Perspectives on improving photosynthesis to increase crop yield

Engineering Rubisco condensation in chloroplasts to manipulate plant photosynthesis

Although Rubisco is the most abundant enzyme globally, it is inefficient for carbon fixation because of its low turnover rate and limited ability to distinguish CO2 and O2, especially under high O2 conditions. To address these limitations, phytoplankton, including cyanobacteria and algae, have evolved CO2-concentrating mechanisms (CCM) that involve compartmentalizing Rubisco within specific structures, such as carboxysomes in cyanobacteria or pyrenoids in algae. Engineering plant chloroplasts to establish similar structures for compartmentalizing Rubisco has attracted increasing interest for improving photosynthesis and carbon assimilation in crop plants. Here, we present a method to effectively induce the condensation of endogenous Rubisco within tobacco (Nicotiana tabacum) chloroplasts by genetically fusing superfolder green fluorescent protein (sfGFP) to the tobacco Rubisco large subunit (RbcL). By leveraging the intrinsic oligomerization feature of sfGFP, we successfully created pyrenoid-like Rubisco condensates that display dynamic, liquid-like properties within chloroplasts without affecting Rubisco assembly and catalytic function. The transgenic tobacco plants demonstrated comparable autotrophic growth rates and full life cycles in ambient air relative to the wild-type plants. Our study offers a promising strategy for modulating endogenous Rubisco assembly and spatial organization in plant chloroplasts via phase separation, which provides the foundation for generating synthetic organelle-like structures for carbon fixation, such as carboxysomes and pyrenoids, to optimize photosynthetic efficiency.

Synthetic crassulacean acid metabolism (SynCAM) for improving water-use efficiency in plants

The global climate crisis will continue to increase the frequency and duration of drought episodes in agricultural production areas worldwide. Hot and dry conditions create greater water-deficit stresses on crops, lowering their productivity. While multiple engineering strategies have been developed to improve the efficiency of photosynthesis, greater efforts are needed to improve the drought attenuation and water-use efficiency of crops. Crassulacean acid metabolism (CAM) is a naturally occurring elaboration of C3 photosynthesis that allows plants to occupy and thrive in hot and dry environments with limited or intermittent water supply. Creating synthetic versions of bioengineered CAM is one potentially fruitful approach to improving crop productivity while also reducing photorespiration and increasing water-use efficiency. We outline current efforts being undertaken to engineer CAM-like or synthetic versions of CAM (SynCAM) and future advances and strategies that might contribute to the optimization of SynCAM engineering in crops.This article is part of the theme issue 'Crops under stress: can we mitigate the impacts of climate change on agriculture and launch the 'Resilience Revolution'?'.

Structure, regulation and assembly of the photosynthetic electron transport chain

The electron transfer chain of chloroplast thylakoid membranes uses solar energy to split water into electrons and protons, creating energetic gradients that drive the formation of photosynthetic fuel in the form of NADPH and ATP. These metabolites are then used to power the fixation of carbon dioxide into biomass through the Calvin-Benson-Bassham cycle in the chloroplast stroma. Recent advances in molecular genetics, structural biology and spectroscopy have provided an unprecedented understanding of the molecular events involved in photosynthetic electron transfer from photon capture to ATP production. Specifically, we have gained insights into the assembly of the photosynthetic complexes into larger supercomplexes, thylakoid membrane organization and the mechanisms underpinning efficient light harvesting, photoprotection and oxygen evolution. In this Review, I focus on the angiosperm plant thylakoid system, outlining our current knowledge on the structure, function, regulation and assembly of each component of the photosynthetic chain. I explain how solar energy is harvested and converted into chemical energy by the photosynthetic electron transfer chain, how its components are integrated into a complex membrane macrostructure and how this organization contributes to regulation and photoprotection.

Optimizing carbon and nitrogen metabolism in plants: From fundamental principles to practical applications

Carbon (C) and nitrogen (N) are fundamental elements essential for plant growth and development, serving as the structural and functional backbone of organic compounds and driving essential biological processes such as photosynthesis, carbohydrate metabolism, and N assimilation. The metabolism and transport of C involve the movement of sugars between shoots and roots through xylem and phloem transport systems, regulated by a sugar-signaling hub. Nitrogen uptake, transport, and metabolism are equally critical, with plants assimilating nitrate and ammonium through specialized transporters and enzymes in response to varying N levels to optimize growth and development. The coordination of C and N metabolism is key to plant productivity and the maintaining of agroecosystem stability. However, inefficient utilization of N fertilizers results in substantial environmental and economic challenges, emphasizing the urgent need to improve N use efficiency (NUE) in crops. Integrating efficient photosynthesis with N uptake offers opportunities for sustainable agricultural practices. This review discusses recent advances in understanding C and N transport, metabolism, and signaling in plants, with a particular emphasis on NUE-related genes in rice, and explores breeding strategies to enhance crop efficiency and agricultural sustainability.

