Systems analysis of long-term heat stress responses in the C4 grass Setaria viridis.

Many C4 plants are used as food and fodder crops and often display improved resource use efficiency compared to C3 plants. However, the response of C4 plants to future extreme conditions such as heatwaves is less understood. Here, Setaria viridis, an emerging C4 model grass, was grown under long-term high temperature stress for two weeks (42°C, compared to 28°C).

Novel resources to investigate leaf plasmodesmata formation in C and C monocots.

Plasmodesmata (PD) are nanochannels that facilitate cell-to-cell transport in plants. More productive and photosynthetically efficient C plants form more PD at the mesophyll (M)-bundle sheath (BS) interface in their leaves than their less efficient C relatives. In C leaves, PD play an essential role in facilitating the rapid metabolite exchange between the M and BS cells to operate a biochemical CO concentrating mechanism, which increases the CO partial pressure at the site of Rubisco in the BS cells and hence photosynthetic efficiency.

Chloroplast NADH dehydrogenase-like complex-mediated cyclic electron flow is the main electron transport route in C bundle sheath cells.

The superior productivity of C plants is achieved via a metabolic C cycle which acts as a CO pump across mesophyll and bundle sheath (BS) cells and requires an additional input of energy in the form of ATP. The importance of chloroplast NADH dehydrogenase-like complex (NDH) operating cyclic electron flow (CEF) around Photosystem I (PSI) for C photosynthesis has been shown in reverse genetics studies but the contribution of CEF and NDH to cell-level electron fluxes remained unknown. We have created gene-edited Setaria viridis with null ndhO alleles lacking functional NDH and developed methods for quantification of electron flow through NDH in BS and mesophyll cells.

Variation in leaf dark respiration among C3 and C4 grasses is associated with use of different substrates.

Measurements of respiratory properties have often been made at a single time point either during daytime using dark-adapted leaves or during nighttime. The influence of the day-night cycle on respiratory metabolism has received less attention but is crucial to understand photosynthesis and photorespiration. Here, we examined how CO2- and O2-based rates of leaf dark respiration (Rdark) differed between midday (after 30-min dark adaptation) and midnight in 8 C3 and C4 grasses.

Photosynthesis and food security: the evolving story of C rice.

Traditional "Green Revolution" cereal breeding strategies to improve yield are now reaching a plateau in our principal global food crop rice. Photosynthesis has now become a major target of international consortia to increase yield potential. Synthetic biology is being used across multiple large projects to improve photosynthetic efficiency.

Faster induction of photosynthesis increases biomass and grain yield in glasshouse-grown transgenic Sorghum bicolor overexpressing Rieske FeS.

Sorghum is one of the most important crops providing food and feed in many of the world's harsher environments. Sorghum utilizes the C pathway of photosynthesis in which a biochemical carbon-concentrating mechanism results in high CO assimilation rates. Overexpressing the Rieske FeS subunit of the Cytochrome b f complex was previously shown to increase the rate of photosynthetic electron transport and stimulate CO assimilation in the model C plant Setaria viridis.

Increased sedoheptulose-1,7-bisphosphatase content in Setaria viridis does not affect C4 photosynthesis.

Sedoheptulose-1,7-bisphosphatase (SBPase) is one of the rate-limiting enzymes of the Calvin cycle, and increasing the abundance of SBPase in C3 plants provides higher photosynthetic rates and stimulates biomass and yield. C4 plants usually have higher photosynthetic rates because they operate a biochemical CO2-concentrating mechanism between mesophyll and bundle sheath cells. In the C4 system, SBPase and other enzymes of the Calvin cycle are localized to the bundle sheath cells.

Rieske FeS overexpression in tobacco provides increased abundance and activity of cytochrome b f.

Photosynthesis is fundamental for plant growth and yield. The cytochrome b f complex catalyses a rate-limiting step in thylakoid electron transport and therefore represents an important point of regulation of photosynthesis. Here we show that overexpression of a single core subunit of cytochrome b f, the Rieske FeS protein, led to up to a 40% increase in the abundance of the complex in Nicotiana tabacum (tobacco) and was accompanied by an enhanced in vitro cytochrome f activity, indicating a full functionality of the complex.

A cross-scale analysis to understand and quantify the effects of photosynthetic enhancement on crop growth and yield across environments.

