Feeding the world: improving photosynthetic efficiency for sustainable crop production

Nitric oxide signal is required for glutathione-induced enhancement of photosynthesis in salt-stressed Solanum lycopersicum L

Reduced glutathione (γ-glutamyl-cysteinyl-glycine, GSH), the primary non-protein sulfhydryl group in organisms, plays a pivotal role in the plant salt stress response. This study aimed to explore the impact of GSH on the photosynthetic apparatus, and carbon assimilation in tomato plants under salt stress, and then investigate the role of nitric oxide (NO) in this process. The investigation involved foliar application of 5 mM GSH, 0.1% (w/v) hemoglobin (Hb, a nitric oxide scavenger), and GSH+Hb on the endogenous NO levels, rapid chlorophyll fluorescence, enzyme activities, and gene expression related to the Calvin cycle in tomato seedlings (Solanum lycopersicum L. cv. 'Zhongshu No. 4') subjected short-term salt stress (100 mM NaCl) for 24, 48 and 72 hours. GSH treatment notably boosted nitrate reductase (NR) and NO synthase (NOS) activities, elevating endogenous NO signaling in salt-stressed tomato seedling leaves. It also mitigated chlorophyll fluorescence (OJIP) curve distortion and damage to the oxygen-evolving complex (OEC) induced by salt stress. Furthermore, GSH improved photosystem II (PSII) electron transfer efficiency, reduced QA - accumulation, and countered salt stress effects on photosystem I (PSI) redox properties, enhancing the light energy absorption index (PIabs). Additionally, GSH enhanced key enzyme activities in the Calvin cycle and upregulated their genes. Exogenous GSH optimized PSII energy utilization via endogenous NO, safeguarded the photosynthetic reaction center, improved photochemical and energy efficiency, and boosted carbon assimilation, ultimately enhancing net photosynthetic efficiency (Pn) in salt-stressed tomato seedling leaves. Conversely, Hb hindered Pn reduction and NO signaling under salt stress and weakened the positive effects of GSH on NO levels, photosynthetic apparatus, and carbon assimilation in tomato plants. Thus, the positive regulation of photosynthesis in tomato seedlings under salt stress by GSH requires the involvement of NO.

Central transcriptional regulator controls photosynthetic growth and carbon storage in response to high light

Carbon capture and biochemical storage are some of the primary drivers of photosynthetic yield and productivity. To elucidate the mechanisms governing carbon allocation, we designed a photosynthetic light response test system for genetic and metabolic carbon assimilation tracking, using microalgae as simplified plant models. The systems biology mapping of high light-responsive photophysiology and carbon utilization dynamics between two variants of the same Picochlorum celeri species, TG1 and TG2 elucidated metabolic bottlenecks and transport rates of intermediates using instationary 13C-fluxomics. Simultaneous global gene expression dynamics showed 73% of the annotated genes responding within one hour, elucidating a singular, diel-responsive transcription factor, closely related to the CCA1/LHY clock genes in plants, with significantly altered expression in TG2. Transgenic P. celeri TG1 cells expressing the TG2 CCA1/LHY gene, showed 15% increase in growth rates and 25% increase in storage carbohydrate content, supporting a coordinating regulatory function for a single transcription factor.

Contribution of Antioxidant System Components to the Long-Term Physiological and Protective Effect of Salicylic Acid on Wheat under Salinity Conditions

Salicylic acid (SA) plays a crucial role in regulating plant growth and development and mitigating the negative effects of various stresses, including salinity. In this study, the effect of 50 μM SA on the physiological and biochemical parameters of wheat plants under normal and stress conditions was investigated. The results showed that on the 28th day of the growing season, SA pretreatment continued to stimulate the growth of wheat plants. This was evident through an increase in shoot length and leaf area, with the regulation of leaf blade width playing a significant role in this effect. Additionally, SA improved photosynthesis by increasing the content of chlorophyll a (Chl a) and carotenoids (Car), resulting in an increased TAP (total amount of pigments) index in the leaves. Furthermore, SA treatment led to a balanced increase in the levels of reduced glutathione (GSH) and oxidized glutathione (GSSG) in the leaves, accompanied by a slight but significant accumulation of ascorbic acid (ASA), hydrogen peroxide (H2O2), proline, and the activation of glutathione reductase (GR) and ascorbate peroxidase (APX). Exposure to salt stress for 28 days resulted in a reduction in length and leaf area, photosynthetic pigments, and GSH and ASA content in wheat leaves. It also led to the accumulation of H2O2 and proline and significant activation of GR and APX. However, SA pretreatment exhibited a long-term growth-stimulating and protective effect under stress conditions. It significantly mitigated the negative impacts of salinity on leaf area, photosynthetic pigments, proline accumulation, lipid peroxidation, and H2O2. Furthermore, SA reduced the salinity-induced depletion of GSH and ASA levels, which was associated with the modulation of GR and APX activities. In small-scale field experiments conducted under natural growing conditions, pre-sowing seed treatment with 50 μM SA improved the main indicators of grain yield and increased the content of essential amino acids in wheat grains. Thus, SA pretreatment can be considered an effective approach for providing prolonged protection to wheat plants under salinity and improving grain yield and quality.

Cell-type-specific transcriptomics uncovers spatial regulatory networks in bioenergy sorghum stems

Bioenergy sorghum is a low-input, drought-resilient, deep-rooting annual crop that has high biomass yield potential enabling the sustainable production of biofuels, biopower, and bioproducts. Bioenergy sorghum's 4-5 m stems account for ~80% of the harvested biomass. Stems accumulate high levels of sucrose that could be used to synthesize bioethanol and useful biopolymers if information about cell-type gene expression and regulation in stems was available to enable engineering. To obtain this information, laser capture microdissection was used to isolate and collect transcriptome profiles from five major cell types that are present in stems of the sweet sorghum Wray. Transcriptome analysis identified genes with cell-type-specific and cell-preferred expression patterns that reflect the distinct metabolic, transport, and regulatory functions of each cell type. Analysis of cell-type-specific gene regulatory networks (GRNs) revealed that unique transcription factor families contribute to distinct regulatory landscapes, where regulation is organized through various modes and identifiable network motifs. Cell-specific transcriptome data was combined with known secondary cell wall (SCW) networks to identify the GRNs that differentially activate SCW formation in vascular sclerenchyma and epidermal cells. The spatial transcriptomic dataset provides a valuable source of information about the function of different sorghum cell types and GRNs that will enable the engineering of bioenergy sorghum stems, and an interactive web application developed during this project will allow easy access and exploration of the data (https://mc-lab.shinyapps.io/lcm-dataset/).

Improving Crop Yield through Increasing Carbon Gain and Reducing Carbon Loss

Photosynthesis is a process where solar energy is utilized to convert atmospheric CO2 into carbohydrates, which forms the basis for plant productivity. The increasing demand for food has created a global urge to enhance yield. Earlier, the plant breeding program was targeting the yield and yield-associated traits to enhance the crop yield. However, the yield cannot be further improved without improving the leaf photosynthetic rate. Hence, in this review, various strategies to enhance leaf photosynthesis were presented. The most promising strategies were the optimization of Rubisco carboxylation efficiency, the introduction of a CO2 concentrating mechanism in C3 plants, and the manipulation of photorespiratory bypasses in C3 plants, which are discussed in detail. Improving Rubisco's carboxylation efficiency is possible by engineering targets such as Rubisco subunits, chaperones, and Rubisco activase enzyme activity. Carbon-concentrating mechanisms can be introduced in C3 plants by the adoption of pyrenoid and carboxysomes, which can increase the CO2 concentration around the Rubisco enzyme. Photorespiration is the process by which the fixed carbon is lost through an oxidative process. Different approaches to reduce carbon and nitrogen loss were discussed. Overall, the potential approaches to improve the photosynthetic process and the way forward were discussed in detail.