The diversity of physiology and metabolism in chlorophototrophic bacteria

Photosynthesis by (bacterio)chlorophyll-producing organisms ("chlorophototrophy") sustains virtually all life on Earth, providing the biosphere with food and energy. The oxygenic process carried out by plants, algae and cyanobacteria also generates the oxygen we breathe, and ancient cyanobacteria were responsible for oxygenating the atmosphere, creating the conditions that allowed the evolution of complex life. Cyanobacteria were also the endosymbiotic progenitors of chloroplasts, play major roles in biogeochemical cycles and as primary producers in aquatic ecosystems, and act as genetically tractable model organisms for studying oxygenic photosynthesis. In addition to the Cyanobacteriota, eight other bacterial phyla, namely Proteobacteria/Pseudomonadota, Chlorobiota, Chloroflexota, Bacillota, Acidobacteriota, Gemmatimonadota, Vulcanimicrobiota and Myxococcota contain at least one putative chlorophototrophic species, all of which perform a variant of anoxygenic photosynthesis, which does not yield oxygen as a by-product. These chlorophototrophic organisms display incredible diversity in the habitats that they colonise, and in their biochemistry, physiology and metabolism, with variation in the light-harvesting complexes and pigments they produce to utilise solar energy. Whilst some are very well understood, such as the proteobacterial 'purple bacteria', others have only been identified in the last few years and therefore relatively little is known about them - especially those that have not yet been isolated and cultured. In this chapter, we aim to summarise and compare the photosynthetic physiology and central metabolic processes of chlorophototrophic members from the nine phyla in which they are found, giving both a short historical perspective and highlighting gaps in our understanding.

The next Green Revolution: integrating crop architectype and physiotype

In the middle of the last century, the Green Revolution dramatically increased crop yields and transformed global agriculture. As current food production is increasingly challenged by the demands of the growing population, climate change, and environmental degradation, a new Green Revolution is urgently needed. This Review highlights recent progress in defining the morphological ideotypes of four major crops, and proposes essential physiological traits critical for crop improvement and environmental adaptation. We introduce two concepts: the 'architectype' representing optimized morphological features, and the 'physiotype' encompassing improved physiological traits. By integrating these concepts through advanced genomic technologies and precision management practices, the next Green Revolution could potentially enhance crop yields and resource use efficiency by over 20-30%, thereby ensuring sustainable food production.

Photosynthetic Responses of Pontederia cordata to Cadmium Stress: Anatomical Structure, Ultrastructure, Physiology, and Gene Expression

Pontederia cordata, a horticulturally valuable ornamental plant, exhibits cadmium (Cd) tolerance, but its photosynthetic response to Cd stress has not been fully elucidated. Here, we employed hydroponics to investigate the effects of varying Cd concentrations on the leaf morphology, anatomy, photosynthetic physiology, and carbon metabolism enzymes in P. cordata. At 0.1 mM Cd, the plants grew well and showed no toxicity, with a normal chloroplast ultrastructure and chlorophyll a fluorescence parameters. Higher Cd concentrations (0.2-0.4 mM) disrupted chloroplasts, reduced chlorophyll content, and suppressed photosynthetic enzyme expression, thereby impairing light energy conversion efficiency and photosynthetic performance. In response, P. cordata adapted by maintaining the thickness of the palisade tissue, increasing the ratio of palisade tissue thickness to spongy tissue thickness, stabilizing carotenoid levels, enhancing non-photochemical quenching processes, and increasing the content of key photosynthetic enzymes and soluble sugars. These findings advance the theoretical understanding of photosynthetic adaptation mechanisms to heavy metal stress.

Evaluating photosynthetic models and their potency in assessing plant responses to changing oxygen concentrations: a comparative analysis of A n-C a and A n-C i curves in Lolium perenne and Triticum aestivum

Accurate determination of photosynthetic parameters is essential for understanding how plants respond to environmental changes. In this study, we evaluated the performance of the Farquhar-von Caemmerer-Berry (FvCB) model and introduced a novel model to fit photosynthetic rates against ambient CO2 concentration (A n -C a) and intercellular CO2 concentration (A n -C i) curves for Lolium perenne and Triticum aestivum under 2% and 21% O2 conditions. We observed significant discrepancies in the FvCB model's fitting capacity for A n -C a and A n -C a curves across different oxygen regimes, particularly in estimates of key parameters such as the maximum carboxylation rate (V cmax), the day respiratory rate (R day), and the maximum electron transport rate for carbon assimilation (J A-max). Notably, under 2% and 21% O2 conditions, the values of V cmax and R day derived from A n -C a curves using the FvCB model were 46.98%, 44.37%, 46.63%, and 37.66% lower than those from A n -C i curves for L. perenne, and 47.10%, 44.30%, 47.03%, and 37.36% lower for T. aestivum, respectively. These results highlight that the FvCB model yields significantly different V cmax and R day values when fitting A n -C a versus A n -C i curves for these two C3 plants. In contrast, the novel model demonstrated superior fitting capabilities for both A n -C a and A n -C i curves under 2% and 21% O2 conditions, achieving high determination coefficients (R 2≥ 0.989). Key parameters such as the maximum net photosynthetic rate (A max) and the CO2 compensation point (Γ) in the presence of R day, showed no significant differences across oxygen concentrations. However, the apparent photorespiratory rate (R pa0) and photorespiratory rate (R p0) derived from A n -C i curves consistently exceeded those from A n -C a curves for both plant species. Furthermore, R pa0 values derived from A n -C a curves closely matched observed values, suggesting that A n -C a curves more accurately reflect the physiological state of plants, particularly for estimating photorespiratory rates. This study underscores the importance of selecting appropriate CO2-response curves to investigate plant photosynthesis and photorespiration under diverse environmental conditions, thereby ensuring a more accurate understanding of plant responses to changing environments.