Photosynthetic manipulation provides new opportunities for enhancing crop yield. However, understanding and quantifying the importance of individual and multiple manipulations on the seasonal biomass growth and yield performance of target crops across variable production environments is limited. Using a state-of-the-art cross-scale model in the APSIM platform we predicted the impact of altering photosynthesis on the enzyme-limited (A ) and electron transport-limited (A ) rates, seasonal dynamics in canopy photosynthesis, biomass growth, and yield formation via large multiyear-by-location crop growth simulations.

Enhanced abundance and activity of the chloroplast ATP synthase in rice through the overexpression of the AtpD subunit.

ATP, produced by the light reactions of photosynthesis, acts as the universal cellular energy cofactor fuelling all life processes. Chloroplast ATP synthase produces ATP using the proton motive force created by solar energy-driven thylakoid electron transport reactions. Here we investigate how increasing abundance of ATP synthase affects leaf photosynthesis and growth of rice, Oryza sativa variety Kitaake.

A single promoter-TALE system for tissue-specific and tuneable expression of multiple genes in rice.

In biological discovery and engineering research, there is a need to spatially and/or temporally regulate transgene expression. However, the limited availability of promoter sequences that are uniquely active in specific tissue-types and/or at specific times often precludes co-expression of multiple transgenes in precisely controlled developmental contexts. Here, we developed a system for use in rice that comprises synthetic designer transcription activator-like effectors (dTALEs) and cognate synthetic TALE-activated promoters (STAPs).

Mesophyll conductance is unaffected by expression of Arabidopsis PIP1 aquaporins in the plasmalemma of Nicotiana.

In plants with C3 photosynthesis, increasing the diffusion conductance for CO2 from the substomatal cavity to chloroplast stroma (mesophyll conductance) can improve the efficiencies of both CO2 assimilation and photosynthetic water use. In the diffusion pathway from substomatal cavity to chloroplast stroma, the plasmalemma and chloroplast envelope membranes impose a considerable barrier to CO2 diffusion, limiting photosynthetic efficiency. In an attempt to improve membrane permeability to CO2, and increase photosynthesis in tobacco, we generated transgenic lines in Nicotiana tabacum L.

Dark respiration rates are not determined by differences in mitochondrial capacity, abundance and ultrastructure in C leaves.

Our understanding of the regulation of respiration in C plants, where mitochondria play different roles in the different types of C photosynthetic pathway, remains limited. We examined how leaf dark respiration rates (R ), in the presence and absence of added malate, vary in monocots representing the three classical biochemical types of C photosynthesis (NADP-ME, NAD-ME and PCK) using intact leaves and extracted bundle sheath strands. In particular, we explored to what extent rates of R are associated with mitochondrial number, volume and ultrastructure.

Expression of a CO-permeable aquaporin enhances mesophyll conductance in the C species .

A fundamental limitation of photosynthetic carbon fixation is the availability of CO. In C plants, primary carboxylation occurs in mesophyll cytosol, and little is known about the role of CO diffusion in facilitating C photosynthesis. We have examined the expression, localization, and functional role of selected plasma membrane intrinsic aquaporins (PIPs) from (foxtail millet) and discovered that SiPIP2;7 is CO-permeable.

The crucial roles of mitochondria in supporting C photosynthesis.

C photosynthesis involves a series of biochemical and anatomical traits that significantly improve plant productivity under conditions that reduce the efficiency of C photosynthesis. We explore how evolution of the three classical biochemical types of C photosynthesis (NADP-ME, NAD-ME and PCK types) has affected the functions and properties of mitochondria. Mitochondria in C NAD-ME and PCK types play a direct role in decarboxylation of metabolites for C photosynthesis.

Updating the steady-state model of C4 photosynthesis.

C4 plants play a key role in world agriculture. For example, C4 crops such as maize and sorghum are major contributors to food production in both developed and developing countries, and the C4 grasses sugarcane, miscanthus, and switchgrass are major plant sources of bioenergy. In the challenge to manipulate and enhance C4 photosynthesis, steady-state models of leaf photosynthesis provide an important tool for gas exchange analysis and thought experiments that can explore photosynthetic pathway changes.

Upregulation of bundle sheath electron transport capacity under limiting light in C Setaria viridis.

