The case for improving crop carbon sink strength or plasticity for a CO2-rich future

The link between changing in host carbon allocation and resistance to Magnaporthe oryzae: a possible tactic for mitigating the rice blast fungus

One of the most destructive diseases affecting rice is rice blast, which is brought on by the rice blast fungus Magnaporthe oryzae. The preventive measures, however, are not well established. To effectively reduce the negative effects of rice blasts on crop yields, it is imperative to comprehend the dynamic interactions between pathogen resistance and patterns of host carbon allocation. This review explores the relationship between variations in carbon allocation and rice plants' ability to withstand the damaging effects of M. oryzae. The review highlights potential strategies for altering host carbon allocation including transgenic, selective breeding, crop rotation, and nutrient management practices as a promising avenue for enhancing rice blast resistance. This study advances our knowledge of the interaction between plants' carbon allocation and M. oryzae resistance and provides stakeholders and farmers with practical guidance on mitigating the adverse effects of the rice blast globally. This information may be used in the future to create varieties that are resistant to M. oryzae.

Advancements in technology and innovation for sustainable agriculture: Understanding and mitigating greenhouse gas emissions from agricultural soils

In recent decades, Technology and Innovation (TI) have shown tremendous potential for improving agricultural productivity and environmental sustainability. However, the adoption and implementation of TI in the agricultural sector and its impact on the environment remain limited. To gain deeper insights into the significance of TI in enhancing agricultural productivity while maintaining environmental balance, this study investigates 21 agriculture-dependent Asian countries. Two machine learning techniques, LASSO (Least Absolute Shrinkage and Selection Operator) and Elastic-Net, are employed to analyze the data, which is categorized into three regional groups: ASEAN (Association of Southeast Asian Nations), SAARC (South Asian Association for Regional Cooperation), and GCC (Gulf Cooperation Council). The findings of this study highlight the heterogeneous nature of technology adoption and its environmental implications across the three country groups. ASEAN countries emerge as proactive adopters of relevant technologies, effectively enhancing agricultural production while simultaneously upholding environmental quality. Conversely, SAARC countries exhibit weaker technology adoption, leading to significant fluctuations in environmental quality, which in turn impact agricultural productivity. Notably, agricultural emissions of N2O (nitrous oxide) and CO2 (carbon dioxide) in SAARC countries show a positive association with agricultural production, while CH4 (methane) emissions have an adverse effect. In contrast, the study reveals a lack of evidence regarding technological adoption in agriculture among GCC countries. Surprisingly, higher agricultural productivity in these countries is correlated with increased N2O emissions. Moreover, the results indicate that deforestation and expansion of cropland contribute to increased agricultural production; however, this expansion is accompanied by higher emissions related to agricultural activities. This research represents a pioneering empirical analysis of the impact of TI and environmental emission gases on agricultural productivity in the three aforementioned country groups. It underscores the imperative of embracing relevant technologies to enhance agricultural output while concurrently ensuring environmental sustainability. The findings of this study provide valuable insights for policymakers and stakeholders in formulating strategies to promote sustainable agriculture and technological advancement in the context of diverse regional dynamics.

Triose phosphate utilization in leaves is modulated by whole-plant sink-source ratios and nitrogen budgets in rice

Triose phosphate utilization (TPU) is a biochemical process indicating carbon sink-source (im)balance within leaves. When TPU limits leaf photosynthesis, photorespiration-associated amino acid exports probably provide an additional carbon outlet and increase leaf CO2 uptake. However, whether TPU is modulated by whole-plant sink-source relations and nitrogen (N) budgets remains unclear. We address this question by model analyses of gas-exchange data measured on leaves at three growth stages of rice plants grown at two N levels. Sink-source ratio was manipulated by panicle pruning, by using yellower-leaf variant genotypes, and by measuring photosynthesis on adaxial and abaxial leaf sides. Across all these treatments, higher leaf N content resulted in the occurrence of TPU limitation at lower intercellular CO2 concentrations. Photorespiration-associated amino acid export was greater in high-N leaves, but was smaller in yellower-leaf genotypes, panicle-pruned plants, and for abaxial measurement. The feedback inhibition of panicle pruning on rates of TPU was not always observed, presumably because panicle pruning blocked N remobilization from leaves to grains and the increased leaf N content masked feedback inhibition. The leaf-level TPU limitation was thus modulated by whole-plant sink-source relations and N budgets during rice grain filling, suggesting a close link between within-leaf and whole-plant sink limitations.