Exciton-Diffusion Enhanced Energy Capture in an Integrated Nanoscale Platform

Harnessing solar energy through biologically inspired nanoscale platforms presents a promising route for sustainable energy conversion. Biohybrid systems take advantage of the design and performance of natural systems while also enabling the optimized organization of the protein components. Until now, such systems have usually been made from components of the same species, limiting the range of properties and interactions that can be generated. Here, we introduce a nanoscale platform of biomolecular films containing cross-species antenna/reaction center proteins. We demonstrated a long-range exciton diffusion of ∼200 nm through the antenna light-harvesting complex II (LHCII) from green plants and quantified the underlying diffusivity at 3 × 10-2 μm2 ns-1 using complementary simulations. The LHCII micropattern also induced directional exciton diffusion as a crucial mechanism for enhanced energy capture, yielding a ∼30% energy transfer efficiency to the reaction center-light-harvesting complex 1 complex from purple bacteria. This platform provides a proof-of-concept for an operation-ready, hybrid energy harvesting system capable of spanning the entire visible spectrum. The integration of diverse photosynthetic proteins into biofilm platforms offers new potential for solar energy capture and conversion.

Engineering of photorespiration-dependent glycine betaine biosynthesis improves photosynthetic carbon fixation and panicle architecture in rice

In C3 plants, photorespiration is an energy expensive pathway that competes with photosynthetic CO2 assimilation and releases CO2 into the atmosphere, potentially reducing C3 plant productivity by 20%-50%. Consequently, reducing the flux through photorespiration has been recognized as a major way to improve C3 crop photosynthetic carbon fixation and productivity. While current research efforts in engineering photorespiration are mainly based on the modification of chloroplast glycolate metabolic steps, only limited studies have explored optimizations in other photorespiratory metabolic steps. Here, we engineered an imGS bypass within the rice mitochondria to bypass the photorespiratory glycine toward glycine betaine, thereby, improving the photosynthetic carbon fixation in rice. The imGS transgenic rice plants exhibited significant accumulation of glycine betaine, reduced photorespiration, and elevated photosynthesis and photosynthate levels. Additionally, the introduction of imGS bypass into rice leads to an increase in the number of branches and grains per panicle which may be related to cytokinin and gibberellin signaling pathways. Taken together, these results suggest diverting mitochondrial glycine from photorespiration toward glycine betaine synthesis can effectively enhance carbon fixation and panicle architecture in rice, offering a promising strategy for developing functional mitochondrial photorespiratory bypasses with the potential to enhance plant productivity.

Engineering carbon assimilation in plants

Carbon assimilation is a crucial part of the photosynthetic process, wherein inorganic carbon, typically in the form of CO2, is converted into organic compounds by living organisms, including plants, algae, and a subset of bacteria. Although several carbon fixation pathways have been elucidated, the Calvin-Benson-Bassham (CBB) cycle remains fundamental to carbon metabolism, playing a pivotal role in the biosynthesis of starch and sucrose in plants, algae, and cyanobacteria. However, Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), the key carboxylase enzyme of the CBB cycle, exhibits low kinetic efficiency, low substrate specificity, and high temperature sensitivity, all of which have the potential to limit flux through this pathway. Consequently, RuBisCO needs to be present at very high concentrations, which is one of the factors contributing to its status as the most prevalent protein on Earth. Numerous attempts have been made to optimize the catalytic efficiency of RuBisCO and thereby promote plant growth. Furthermore, the limitations of this process highlight the potential benefits of engineering or discovering more efficient carbon fixation mechanisms, either by improving RuBisCO itself or by introducing alternative pathways. Here, we review advances in artificial carbon assimilation engineering, including the integration of synthetic biology, genetic engineering, metabolic pathway optimization, and artificial intelligence in order to create plants capable of performing more efficient photosynthesis. We additionally provide a perspective of current challenges and potential solutions alongside a personal opinion of the most promising future directions of this emerging field.

Effects of DA-6 and MC on the growth, physiology, and yield characteristics of soybean

BACKGROUND

As a grain and oil crop, soybean presents a much lower yield than other staple crops. However, crop yields can be improved by applying modern agricultural technology, such as diethylaminoethyl hexanoate (DA-6) and mepiquat chloride (MC), which are important plant-growth regulators that substantially affect crop growth and yield.

METHODS

This study examined the effects of DA-6 (30, 60, or 90 mg L-1) and MC (100, 200, or 400 mg L-1) on soybean growth, development, root structure, photosynthetic physiology, osmotic regulation, and yield via field and pot experiments.