From leaf to multiscale models of photosynthesis: applications and challenges for crop improvement

To keep up with the growth of human population and to circumvent deleterious effects of global climate change, it is essential to enhance crop yield to achieve higher production. Here we review mathematical models of oxygenic photosynthesis that are extensively used, and discuss in depth a subset that accounts for diverse approaches providing solutions to our objective. These include models (1) to study different ways to enhance photosynthesis, such as fine-tuning antenna size, photoprotection and electron transport; (2) to bioengineer carbon metabolism; and (3) to evaluate the interactions between the process of photosynthesis and the seasonal crop dynamics, or those that have included statistical whole-genome prediction methods to quantify the impact of photosynthesis traits on the improvement of crop yield. We conclude by emphasizing that the results obtained in these studies clearly demonstrate that mathematical modelling is a key tool to examine different approaches to improve photosynthesis for better productivity, while effective multiscale crop models, especially those that also include remote sensing data, are indispensable to verify different strategies to obtain maximized crop yields.

The Calvin-Benson-Bassham cycle in C4 and Crassulacean acid metabolism species

The Calvin-Benson-Bassham (CBB) cycle is the ancestral CO2 assimilation pathway and is found in all photosynthetic organisms. Biochemical extensions to the CBB cycle have evolved that allow the resulting pathways to act as CO2 concentrating mechanisms, either spatially in the case of C4 photosynthesis or temporally in the case of Crassulacean acid metabolism (CAM). While the biochemical steps in the C4 and CAM pathways are known, questions remain on their integration and regulation with CBB cycle activity. The application of omic and transgenic technologies is providing a more complete understanding of the biochemistry of C4 and CAM species and will also provide insight into the CBB cycle in these plants. As the global population increases, new solutions are required to increase crop yields and meet demands for food and other bioproducts. Previous work in C3 species has shown that increasing carbon assimilation through genetic manipulation of the CBB cycle can increase biomass and yield. There may also be options to improve photosynthesis in species using C4 photosynthesis and CAM through manipulation of the CBB cycle in these plants. This is an underexplored strategy and requires more basic knowledge of CBB cycle operation in these species to enable approaches for increased productivity.

Perspectives on improving crop Rubisco by directed evolution

Rubisco catalyses the entry of almost all CO2 into the biosphere and is often the rate-limiting step in plant photosynthesis and growth. Its notoriety as the most abundant protein on Earth stems from the slow and error-prone catalytic properties that require plants, cyanobacteria, algae and photosynthetic bacteria to produce it in high amounts. Efforts to improve the CO2-fixing properties of plant Rubisco has been spurred on by the discovery of more effective isoforms in some algae with the potential to significantly improve crop productivity. Incompatibilities between the protein folding machinery of leaf and algae chloroplasts have, so far, prevented efforts to transplant these more effective Rubisco variants into plants. There is therefore increasing interest in improving Rubisco catalysis by directed (laboratory) evolution. Here we review the advances being made in, and the ongoing challenges with, improving the solubility and/or carboxylation activity of differing non-plant Rubisco lineages. We provide perspectives on new opportunities for the directed evolution of crop Rubiscos and the existing plant transformation capabilities available to evaluate the extent to which Rubisco activity improvements can benefit agricultural productivity.

Creating new-to-nature carbon fixation: A guide

Synthetic biology aims at designing new biological functions from first principles. These new designs allow to expand the natural solution space and overcome the limitations of naturally evolved systems. One example is synthetic CO2-fixation pathways that promise to provide more efficient ways for the capture and conversion of CO2 than natural pathways, such as the Calvin Benson Bassham (CBB) cycle of photosynthesis. In this review, we provide a practical guideline for the design and realization of such new-to-nature CO2-fixation pathways. We introduce the concept of "synthetic CO2-fixation", and give a general overview over the enzymology and topology of synthetic pathways, before we derive general principles for their design from their eight naturally evolved analogs. We provide a comprehensive summary of synthetic carbon-assimilation pathways and derive a step-by-step, practical guide from the theoretical design to their practical implementation, before ending with an outlook on new developments in the field.

Contrasting leaf-scale photosynthetic low-light response and its temperature dependency are key to differences in crop-scale radiation use efficiency

Radiation use efficiency (RUE) is a key crop adaptation trait that quantifies the potential amount of aboveground biomass produced by the crop per unit of solar energy intercepted. But it is unclear why elite maize and grain sorghum hybrids differ in their RUE at the crop level. Here, we used a non-traditional top-down approach via canopy photosynthesis modelling to identify leaf-level photosynthetic traits that are key to differences in crop-level RUE. A novel photosynthetic response measurement was developed and coupled with use of a Bayesian model fitting procedure, incorporating a C4 leaf photosynthesis model, to infer cohesive sets of photosynthetic parameters by simultaneously fitting responses to CO2 , light, and temperature. Statistically significant differences between leaf photosynthetic parameters of elite maize and grain sorghum hybrids were found across a range of leaf temperatures, in particular for effects on the quantum yield of photosynthesis, but also for the maximum enzymatic activity of Rubisco and PEPc. Simulation of diurnal canopy photosynthesis predicted that the leaf-level photosynthetic low-light response and its temperature dependency are key drivers of the performance of crop-level RUE, generating testable hypotheses for further physiological analysis and bioengineering applications.

Fast Assimilation-Temperature Response: a FAsTeR method for measuring the temperature dependence of leaf-level photosynthesis

We present the Fast Assimilation-Temperature Response (FAsTeR) method, a new method for measuring plant assimilation-temperature (AT) response that reduces measurement time and increases data density compared with conventional methods. The FAsTeR method subjects plant leaves to a linearly increasing temperature ramp while taking rapid, nonequilibrium measurements of gas exchange variables. Two postprocessing steps are employed to correct measured assimilation rates for nonequilibrium effects and sensor calibration drift. Results obtained with the new method are compared with those from two conventional stepwise methods. Our new method accurately reproduces results obtained from conventional methods, reduces measurement time by a factor of c. 3.3 (from c. 90 to 27 min), and increases data density by a factor of c. 55 (from c. 10 to c. 550 observations). Simulation results demonstrate that increased data density substantially improves confidence in parameter estimates and drastically reduces the influence of noise. By improving measurement speed and data density, the FAsTeR method enables users to ask fundamentally new kinds of ecological and physiological questions, expediting data collection in short-field campaigns, and improving the representativeness of data across species in the literature.

CLAW: An automated Snakemake workflow for the assembly of chloroplast genomes from long-read data

Chloroplasts are photosynthetic organelles in algal and plant cells that contain their own genome. Chloroplast genomes are commonly used in evolutionary studies and taxonomic identification and are increasingly becoming a target for crop improvement studies. As DNA sequencing becomes more affordable, researchers are collecting vast swathes of high-quality whole-genome sequence data from laboratory and field settings alike. Whole tissue read libraries sequenced with the primary goal of understanding the nuclear genome will inadvertently contain many reads derived from the chloroplast genome. These whole-genome, whole-tissue read libraries can additionally be used to assemble chloroplast genomes with little to no extra cost. While several tools exist that make use of short-read second generation and third-generation long-read sequencing data for chloroplast genome assembly, these tools may have complex installation steps, inadequate error reporting, poor expandability, and/or lack scalability. Here, we present CLAW (Chloroplast Long-read Assembly Workflow), an easy to install, customise, and use Snakemake tool to assemble chloroplast genomes from chloroplast long-reads found in whole-genome read libraries (https://github.com/aaronphillips7493/CLAW). Using 19 publicly available reference chloroplast genome assemblies and long-read libraries from algal, monocot and eudicot species, we show that CLAW can rapidly produce chloroplast genome assemblies with high similarity to the reference assemblies. CLAW was designed such that users have complete control over parameterisation, allowing individuals to optimise CLAW to their specific use cases. We expect that CLAW will provide researchers (with varying levels of bioinformatics expertise) with an additional resource useful for contributing to the growing number of publicly available chloroplast genome assemblies.

Plants and global warming: challenges and strategies for a warming world

KEY MESSAGE

In this review, we made an attempt to create a holistic picture of plant response to a rising temperature environment and its impact by covering all aspects from temperature perception to thermotolerance. This comprehensive account describing the molecular mechanisms orchestrating these responses and potential mitigation strategies will be helpful for understanding the impact of global warming on plant life. Organisms need to constantly recalibrate development and physiology in response to changes in their environment. Climate change-associated global warming is amplifying the intensity and periodicity of these changes. Being sessile, plants are particularly vulnerable to variations happening around them. These changes can cause structural, metabolomic, and physiological perturbations, leading to alterations in the growth program and in extreme cases, plant death. In general, plants have a remarkable ability to respond to these challenges, supported by an elaborate mechanism to sense and respond to external changes. Once perceived, plants integrate these signals into the growth program so that their development and physiology can be modulated befittingly. This multifaceted signaling network, which helps plants to establish acclimation and survival responses enabled their extensive geographical distribution. Temperature is one of the key environmental variables that affect all aspects of plant life. Over the years, our knowledge of how plants perceive temperature and how they respond to heat stress has improved significantly. However, a comprehensive mechanistic understanding of the process still largely elusive. This review explores how an increase in the global surface temperature detrimentally affects plant survival and productivity and discusses current understanding of plant responses to high temperature (HT) and underlying mechanisms. We also highlighted potential resilience attributes that can be utilized to mitigate the impact of global warming.

