Enhanced leaf photosynthesis as a target to increase grain yield: insights from transgenic rice lines with variable Rieske FeS protein content in the cytochrome b6 /f complex

Ectopic Expression of a Transmembrane Protein KaCyt b6 from a Red Seaweed Kappaphycus alvarezii in Transgenic Tobacco Augmented the Photosynthesis and Growth

Cytochrome b6f complex is a thylakoid membrane-localized protein and catalyses the transfer of electrons from plastoquinol to plastocyanin in photosynthetic electron transport chain. In the present study, Cytochrome b6 (KaCyt b6) gene from Kappaphycus alvarezii (a red seaweed) was overexpressed in tobacco. A 935 base pair (bp) long KaCyt b6 cDNA contained an open reading frame of 648 bp encoding a protein of 215 amino acids with an expected isoelectric point of 8.67 and a molecular mass of 24.37 kDa. The KaCyt b6 gene was overexpressed in tobacco under control of CaMV35S promoter. The transgenic tobacco had higher electron transfer rate and photosynthetic yield over wild-type and vector control tobacco. The KaCyt b6 tobacco also exhibited significantly higher photosynthetic gas exchange (PN) and improved water use efficiency. The transgenic plants had higher ratio of PN and intercellular CO2. The KaCyt b6 transgenic tobacco showed higher estimates of photosystem II quantum yield, higher activity of the water-splitting complex, PSII photochemistry, and photochemical quenching. The basal quantum yield of nonphotochemical processes in PSII was recorded lower in KaCyt b6 tobacco. Transgenic tobacco contained higher contents of carotenoids and total chlorophyll and also had better ratios of chlorophyll a and b, and carotenoids and total chlorophyll contents hence improved photosynthetic efficiency and production of sugar and starch. The KaCyt b6 transgenic plants performed superior under control and greenhouse conditions. To the best of our knowledge through literature survey, this is the first report on characterization of KaCyt b6 gene from K. alvarezii for enhanced photosynthetic efficiency and growth in tobacco.

High photosynthesis rates in Brassiceae species are mediated by leaf anatomy enabling high biochemical capacity, rapid CO2 diffusion and efficient light use

Certain species in the Brassicaceae family exhibit high photosynthesis rates, potentially providing a valuable route toward improving agricultural productivity. However, factors contributing to their high photosynthesis rates are still unknown. We compared Hirschfeldia incana, Brassica nigra, Brassica rapa and Arabidopsis thaliana, grown under two contrasting light intensities. Hirschfeldia incana matched B. nigra and B. rapa in achieving very high photosynthesis rates under high growth-light condition, outperforming A. thaliana. Photosynthesis was relatively more limited by maximum photosynthesis capacity in H. incana and B. rapa and by mesophyll conductance in A. thaliana and B. nigra. Leaf traits such as greater exposed mesophyll specific surface enabled by thicker leaf or high-density small palisade cells contributed to the variation in mesophyll conductance among the species. The species exhibited contrasting leaf construction strategies and acclimation responses to low light intensity. High-light plants distributed Chl deeper in leaf tissue, ensuring even distribution of photosynthesis capacity, unlike low-light plants. Leaf anatomy of H. incana, B. nigra and B. rapa facilitated effective CO2 diffusion, efficient light use and provided ample volume for their high maximum photosynthetic capacity, indicating that a combination of adaptations is required to increase CO2-assimilation rates in plants.

Natural genetic variation in dynamic photosynthesis is correlated with stomatal anatomical traits in diverse tomato species across geographical habitats

Plants grown under field conditions experience fluctuating light. Understanding the natural genetic variations for a similarly dynamic photosynthetic response among untapped germplasm resources, as well as the underlying mechanisms, may offer breeding strategies to improve production using molecular approaches. Here, we measured gas exchange under fluctuating light, along with stomatal density and size, in eight wild tomato species and two tomato cultivars. The photosynthetic induction response showed significant diversity, with some wild species having faster induction rates than the two cultivars. Species with faster photosynthetic induction rates had higher daily integrated photosynthesis, but lower average water use efficiency because of high stomatal conductance under natural fluctuating light. The variation in photosynthetic induction was closely associated with the speed of stomatal responses, highlighting its critical role in maximizing photosynthesis under fluctuating light conditions. Moreover, stomatal size was negatively correlated with stomatal density within a species, and plants with smaller stomata at a higher density had a quicker photosynthetic response than those with larger stomata at lower density. Our findings show that the response of stomatal conductance plays a pivotal role in photosynthetic induction, with smaller stomata at higher density proving advantageous for photosynthesis under fluctuating light in tomato species. The interspecific variation in the rate of stomatal responses could offer an untapped resource for optimizing dynamic photosynthetic responses under field conditions.