RESULTS

The results showed that DA-6 effectively promoted the growth of soybean and increased parameters such as plant height, leaf area, and leaf dry weight in different growth stages by 21.0%, 18.7%, and 66.4%, respectively. In contrast, MC inhibited the growth and other parameters, decreasing the plant height, leaf area, and leaf dry weight in different growth stages by up to 15.7%, 11.9%, and 10.1%, respectively. Both DA-6 and MC promoted root development by increasing the dry weight, length, surface area, volume, tip number, branch number, and cross number. In terms of physiology, DA-6, and MC increased photosynthetic parameters, such as steady-state fluorescence (Fs), maximum fluorescence (Fm'), and photosynthetic system II (Phi2), increased the soluble protein contents, with maximum increases of 27.7% and 28.1% at different periods, and increased the soluble sugar contents by 38.2% and 58.3%. Regarding yield characteristics, DA-6 and MC considerably increased the yield, 100-grain weight, and number of effective pods. DA-6 increased the number of two- and three-seed pods, whereas MC increased the number of one-, two-, and three-seed pods. MC performed better than DA-6; however, they exerted different effects on the two varieties and at different concentrations. DA-6 was most effective at 30-60 mg L-1, while MC was most effective at 100-200 mg L-1.

CONCLUSIONS

This study revealed the effects of DA-6 and MC on soybean morphology, physiology, and yield characteristics and the appropriate concentrations for application in soybean productions. Thus, these findings provide guidance for the rational application of the two regulators for soybean high-yield cultivation and stress resistance.

Engineering nitrogen and carbon fixation for next-generation plants

Improving plant nitrogen (N) and carbon (C) acquisition and assimilation is a major challenge for global agriculture, food security, and ecological sustainability. Emerging synthetic biology techniques, including directed evolution, artificial intelligence (AI)-guided enzyme design, and metabolic engineering, have opened new avenues for optimizing nitrogenase to fix atmospheric N2 in plants, engineering Rhizobia or other nitrogen-fixing bacteria for symbiotic associations with both legume and nonlegume crops, and enhancing carbon fixation to improve photosynthetic efficiency and source-to-sink assimilate fluxes. Here, we discuss the potential for engineering nitrogen fixation and carbon fixation mechanisms in plants, from rational and AI-driven optimization of nitrogen and carbon fixation cycles. Furthermore, we discuss strategies for modifying source-to-sink relationships to promote robust growth in extreme conditions, such as arid deserts, saline-alkaline soils, or even extraterrestrial environments like Mars. The combined engineering of N and C pathways promises a new generation of crops with enhanced productivity, resource-use efficiency, and resilience. Finally, we explore future perspectives, focusing on the integration of enzyme engineering via directed evolution and computational design to accelerate metabolic innovation in plants.

Knowledge of microalgal Rubiscos helps to improve photosynthetic efficiency of crops

MAIN CONCLUSION

A comprehensive understanding of microalgal Rubiscos offers opportunities to enhance photosynthetic efficiency of crops. As food production fails to meet the needs of the expanding population, there is increasing concern about Ribulose-1, 5-diphosphate (RuBP) carboxylase/oxygenase (Rubisco), the enzyme that catalyzes CO2 fixation in photosynthesis. There have been many attempts to optimize Rubisco in crops, but the complex multicellular structure of higher plants makes optimization more difficult. Microalgae have the characteristics of rapid growth, simple structure and easy molecular modification, and the function and properties of their Rubiscos are basically the same as those of higher plants. Research on microalgal Rubiscos helps to broaden the understanding of Rubiscos of higher plants. Also, transferring all or part of better microalgal Rubiscos into crop cells or giving crop Rubiscos the advantages of microalgal Rubiscos can help improve the photosynthesis of crops. In this review, the distribution, origin, evolution, molecular structure, folding, assembly, activation and kinetic properties of microalgal Rubiscos are summarized. Moreover, the development of some effective methods to improve the properties and application of Rubiscos in microalgae are also described.

New avenues in photosynthesis: from light harvesting to global modeling

Photosynthesis underpins life on Earth, serving as the primary energy source while regulating global carbon and water cycles, thereby shaping climate and vegetation. Advancing photosynthesis research is essential for improving crop productivity and refining photosynthesis models across scales, ultimately addressing critical global challenges such as food security and environmental sustainability. This minireview synthesizes a selection of recent advancements presented at the 2nd European Congress of Photosynthesis Research, focusing on improving photosynthesis efficiency and modelling across the scales. We explore strategies to optimize light harvesting and carbon fixation, leading to canopy level improvements. Alongside synthetic biology, we examine recent advances in harnessing natural variability in key photosynthetic traits, considering both methodological innovations and the vast reservoir of opportunities they present. Additionally, we highlight unique insights gained from plants adapted to extreme environments, offering pathways to improve photosynthetic efficiency and resilience simultaneously. We emphasize the importance of a holistic approach, integrating dynamic modeling of metabolic processes to bridge these advancements. Beyond photosynthesis improvements, we discuss the progress of improving photosynthesis simulations, particularly through improved parametrization of mesophyll conductance, crucial for enhancing leaf-to-global scale simulations. Recognizing the need for greater interdisciplinary collaboration to tackle the grand challenges put on photosynthesis research, we highlight two initiatives launched at the congress-an open science platform and a dedicated journal for plant ecophysiology. We conclude this minireview with a forward-looking outline, highlighting key next steps toward achieving meaningful improvements in photosynthesis, yield, resilience and modeling.