Kinetic modeling identifies targets for engineering improved photosynthetic efficiency in potato (Solanum tuberosum cv. Solara)

Potato (Solanum tuberosum) is a significant non-grain food crop in terms of global production. However, its yield potential might be raised by identifying means to release bottlenecks within photosynthetic metabolism, from the capture of solar energy to the synthesis of carbohydrates. Recently, engineered increases in photosynthetic rates in other crops have been directly related to increased yield - how might such increases be achieved in potato? To answer this question, we derived the photosynthetic parameters Vcmax and Jmax to calibrate a kinetic model of leaf metabolism (e-Photosynthesis) for potato. This model was then used to simulate the impact of manipulating the expression of genes and their protein products on carbon assimilation rates in silico through optimizing resource investment among 23 photosynthetic enzymes, predicting increases in photosynthetic CO2 uptake of up to 67%. However, this number of manipulations would not be practical with current technologies. Given a limited practical number of manipulations, the optimization indicated that an increase in amounts of three enzymes - Rubisco, FBP aldolase, and SBPase - would increase net assimilation. Increasing these alone to the levels predicted necessary for optimization increased photosynthetic rate by 28% in potato.

Spectral Reflectance Measurements

This chapter provides a methodology for evaluating plant health and leaf characteristics using spectral reflectance. It provides a step-by-step guide to using spectrometers for high-resolution point measurements of leaf spectral reflectance and multispectral imaging for capturing spatial data, emphasizing the importance of consistent measurement conditions. The chapter further explores the intricacies of multispectral imaging, including calibration, data collection, and image processing. Finally, this chapter delves into the application of various spectral indices for the quantification of key traits such as pigment content, the status of the xanthophyll cycle, water content, and how to identify spectral regions of interest for further research and development. Serving as a guide for researchers and practitioners in plant science, this chapter provides a straightforward framework for plant health assessment using spectral reflectance.

Photosynthesis governed by nanoparticulate titanium dioxide. The Pisum sativum L. case study

Wide availability of anthropogenic TiO2 nanoparticles facilitates their penetration into environment and prompts interactions with plants. They alter plants growth and change their nutritional status. In particular, metabolic processes are affected. In this work the effect of nanometric TiO2 on photosynthesis efficiency in green pea (Pisum sativum L.) was studied. Hydroponic cultivations with three Ti levels (10; 50 and 100 mg L-1) were applied. At all concentrations nanoparticles penetrated into plant tissues and were detected by the single particle ICP-MS/MS method. Nanoparticles altered the CO2 assimilation rate and gas exchange parameters (i.e. transpiration, stomatal conductance, sub-stomatal CO2 concentration). The most pronounced effects were observed for Ti 50 mg L-1 cultivation where photosynthesis efficiency, transpiration and stomatal conductance were increased by 14.69%, 4.58% and 8.92%, respectively. They were further confirmed by high maximum ribulose 1,5-bisphosphate carboxylation rate (27.40% increase), maximum electron transport rate (21.51% increase) and the lowest CO2 compensation point (45.19% decrease). Furthermore, concentrations of Cu, Mn, Zn, Fe, Mg, Ca, K and P were examined with the most pronounced changes observed for elements directly involved in photosynthesis (Cu, Zn, Mn, and Fe). The Cu concentrations in roots, stems and leaves for Ti 50 mg L-1 cultivation were below the control by 33.15%, 38.28% and 10.76%, respectively. The Zn content in analogous treatment and organs decreased by 30.24%, 26.69% and 13.35%. The Mn and Fe levels in leaves were increased by 72.22% and 50.32%, respectively. Our results indicated that plant defence mechanisms which restrain the water uptake have been overcome in pea by photocatalytic activity of nanoparticulate TiO2 which stimulated photosynthesis. On the contrary to the substantial stomatal conductance, the transpiration has been reduced because exceptional part of water flow was already consumed in chloroplasts and could not have been freed to the atmosphere.

Nitrogen-potassium balance improves leaf photosynthetic capacity by regulating leaf nitrogen allocation in apple

Nitrogen (N) and potassium (K) are two important mineral nutrients in regulating leaf photosynthesis. However, the influence of N and K interaction on photosynthesis is still not fully understood. Using a hydroponics approach, we studied the effects of different N and K conditions on the physiological characteristics, N allocation and photosynthetic capacity of apple rootstock M9T337. The results showed that high N and low K conditions significantly reduced K content in roots and leaves, resulting in N/K imbalance, and allocated more N in leaves to non-photosynthetic N. Low K conditions increased biochemical limitation (BL), mesophyll limitation (MCL), and stomatal limitation (SL). By setting different N supplies, lowering N levels under low K conditions increased the proportion of water-soluble protein N (Nw) and sodium dodecyl sulfate-soluble proteins (Ns) by balancing N/K and increased the proportion of carboxylation N and electron transfer N. This increased the maximum carboxylation rate and mesophyll conductance, which reduced MCL and BL and alleviated the low K limitation of photosynthesis in apple rootstocks. In general, our results provide new insights into the regulation of photosynthetic capacity by N/K balance, which is conducive to the coordinated supply of N and K nutrients.

Quantifying the role of genome size and repeat content in adaptive variation and the architecture of flowering time in Amaranthus tuberculatus

Genome size variation, largely driven by repeat content, is poorly understood within and among populations, limiting our understanding of its significance for adaptation. Here we characterize intraspecific variation in genome size and repeat content across 186 individuals of Amaranthus tuberculatus, a ubiquitous native weed that shows flowering time adaptation to climate across its range and in response to agriculture. Sequence-based genome size estimates vary by up to 20% across individuals, consistent with the considerable variability in the abundance of transposable elements, unknown repeats, and rDNAs across individuals. The additive effect of this variation has important phenotypic consequences-individuals with more repeats, and thus larger genomes, show slower flowering times and growth rates. However, compared to newly-characterized gene copy number and polygenic nucleotide changes underlying variation in flowering time, we show that genome size is a marginal contributor. Differences in flowering time are reflected by genome size variation across sexes and marginally, habitats, while polygenic variation and a gene copy number variant within the ATP synthesis pathway show consistently stronger environmental clines than genome size. Repeat content nonetheless shows non-neutral distributions across the genome, and across latitudinal and environmental gradients, demonstrating the numerous governing processes that in turn influence quantitative genetic variation for phenotypes key to plant adaptation.

Prospects of chloroplast metabolic engineering for developing nutrient-dense food crops

Addressing nutritional deficiencies in food crops through biofortification is a sustainable approach to tackling malnutrition. Biofortification is continuously being attempted through conventional breeding as well as through various plant biotechnological interventions, ranging from molecular breeding to genetic engineering and genome editing for enriching crops with various health-promoting metabolites. Genetic engineering is used for the rational incorporation of desired nutritional traits in food crops and predominantly operates through nuclear and chloroplast genome engineering. In the recent past, chloroplast engineering has been deployed as a strategic tool to develop model plants with enhanced nutritional traits due to the various advantages it offers over nuclear genome engineering. However, this approach needs to be extended for the nutritional enhancement of major food crops. Further, this platform could be combined with strategies, such as synthetic biology, chloroplast editing, nanoparticle-mediated rapid chloroplast transformation, and horizontal gene transfer through grafting for targeting endogenous metabolic pathways for overproducing native nutraceuticals, production of biopharmaceuticals, and biosynthesis of designer nutritional compounds. This review focuses on exploring various features of chloroplast genome engineering for nutritional enhancement of food crops by enhancing the levels of existing metabolites, restoring the metabolites lost during crop domestication, and introducing novel metabolites and phytonutrients needed for a healthy daily diet.