Predicting corn tiller development in restrictive environments can be achieved to enhance defensive management decision tools for producers

Introduction

While globally appreciated for reliable, intensification-friendly phenotypes, modern corn (Zea mays L.) genotypes retain crop plasticity potential. For example, weather and heterogeneous field conditions can overcome phenotype uniformity and facilitate tiller expression. Such plasticity may be of interest in restrictive or otherwise variable environments around the world, where corn production is steadily expanding. No substantial effort has been made in available literature to predict tiller development in field scenarios, which could provide insight on corn plasticity capabilities and drivers. Therefore, the objectives of this investigation are as follows: 1) identify environment, management, or combinations of these factors key to accurately predict tiller density dynamics in corn; and 2) test outof-season prediction accuracy for identified factors.

Methods

Replicated field trials were conducted in 17 diverse site-years in Kansas (United States) during the 2019, 2020, and 2021 seasons. Two modern corn genotypes were evaluated with target plant densities of 25000, 42000, and 60000 plants ha -1. Environmental, phenological, and morphological data were recorded and evaluated with generalized additive models.

Results

Plant density interactions with cumulative growing degree days, photothermal quotient, mean minimum and maximum daily temperatures, cumulative vapor pressure deficit, soil nitrate, and soil phosphorus were identified as important predictive factors of tiller density. Many of these factors had stark non-limiting thresholds. Factors impacting growth rates and photosynthesis (specifically vapor pressure deficit and maximum temperatures) were most sensitive to changes in plant density. Out-of-season prediction errors were seasonally variable, highlighting model limitations due to training datasets.

Discussion

This study demonstrates that tillering is a predictable plasticity mechanism in corn, and therefore could be incorporated into decision tools for restrictive growing regions. While useful for diagnostics, these models are limited in forecast utility and should be coupled with appropriate decision theory and risk assessments for producers in climatically and socioeconomically vulnerable environments.

Elevated [CO2] negatively impacts C4 photosynthesis under heat and water stress without penalizing biomass

Elevated [CO2] (eCO2) and water stress reduce leaf stomatal conductance (gs), which may affect leaf thermoregulation during heat waves (heat stress). Two sorghum lines, with different leaf width were grown in a glasshouse at a mean day temperature of 30 °C, under different [CO2] and watering levels, and subjected to heat stress (43 °C) for 6 d at the start of the reproductive stage. We measured leaf photosynthetic and stomatal responses to light transients before harvesting the plants. Photosynthesis at growth conditions (Agrowth) and biomass accumulation were enhanced by eCO2 under control conditions. Heat stress increased gs, especially in wider leaves, and reduced the time constant of stomatal opening (kopen) at ambient [CO2] but not eCO2. However, heat stress reduced photosynthesis under water stress and eCO2 due to increased leaf temperature and reduced evaporative cooling. eCO2 prevented the reduction of biomass under both water and heat stress, possibly due to improved plant and soil water status as a result of reduced gs. Our results suggest that the response of the C4 crop sorghum to future climate conditions depends on the trade-off between low gs needed for high water use efficiency and drought tolerance, and the high gs needed for improved thermoregulation and heat tolerance under an eCO2 future.