Chemometric Modeling Revealed Oleic and Linoleic Acids as Varietal Biomarkers for Six Sesame Varieties-In Vitro and UHPLC Analyses

Pakistan once considered self-sufficient for edible oil production now became the major importer with 88.6% imports and producing only the minor portion. Scientific negligence in oil seed crops led to a dramatic decrease in edible oil production depending mainly on only the imports. Sesamum indicum L., "Queen of Oil seeds" with 50-55% oil, is cultivated in various geographical regions of Pakistan, but farmers are not considering this crop because of insufficient knowledge, poor crop management practices, and low yielding varieties. This study was conducted to check the nutritional, biochemical, antioxidant, and yield potentials of six major varieties, i.e., TS-5, TH-6, Til-18, NIAB-Mil, NIAB-Pearl, and NS-16, and to compare the nutritionals, oil quality, and oil yield potential of these varieties. Field experiment was conducted, and various crop growth biomarkers were analyzed. Chlorophyll content and superoxide dismutase activity were found to be highest in NIAB-Mil followed by NIAB-Pearl and comparable to those of Til-18, while APX, Cat, and GPX activity was found to be highest in Til-18 with 25.6 and 5.9 and 6.02 mg/g, respectively. Seed antioxidant parameters showed a mixed response, but NIAB-Mil, NIAB pearl, and Til-18 were found to be highest in all antioxidant parameters. UHPLC analysis of seed oil resulted in a total of 14 triacylglycerols (TAGs), and principal component analysis and OPLS-Da analysis showed seven TAG biomarkers responsible for the separation of sesame varieties. Til-18 was found to be highest in oil content (53.3%) more abundant with oleic acid, while NIAB-Pearl, NIAB-Mil, and NS-16 were found to be abundant with linoleic acid, both considered as potential TAG biomarkers for sesame oil separation. This study concluded that, in general, Til-18 variety is more resistant with high nutritional status, high antioxidant activity, and oil yielding variety, followed by NIAB-Mil and NIAB-Pearl.

The atypical Dof transcriptional factor OsDes1 contributes to stay-green, grain yield, and disease resistance in rice

The regulation of leaf senescence and disease resistance plays a crucial role in determining rice grain yield and quality, which are important to meet the ever-increasing food demands of the world. Here, we identified an atypical Dof transcriptional factor OsDes1 that contributes to the stay-green phenotype, grain yield, and disease resistance in rice. The expression level of OsDes1 is positively associated with stay-green in natural variations of japonica rice, suggesting that OsDes1 would be alternatively used in breeding programs. Mechanistically, OsDes1 targets the promoter of the Rieske FeS protein gene OsPetC to activate its expression and interacts with OsPetC to protect against its degradation, thus promoting stay-green and ultimately improving the grain yield. OsDes1 also binds to the promoter region of defense-related genes, such as OsPR1b, and activates their expression, leading to enhanced disease resistance. These findings offer a potential strategy for breeding rice to enhance grain yield and disease resistance.

Enhancing Photosynthesis and Plant Productivity through Genetic Modification

Enhancing crop photosynthesis through genetic engineering technologies offers numerous opportunities to increase plant productivity. Key approaches include optimizing light utilization, increasing cytochrome b6f complex levels, and improving carbon fixation. Modifications to Rubisco and the photosynthetic electron transport chain are central to these strategies. Introducing alternative photorespiratory pathways and enhancing carbonic anhydrase activity can further increase the internal CO2 concentration, thereby improving photosynthetic efficiency. The efficient translocation of photosynthetically produced sugars, which are managed by sucrose transporters, is also critical for plant growth. Additionally, incorporating genes from C4 plants, such as phosphoenolpyruvate carboxylase and NADP-malic enzymes, enhances the CO2 concentration around Rubisco, reducing photorespiration. Targeting microRNAs and transcription factors is vital for increasing photosynthesis and plant productivity, especially under stress conditions. This review highlights potential biological targets, the genetic modifications of which are aimed at improving photosynthesis and increasing plant productivity, thereby determining key areas for future research and development.

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.

Carbon nanosol promotes plant growth and broad-spectrum resistance

Carbon nanosol (CNS) is a carbon-based nanomaterial capable of promoting plant growth while the underlying mechanism involved in this process remains unknown. This study demonstrates that CNS promotes rice seedling growth under restricted concentrations. Macroelement transporter mutants were investigated to further investigate the CNS-mediated promotion of rice seedling growth. The genetic and physiological findings revealed that nitrate transporter 1.1B (NRT1.1B) and ammonium transporter 1 (AMT1) mutants inhibited the CNS-induced growth development of rice seedlings, whereas potassium transporter (AKT1) and phosphate transporter 8 (PT8) did not exhibit any inhibitory effects. Further investigations demonstrated the inhibition of CNS-mediated growth promotion via glutamine synthetase 1;1 (gs1;1) mutants. Additionally, the administration of CNS resulted in enhanced accumulation of chlorophyll in plants, and the promotion of CNS-induced growth was inhibited by yellow-green leaf 8 (YGL8) mutants and the chlorophyll biosynthetic gene divinyl reductase (DVR) mutants. According to these findings, the CNS promotes plant growth by stimulating chlorophyll biosynthesis. Furthermore, the presence of CNS enhanced the ability of rice to withstand blast, sheath blight (ShB), and bacterial blight. The nrt1.1b, amt1, dvr, and ygl8 mutants did not exhibit a broad spectrum effect. The positive regulation of broad-spectrum resistance in rice by GS1;1 suggests the requirement of N assimilation for CNS-mediated broad-spectrum resistance. In addition, an in vitro assay demonstrated that CNS inhibits the growth of pathogens responsible for blast, ShB, and bacterial blight, namely Magnaporthe oryzae, Rhizoctonia solani AG1-IA, and Xanthomonas oryzae pv. Oryzae, respectively. CNS application may also induce broad-spectrum resistance against bacterial and fungal pathogens, indicating that in addition to its antifungal and antibacterial properties, CNS application may also stimulate N assimilation. Collectively, the results indicate that CNS may be a potential nano-therapeutic agent for improved plant growth promotion while also providing broad-spectrum resistance.