Effects of exogenous zinc (ZnSO4·7H2O) on photosynthetic characteristics and grain quality of hybrid rice

Rice is an important food crop and zinc (Zn) is a beneficial microelement. However, there are few reports on the effect of zinc on yield and physiological characteristics of rice. In this study, exogenous zinc (ZnSO4·7H2O) was applied on plant to explore the effects of zinc on rice yield, quality and photosynthetic capacity. The results showed that appropriate concentration of zinc could increase the net photosynthetic rate (Pn) of rice leaves, and Zn2 (2 mg/L ZnSO4•7H2O) treatment was the most significant. However, the Zn treatment had no positive effect on rice yield except under the concentration of Zn2. Meanwhile, the result showed that Zn treatment could increase chalkiness degree (CD) and chalky grain rate (CGR), decreased amylose content (AC), increased protein content and changed protein composition of rice. The above indexes were most significant in Zn2 treatment. In addition, the Zn2 treatment significantly increased rapid viscosity analyzer (RVA) of rice. In conclusion, the results of this study suggested that Zn treatment could enhance the photosynthetic capacity of rice leaves, and improve the processing quality, taste quality and nutritional quality of rice. However, it will have a negative impact on the appearance quality of rice and cannot be used to increase rice production. This study will provide a basis for the application of zinc in rice production.

Expression of the plastocyanin gene PETE2 in Camelina sativa improves seed yield and salt tolerance

Plastocyanin functions as an electron carrier in the photosynthetic electron transport chain, located at the thylakoid membrane. In several species, endogenous plastocyanin levels are correlated with the photosynthetic electron transport rate. Overexpression of plastocyanin genes in Arabidopsis thaliana increases plant size, but this phenomenon has not been observed in crop species. Here, we investigated the effects of heterologous expression of a gene encoding a plastocyanin isoform from Arabidopsis, AtPETE2, in the oil seed crop Camelina sativa under standard growth conditions and under salt stress. AtPETE2 heterologous expression enhanced photosynthetic activity in Camelina, accelerating plant development and improving seed yield under standard growth conditions. Additionally, CsPETE2 from Camelina was induced by salt stress and AtPETE2 expression lines had larger primary roots and more lateral roots than the wild type. AtPETE2 expression lines also had larger seeds and higher total seed yield under long-term salt stress compared with non-transgenic Camelina. Our results demonstrate that increased plastocyanin levels in Camelina can enhance photosynthesis and productivity, as well as tolerance to osmotic and salt stresses. Heterologous expression of plastocyanin may be a useful strategy to mitigate crop stress in saline soils.

Machine learning in photosynthesis: Prospects on sustainable crop development

Improving photosynthesis is a promising avenue to increase food security. Studying photosynthetic traits with the aim to improve efficiency has been one of many strategies to increase crop yield but analyzing large data sets presents an ongoing challenge. Machine learning (ML) represents a ubiquitous tool that can provide a more elaborate data analysis. Here we review the application of ML in various domains of photosynthetic research, as well as in photosynthetic pigment studies. We highlight how correlating hyperspectral data with photosynthetic parameters to improve crop yield could be achieved through various ML algorithms. We also propose strategies to employ ML in promoting photosynthetic pigment research for furthering crop yield.

Metabolic pathways engineering for drought or/and heat tolerance in cereals

Drought (D) and heat (H) are the two major abiotic stresses hindering cereal crop growth and productivity, either singly or in combination (D/+H), by imposing various negative impacts on plant physiological and biochemical processes. Consequently, this decreases overall cereal crop production and impacts global food availability and human nutrition. To achieve global food and nutrition security vis-a-vis global climate change, deployment of new strategies for enhancing crop D/+H stress tolerance and higher nutritive value in cereals is imperative. This depends on first gaining a mechanistic understanding of the mechanisms underlying D/+H stress response. Meanwhile, functional genomics has revealed several stress-related genes that have been successfully used in target-gene approach to generate stress-tolerant cultivars and sustain crop productivity over the past decades. However, the fast-changing climate, coupled with the complexity and multigenic nature of D/+H tolerance suggest that single-gene/trait targeting may not suffice in improving such traits. Hence, in this review-cum-perspective, we advance that targeted multiple-gene or metabolic pathway manipulation could represent the most effective approach for improving D/+H stress tolerance. First, we highlight the impact of D/+H stress on cereal crops, and the elaborate plant physiological and molecular responses. We then discuss how key primary metabolism- and secondary metabolism-related metabolic pathways, including carbon metabolism, starch metabolism, phenylpropanoid biosynthesis, γ-aminobutyric acid (GABA) biosynthesis, and phytohormone biosynthesis and signaling can be modified using modern molecular biotechnology approaches such as CRISPR-Cas9 system and synthetic biology (Synbio) to enhance D/+H tolerance in cereal crops. Understandably, several bottlenecks hinder metabolic pathway modification, including those related to feedback regulation, gene functional annotation, complex crosstalk between pathways, and metabolomics data and spatiotemporal gene expressions analyses. Nonetheless, recent advances in molecular biotechnology, genome-editing, single-cell metabolomics, and data annotation and analysis approaches, when integrated, offer unprecedented opportunities for pathway engineering for enhancing crop D/+H stress tolerance and improved yield. Especially, Synbio-based strategies will accelerate the development of climate resilient and nutrient-dense cereals, critical for achieving global food security and combating malnutrition.

Photosynthetic Response of Blueberries Grown in Containers

Recently, there has been increased interest in container blueberry production as a viable alternative to open-field blueberry planting. Container production of blueberries offers numerous advantages, among these, a lack of limitation by suboptimal soil conditions in the open field and the ability to control substrate pH, drainage, and organic matter. The photosynthetic response for three container-grown Southern highbush blueberry (interspecific Vaccinium hybrids) cultivars including 'Jewel', 'Meadowlark', and 'Victoria' and a rabbiteye blueberry (Vaccinium virgatum) 'Baldwin', were measured during the spring and summer of 2022. It was hypothesized that the three cultivars evaluated would have different photosynthetic responses. The objective of this study was to determine the photosynthetic activity of different blueberry cultivars during the first year of crop establishment. A series of measurements were conducted every 2 h throughout the day and for different dates using a gas exchange data analyzer on newly matured fully expanded leaves located in the top middle section of the canopy for each cultivar. The response curves showed that net photosynthesis (A) became saturated at moderate light, with saturation occurring at a photosynthetic photon flux density (PPFD) of 1932 µmol m-2 s-1. At this point, the rate of CO2 assimilation was approximately 16.84 µmol CO2 m-2 s-1. No differences in (A) were found among cultivars. Overall, the attained values of photosynthesis provide a strong conceptual basis for understanding the cultivar variation response when grown in containers; therefore, the containerized system may serve as a production system for early fruiting blueberries in Alabama, USA.

Enhancing photosynthetic CO2 fixation by assembling metal-organic frameworks on Chlorella pyrenoidosa

The CO2 concentration at ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is crucial to improve photosynthetic efficiency for biomass yield. However, how to concentrate and transport atmospheric CO2 towards the Rubisco carboxylation is a big challenge. Herein, we report the self-assembly of metal-organic frameworks (MOFs) on the surface of the green alga Chlorella pyrenoidosa that can greatly enhance the photosynthetic carbon fixation. The chemical CO2 concentrating approach improves the apparent photo conversion efficiency to about 1.9 folds, which is up to 9.8% in ambient air from an intrinsic 5.1%. We find that the efficient carbon fixation lies in the conversion of the captured CO2 to the transportable HCO3- species at bio-organic interface. This work demonstrates a chemical approach of concentrating atmospheric CO2 for enhancing biomass yield of photosynthesis.

Is chloroplast size optimal for photosynthetic efficiency?

Improving photosynthetic efficiency has recently emerged as a promising way to increase crop production in a sustainable manner. While chloroplast size may affect photosynthetic efficiency in several ways, we aimed to explore whether chloroplast size manipulation can be a viable approach to improving photosynthetic performance. Several tobacco (Nicotiana tabacum) lines with contrasting chloroplast sizes were generated via manipulation of chloroplast division genes to assess photosynthetic performance under steady-state and fluctuating light. A selection of lines was included in a field trial to explore productivity. Lines with enlarged chloroplasts underperformed in most of the measured traits. Lines with smaller and more numerous chloroplasts showed a similar efficiency compared with wild-type (WT) tobacco. Chloroplast size only weakly affected light absorptance and light profiles within the leaf. Increasing chloroplast size decreased mesophyll conductance (gm ) but decreased chloroplast size did not increase gm . Increasing chloroplast size reduced chloroplast movements and enhanced non-photochemical quenching. The chloroplast smaller than WT appeared to be no better than WT for photosynthetic efficiency and productivity under field conditions. The results indicate that chloroplast size manipulations are therefore unlikely to lead to higher photosynthetic efficiency or growth.