The decline of plant mineral nutrition under rising CO2: physiological and molecular aspects of a bad deal

The elevation of atmospheric CO₂ concentration has a strong impact on the physiology of C3 plants, far beyond photosynthesis and C metabolism. In particular, it reduces the concentrations of most mineral nutrients in plant tissues, posing major threats on crop quality, nutrient cycles, and carbon sinks in terrestrial agro-ecosystems. The causes of the detrimental effect of high CO₂ levels on plant mineral status are not understood. We provide an update on the main hypotheses and review the increasing evidence that, for nitrogen, this detrimental effect is associated with direct inhibition of key mechanisms of nitrogen uptake and assimilation. We also mention promising strategies for identifying genotypes that will maintain robust nutrient status in a future high-CO₂ world.

Sustaining productivity gains in the face of climate change: A research agenda for US wheat

Wheat is a globally important crop and one of the "big three" US field crops. But unlike the other two (maize and soybean), in the United States its development is commercially unattractive, and so its breeding takes place primarily in public universities. Troublingly, the incentive structures within these universities may be hindering genetic improvement just as climate change is complicating breeding efforts. "Business as usual" in the US public wheat-breeding infrastructure may not sustain productivity increases. To address this concern, we held a multidisciplinary conference in which researchers from 12 US (public) universities and one European university shared the current state of knowledge in their disciplines, aired concerns, and proposed initiatives that could facilitate maintaining genetic improvement of wheat in the face of climate change. We discovered that climate-change-oriented breeding efforts are currently considered too risky and/or costly for most university wheat breeders to undertake, leading to a relative lack of breeding efforts that focus on abiotic stressors such as drought and heat. We hypothesize that this risk/cost burden can be reduced through the development of appropriate germplasm, relevant screening mechanisms, consistent germplasm characterization, and innovative models predicting the performance of germplasm under projected future climate conditions. However, doing so will require coordinated, longer-term, inter-regional efforts to generate phenotype data, and the modification of incentive structures to consistently reward such efforts.

Bacterial Form II Rubisco can support wild-type growth and productivity in Solanum tuberosum cv. Desiree (potato) under elevated CO2

The last decade has seen significant advances in the development of approaches for improving both the light harvesting and carbon fixation pathways of photosynthesis by nuclear transformation, many involving multigene synthetic biology approaches. As efforts to replicate these accomplishments from tobacco into crops gather momentum, similar diversification is needed in the range of transgenic options available, including capabilities to modify crop photosynthesis by chloroplast transformation. To address this need, here we describe the first transplastomic modification of photosynthesis in a crop by replacing the native Rubisco in potato with the faster, but lower CO₂-affinity and poorer CO₂/O₂ specificity Rubisco from the bacterium Rhodospirillum rubrum. High level production of R. rubrum Rubisco in the potRr genotype (8 to 10 µmol catalytic sites m²) allowed it to attain wild-type levels of productivity, including tuber yield, in air containing 0.5% (v/v) CO₂. Under controlled environment growth at 25°C and 350 µmol photons m² PAR, the productivity and leaf biochemistry of wild-type potato at 0.06%, 0.5%, or 1.5% (v/v) CO₂ and potRr at 0.5% or 1.5% (v/v) CO₂ were largely indistinguishable. These findings suggest that increasing the scope for enhancing productivity gains in potato by improving photosynthate production will necessitate improvement to its sink-potential, consistent with current evidence productivity gains by eCO₂ fertilization for this crop hit a ceiling around 560 to 600 ppm CO₂.

Climate change challenges, plant science solutions

Climate change is a defining challenge of the 21st century, and this decade is a critical time for action to mitigate the worst effects on human populations and ecosystems. Plant science can play an important role in developing crops with enhanced resilience to harsh conditions (e.g. heat, drought, salt stress, flooding, disease outbreaks) and engineering efficient carbon-capturing and carbon-sequestering plants. Here, we present examples of research being conducted in these areas and discuss challenges and open questions as a call to action for the plant science community.