The SbbHLH041-SbEXPA11 Module Enhances Cadmium Accumulation and Rescues Biomass by Increasing Photosynthetic Efficiency in Sorghum

In plants, expansin genes are responsive to heavy metal exposure. To study the bioremediary potential of this important gene family, we discovered a root-expressed expansin gene in sorghum, SbEXPA11, which is notably upregulated following cadmium (Cd) exposure. However, the mechanism underlying the Cd detoxification and accumulation mediated by SbEXPA11 in sorghum remains unclear. We overexpressed SbEXPA11 in sorghum and compared wild-type (WT) and SbEXPA11-overexpressing transgenic sorghum in terms of Cd accumulation and physiological indices following Cd. Compared with the WT, we found that SbEXPA11 mediates Cd tolerance by exerting reactive oxygen species (ROS)-scavenging effects through upregulating the expression of antioxidant enzymes. Moreover, the overexpression of SbEXPA11 rescued biomass production by increasing the photosynthetic efficiency of transgenic plants. In the pot experiment with a dosage of 10 mg/kg Cd, transgenic sorghum plants demonstrated higher efficacy in reducing the Cd content of the soil (8.62 mg/kg) compared to WT sorghum plants (9.51 mg/kg). Subsequent analysis revealed that the SbbHLH041 transcription factor has the ability to induce SbEXPA11 expression through interacting with the E-box located within the SbEXPA11 promoter. These findings suggest that the SbbHLH041-SbEXPA11 cascade module may be beneficial for the development of phytoremediary sorghum varieties.

Genome-wide association study of soybean (Glycine max [L.] Merr.) germplasm for dissecting the quantitative trait nucleotides and candidate genes underlying yield-related traits

Soybean (Glycine max [L.] Merr.) is one of the most significant crops in the world in terms of oil and protein. Owing to the rising demand for soybean products, there is an increasing need for improved varieties for more productive farming. However, complex correlation patterns among quantitative traits along with genetic interactions pose a challenge for soybean breeding. Association studies play an important role in the identification of accession with useful alleles by locating genomic sites associated with the phenotype in germplasm collections. In the present study, a genome-wide association study was carried out for seven agronomic and yield-related traits. A field experiment was conducted in 2015/2016 at two locations that include 155 diverse soybean germplasm. These germplasms were genotyped using SoySNP50K Illumina Infinium Bead-Chip. A total of 51 markers were identified for node number, plant height, pods per plant, seeds per plant, seed weight per plant, hundred-grain weight, and total yield using a multi-locus linear mixed model (MLMM) in FarmCPU. Among these significant SNPs, 18 were putative novel QTNs, while 33 co-localized with previously reported QTLs. A total of 2,356 genes were found in 250 kb upstream and downstream of significant SNPs, of which 17 genes were functional and the rest were hypothetical proteins. These 17 candidate genes were located in the region of 14 QTNs, of which ss715580365, ss715608427, ss715632502, and ss715620131 are novel QTNs for PH, PPP, SDPP, and TY respectively. Four candidate genes, Glyma.01g199200, Glyma.10g065700, Glyma.18g297900, and Glyma.14g009900, were identified in the vicinity of these novel QTNs, which encode lsd one like 1, Ergosterol biosynthesis ERG4/ERG24 family, HEAT repeat-containing protein, and RbcX2, respectively. Although further experimental validation of these candidate genes is required, several appear to be involved in growth and developmental processes related to the respective agronomic traits when compared with their homologs in Arabidopsis thaliana. This study supports the usefulness of association studies and provides valuable data for functional markers and investigating candidate genes within a diverse germplasm collection in future breeding programs.

Selenite affected photosynthesis of Oryza sativa L. exposed to antimonite: Electron transfer, carbon fixation, pigment synthesis via a combined analysis of physiology and transcriptome

Selenium (Se) is a microelement that can counteract (a)biotic stresses in plants. Excess antimony (Sb) will inhibit plant photosynthesis, which can be alleviated by appropriate doses of Se but the associated mechanisms at the molecular levels have not been fully explored. Here, a rice variety (Yongyou 9) was exposed to selenite [Se(IV), 0.2 and 0.8 mg L-1] alone or combined with antimonite [Sb(III), 5 and 10 mg L-1]. When compared to the 10 mg L-1 Sb treatment alone, addition of Se in a dose-dependent manner 1) reduced the heat dissipation efficiency resulting from the inhibited donors, Sb concentrations in shoots and roots, leaf concentrations of fructose, H2O2 and O2•-; 2) enhanced heat dissipation efficiency resulting from the inhibited accepters value, concentrations of Chl a, sucrose and starch, and the enzyme activity of adenosine diphosphate glucose pyrophosphorylase, sucrose phosphate synthase, and sucrose synthase; but 3) did not alter gas exchange parameters, concentrations of Chl b and total Chl, enzyme activity of soluble acid invertase, and values of maximum P700 signal, photochemical efficiency of PSI and electron transport rate of PSI. Se alleviated the damage caused by Sb to the oxygen-evolving complex and promoted the transfer of electrons from QA to QB. When compared to the 10 mg L-1 Sb treatment alone, addition of Se 1) up-regulated genes correlated to synthesis pathways of Chl, carotenoid, sucrose and glucose; 2) disturbed signal transduction pathway of abscisic acid; and 3) upregulated gene expression correlated to photosynthetic complexes (OsFd1, OsFER1 and OsFER2).