Phosphoribulokinase abundance is not limiting the Calvin-Benson-Bassham cycle in Chlamydomonas reinhardtii

Improving photosynthetic efficiency in plants and microalgae is of utmost importance to support the growing world population and to enable the bioproduction of energy and chemicals. Limitations in photosynthetic light conversion efficiency can be directly attributed to kinetic bottlenecks within the Calvin-Benson-Bassham cycle (CBBC) responsible for carbon fixation. A better understanding of these bottlenecks in vivo is crucial to overcome these limiting factors through bio-engineering. The present study is focused on the analysis of phosphoribulokinase (PRK) in the unicellular green alga Chlamydomonas reinhardtii. We have characterized a PRK knock-out mutant strain and showed that in the absence of PRK, Chlamydomonas cannot grow photoautotrophically while functional complementation with a synthetic construct allowed restoration of photoautotrophy. Nevertheless, using standard genetic elements, the expression of PRK was limited to 40% of the reference level in complemented strains and could not restore normal growth in photoautotrophic conditions suggesting that the CBBC is limited. We were subsequently able to overcome this initial limitation by improving the design of the transcriptional unit expressing PRK using diverse combinations of DNA parts including PRK endogenous promoter and introns. This enabled us to obtain strains with PRK levels comparable to the reference strain and even overexpressing strains. A collection of strains with PRK levels between 16% and 250% of WT PRK levels was generated and characterized. Immunoblot and growth assays revealed that a PRK content of ≈86% is sufficient to fully restore photoautotrophic growth. This result suggests that PRK is present in moderate excess in Chlamydomonas. Consistently, the overexpression of PRK did not increase photosynthetic growth indicating that that the endogenous level of PRK in Chlamydomonas is not limiting the Calvin-Benson-Bassham cycle under optimal conditions.

Coping with the cold: unveiling cryoprotectants, molecular signaling pathways, and strategies for cold stress resilience

Low temperature stress significantly threatens crop productivity and economic sustainability. Plants counter this by deploying advanced molecular mechanisms to perceive and respond to cold stress. Transmembrane proteins initiate these responses, triggering a series of events involving secondary messengers such as calcium ions (Ca2+), reactive oxygen species (ROS), and inositol phosphates. Of these, calcium signaling is paramount, activating downstream phosphorylation cascades and the transcription of cold-responsive genes, including cold-regulated (COR) genes. This review focuses on how plants manage freeze-induced damage through dual strategies: cold tolerance and cold avoidance. Tolerance mechanisms involve acclimatization to decreasing temperatures, fostering gradual accumulation of cold resistance. In contrast, avoidance mechanisms rely on cryoprotectant molecules like potassium ions (K+), proline, glycerol, and antifreeze proteins (AFPs). Cryoprotectants modulate intracellular solute concentration, lower the freezing point, inhibit ice formation, and preserve plasma membrane fluidity. Additionally, these molecules demonstrate antioxidant activity, scavenging ROS, preventing protein denaturation, and subsequently mitigating cellular damage. By forming extensive hydrogen bonds with water molecules, cryoprotectants also limit intercellular water movement, minimizing extracellular ice crystal formation, and cell dehydration. The deployment of cryoprotectants is a key adaptive strategy that bolsters plant resilience to cold stress and promotes survival in freezing environments. However, the specific physiological and molecular mechanisms underlying these protective effects remain insufficiently understood. Therefore, this review underscores the need for further research to elucidate these mechanisms and assess their potential impact on crop productivity and sustainability, contributing to the progressive discourse in plant biology and environmental science.

Glyceraldehyde-3-phosphate dehydrogenase subunits A and B are essential to maintain photosynthetic efficiency

In plants, glyceraldehyde-3-phosphate dehydrogenase (GAPDH; EC 1.2.1.12) reversibly converts 1,3-bisphosphoglycerate to glyceraldehyde-3-phosphate coupled with the reduction of NADPH to NADP+. The GAPDH enzyme that functions in the Calvin-Benson cycle is assembled either from 4 glyceraldehyde-3-phosphate dehydrogenase A (GAPA) subunit proteins forming a homotetramer (A4) or from 2 GAPA and 2 glyceraldehyde-3-phosphate dehydrogenase B (GAPB) subunit proteins forming a heterotetramer (A2B2). The relative importance of these 2 forms of GAPDH in determining the rate of photosynthesis is unknown. To address this question, we measured the photosynthetic rates of Arabidopsis (Arabidopsis thaliana) plants containing reduced amounts of the GAPDH A and B subunits individually and jointly, using T-DNA insertion lines of GAPA and GAPB and transgenic GAPA and GAPB plants with reduced levels of these proteins. Here, we show that decreasing the levels of either the A or B subunits decreased the maximum efficiency of CO2 fixation, plant growth, and final biomass. Finally, these data showed that the reduction in GAPA protein to 9% wild-type levels resulted in a 73% decrease in carbon assimilation rates. In contrast, eliminating GAPB protein resulted in a 40% reduction in assimilation rates. This work demonstrates that the GAPA homotetramer can compensate for the loss of GAPB, whereas GAPB alone cannot compensate fully for the loss of the GAPA subunit.

Quantifying Contributions of Different Factors to Canopy Photosynthesis in 2 Maize Varieties: Development of a Novel 3D Canopy Modeling Pipeline

Crop yield potential is intrinsically related to canopy photosynthesis; therefore, improving canopy photosynthetic efficiency is a major focus of current efforts to enhance crop yield. Canopy photosynthesis rate (Ac) is influenced by several factors, including plant architecture, leaf chlorophyll content, and leaf photosynthetic properties, which interact with each other. Identifying factors that restrict canopy photosynthesis and target adjustments to improve canopy photosynthesis in a specific crop cultivar pose an important challenge for the breeding community. To address this challenge, we developed a novel pipeline that utilizes factorial analysis, canopy photosynthesis modeling, and phenomics data collected using a 64-camera multi-view stereo system, enabling the dissection of the contributions of different factors to differences in canopy photosynthesis between maize cultivars. We applied this method to 2 maize varieties, W64A and A619, and found that leaf photosynthetic efficiency is the primary determinant (17.5% to 29.2%) of the difference in Ac between 2 maize varieties at all stages, and plant architecture at early stages also contribute to the difference in Ac (5.3% to 6.7%). Additionally, the contributions of each leaf photosynthetic parameter and plant architectural trait were dissected. We also found that the leaf photosynthetic parameters were linearly correlated with Ac and plant architecture traits were non-linearly related to Ac. This study developed a novel pipeline that provides a method for dissecting the relationship among individual phenotypes controlling the complex trait of canopy photosynthesis.

Effect of cornstalk biochar on phytoremediation of Pb-contaminated soil by females and males of Populus deltoides (Salicaceae)

Soil pollution with lead (Pb) has become a serious global concern, adversely affecting the forest ecosystem. This study was conducted to investigate the effects of corn straw on the remediation efficiency of Pb-contaminated soil using Populus deltoides. Female and male P. deltoides cuttings were subjected to soil spiked with 900 mg kg-1 Pb and amended with 5% (v/v) corn straw biochar for 90 days. Under Pb stress, the addition of biochar significantly increased the total biomass accumulation by 29% in females and 26% in males. However, without the addition of biochar, the biomass accumulation was significantly reduced by 11% in females and 3% in males under Pb stress. Females showed a higher uptake and accumulation of Pb in roots and leaves, while males accumulated more Pb in roots and stems and exhibited an increased anti-oxidative capacity. Biochar addition alleviated Pb toxicity in both male and female P. deltoides by immobilizing Pb ion in the soil, reducing Pb uptake and translocation, promoting nutrient uptake, and improving the diversity and stability of the soil bacteria community. Under Pb stress, the relative abundances of metal-resistance bacteria significantly increased, such as the abundance of Bacteroidetes in females and the abundances of Actinobacteria, Firmicutes, and Planctomycetes in males. In brief, the males under biochar addition exhibited promising potential as candidates for phytoremediation of Pb-contaminated soil. This study provides new insights into mechanisms underlying sexually differential responses to Pb stress in the presence of biochar amendment.