The time course of acclimation to the stress of triose phosphate use limitation

Triose phosphate utilisation (TPU) limits the maximum rate at which plants can photosynthesise. However, TPU is almost never found to be limiting photosynthesis under ambient conditions for plants. This, along with previous results showing adaptability of TPU at low temperature, suggest that TPU capacity is regulated to be just above the photosynthetic rate achievable under the prevailing conditions. A set of experiments were performed to study the adaptability of TPU capacity when plants are acclimated to elevated CO₂ concentrations. Plants held at 1500 ppm CO₂ were initially TPU limited. After 30 h they no longer exhibited TPU limitations but they did not elevate their TPU capacity. Instead, the maximum rates of carboxylation and electron transport declined. A timecourse of regulatory responses was established. A step increase of CO₂ first caused PSI to be oxidised but after 40 s both PSI and PSII had excess electrons as a result of acceptor-side limitations. Electron flow to PSI slowed and the proton motive force increased. Eventually, non-photochemical quenching reduced electron flow sufficiently to balance the TPU limitation. Over several minutes rubisco deactivated contributing to regulation of metabolism to overcome the TPU limitation.

Improving crop yield potential: Underlying biological processes and future prospects

The growing world population and global increases in the standard of living both result in an increasing demand for food, feed and other plant-derived products. In the coming years, plant-based research will be among the major drivers ensuring food security and the expansion of the bio-based economy. Crop productivity is determined by several factors, including the available physical and agricultural resources, crop management, and the resource use efficiency, quality and intrinsic yield potential of the chosen crop. This review focuses on intrinsic yield potential, since understanding its determinants and their biological basis will allow to maximize the plant's potential in food and energy production. Yield potential is determined by a variety of complex traits that integrate strictly regulated processes and their underlying gene regulatory networks. Due to this inherent complexity, numerous potential targets have been identified that could be exploited to increase crop yield. These encompass diverse metabolic and physical processes at the cellular, organ and canopy level. We present an overview of some of the distinct biological processes considered to be crucial for yield determination that could further be exploited to improve future crop productivity.

Wheat yield potential can be maximized by increasing red to far-red light conditions at critical developmental stages

Sensing of neighbours via the Red to Far-Red light ratio (R:FR) may exert a cap to yield potential in wheat. The effects of an increased R:FR inside the canopy were studied in dense wheat mini canopies grown in controlled environments by lowering FR. To distinguish between effects exerted by light sensing and assimilate supply, the treatments were complemented with elevated CO₂ , applied between different developmental timepoints to specifically impact tillering, spike growth, floret fertility and grain filling, in different combinations. The yield response to high R:FR was strongly dependent on the developmental stage in all three cultivars and pivoted between positive if applied after the start of stem elongation, and negative or null if applied before. Yield gains of up to 70% and 120% were observed, respectively, in two cultivars, associated with a higher number of tiller spikes and grains per spike in the main shoot. The response to the combination of high R:FR and elevated CO₂ or CO₂ alone were cultivar dependent. Taken together, our results suggest that R:FR exerts a significant control on yield potential in wheat and achieving a high R:FR from stem elongation to maturity is a promising lever towards a significant increase in grain yield.

A model-guided holistic review of exploiting natural variation of photosynthesis traits in crop improvement

Breeding for improved leaf photosynthesis is considered as a viable approach to increase crop yield. Whether it should be improved in combination with other traits has not been assessed critically. Based on the quantitative crop model GECROS that interconnects various traits to crop productivity, we review natural variation in relevant traits, from biochemical aspects of leaf photosynthesis to morpho-physiological crop characteristics. While large phenotypic variations (sometimes >2-fold) for leaf photosynthesis and its underlying biochemical parameters were reported, few quantitative trait loci (QTL) were identified, accounting for a small percentage of phenotypic variation. More QTL were reported for sink size (that feeds back on photosynthesis) or morpho-physiological traits (that affect canopy productivity and duration), together explaining a much greater percentage of their phenotypic variation. Traits for both photosynthetic rate and sustaining it during grain filling were strongly related to nitrogen-related traits. Much of the molecular basis of known photosynthesis QTL thus resides in genes controlling photosynthesis indirectly. Simulation using GECROS demonstrated the overwhelming importance of electron transport parameters, compared with the maximum Rubisco activity that largely determines the commonly studied light-saturated photosynthetic rate. Exploiting photosynthetic natural variation might significantly improve crop yield if nitrogen uptake, sink capacity, and other morpho-physiological traits are co-selected synergistically.