Far-Red Absorbing LHCII Incorporating Chlorophyll d Preserves Photoprotective Carotenoid Triplet-Triplet Energy Transfer Pathways

Chlorophyll d (Chl d) can be successfully introduced in reconstituted LHCII with minimal interference with the energy equilibration processes within the complex, thereby facilitating the development of plant light-harvesting complexes (LHCs) with enhanced capabilities for light absorption in the far-red spectrum. In this study, we address whether Chl d introduction affects LHCII's ability to protect itself from photo-oxidation, a crucial point for successfully exploiting modified complexes to extend light harvesting in plants. Here we focus on incorporating Chl d into Lhcb1 (the monomeric unit of LHCII), specifically studying the Chl triplet quenching by carotenoids using time-resolved electron paramagnetic resonance (TR-EPR) and optically detected magnetic resonance (ODMR). We also characterize the A2 mutant of LHCII, in which the Chl 612 is removed, to assist in determining the triplet quenching sites on the Lhcb1 complex reconstituted with Chl d. We found that far-red absorbing LHCII incorporating Chl d maintains the efficiency of the photoprotective process.

Unveiling Drought Tolerant Cotton Genotypes: Insights from Morpho-Physiological and Biochemical Markers at Flowering

Drought stress substantially restricts cotton growth, decreasing cotton production potential worldwide. This study evaluated cotton genotypes at the flowering stage to identify drought-resilient genotypes under moderate and severe drought conditions using physio-morphic and biochemical markers. Five genotypes were examined in a completely randomized design with three replicates across three treatments. Growth and biochemical traits were measured after 14 days of drought stress. The Multi-trait Genotype-Ideotype Distance Index (MGIDI) identified the most drought-tolerant genotypes. Severe drought had a pronounced negative effect on growth and biochemical traits, followed by moderate drought. Among the genotypes, FH-912 exhibited the strongest resilience, with significant increases in proline, peroxidase, catalase, and total chlorophyll. In contrast, chlorophyll a and transpiration rates were largely unaffected. Genotypes VH-351, VH-281, and GH-99 showed moderate drought tolerance, while FH-556 was highly sensitive to water stress. Statistical analyses, including ANOVA, PCA, and heatmaps, confirmed FH-912's superior performance under drought stress. The drought-resilient genotype, FH-912, holds promise for breeding drought-tolerant cotton varieties to sustain cotton productivity in water-limited environments, especially in drought-prone regions.

Responses of Tomato Photosystem II Photochemistry to Pegylated Zinc-Doped Ferrite Nanoparticles

Various metal-based nanomaterials have been the focus of research regarding their use in controlling pests and diseases and in improving crop yield and quality. In this study, we synthesized via a solvothermal procedure pegylated zinc-doped ferrite (ZnFer) NPs and characterized their physicochemical properties by X-ray diffraction (XRD), vibrating sample magnetometry (VSM), thermogravimetric analysis (TGA), FT-IR and UV-Vis spectroscopies, as well as transmission electron microscopy (TEM). Subsequently, their impact on tomato photosynthetic efficiency was evaluated by using chlorophyll a fluorescence imaging analysis to estimate the light energy use efficiency of photosystem II (PSII), 30, 60, and 180 min after foliar spray of tomato plants with distilled water (control plants) or 15 mg L-1 and 30 mg L-1 ZnFer NPs. The PSII responses of tomato leaves to foliar spray with ZnFer NPs showed time- and dose-dependent biphasic hormetic responses, characterized by a short-time inhibitory effect by the low dose and stimulatory effect by the high dose, while at a longer exposure period, the reverse phenomenon was recorded by the low and high doses. An inhibitory effect on PSII function was observed after more than ~120 min exposure to both ZnFer NPs concentrations, implying a negative effect on PSII photochemistry. We may conclude that the synthesized ZnFer NPs, despite their ability to induce hormesis of PSII photochemistry, have a negative impact on photosynthetic function.

Wheat2035: Integrating pan-omics and advanced biotechnology for future wheat design

Wheat (Triticum aestivum) production is vital for global food security, providing energy and protein to millions of people worldwide. Recent advancements in wheat research have led to significant increases in production, fueled by technological and scientific innovation. Here, we summarize the major advancements in wheat research, particularly the integration of biotechnologies and a deeper understanding of wheat biology. The shift from multi-omics to pan-omics approaches in wheat research has greatly enhanced our understanding of the complex genome, genomic variations, and regulatory networks to decode complex traits. We also outline key scientific questions, potential research directions, and technological strategies for improving wheat over the next decade. Since global wheat production is expected to increase by 60% in 2050, continued innovation and collaboration are crucial. Integrating biotechnologies and a deeper understanding of wheat biology will be essential for addressing future challenges in wheat production, ensuring sustainable practices and improved productivity.