Fruit Photosynthesis: More to Know about Where, How and Why

Not only leaves but also other plant organs and structures typically considered as carbon sinks, including stems, roots, flowers, fruits and seeds, may exhibit photosynthetic activity. There is still a lack of a coherent and systematized body of knowledge and consensus on the role(s) of photosynthesis in these "sink" organs. With regard to fruits, their actual photosynthetic activity is influenced by a range of properties, including fruit anatomy, histology, physiology, development and the surrounding microclimate. At early stages of development fruits generally contain high levels of chlorophylls, a high density of functional stomata and thin cuticles. While some plant species retain functional chloroplasts in their fruits upon subsequent development or ripening, most species undergo a disintegration of the fruit chloroplast grana and reduction in stomata functionality, thus limiting gas exchange. In addition, the increase in fruit volume hinders light penetration and access to CO₂, also reducing photosynthetic activity. This review aimed to compile information on aspects related to fruit photosynthesis, from fruit characteristics to ecological drivers, and to address the following challenging biological questions: why does a fruit show photosynthetic activity and what could be its functions? Overall, there is a body of evidence to support the hypothesis that photosynthesis in fruits is key to locally providing: ATP and NADPH, which are both fundamental for several demanding biosynthetic pathways (e.g., synthesis of fatty acids); O₂, to prevent hypoxia in its inner tissues including seeds; and carbon skeletons, which can fuel the biosynthesis of primary and secondary metabolites important for the growth of fruits and for spreading, survival and germination of their seed (e.g., sugars, flavonoids, tannins, lipids). At the same time, both primary and secondary metabolites present in fruits and seeds are key to human life, for instance as sources for nutrition, bioactives, oils and other economically important compounds or components. Understanding the functions of photosynthesis in fruits is pivotal to crop management, providing a rationale for manipulating microenvironmental conditions and the expression of key photosynthetic genes, which may help growers or breeders to optimize development, composition, yield or other economically important fruit quality aspects.

Response of in situ root phenotypes to potassium stress in cotton

Potassium plays a significant role in the basic functions of plant growth and development. Potassium uptake is closely associated with morphological characteristics of the roots. However, the dynamic characteristics of phenotype and lifespan of cotton (Gossypium hirsutum L.) lateral roots and root hairs under low and high potassium stress remain unclear. In this study, potassium stress experiments (low and high potassium, medium potassium as control) were conducted using RhizoPot (an in situ root observation device) to determine the response characteristics of lateral roots and root hairs in cotton under potassium stress. The plant morphology, photosynthetic characteristics, root phenotypic changes, and lifespan of lateral roots and root hairs were measured. Potassium accumulation, aboveground phenotype, photosynthetic capacity, root length density, root dry weight, root diameter, lateral root lifespan, and root hair lifespan under low potassium stress were significantly decreased compared to medium potassium treatment. However, the root hair length of the former was significantly increased than that of the latter. Potassium accumulation and the lateral root lifespan were significantly increased under high potassium treatment, while root length density, root dry weight, root diameter, root hair length, and root hair lifespan were significantly decreased compared to the medium potassium treatment. Notably, there were no significant differences in aboveground morphology and photosynthetic characters. Principal component analysis revealed that lateral root lifespan, root hair lifespan of the first lateral root, and root hair length significantly correlated with potassium accumulation. The root had similar regularity responses to low and high potassium stress except for lifespan and root hair length. The findings of this study enhance the understanding of the phenotype and lifespan of cotton's lateral roots and root hairs under low and high potassium stress.

Concurrence of microplastics and heat waves reduces rice yields and disturbs the agroecosystem nitrogen cycle

Microplastic pollution and heat waves, as damaging aspects of human activities, have been found to affect crop production and nitrogen (N) cycling in agroecosystems. However, the impacts of the combination of heat waves and microplastics on crop production and quality have not been analyzed. We found that heat waves or microplastics alone had slight effects on rice physiological parameters and soil microbial communities. However, under heat wave conditions, the typical low-density polyethylene (LDPE) and polylactic acid (PLA) microplastics decreased the rice yields by 32.1% and 32.9%, decreased the grain protein level by 4.5% and 2.8%, and decreased the lysine level by 91.1% and 63.6%, respectively. In the presence of heat waves, microplastics increased the allocation and assimilation of N in roots and stems but decreased those in leaves, which resulted in a reduction in photosynthesis. In soil, the concurrence of microplastics and heat waves induced the leaching of microplastics, which resulted in decreased microbial N functionality and disturbed N metabolism. In summary, heat waves amplified the disturbance induced by microplastics on the agroecosystem N cycle and therefore exacerbated the decreases in rice yield and nutrients induced by microplastics, which indicates that the environmental and food risks of microplastics deserve to be reconsidered.

Grafting Rhodobacter sphaeroides with red algae Rubisco to accelerate catalysis and plant growth

Improving the carboxylation properties of Rubisco has primarily arisen from unforeseen amino acid substitutions remote from the catalytic site. The unpredictability has frustrated rational design efforts to enhance plant Rubisco towards the prized growth-enhancing carboxylation properties of red algae Griffithsia monilis GmRubisco. To address this, we determined the crystal structure of GmRubisco to 1.7 Å. Three structurally divergent domains were identified relative to the red-type bacterial Rhodobacter sphaeroides RsRubisco that, unlike GmRubisco, are expressed in Escherichia coli and plants. Kinetic comparison of 11 RsRubisco chimaeras revealed that incorporating C329A and A332V substitutions from GmRubisco Loop 6 (corresponding to plant residues 328 and 331) into RsRubisco increased the carboxylation rate (kcatc) by 60%, the carboxylation efficiency in air by 22% and the CO2/O2 specificity (Sc/o) by 7%. Plastome transformation of this RsRubisco Loop 6 mutant into tobacco enhanced photosynthesis and growth up to twofold over tobacco producing wild-type RsRubisco. Our findings demonstrate the utility of RsRubisco for the identification and in planta testing of amino acid grafts from algal Rubisco that can enhance the enzyme's carboxylase potential.

Modelling plants across scales of biological organisation for guiding crop improvement

Grain yield improvement in globally important staple crops is critical in the coming decades if production is to keep pace with growing demand; so there is increasing interest in understanding and manipulating plant growth and developmental traits for better crop productivity. However, this is confounded by complex cross-scale feedback regulations and a limited ability to evaluate the consequences of manipulation on crop production. Plant/crop modelling could hold the key to deepening our understanding of dynamic trait-crop-environment interactions and predictive capabilities for supporting genetic manipulation. Using photosynthesis and crop growth as an example, this review summarises past and present experimental and modelling work, bringing about a model-guided crop improvement thrust, encompassing research into: (1) advancing cross-scale plant/crop modelling that connects across biological scales of organisation using a trait dissection-integration modelling principle; (2) improving the reliability of predicted molecular-trait-crop-environment system dynamics with experimental validation; and (3) innovative model application in synergy with cross-scale experimentation to evaluate G×M×E and predict yield outcomes of genetic intervention (or lack of it) for strategising further molecular and breeding efforts. The possible future roles of cross-scale plant/crop modelling in maximising crop improvement are discussed.

Research Progress in Improving Photosynthetic Efficiency

Photosynthesis is the largest mass- and energy-conversion process on Earth, and it is the material basis for almost all biological activities. The efficiency of converting absorbed light energy into energy substances during photosynthesis is very low compared to theoretical values. Based on the importance of photosynthesis, this article summarizes the latest progress in improving photosynthesis efficiency from various perspectives. The main way to improve photosynthetic efficiency is to optimize the light reactions, including increasing light absorption and conversion, accelerating the recovery of non-photochemical quenching, modifying enzymes in the Calvin cycle, introducing carbon concentration mechanisms into C₃ plants, rebuilding the photorespiration pathway, de novo synthesis, and changing stomatal conductance. These developments indicate that there is significant room for improvement in photosynthesis, providing support for improving crop yields and mitigating changes in climate conditions.