Carbon dioxide responsiveness mitigates rice yield loss under high night temperature

Increasing night-time temperatures are a major threat to sustaining global rice (Oryza sativa L.) production. A simultaneous increase in [CO2] will lead to an inevitable interaction between elevated [CO2] (e[CO2]) and high night temperature (HNT) under current and future climates. Here, we conducted field experiments to identify [CO2] responsiveness from a diverse indica panel comprising 194 genotypes under different planting geometries in 2016. Twenty-three different genotypes were tested under different planting geometries and e[CO2] using a free-air [CO2] enrichment facility in 2017. The most promising genotypes and positive and negative controls were tested under HNT and e[CO2] + HNT in 2018. [CO2] responsiveness, measured as a composite response index on different yield components, grain yield, and photosynthesis, revealed a strong relationship (R2 = 0.71) between low planting density and e[CO2]. The most promising genotypes revealed significantly lower (P < 0.001) impact of HNT in high [CO2] responsive (HCR) genotypes compared to the least [CO2] responsive genotype. [CO2] responsiveness was the major driver determining grain yield and related components in HCR genotypes with a negligible yield loss under HNT. A systematic investigation highlighted that active selection and breeding for [CO2] responsiveness can lead to maintained carbon balance and compensate for HNT-induced yield losses in rice and potentially other C3 crops under current and future warmer climates.

Impact of Elevated CO2 and Reducing the Source-Sink Ratio by Partial Defoliation on Rice Grain Quality - A 3-Year Free-Air CO2 Enrichment Study

Evaluating the impact of increasing CO₂ on rice quality is becoming a global concern. However, whether adjusting the source-sink ratio will affect the response of rice grain quality to elevated CO₂ concentrations remains unknown. In 2016-2018, we conducted a free-air CO₂ enrichment experiment using a popular japonica cultivar grown at ambient and elevated CO₂ levels (eCO₂, increased by 200 ppm), reducing the source-sink ratio via cutting leaves (LC) at the heading stage, to investigate the effects of eCO₂ and LC and their interactions on rice processing, appearance, nutrition, and eating quality. Averaged across 3 years, eCO₂ significantly decreased brown rice percentage (-0.5%), milled rice percentage (-2.1%), and head rice percentage (-4.2%) but increased chalky grain percentage (+ 22.3%) and chalkiness degree (+ 26.3%). Markedly, eCO₂ increased peak viscosity (+ 2.9%) and minimum viscosity (+ 3.8%) but decreased setback (-96.1%) of powder rice and increased the appearance (+ 4.5%), stickiness (+ 3.5%) and balance degree (+ 4.8%) of cooked rice, while decreasing the hardness (-6.7%), resulting in better palatability (+ 4.0%). Further, eCO₂ significantly decreased the concentrations of protein, Ca, S, and Cu by 5.3, 4.7, 2.2, and 9.6%, respectively, but increased K concentration by 3.9%. Responses of nutritional quality in different grain positions (brown and milled rice) to eCO₂ showed the same trend. Compared with control treatment, LC significantly increased chalky grain percentage, chalkiness degree, protein concentration, mineral element levels (except for B and Mn), and phytic acid concentration. Our results indicate that eCO₂ reduced rice processing suitability, appearance, and nutritional quality but improved the eating quality. Rice quality varied significantly among years; however, few CO₂ by year, CO₂ by LC, or CO₂ by grain position interactions were detected, indicating that the effects of eCO₂ on rice quality varied little with the growing seasons, the decrease in the source-sink ratios or the different grain positions.