Cloning and functional study of GmRPI2, which is the critical gene of photosynthesis in soybean

Light provides energy for photosynthesis and is also an important environmental signal that regulates plant growth and development. Ribose-5-phosphate isomerase plays a crucial role in photosynthesis. However, ribose-5-phosphate isomerase has yet to be studied in soybean photosynthesis. To understand the biological function of GmRPI2, in this study, GmRPI2 was cloned, plant overexpression vectors and gene editing vectors were successfully constructed, and transformed into recipient soybean JN74 using the Agrobacterium-mediated method. Using qRT-PCR, we analyzed that GmRPI2 gene expression was highest in leaves, second highest in roots, and lowest in stems. Promoter analysis revealed the presence of multiple cis-acting elements related to light response in the promoter region of GmRPI2. Compared with the control soybean plants, the net photosynthetic rate and transpiration rate of the overexpression lines were higher than those of the control and gene editing lines, while the intercellular CO2 concentration was significantly lower than that of the control and gene editing lines; the total chlorophyll, chlorophyll a, chlorophyll b contents and soluble sugar contents of the overexpression plants were significantly higher than those of the recipient and editing plants, indicating that the GmRPI2 gene can increase The GmRPI2 gene can increase the photosynthetic capacity of soybean plants, providing a theoretical basis and genetic resources for improving soybean yield by regulating photosynthetic efficiency.

Grafting enhances drought tolerance by regulating and mobilizing proteome, transcriptome and molecular physiology in okra genotypes

Drought stress poses a serious concern to the growth, development, and quality of the okra crop due to factors including decreased yield, inadequate development of dietary fibre, increased mite infestation, and decreased seed viability. Grafting is one of the strategies that have been developed to increase the drought stress tolerance of crops. We conducted proteomics, transcriptomics and integrated it with molecular physiology to assess the response of sensitive okra genotypes; NS7772 (G1), Green gold (G2) and OH3312 (G3) (scion) grafted to NS7774 (rootstock). In our studies we observed that sensitive okra genotypes grafted to tolerant genotypes mitigated the deleterious effects of drought stress through an increase in physiochemical parameters, and lowered reactive oxygen species. A comparative proteomic analysis showed a stress responsive proteins related to Photosynthesis, energy and metabolism, defence response, protein and nucleic acid biosynthesis. A proteomic investigation demonstrated that scions grafted onto okra rootstocks increased more photosynthesis-related proteins during drought stress, indicating an increase in photosynthetic activity when plants were subjected to drought stress. Furthermore, transcriptome of RD2, PP2C, HAT22, WRKY and DREB increased significantly, specifically for grafted NS7772 genotype. Furthermore, our study also indicated that grafting improved the yield components such as number of pods and seeds per plant, maximum fruit diameter, and maximum plant height in all genotypes which directly contributed towards their high resistance towards drought stress.

Identification of photosynthetic parameters for superior yield of two super hybrid rice varieties: A cross-scale study from leaf to canopy

Enhancing photosynthetic capacity is widely accepted as critical to advancing crop yield. Therefore, identifying photosynthetic parameters positively related to biomass accumulation in elite cultivars is the major focus of current rice research. In this work, we assessed leaf photosynthetic performance, canopy photosynthesis, and yield attributes of super hybrid rice cultivars Y-liangyou 3218 (YLY3218) and Y-liangyou 5867 (YLY5867) at tillering stage and flowering stage, using inbred super rice cultivars Zhendao11(ZD11) and Nanjing 9108 (NJ9108) as control. A diurnal canopy photosynthesis model was applied to estimate the influence of key environmental factors, canopy attributes, and canopy nitrogen status on daily aboveground biomass increment (AMDAY). Results showed that primarily the light-saturated photosynthetic rate at tillering stage contributed to the advancing yield and biomass of super hybrid rice in comparison to inbred super rice, and the light-saturated photosynthetic rate between them was similar at flowering stage. At tillering stage, the higher CO2 diffusion capacity, together with higher biochemical capacity (i.e., maximum carboxylation rate of Rubisco, maximum electron transport rate (J max), and triose phosphate utilization rate) favored leaf photosynthesis of super hybrid rice. Similarly, AMDAY in super hybrid rice was higher than inbred super rice at tillering stage, and comparable at flowering stage partially due to increased canopy nitrogen concentration (SLNave) of inbred super rice. At tillering stage, model simulation revealed that replacement of J max and g m in inbred super rice by super hybrid rice always had a positive effect on AMDAY, and the averaged AMDAY increment was 5.7% and 3.4%, respectively. Simultaneously, the 20% enhancement of total canopy nitrogen concentration through the improvement of SLNave (TNC-SLNave) resulted in the highest AMDAY across cultivars, with an average increase of 11.2%. In conclusion, the advancing yield performance of YLY3218 and YLY5867 was due to the higher J max and g m at tillering stage, and TCN-SLNave is a promising target for future super rice breeding programs.