Photosynthetic modification of plants through recent technologies: a valuable way to ensure crop fortification

The 2030 Sustainable Development Goals of the United Nations include a strong emphasis on ending hunger worldwide. According to the 2019 Global Food Security Index, while 88% of countries claim there is sufficient food supply in their country, the sad reality is that 1 in 3 countries is facing insufficient availability of food supply, which means that in those countries, more than 10% of the population is malnourished. Since nutrition is crucial to leading a healthy life and satisfying food security needs, several governments have turned to national nutrition surveys to gauge the extent of malnutrition in their populations. Plants are able to grow, develop, and store nutrients by photosynthesis, which convert light into chemical energy through cell redox regulatory networks. A photosynthesis system's electron flow may be adjusted to accommodate varying light and environmental circumstances. Many techniques exist for controlling the flow of electrons emitted during light processes in order to save or waste energy. The two protein molecules TROL and flavoenzyme ferredoxin (oxidoreductase+NADP) (FNR) interact dynamically to form an excellent molecular switch capable of splitting electrons from the photosystem. The TROL-FNR bifurcation may be limited by either generating NADPH or preventing reactive oxygen species from propagating. TROL-based genome editing is an experimental method for enhancing plant stress and defensive responses, efficiency, and ultimately agricultural production.

Seasonal climate conditions impact the effectiveness of improving photosynthesis to increase soybean yield

Context

Photosynthetic stimulations have shown promising outcomes in improving crop photosynthesis, including soybean. However, it is still unclear to what extent these changes can impact photosynthetic assimilation and yield under long-term field climate conditions.

Objective

In this paper, we present a systematic evaluation of the response of canopy photosynthesis and yield to two critical parameters in leaf photosynthesis: the maximum carboxylation rate of ribulose-1,5-bisphosphate carboxylase/oxygenase (Vcmax) and the maximum electron transport of the ribulose-1,5-bisphosphate regeneration rate (Jmax).

Methods

Using the field-scale crop model Soybean-BioCro and ten years of observed climate data in Urbana, Illinois, U.S., we conducted sensitivity experiments to estimate the changes in canopy photosynthesis, leaf area index, and biomass due to the changes in Vcmax and Jmax.

Results

The results show that 1) Both the canopy photosynthetic assimilation (An) and pod biomass yields were more sensitive to the changes in Jmax, particularly at high atmospheric carbon-dioxide concentrations ([CO2]); 2) Higher [CO2] undermined the effectiveness of increasing the two parameters to improve An and yield; 3) Under the same [CO2], canopy light interception and canopy respiration were key factors that undermined improvements in An and yield; 4) A canopy with smaller leaf area index tended to have a higher yield improvement, and 5) Increases in assimilations and yields were highly dependent on growing-season climatic conditions. The solar radiation, temperature, and relative humidity were the main climate drivers that impacted the yield improvement, and they had opposite correlations with improved yield during the vegetative phase compared to the reproductive phase.

Conclusions

In a world with elevated [CO2], genetic engineering crop photosynthesis should focus more on improving Jmax. Further, long-term climate conditions and seasonal variations must be considered to determine the improvements in soybean canopy photosynthesis and yield at the field scale.

Implications

Quantifying the effectiveness of changing Vcmax and Jmax helps understand their individual and combined contributions to potential improvements in assimilation and yield. This work provides a framework for evaluating how altering the photosynthetic rate parameters impacts soybean yield and assimilation under different seasonal climate scenarios at the field scale.

Seed priming with NaCl helps to improve tissue tolerance, potassium retention ability of plants, and protects the photosynthetic ability in two different legumes, chickpea and lentil, under salt stress

MAIN CONCLUSION

Seed priming with NaCl mimicked the conditions of natural priming to improve the tissue tolerance nature of sensitive legumes, which helps to maintain survivability and yield in mildly saline areas. Seed priming with NaCl is a seed invigoration technique that helps to improve plant growth by altering Na⁺ and K⁺ content under salt stress. Legumes are overall sensitive to salt and salinity hampers their growth and yield. Therefore, a priming (50 mM NaCl) experiment was performed with two different legume members [Cicer arietinum cv. Anuradha and Lens culinaris cv. Ranjan] and different morpho-physiological, biochemical responses at 50 mM, 100 mM, and 150 mM NaCl and molecular responses at 150 mM NaCl were studied in hydroponically grown nonprimed and primed members. Similarly, a pot experiment was performed at 80 mM Na⁺, to check the yield. Tissue Na⁺ and K⁺ content suggested NaCl-priming did not significantly alter the accumulation of Na⁺ among nonprimed and primed members but retained more K⁺ in cells, thus maintaining a lower cellular Na⁺/K⁺ ratio. Low osmolyte content (e.g., proline) in primed members suggested priming could minimize their overall osmolytic requirement. Altogether, these implied tissue tolerance (TT) nature might have improved in case of NaCl-priming as was also reflected by a better TT score (LC₅₀ value). An improved TT nature enabled the primed plants to maintain a significantly higher photosynthetic rate through better stomatal conductance. Along with this, a higher level of chlorophyll content and competent functioning of the photosynthetic subunits improved photosynthetic performance that ensured yield under stress. Overall, this study explores the potential of NaCl-priming and creates possibilities for considerably sensitive members; those in their nonprimed forms have no prospect in mildly saline agriculture.

Root zone temperature regulates potassium absorption and photosynthesis in maize (Zea mays)

Affected by climate warming, the impact of crop root zone warming (RZW) on maize seedling growth and nutrient uptake deserve attention. The characteristics of K uptake in maize under root zone warming and the combined impacts of potassium deficiency and RZW are still unclear. The present study aimed to investigate the effects of RZW on potassium absorption and photosynthesis of maize seedlings under the difference in potassium. The results showed that RZW and low potassium treatment significantly affected root shoot development and photosynthetic physiological characteristics of maize seedlings. Moreover, the interaction of RZW and potassium content had striking influence on maize seedlings. Under the normal potassium with root zone medium temperature treatment, the development of maize was the most vigorous. Under the dual stress of high root zone temperature and low potassium, the root absorption area, total potassium content and root activity were significantly reduced, which then influenced the light energy use efficiency and dry matter accumulation. Securing the supply of potassium fertilizer under high root zone temperature stress is useful to alleviate the impact of high temperature stress.

Dynamic responses of carbon assimilation and stomatal conductance in the future climate

This article comments on:

Wall S, Cockram J, Vialet-Chabrand S, Van Rie J, Galle A, Lawson T. 2023. The impact of growth at elevated [CO2] on stomatal anatomy and behavior differs between wheat species and cultivars. Journal of Experimental Botany 74, 2860–2874

Plants exposed to titanium dioxide nanoparticles acquired contrasting photosynthetic and morphological strategies depending on the growing light intensity: a case study in radish

Due to the photocatalytic property of titanium dioxide (TiO₂), its application may be dependent on the growing light environment. In this study, radish plants were cultivated under four light intensities (75, 150, 300, and 600 μmol m^-2 s^-1 photosynthetic photon flux density, PPFD), and were weekly sprayed (three times in total) with TiO₂ nanoparticles at different concentrations (0, 50, and 100 μmol L^-1). Based on the obtained results, plants used two contrasting strategies depending on the growing PPFD. In the first strategy, as a result of exposure to high PPFD, plants limited their leaf area and send the biomass towards the underground parts to limit light-absorbing surface area, which was confirmed by thicker leaves (lower specific leaf area). TiO₂ further improved the allocation of biomass to the underground parts when plants were exposed to higher PPFDs. In the second strategy, plants dissipated the absorbed light energy into the heat (NPQ) to protect the photosynthetic apparatus from high energy input due to carbohydrate and carotenoid accumulation as a result of exposure to higher PPFDs or TiO₂ concentrations. TiO₂ nanoparticle application up-regulated photosynthetic functionality under low, while down-regulated it under high PPFD. The best light use efficiency was noted at 300 m^-2 s^-1 PPFD, while TiO₂ nanoparticle spray stimulated light use efficiency at 75 m^-2 s^-1 PPFD. In conclusion, TiO₂ nanoparticle spray promotes plant growth and productivity, and this response is magnified as cultivation light intensity becomes limited.

Sequence Characteristics and Expression Analysis of the Gene Encoding Sedoheptulose-1,7-Bisphosphatase, an Important Calvin Cycle Enzyme in Upland Cotton (Gossypium hirsutum L.)