C photosynthesis is a biochemical pathway that operates across mesophyll and bundle sheath (BS) cells to increase CO concentration at the site of CO fixation. C plants benefit from high irradiance but their efficiency decreases under shade, causing a loss of productivity in crop canopies. We investigated shade acclimation responses of Setaria viridis, a model monocot of NADP-dependent malic enzyme subtype, focussing on cell-specific electron transport capacity.

Bundle sheath suberisation is required for C photosynthesis in a Setaria viridis mutant.

C photosynthesis provides an effective solution for overcoming the catalytic inefficiency of Rubisco. The pathway is characterised by a biochemical CO concentrating mechanism that operates across mesophyll and bundle sheath (BS) cells and relies on a gas tight BS compartment. A screen of a mutant population of Setaria viridis, an NADP-malic enzyme type C monocot, generated using N-nitroso-N-methylurea identified a mutant with an amino acid change in the gene coding region of the ABCG transporter, a step in the suberin synthesis pathway.

CO diffusion in tobacco: a link between mesophyll conductance and leaf anatomy.

The partial pressure of CO at the sites of carboxylation within chloroplasts depends on the conductance to CO diffusion from intercellular airspace to the sites of carboxylation, termed mesophyll conductance ( ). We investigated how varies with leaf age and through a tobacco () canopy by combining gas exchange and carbon isotope measurements using tunable diode laser spectroscopy. We combined these measurements with the anatomical characterization of leaves.

A low CO2-responsive mutant of Setaria viridis reveals that reduced carbonic anhydrase limits C4 photosynthesis.

In C4 species, β-carbonic anhydrase (CA), localized to the cytosol of the mesophyll cells, accelerates the interconversion of CO2 to HCO3-, the substrate used by phosphoenolpyruvate carboxylase (PEPC) in the first step of C4 photosynthesis. Here we describe the identification and characterization of low CO2-responsive mutant 1 (lcr1) isolated from an N-nitroso-N-methylurea- (NMU) treated Setaria viridis mutant population. Forward genetic investigation revealed that the mutated gene Sevir.

Installation of C photosynthetic pathway enzymes in rice using a single construct.

Introduction of a C photosynthetic mechanism into C 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 C 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.

Rubisco carboxylase/oxygenase: From the enzyme to the globe: A gas exchange perspective.

Rubisco is the primary carboxylase of the photosynthetic process, the most abundant enzyme in the biosphere, and also one of the best-characterized enzymes. Rubisco also functions as an oxygenase, a discovery made 50 years ago by Bill Ogren. Carboxylation of ribulose bisphosphate (RuBP) is the first step of the photosynthetic carbon reduction cycle and leads to the assimilation of CO, whereas the oxygenase activity necessitates the recycling of phosphoglycolate through the photorespiratory carbon oxidation cycle with concomitant loss of CO.

A wish list for synthetic biology in photosynthesis research.

This perspective summarizes the presentations and discussions at the ' International Symposium on Synthetic Biology in Photosynthesis Research', which was held in Shanghai in 2018. Leveraging the current advanced understanding of photosynthetic systems, the symposium brain-stormed about the redesign and engineering of photosynthetic systems for translational goals and evaluated available new technologies/tools for synthetic biology as well as technological obstacles and new tools that would be needed to overcome them. Four major research areas for redesigning photosynthesis were identified: (i) mining natural variations of photosynthesis; (ii) coordinating photosynthesis with pathways utilizing photosynthate; (iii) reconstruction of highly efficient photosynthetic systems in non-host species; and (iv) development of new photosynthetic systems that do not exist in nature.

On the road to C rice: advances and perspectives.

The international C rice consortium aims to introduce into rice a high capacity photosynthetic mechanism, the C pathway, to increase yield. The C pathway is characterised by a complex combination of biochemical and anatomical specialisation that ensures high CO partial pressure at RuBisCO sites in bundle sheath (BS) cells. Here we report an update of the progress of the C rice project.

Overexpression of the Rieske FeS protein of the Cytochrome complex increases C photosynthesis in .

C photosynthesis is characterised by a CO concentrating mechanism that operates between mesophyll and bundle sheath cells increasing CO partial pressure at the site of Rubisco and photosynthetic efficiency. Electron transport chains in both cell types supply ATP and NADPH for C photosynthesis. Cytochrome is a key control point of electron transport in C plants.