Evolution of a biochemical model of steady-state photosynthesis

On the occasion of the 40th anniversary of the publication of the landmark model by Farquhar, von Caemmerer & Berry on steady-state C₃ photosynthesis (known as the "FvCB model"), we review three major further developments of the model. These include: (1) limitation by triose phosphate utilization, (2) alternative electron transport pathways, and (3) photorespiration-associated nitrogen and C₁ metabolisms. We discussed the relation of the third extension with the two other extensions, and some equivalent extensions to model C₄ photosynthesis. In addition, the FvCB model has been coupled with CO₂ -diffusion models. We review how these extensions and integration have broadened the use of the FvCB model in understanding photosynthesis, especially with regard to bioenergetic stoichiometries associated with photosynthetic quantum yields. Based on the new insights, we present caveats in applying the FvCB model. Further research needs are highlighted.

Physiological and Expressional Regulation on Photosynthesis, Starch and Sucrose Metabolism Response to Waterlogging Stress in Peanut

Waterlogging has negative effects on crop yield. Physiological and transcriptome data of two peanut cultivars [Zhongkaihua 1 (ZKH 1) and Huayu 39 (HY 39)] were studied under normal water supply and waterlogging stress for 5 or 10 days at the flowering stage. The results showed that the main stem height, the number of lateral branches, lateral branch length, and the stem diameter increased under waterlogging stress, followed by an increase in dry matter accumulation, which was correlated with the increase in the soil and plant analysis development (SPAD) and net photosynthetic rate (Pn) and the upregulation of genes related to porphyrin and chlorophyll metabolism and photosynthesis. However, the imbalance of the source-sink relationship under waterlogging was the main cause of yield loss, and waterlogging caused an increase in the sucrose and soluble sugar contents and a decrease in the starch content; it also decreased the activities of sucrose synthetase (SS) and sucrose phosphate synthetase (SPS), which may be due to the changes in the expression of genes related to starch and sucrose metabolism. However, the imbalance of the source-sink relationship led to the accumulation of photosynthate in the stems and leaves, which resulted in the decrease of the ratio of pod dry weight to total dry weight (PDW/TDW) and yield. Compared with ZKH 1, the PDW of HY 39 decreased more probably because more photosynthate accumulated in the stem and leaves of HY 39 and could not be effectively transported to the pod.

Alterations in Source-Sink Relations Affect Rice Yield Response to Elevated CO2: A Free-Air CO2 Enrichment Study

To understand the effects of source-sink relationships on rice yield response to elevated CO₂ levels (eCO₂), we conducted a field study using a popular japonica cultivar grown in a free-air CO₂ enrichment environment in 2017-2018. The source-sink ratio of rice was set artificially via source-sink treatments (SSTs) at the heading stage. Five SSTs were performed in 2017 (EXP1): cutting off the flag leaf (LC1) and the top three functional leaves (LC3), removing one branch in every three branches of a panicle (SR1/3) and one branch in every two branches of a panicle (SR1/2), and the control (CK) without any leaf cutting or spikelet removal. The eCO₂ significantly increased grain yield by 15.7% on average over all treatments; it significantly increased grain yield of CK, LC1, LC3, SR1/3, and SR1/2 crops by 13.9, 18.1, 25.3, 12.0, and 10.9%, respectively. The yield response to eCO₂ was associated with a significant increase of panicle number and fully-filled grain percentage (FGP), and the response of crops under different SSTs was significantly positively correlated with FGP and the average grain weight of the seeds. Two SSTs (CK and LC3) were performed in 2018 (EXP2), which confirmed that the yield response of LC3 crops (25.1%) to eCO₂ was significantly higher than that of CK (15.9%). Among the different grain positions, yield response to eCO₂ of grains attached to the lower secondary rachis was greater than that of grains attached to the upper primary rachis. Reducing the source-sink ratio via leaf-cutting enhanced the net photosynthetic rate response of the remaining leaves to eCO₂ and increased the grain filling ability. Conversely, spikelet removal increased the non-structural carbohydrate (NSC) content of the stem, causing feedback inhibition and photosynthetic down-regulation. This study suggests that reducing the source-sink ratio by adopting appropriate management measures can increase the response of rice to eCO₂.