Boosting photosynthesis opens new opportunities for agriculture sustainability and circular economy: The BEST-CROP research and innovation action

There is a need for ground-breaking technologies to boost crop yield, both grains and biomass, and their processing into economically competitive materials. Novel cereals with enhanced photosynthesis and assimilation of greenhouse gasses, such as carbon dioxide and ozone, and tailored straw suitable for industrial manufacturing, open a new perspective for the circular economy. Here we describe the vision, strategies, and objectives of BEST-CROP, a Horizon-Europe and United Kingdom Research and Innovation (UKRI) funded project that relies on an alliance of academic plant scientists teaming up with plant breeding companies and straw processing companies to use the major advances in photosynthetic knowledge to improve barley biomass and to exploit the variability of barley straw quality and composition. We adopt the most promising strategies to improve the photosynthetic properties and ozone assimilation capacity of barley: (i) tuning leaf chlorophyll content and modifying canopy architecture; (ii) increasing the kinetics of photosynthetic responses to changes in irradiance; (iii) introducing photorespiration bypasses; (iv) modulating stomatal opening, thus increasing the rate of carbon dioxide fixation and ozone assimilation. We expect that by improving our targeted traits we will achieve increases in aboveground total biomass production without modification of the harvest index, with added benefits in sustainability via better resource-use efficiency of water and nitrogen. In parallel, the resulting barley straw is tailored to: (i) increase straw protein content to make it suitable for the development of alternative biolubricants and feed sources; (ii) control cellulose/lignin contents and lignin properties to develop straw-based construction panels and polymer composites. Overall, by exploiting natural- and induced-genetic variability as well as gene editing and transgenic engineering, BEST-CROP will lead to multi-purpose next generation barley cultivars supporting sustainable agriculture and capable of straw-based applications.

Coenzyme M: An Archaeal Antioxidant as an Agricultural Biostimulant

Rising global food demand necessitates improved crop yields. Biostimulants offer a potential solution to meet these demands. Among them, antioxidants have shown potential to improve yield, nutritional quality, and resilience to climate change. However, large-scale production of many antioxidants is challenging. Here, we investigate Coenzyme M (CoM), a small, achiral antioxidant from archaea, as a potential biostimulant, investigating its effects on growth and physiology. CoM significantly increased shoot mass and root length of the model plant, Arabidopsis thaliana, in a concentration-dependent manner. Sulfur-containing CoM supplementation restored growth under sulfur-limited conditions in Arabidopsis, whereas similar recovery was not observed for other macronutrient deficiencies, consistent with it being metabolized. In tobacco, CoM increased photosynthetic light capture capacity, consistent with observed growth improvements. Interestingly, this effect was independent of carbon capture rates. Furthermore, CoM promoted early-stage shoot growth in various crops species, including tobacco, basil, cannabis, and soybean. Our results suggest CoM is a promising, scalable biostimulant with potential to modify photosynthesis and enhance crop productivity.

In vivo two-photon FLIM resolves photosynthetic properties of maize bundle sheath cells

Maize (Zea mays L.) performs highly efficient C4 photosynthesis by dividing photosynthetic metabolism between mesophyll and bundle sheath cells. In vivo physiological measurements are indispensable for C4 photosynthesis research as photosynthetic activities are easily interrupted by leaf section or cell isolation. Yet, direct in vivo observation regarding bundle sheath cells in the delicate anatomy of the C4 leaf is still challenging. In the current work, we used two-photon fluorescence-lifetime imaging microscopy (two-photon-FLIM) to access the photosynthetic properties of bundle sheath cells on intact maize leaves. The results provide spectroscopic evidence for the diminished total PSII activity in bundle sheath cells at its physiological level and show that the single PSIIs could undergo charge separation as usual. We also report an acetic acid-induced chlorophyll fluorescence quenching on intact maize leaves, which might be a physiological state related to the nonphotochemical quenching mechanism.

Modification of Non-photochemical Quenching Pathways in the C4 Model Plant Setaria viridis Revealed Shared and Unique Photoprotection Mechanisms as Compared to C3 Plants

Light is essential for photosynthesis; however, excess light can increase the accumulation of photoinhibitory reactive oxygen species that reduce photosynthetic efficiency. Plants have evolved photoprotective non-photochemical quenching (NPQ) pathways to dissipate excess light energy. In tobacco and soybean (C3 plants), overexpression of three NPQ genes, violaxanthin de-epoxidase (VDE), Photosystem II Subunit S (PsbS), and zeaxanthin epoxidase (ZEP), hereafter VPZ, resulted in faster NPQ induction and relaxation kinetics, and increased crop yields in field conditions. NPQ is well-studied in C3 plants; however, NPQ and the translatability of the VPZ approach in C4 plants is poorly understood. The green foxtail Setaria viridis is an excellent model to study photosynthesis and photoprotection in C4 plants. To understand the regulation of NPQ and photosynthesis in C4 plants, we performed transient overexpression in Setaria protoplasts and generated (and employed) stable transgenic Setaria plants overexpressing one of the three Arabidopsis NPQ genes or all three NPQ genes (AtVPZ lines). Overexpressing (OE) AtVDE and AtZEP in Setaria produced similar results as in C3 plants, with increased or reduced zeaxanthin (thus NPQ), respectively. However, overexpressing AtPsbS appeared to be challenging in Setaria, with largely reduced NPQ in protoplasts and under-represented homozygous AtPsbS-OE lines, potentially due to competitive and tight heterodimerization of AtPsbS and SvPsbS proteins. Furthermore, Setaria AtVPZ lines had increased zeaxanthin, faster NPQ induction, higher NPQ level, but slower NPQ relaxation. Despite this, AtVPZ lines had improved growth as compared to wildtype under several conditions, especially high temperatures, which is not related to the faster relaxation of NPQ but may be attributable to increased zeaxanthin and NPQ in C4 plants. Our results identified shared and unique characteristics of the NPQ pathway in C4 model Setaria as compared to C3 plants and provide insights to improve C4 crop yields under fluctuating environmental conditions.