Phosphorus Availability Affects the Photosynthesis and Antioxidant System of Contrasting Low-P-Tolerant Cotton Genotypes

Phosphorus (P) is an essential macronutrient, and an important component of plant metabolism. However, little is known about the effects of low P availability on P absorption, the photosynthetic electron transport chain, and the antioxidant system in cotton. This study used cotton genotypes (sensitive FJA and DLNTDH and tolerant BX014 and LuYuan343) with contrasting low-P tolerance in a hydroponic experiment under 15 µM, 50 µM, and 500 μM P concentrations. The results showed that low P availability reduced plant development and leaf area, shoot length, and dry weight in FJA and DLNADH, compared to BX014 and LuYuan343. The low P availability decreased the gas-exchange parameters such as the net photosynthetic rate, transpiration rate, and stomatal conductance, and increased the intercellular CO₂ concentration. Chlorophyll a fluorescence demonstrated that the leaves' absorption and trapped-energy flux were largely steady. In contrast, considerable gains in absorption and trapped-energy flux per reaction center resulted from decreases in the electron transport per reaction center under low-P conditions. In addition, low P availability reduced the activities of antioxidant enzymes and increased the content of malondialdehyde in the cotton genotypes, especially in FJA and DLNTDH. Moreover, low P availability reduced the activity of PEPC and generated a decline in the content of ATP and NADPH. Our research can provide a theoretical physiological basis for the growth and tolerance of cotton under low-P conditions.

Improving plant heat tolerance through modification of Rubisco activase in C3 plants to secure crop yield and food security in a future warming world

The world's population may reach 10 billion by 2050, but 10% still suffer from food shortages. At the same time, global warming threatens food security by decreasing crop yields, so it is necessary to develop crops with enhanced resistance to high temperatures in order to secure the food supply. In this review, the role of Rubisco activase as an important factor in plant heat tolerance is summarized, based on the conclusions of recent findings. Rubisco activase is a molecular chaperone determining the activation of Rubisco, whose heat sensitivity causes reductions of photosynthesis at high temperatures. Thus, the thermostability of Rubisco activase is considered to be critical for improving plant heat tolerance. It has been shown that the introduction of thermostable Rubisco activase through gene editing into Arabidopsis thaliana and from heat-adapted wild Oryza species or C4Zea mays into Oryza sativa improves Rubisco activation, photosynthesis, and plant growth at high temperatures. We propose that developing a universal thermostable Rubisco activase could be a promising direction for further studies.

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.

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

ATP, produced by the light reactions of photosynthesis, acts as the universal cellular energy cofactor fuelling all life processes. Chloroplast ATP synthase produces ATP using the proton motive force created by solar energy-driven thylakoid electron transport reactions. Here we investigate how increasing abundance of ATP synthase affects leaf photosynthesis and growth of rice, Oryza sativa variety Kitaake. We show that overexpression of AtpD, the nuclear-encoded subunit of the chloroplast ATP synthase, stimulates both abundance of the complex, confirmed by immunodetection of thylakoid complexes separated by Blue Native-PAGE, and ATP synthase activity, detected as higher proton conductivity of the thylakoid membrane. Plants with increased AtpD content had higher CO2 assimilation rates when a stepwise increase in CO2 partial pressure was imposed on leaves at high irradiance. Fitting of the CO2 response curves of assimilation revealed that plants overexpressing AtpD had a higher electron transport rate (J) at high CO2, despite having wild-type-like abundance of the cytochrome b6f complex. A higher maximum carboxylation rate (Vcmax) and lower cyclic electron flow detected in transgenic plants both pointed to an increased ATP production compared with wild-type plants. Our results present evidence that the activity of ATP synthase modulates the rate of electron transport at high CO2 and high irradiance.

Rieske FeS overexpression in tobacco provides increased abundance and activity of cytochrome b6 f

Photosynthesis is fundamental for plant growth and yield. The cytochrome b₆ f complex catalyses a rate-limiting step in thylakoid electron transport and therefore represents an important point of regulation of photosynthesis. Here we show that overexpression of a single core subunit of cytochrome b₆ f, the Rieske FeS protein, led to up to a 40% increase in the abundance of the complex in Nicotiana tabacum (tobacco) and was accompanied by an enhanced in vitro cytochrome f activity, indicating a full functionality of the complex. Analysis of transgenic plants overexpressing Rieske FeS by the light-induced fluorescence transients technique revealed a more oxidised primary quinone acceptor of photosystem II (Q_A ) and plastoquinone pool and faster electron transport from the plastoquinone pool to photosystem I upon changes in irradiance, compared to control plants. A faster establishment of q_E , the energy-dependent component of nonphotochemical quenching, in transgenic plants suggests a more rapid buildup of the transmembrane proton gradient, also supporting the increased in vivo cytochrome b₆ f activity. However, there was no consistent increase in steady-state rates of electron transport or CO₂ assimilation in plants overexpressing Rieske FeS grown in either laboratory conditions or field trials, suggesting that the in vivo activity of the complex was only transiently increased upon changes in irradiance. Our results show that overexpression of Rieske FeS in tobacco enhances the abundance of functional cytochrome b₆ f and may have the potential to increase plant productivity if combined with other traits.