Tuber and Tuberous Root Development

Root and tuber crops have been an important part of human nutrition since the early days of humanity, providing us with essential carbohydrates, proteins, and vitamins. Today, they are especially important in tropical and subtropical regions of the world, where they help to feed an ever-growing population. Early induction and storage organ size are important agricultural traits, as they determine yield over time. During potato tuberization, environmental and metabolic status are sensed, ensuring proper timing of tuberization mediated by phloem-mobile signals. Coordinated cellular restructuring and expansion growth, as well as controlled storage metabolism in the tuber, are executed. This review summarizes our current understanding of potato tuber development and highlights similarities and differences to important tuberous root crop species like sweetpotato and cassava. Finally, we point out knowledge gaps that need to be filled before a complete picture of storage organ development can emerge.

Dissecting Source-Sink Relationship of Subtending Leaf for Yield and Fiber Quality Attributes in Upland Cotton (Gossypium hirsutum L.)

Photosynthesis as a source is a significant contributor to the reproductive sink affecting cotton yield and fiber quality. Moreover, carbon assimilation from subtending leaves adds up a significant proportion to the reproductive sink. Therefore, this study aimed to address the source-sink relationship of boll subtending leaf with fiber quality and yield related traits in upland cotton. A core collection of 355 upland cotton accessions was subjected to subtending leaf removal treatment effects across 2 years. The analysis of variance suggested a significant effect range in the source-sink relationship under subtending leaf removal effects at different growth stages. Further insight into the variation was provided by the correlation analysis and principal component analysis. A significant positive correlation between different traits was observed and the multivariate analysis including hierarchical clustering and principal component analysis (PCA) categorised germplasm accessions into three groups on the basis of four subtending leaf removal treatment effects across 2 years. A set of genotypes with the lowest and highest treatment effects has been identified. Selected accessions and the outcome of the current study may provide a basis for a further study to explore the molecular mechanism of source-sink relationship of boll subtending leaf and utilization of breeding programs focused on cotton improvement.

Changes in Leaf-Level Nitrogen Partitioning and Mesophyll Conductance Deliver Increased Photosynthesis for Lolium perenne Leaves Engineered to Accumulate Lipid Carbon Sinks

Diacylglycerol acyl-transferase (DGAT) and cysteine oleosin (CO) expression confers a novel carbon sink (of encapsulated lipid droplets) in leaves of Lolium perenne and has been shown to increase photosynthesis and biomass. However, the physiological mechanism by which DGAT + CO increases photosynthesis remains unresolved. To evaluate the relationship between sink strength and photosynthesis, we examined fatty acids (FA), water-soluble carbohydrates (WSC), gas exchange parameters and leaf nitrogen for multiple DGAT + CO lines varying in transgene accumulation. To identify the physiological traits which deliver increased photosynthesis, we assessed two important determinants of photosynthetic efficiency, CO₂ conductance from atmosphere to chloroplast, and nitrogen partitioning between different photosynthetic and non-photosynthetic pools. We found that DGAT + CO accumulation increased FA at the expense of WSC in leaves of L. perenne and for those lines with a significant reduction in WSC, we also observed an increase in photosynthesis and photosynthetic nitrogen use efficiency. DGAT + CO L. perenne displayed no change in rubisco content or V_cmax but did exhibit a significant increase in specific leaf area (SLA), stomatal and mesophyll conductance, and leaf nitrogen allocated to photosynthetic electron transport. Collectively, we showed that increased carbon demand via DGAT+CO lipid sink accumulation can induce leaf-level changes in L. perenne which deliver increased rates of photosynthesis and growth. Carbon sinks engineered within photosynthetic cells provide a promising new strategy for increasing photosynthesis and crop productivity.