Sedoheptulose-1,7-bisphosphatase (SBPase, EC 3.1.3.37) is a key enzyme in the plant Calvin cycle and one of the main rate-limiting enzymes in the plant photosynthesis pathway. Many studies have demonstrated that the SBPase gene plays an important role in plant photosynthetic efficiency, yield, and stress responses; however, few studies have been conducted on the function and expression of the GhSBPase gene in upland cotton. In this study, our results showed that the coding sequence (CDS) of GhSBPase gene was 1182 bp, encoding a protein with 393 amino acids. The GhSBPase protein had adenosine monophosphate (AMP) binding site and a FIG (FBPase/IMPase/glpX) domain, and had six Cys residues and a CGGT(A/Q)C motif that were involved in redox regulation in plants. Evolutionarily, the GhSBPase protein clustered into the dicotyledon subgroup and was most closely related to the tomato SlSBPase protein. Western-blot analysis further indicated that the GhSBPase gene was indeed the gene encoding the SBPase protein in upland cotton. The GhSBPase protein was localized in chloroplast, which was consistent with its function as a key enzyme in photosynthesis. The GhSBPase gene was specifically highly expressed in leaves, and its expression level was significantly lower in a yellow-green leaf mutant than in the wild type. Moreover, the GhSBPase expression was in response to drought, salt, high- and low-temperature stress, and exhibits different expression patterns. The GhSBPase promoter had the cis-acting elements in response to abiotic stress, phytohormone, and light. In addition, the GhSBPase expression was positively correlated with the chlorophyll fluorescence parameters, suggesting that changes in the expression of the GhSBPase had potential applicability in breeding for enhanced cotton photosynthetic efficiency. These results will help to understand the function of the GhSBPase gene in photosynthesis and the adaptability of plants to external stress and provide important gene information for the high-yield breeding of crops in the future.

Feeding the world: impacts of elevated [CO2] on nutrient content of greenhouse grown fruit crops and options for future yield gains

Several long-term studies have provided strong support demonstrating that growing crops under elevated [CO2] can increase photosynthesis and result in an increase in yield, flavour and nutritional content (including but not limited to Vitamins C, E and pro-vitamin A). In the case of tomato, increases in yield by as much as 80% are observed when plants are cultivated at 1000 ppm [CO2], which is consistent with current commercial greenhouse production methods in the tomato fruit industry. These results provide a clear demonstration of the potential for elevating [CO2] for improving yield and quality in greenhouse crops. The major focus of this review is to bring together 50 years of observations evaluating the impact of elevated [CO2] on fruit yield and fruit nutritional quality. In the final section, we consider the need to engineer improvements to photosynthesis and nitrogen assimilation to allow plants to take greater advantage of elevated CO2 growth conditions.

Adaptive nitrogen inputs sustain water-nitrogen use and improve maize productivity with varied precipitation conditions on a semi-arid agroecosystem

BACKGROUND

Maize productivity in semi-arid regions is increasingly at risk because of the sparse and uneven precipitation, and it is also restricted by excessive or insufficient fertilization management strategies. A 4-year (2016-2019) field experiment was therefore conducted to show the effects of fertilizer with five nitrogen levels (0, 75-90, 150-180, 270, and 360 kg ha^-1 , represented as N₀ , N_75-90 , N_150-180 , N₂₇₀ , N₃₆₀ , respectively) under two variable precipitation patterns (rainy at pre-anthesis in 2016 and 2018 versus dry at pre-anthesis in 2017 and 2019) on soil water storage (SWS), water use efficiency (WUE), nitrogen use efficiency (NUE), and maize yield in the Loess Plateau.

RESULTS

Nitrogen inputs increased the amount of above-ground dry matter and the WUE for dry matter (WUEd). Dry years at pre-anthesis significantly reduced dry matter accumulation and kernel number per plant. However, soil water storage before sowing (SWSs) decreased from 440 mm in 2016 to 384 mm in 2019, and the increase in fertilization resulted in the water imbalance. Both the maximum grain yield and WUE for grain yield were found in N₂₇₀ under rainy years at pre-anthesis, whereas in N_150-180  under dry years at pre-anthesis. The average nitrogen recovery efficiency (NRE), nitrogen agronomy efficiency (NAE) and nitrogen partial factor productivity (NPFP) decreased with increases in N application, compared with N₃₆₀ , the NRE,NAE and NPFP of N_150-180 increased by 63.5%, 189.2% and 135.5%, respectively.

CONCLUSIONS

Reducing basal N fertilizers could enhance maize yield and maintain moderate water and nitrogen productivity in years with less rainfall. © 2023 Society of Chemical Industry.

The combined formulation of brassinolide and pyraclostrobin increases biomass and seed yield by improving photosynthetic capacity in Arabidopsis thaliana

In the context of global food crisis, applying the phytohormone-brassinosteroids (BRs) in combination with the fungicide-pyraclostrobin (Pyr) was beneficial for plant quality and productivity in several field trials. However, in addition to the benefits of disease control due to the innate fungicidal activity of Pyr, it remains to be understood whether the coapplication of BL+ Pyr exerts additional growth-promoting effects. For this purpose, the effects of BL treatment, Pyr treatment, and BL+ Pyr treatment in Arabidopsis thaliana were compared. The results showed that the yield increased at a rate of 25.6% in the BL+Pyr group and 9.7% in the BL group, but no significant change was observed in the Pyr group. Furthermore, the BL+Pyr treatment increased the fresh weight of both the leaves and the inflorescences. In contrast, the Pyr and BL treatments only increased the fresh weight of leaves and inflorescences, respectively. Additionally, the BL + Pyr treatment increased the P_n, G_s, T_r, V_{c, max}, J_max, V_TPU, ETR, F_v'/F_m', ΦPSII, Rd, AYE and Rubisco enzyme activity by 26%, 38%, 40%, 16%, 19%, 15%, 9%, 10%, 17%, 179%, 18% and 32%, respectively. While, these paraments did not change significantly by the BL or Pyr treatments. Treatment with BL + Pyr and Pyr, rather than BL, improved the chlorophyll a and chlorophyll b contents by upregulating genes related to chlorophyll biosynthesis and downregulating genes related to chlorophyll degradation. Additionally, according to transcriptomic and metabolomic analysis, the BL+ Pyr treatment outperformed the individual BL or Pyr treatments in activating the transcription of genes involved in photosynthesis and increasing sugar accumulation. Our results first validated that the combined usage of BL and Pyr exerted striking synergistic effects on enhancing plant biomass and yield by increasing photosynthetic efficiency. These results might provide new understanding for the agricultural effects by the co-application of BL and Pyr, and it might stimulate the efforts to develop new environment-friendly replacement for Pyr to minimize the ecotoxicology of Pyr.

A natural variation in the promoter of GRA117 affects carbon assimilation in rice

GRA117 is crucial in the process of carbon assimilation in rice as it regulates the development of chloroplasts, which in turn facilitates the Calvin-Benson cycle. Carbon assimilation is a critical process for plant growth, and despite numerous relevant studies, there are still unknown constraints. In this study, we isolated a rice mutant, gra117, which exhibited seedling albinism, delayed chloroplast development, decreased chlorophyll content, reduced yield, and seedling stress susceptibility, as compared to WT. Our further investigations revealed that gra117 had a significantly lower net photosynthetic carbon assimilation rate, as well as reduced levels of Rubisco enzyme activity, RUBP, PGA, carbohydrate, protein content, and dry matter accumulation. These findings provide evidence for decreased carbon assimilation in gra117. By mapping cloning, we discovered a 665 bp insertion in the GRA117 promoter region that decreases GRA117 transcriptional activity and causes the gra117 phenotype. GRA117 encodes PfkB-type fructokinase-like 2, which is subcellularly localized in chloroplasts and is widely expressed in various rice tissues, particularly at high levels in leaf tissues. GRA117 transcription is regulated by the core region 1029 bp before the start codon. Our quantitative RT-PCR and Western blot assays showed that GRA117 promotes the expression and translation of photosynthetic genes. RNA-Seq analysis revealed that GRA117 plays a significant role in photosynthetic carbon fixation, carbon metabolism, and chloroplast ribosome-related pathways. Our study supports that GRA117 promotes the Calvin-Benson cycle by regulating chloroplast development, ultimately leading to enhanced carbon assimilation in rice.