Overexpression of Chloroplast Triosephosphate Isomerase Marginally Improves Photosynthesis at Elevated CO2 Levels in Rice

We recently suggested that chloroplast triosephosphate isomerase (cpTPI) has moderate control over the rate of CO2 assimilation (A) at elevated CO2 levels via the capacity for triose phosphate utilization (TPU) in rice (Oryza sativa L.) from its antisense-suppression study. In the present study, the effects of cpTPI overexpression on photosynthesis were examined in transgenic rice plants overexpressing the gene encoding cpTPI. The amounts of cpTPI protein in the two lines of transgenic plants were 4.8- and 12.1-folds higher than in wild-type plants, respectively. The magnitude of the increase approximately corresponded to the increase in transcript levels of cpTPI. A at CO2 levels of 100 and 120 Pa increased by 6-9% in the transgenic plants, whereas those at ambient and low CO2 levels were scarcely affected. Similar increases were observed for TPU capacity estimated from the CO2 response curves of A. These results indicate that the overexpression of cpTPI marginally improved photosynthesis at elevated CO2 levels via improvement in TPU capacity in rice. However, biomass production at a CO2 level of 120 Pa did not increase in transgenic plants, suggesting that the improvement in photosynthesis by cpTPI overexpression was not sufficient to improve biomass production in rice.

Single-molecule real-time sequencing of the full-length transcriptome of Halophila beccarii

Ecologically, Halophila beccarii Asch. is considered as a colonizing or a pioneer seagrass species and a “tiny but mighty” seagrass species, since it may recover quickly from disturbance generally. The use of transcriptome technology can provide a better understanding of the physiological processes of seagrasses. To date, little is known about the genome and transcriptome information of H. beccarii. In this study, we used single molecule real-time (SMRT) sequencing to obtain full-length transcriptome data and characterize the transcriptome structure. A total of 11,773 of the 15,348 transcripts were successfully annotated in seven databases. In addition, 1573 long non-coding RNAs, 8402 simple sequence repeats and 2567 transcription factors were predicted in all the transcripts. A GO analysis showed that 5843 transcripts were divided into three categories, including biological process (BP), cellular component (CC) and molecular function (MF). In these three categories, metabolic process (1603 transcripts), protein-containing complex (515 transcripts) and binding (3233 transcripts) were the primary terms in BP, CC, and MF, respectively. The major types of transcription factors were involved in MYB-related and NF-YB families. To the best of our knowledge, this is the first report of the transcriptome of H. beccarii using SMRT sequencing technology.

Toxicity of different forms of antimony to rice plants: Photosynthetic electron transfer, gas exchange, photosynthetic efficiency, and carbon assimilation combined with metabolome analysis

Antimony (Sb) is a toxic metalloid, and excess Sb causes damage to the plant photosynthetic system. However, the underlying mechanisms of Sb toxicity in the plant photosynthetic system are not clear. Hydroponic culture experiments were conducted to illustrate the toxicity differences of antimonite [Sb(III)] and antimonate [Sb(V)] to the photosynthetic system in a rice plant (Yangdao No. 6). The results showed that Sb(III) showed a higher toxicity than Sb(V), judging from (1) lower shoot and root biomass, leaf water moisture content, water use efficiency, stomatal conductance, net photosynthetic rate, and transpiration rate; (2) higher water vapor deficit, soluble sugar content, starch content, and oligosaccharide content (sucrose, stachyose, and 1-kestose). To further analyze the direction of the photosynthetic products, we conducted a metabonomic analysis. More glycosyls were allocated to the synthesis pathways of oligosaccharides (sucrose, stachyose, and 1-kestose), anthocyanins, salicylic acid, flavones, flavonols, and lignin under Sb stress to quench excess oxygen free radicals (ROS), strengthen the cell wall structure, rebalance the cell membrane, and/or regulate cell permeability. This study provides a complete mechanism to elucidate the toxicity differences of Sb(III) and Sb(V) by exploring their effects on photosynthesis, saccharide synthesis, and the subsequent flow directions of glycosyls.

Nitrogen Reduction Combined with Organic Materials Can Stabilize Crop Yield and Soil Nutrients in Winter Rapeseed and Maize Rotation in Yellow Soil

Objective: To investigate the effect of nitrogen reduction combined with organic materials on crop growth of winter rapeseed and maize rotation in yellow soil. Methods: A 2-year, four-season winter rapeseed and maize rotation experiment using three organic materials (biochar (B), commercial organic fertilizer (O) and straw (S), 3000 kg·hm−2) and three nitrogen application rates (100%, 85% and 70%) was carried out from 2018 to 2020 in Guizhou Province, China. By comprehensively analyzing the crop yield, biomass and nutrient absorption, soil nutrients indicators, and the efficiency of nitrogen fertilizer was calculated. Results: All organic materials could increase the yield of both crops, and 100% N + O treatment was the best, and the 2-year winter rapeseed and maize yields reached 3069 kg·hm−2, 3215 kg·hm−2 and 11,802 kg·hm−2, 11,912 kg·hm−2, respectively. When nitrogen application was reduced by 15%, the addition of the three organic materials could stabilize or increase the yield and biomass, and nitrogen, phosphorus and potassium absorption in both crops showed an increasing trend, which could improve or maintain soil nutrients. When nitrogen application was reduced by 30%, the yields of two crops with organic materials addition were lower than those of 100% N treatment. Through the interaction, it was found that nitrogen and organic material were the main reasons for the increase in yield, respectively. Conclusions: The addition of three organic materials can replace 15% of nitrogen fertilizer. It is recommended to apply 153.0 kg·hm−2 and 127.5 kg·hm−2 of nitrogen fertilizer in winter rapeseed and maize seasons, respectively, in the rotation area of Guizhou yellow soil, with the addition of 3000 kg·hm−2 organic materials, most appropriately commercial organic fertilizer.