Can spatial self-organization inhibit evolutionary adaptation?

Plants often respond to drier climates by slow evolutionary adaptations from fast-growing to stress-tolerant species. These evolutionary adaptations increase the plants' resilience to droughts but involve productivity losses that bear on agriculture and food security. Plants also respond by spatial self-organization, through fast vegetation patterning involving differential plant mortality and increased water availability to the surviving plants. The manners in which these two response forms intermingle and affect productivity and resilience have not been studied. Here we ask: can spatial patterning inhibit undesired evolutionary adaptation without compromising ecosystem resilience? To address this question, we integrate adaptive dynamics and vegetation pattern-formation theories and show that vegetation patterning can inhibit evolutionary adaptations to less productive, more stress-tolerant species over a wide precipitation range while increasing their resilience to water stress. This evolutionary homeostasis results from the high spatial plasticity of vegetation patterns, associated with patch thinning and patch dilution, which maintains steady local water availability despite decreasing precipitation. Spatial heterogeneity expedites the onset of vegetation patterning and induces evolutionary homeostasis at an earlier stage of evolutionary adaptation, thereby mitigating the productivity loss that occurs while the vegetation remains spatially uniform. We conclude by discussing our results in a broader context of evolutionary retardation.

Identifying hub genes and key functional modules in leaf tissue of Populus species based on WGCNA

As one of the most important parts of plants, the genetic mechanisms of photosynthesis or the response of leaf to a single abiotic and biotic stress have been well studied. However, few researches have involved in the integration of data analysis from system level in leaf tissue under multiple abiotic stresses by utilizing biological networks. In this study, the weighted gene co-expression network analysis (WGCNA) strategy was used to integrate multiple data in leaf tissue of Populus species under different sample treatments. The gene co-expression networks were constructed and functional modules were identified by selecting the suitable soft threshold power β in the procedure of WGCNA. The identified hub genes and gene modules were annotated by agriGO, NetAffx Analysis Center, The Plant Genome Integrative Explorer (PlantGenIE) and other annotation tools. The annotation results have displayed that the highly correlated modules and hub genes are involved in the important biological processes or pathways related to module traits. The efficiency of the WGCNA strategy can generate comprehensive understanding of gene module-traits associations in leaf tissue, which will provide novel insight into the genetic mechanism of Populus species.

Photosynthetic characteristics and genetic mapping of a yellow-green leaf mutant jym165 in soybean

BACKGROUND

Leaves are important sites for photosynthesis and can convert inorganic substances into organic matter. Photosynthetic performance is an important factor affecting crop yield. Leaf colour is closely related to photosynthesis, and leaf colour mutants are considered an ideal material for studying photosynthesis.

RESULTS

We obtained a yellow-green leaf mutant jym165, using ethyl methane sulfonate (EMS) mutagenesis. Physiological and biochemical analyses indicated that the contents of chlorophyll a, chlorophyll b, carotenoids, and total chlorophyll in the jym165 mutant decreased significantly compared with those in Jiyu47 (JY47). The abnormal chloroplast development of jym165 led to a decrease in net photosynthetic rate and starch content compared with that of JY47. However, quality traits analysis showed that the sum of oil and protein contents in jym165 was higher than that in JY47. In addition, the regional yield (seed spacing: 5 cm) of jym165 increased by 2.42% compared with that of JY47 under high planting density. Comparative transcriptome analysis showed that the yellow-green leaf phenotype was closely related to photosynthesis and starch and sugar metabolism pathways. Genetic analysis suggests that the yellow-green leaf phenotype is controlled by a single recessive nuclear gene. Using Mutmap sequencing, the candidate regions related of leaf colour was narrowed to 3.44 Mb on Chr 10.

CONCLUSIONS

Abnormal chloroplast development in yellow-green mutants leads to a decrease in the photosynthetic pigment content and net photosynthetic rate, which affects the soybean photosynthesis pathway and starch and sugar metabolism pathways. Moreover, it has the potentiality to increase soybean yield under dense planting conditions. This study provides a useful reference for studying the molecular mechanisms underlying photosynthesis in soybean.

Radiometric determination of rubisco activation state and quantity in leaves

Rubisco is the key enzyme in photosynthesis, catalyzing fixation of carbon dioxide from the atmosphere into energy storage molecules. Several inefficiencies in Rubisco limit the rate of photosynthesis, and, therefore, the growth of the plant. Rubisco is sensitive to light, making deactivation of the enzyme upon sampling likely. Moreover, the indirect methods often used to study its activity make obtaining reliable data difficult. In this Chapter, we describe an approach to generate reliable and repeatable data for Rubisco activities, activation state and abundance in plant leaves. We include methods to sample and extract proteins, minimizing Rubisco degradation and deactivation. We describe radiometric techniques to measure Rubisco activities and calculate its activation state at the time of sampling, and to quantify its abundance.

