diseases. It is determined by the product of the available light energy and by the genetically determined properties: efficiency of light capture ( ℇi), the efficiency of conversion of the intercepted light into biomass ( ℇc) and the proportion of biomass partitioned into grain ( η). Plant breeding brings η and ℇi close to their theoretical maxima, leaving ℇc, primarily determined by photosynthesis, as the only remaining major prospect for improving Yp. Leaf photosynthetic rate, however, is poorly correlated with yield when different genotypes of a crop species are compared. This led to the viewpoint that improvement of leaf photosynthesis has little value for improving Yp. By contrast, the many recent experiments that compare the growth of a genotype in current and future projected elevated [CO2] environments show that increase in leaf photosynthesis is closely associated with similar increases in yield. Are there opportunities to achieve similar increases by genetic manipulation? Six potential routes of increasing ℇc by improving photosynthetic efficiency were explored, ranging from altered canopy architecture to improved regeneration of the acceptor molecule for CO2. Collectively, these changes could improve ℇc and, therefore, Yp by c. 50%. Because some changes could be achieved by transgenic technology, the time of the development of commercial cultivars could be considerably less than by conventional breeding and potentially, within 10–15 years. [ABSTRACT FROM AUTHOR]

This article comments on: Can exploiting natural genetic variation in leaf photosynthesis contribute to increasing rice productivity? A simulation analysis [ABSTRACT FROM AUTHOR]