OsCOMT, encoding a caffeic acid O-methyltransferase in melatonin biosynthesis, increases rice grain yield through dual regulation of leaf senescence and vascular development

Melatonin, a natural phytohormone in plants, plays multiple critical roles in plant growth and stress responses. Although melatonin biosynthesis-related genes have been suggested to possess diverse biological functions, their roles and functional mechanisms in regulating rice grain yield remain largely unexplored. Here, we uncovered the roles of a caffeic acid O-methyltransferase (OsCOMT) gene in mediating rice grain yield through dual regulation of leaf senescence and vascular development. In vitro and in vivo evidence revealed that OsCOMT is involved in melatonin biosynthesis. Transgenic assays suggested that OsCOMT significantly delays leaf senescence at the grain filling stage by inhibiting degradation of chlorophyll and chloroplast, which, in turn, improves photosynthesis efficiency. In addition, the number and size of vascular bundles in the culms and leaves were significantly increased in the OsCOMT-overexpressing plants, while decreased in the knockout plants, suggesting that OsCOMT plays a positive role in vascular development of rice. Further evidence indicated that OsCOMT-mediated vascular development might owe to the crosstalk between melatonin and cytokinin. More importantly, we found that OsCOMT is a positive regulator of grain yield, and overexpression of OsCOMT increase grain yield per plant even in a high-yield variety background, suggesting that OsCOMT can be used as an important target for enhancing rice yield. Our findings shed novel insights into melatonin-mediated leaf senescence and vascular development and provide a possible strategy for genetic improvement of rice grain yield.

Partially functional NARROW LEAF1 balances leaf photosynthesis and plant architecture for greater rice yield

NARROW LEAF1 (NAL1) is an elite gene in rice (Oryza sativa), given its close connection to leaf photosynthesis, hybrid vigor, and yield-related agronomic traits; however, the underlying mechanism by which this gene affects these traits remains elusive. In this study, we systematically measured leaf photosynthetic parameters, leaf anatomical parameters, architectural parameters, and agronomic traits in indica cultivar 9311, in 9311 with the native NAL1 replaced by the Nipponbare NAL1 (9311-NIL), and in 9311 with the NAL1 fully mutated (9311-nal1). Leaf length, width, and spikelet number gradually increased from lowest to highest in 9311-nal1, 9311, and 9311-NIL. In contrast, the leaf photosynthetic rate on a leaf area basis, leaf thickness, and panicle number gradually decreased from highest to lowest in 9311-nal1, 9311, and 9311-NIL. RNA-seq analysis showed that NAL1 negatively regulates the expression of photosynthesis-related genes; NAL1 also influenced expression of many genes related to phytohormone signaling, as also shown by different leaf contents of 3-Indoleacetic acid, jasmonic acid, Gibberellin A3, and isopentenyladenine among these genotypes. Furthermore, field experiments with different planting densities showed that 9311 had a larger biomass and yield advantage under low planting density compared to either 9311-NIL or 9311-nall. This study shows both direct and indirect effects of NAL1 on leaf photosynthesis; furthermore, we show that a partially functional NAL1 allele helps maintain a balanced leaf photosynthesis and plant architecture for increased biomass and grain yield in the field.

Towards improved dynamic photosynthesis in C3 crops by utilizing natural genetic variation

Under field environments, fluctuating light conditions induce dynamic photosynthesis, which affects carbon gain by crop plants. Elucidating the natural genetic variations among untapped germplasm resources and their underlying mechanisms can provide an effective strategy to improve dynamic photosynthesis and, ultimately, improve crop yields through molecular breeding approaches. In this review, we first overview two processes affecting dynamic photosynthesis, namely (i) biochemical processes associated with CO2 fixation and photoprotection and (ii) gas diffusion processes from the atmosphere to the chloroplast stroma. Next, we review the intra- and interspecific variations in dynamic photosynthesis in relation to each of these two processes. It is suggested that plant adaptations to different hydrological environments underlie natural genetic variation explained by gas diffusion through stomata. This emphasizes the importance of the coordination of photosynthetic and stomatal dynamics to optimize the balance between carbon gain and water use efficiency under field environments. Finally, we discuss future challenges in improving dynamic photosynthesis by utilizing natural genetic variation. The forward genetic approach supported by high-throughput phenotyping should be introduced to evaluate the effects of genetic and environmental factors and their interactions on the natural variation in dynamic photosynthesis.

Speed of light-induced stomatal movement is not correlated to initial or final stomatal conductance in rice

In nature, plants are often confronted with wide variations in light intensity, which may cause a massive carbon loss and water waste. Here, we investigated the response of photosynthetic rate and stomatal conductance to fluctuating light among ten rice genotypes and their influence on plant acclimation and intrinsic water-use efficiency (WUEi). Significant differences were observed in photosynthetic induction and stomatal kinetics across rice genotypes. However, no significant correlation was observed between steady-state and non-steady-state gas exchange. Genotypes with a greater range of steady-state and faster response rate of the gas exchange showed stronger adaptability to fluctuating light. Higher stomatal conductance during the initial phase of induction had little effect on the photosynthetic rate but markedly decreased the plant WUEi. Clarification of the mechanism influencing the dynamic gas exchange and synchronization between photosynthesis and stomatal conductance under fluctuating light may contribute to the improvement of photosynthesis and water-use efficiency in the future.