Lighting the way: Compelling open questions in photosynthesis research

Photosynthesis-the conversion of energy from sunlight into chemical energy-is essential for life on Earth. Yet there is much we do not understand about photosynthetic energy conversion on a fundamental level: how it evolved and the extent of its diversity, its dynamics, and all the components and connections involved in its regulation. In this commentary, researchers working on fundamental aspects of photosynthesis including the light-dependent reactions, photorespiration, and C4 photosynthetic metabolism pose and discuss what they view as the most compelling open questions in their areas of research.

Cyclic electron flow and Photosystem II-less photosynthesis

Oxygenic photosynthesis is characterised by the cooperation of two photo-driven complexes, Photosystem II (PSII) and Photosystem I (PSI), sequentially linked through a series of redox-coupled intermediates. Divergent evolution has resulted in photosystems exhibiting complementary redox potentials, spanning the range necessary to oxidise water and reduce CO2 within a single system. Catalysing nature's most oxidising reaction to extract electrons from water is a highly specialised task that limits PSII's metabolic function. In contrast, potential electron donors in PSI span a range of redox potentials, enabling it to accept electrons from various metabolic processes. This metabolic flexibility of PSI underpins the capacity of photosynthetic organisms to balance energy supply with metabolic demands, which is key for adaptation to environmental changes. Here, we review the phenomenon of 'PSII-less photosynthesis' where PSI functions independently of PSII by operating cyclic electron flow using electrons derived from non-photochemical reactions. PSII-less photosynthesis enables supercharged ATP production and is employed, for example, by cyanobacteria's heterocysts to host nitrogen fixation and by bundle sheath cells of C4 plants to boost CO2 assimilation. We discuss the energetic benefits of this arrangement and the prospects of utilising it to improve the productivity and stress resilience of photosynthetic organisms.

Hormetic Response of Photosystem II Function Induced by Nontoxic Calcium Hydroxide Nanoparticles

In recent years, inorganic nanoparticles, including calcium hydroxide nanoparticles [Ca Ca(OH)2 NPs], have attracted significant interest for their ability to impact plant photosynthesis and boost agricultural productivity. In this study, the effects of 15 and 30 mg L-1 oleylamine-coated calcium hydroxide nanoparticles [Ca(OH)2@OAm NPs] on photosystem II (PSII) photochemistry were investigated on tomato plants at their growth irradiance (GI) (580 μmol photons m-2 s-1) and at high irradiance (HI) (1000 μmol photons m-2 s-1). Ca(OH)2@OAm NPs synthesized via a microwave-assisted method revealed a crystallite size of 25 nm with 34% w/w of oleylamine coater, a hydrodynamic size of 145 nm, and a ζ-potential of 4 mV. Compared with the control plants (sprayed with distilled water), PSII efficiency in tomato plants sprayed with Ca(OH)2@OAm NPs declined as soon as 90 min after the spray, accompanied by a higher excess excitation energy at PSII. Nevertheless, after 72 h, the effective quantum yield of PSII electron transport (ΦPSII) in tomato plants sprayed with Ca(OH)2@OAm NPs enhanced due to both an increase in the fraction of open PSII reaction centers (qp) and to the enhancement in the excitation capture efficiency (Fv'/Fm') of these centers. However, the decrease at the same time in non-photochemical quenching (NPQ) resulted in an increased generation of reactive oxygen species (ROS). It can be concluded that Ca(OH)2@OAm NPs, by effectively regulating the non-photochemical quenching (NPQ) mechanism, enhanced the electron transport rate (ETR) and decreased the excess excitation energy in tomato leaves. The delay in the enhancement of PSII photochemistry by the calcium hydroxide NPs was less at the GI than at the HI. The enhancement of PSII function by calcium hydroxide NPs is suggested to be triggered by the NPQ mechanism that intensifies ROS generation, which is considered to be beneficial. Calcium hydroxide nanoparticles, in less than 72 h, activated a ROS regulatory network of light energy partitioning signaling that enhanced PSII function. Therefore, synthesized Ca(OH)2@OAm NPs could potentially be used as photosynthetic biostimulants to enhance crop yields, pending further testing on other plant species.

Microalgae-mediated bioremediation: current trends and opportunities-a review

Environmental pollution poses a critical global challenge, and traditional wastewater treatment methods often prove inadequate in addressing the complexity and scale of this issue. On the other hand, microalgae exhibit diverse metabolic capabilities that enable them to remediate a wide range of pollutants, including heavy metals, organic contaminants, and excess nutrients. By leveraging the unique metabolic pathways of microalgae, innovative strategies can be developed to effectively remediate polluted environments. Therefore, this review paper highlights the potential of microalgae-mediated bioremediation as a sustainable and cost-effective alternative to conventional methods. It also highlights the advantages of utilizing microalgae and algae-bacteria co-cultures for large-scale bioremediation applications, demonstrating impressive biomass production rates and enhanced pollutant removal efficiency. The promising potential of microalgae-mediated bioremediation is emphasized, presenting a viable and innovative alternative to traditional treatment methods in addressing the global challenge of environmental pollution. This review identifies the opportunities and challenges for microalgae-based technology and proposed suggestions for future studies to tackle challenges. The findings of this review advance our understanding of the potential of microalgae-based technology wastewater treatment.