Low Light Increases the Abundance of Light Reaction Proteins: Proteomics Analysis of Maize (Zea mays L.) Grown at High Planting Density

Maize (Zea mays L.) is usually planted at high density, so most of its leaves grow in low light. Certain morphological and physiological traits improve leaf photosynthetic capacity under low light, but how light absorption, transmission, and transport respond at the proteomic level remains unclear. Here, we used tandem mass tag (TMT) quantitative proteomics to investigate maize photosynthesis-related proteins under low light due to dense planting, finding increased levels of proteins related to photosystem II (PSII), PSI, and cytochrome b₆f. These increases likely promote intersystem electron transport and increased PSI end electron acceptor abundance. OJIP transient curves revealed increases in some fluorescence parameters under low light: quantum yield for electron transport (φE_o), probability that an electron moves beyond the primary acceptor Q_A^- (ψ_o), efficiency/probability of electron transfer from intersystem electron carriers to reduction end electron acceptors at the PSI acceptor side (δR_o), quantum yield for reduction of end electron acceptors at the PSI acceptor side (φR_o), and overall performance up to the PSI end electron acceptors (PI_total). Thus, densely planted maize shows elevated light utilization through increased electron transport efficiency, which promotes coordination between PSII and PSI, as reflected by higher apparent quantum efficiency (AQE), lower light compensation point (LCP), and lower dark respiration rate (R_d).

Photosynthetic Induction Under Fluctuating Light Is Affected by Leaf Nitrogen Content in Tomato

The response of photosynthetic CO₂ assimilation to changes of illumination affects plant growth and crop productivity under natural fluctuating light conditions. However, the effects of nitrogen (N) supply on photosynthetic physiology after transition from low to high light are seldom studied. To elucidate this, we measured gas exchange and chlorophyll fluorescence under fluctuating light in tomato (Solanum lycopersicum) seedlings grown with different N conditions. After transition from low to high light, the induction speeds of net CO₂ assimilation (A _N ), stomatal conductance (g _s ), and mesophyll conductance (g _m ) delayed with the decline in leaf N content. The time to reach 90% of maximum A _N , g _s and g _m was negatively correlated with leaf N content. This delayed photosynthetic induction in plants grown under low N concentration was mainly caused by the slow induction response of g _m rather than that of g _s . Furthermore, the photosynthetic induction upon transfer from low to high light was hardly limited by photosynthetic electron flow. These results indicate that decreased leaf N content declines carbon gain under fluctuating light in tomato. Increasing the induction kinetics of g _m has the potential to enhance the carbon gain of field crops grown in infertile soil.

Drought stress memory in rice guard cells: Proteome changes and genomic stability of DNA

Drought is one of the major threats for crop plants among them rice, worldwide. The effects of drought vary depending on the plant growth phase and the occurrence of a previous stress, which can leave a memory of the stress. Stomata guard cells perform many essential functions and are highly responsive to hormonal and environmental stimuli. Therefore, information on how guard cells respond to drought might be useful for selecting drought tolerant plants. In this work, physiological analysis, comparative proteomics, gene expression and 5 - methylcytosine (%) analysis were used to elucidate the effects of drought in single stress event at vegetative or reproductive stage or recurrent at both stages in guard cells from rice plants. Photosynthesis and stomatal conductance decreased when drought was applied at reproductive stage in single and recurrent event. Twelve drought-responsive proteins were identified, belonging to photosynthesis pathway, response to oxidative stress, stress signalling and others. The expression of their encoding genes showed a positive relation with the protein abundance. Drought stress increased the total DNA methylation when applied at vegetative stage in single (35%) and recurrent event (18%) and decreased it in plants stressed at reproductive stage (9.8%), with respect to the levels measured in well-watered ones (13.84%). In conclusion, a first drought event seems to induce adaptation to water-deficit conditions through decreasing energy dissipation, increasing ATP energy provision, reducing oxidative damage in GC. Furthermore, the stress memory is associated with epigenetic markers.

Weed Detection in Rice Fields Using Remote Sensing Technique: A Review

This paper reviewed the weed problems in agriculture and how remote sensing techniques can detect weeds in rice fields. The comparison of weed detection between traditional practices and automated detection using remote sensing platforms is discussed. The ideal stage for controlling weeds in rice fields was highlighted, and the types of weeds usually found in paddy fields were listed. This paper will discuss weed detection using remote sensing techniques, and algorithms commonly used to differentiate them from crops are deliberated. However, weed detection in rice fields using remote sensing platforms is still in its early stages; weed detection in other crops is also discussed. Results show that machine learning (ML) and deep learning (DL) remote sensing techniques have successfully produced a high accuracy map for detecting weeds in crops using RS platforms. Therefore, this technology positively impacts weed management in many aspects, especially in terms of the economic perspective. The implementation of this technology into agricultural development could be extended further.

Overexpression of both Rubisco and Rubisco activase rescues rice photosynthesis and biomass under heat stress

Global warming threatens food security by decreasing crop yields through damage to photosynthetic systems, especially Rubisco activation. We examined whether co-overexpression of Rubisco and Rubisco activase improves the photosynthetic and growth performance of rice under high temperatures. We grew three rice lines-the wild-type (WT), a Rubisco activase-overexpressing line (oxRCA) and a Rubisco- and Rubisco activase-co-overexpressing line (oxRCA-RBCS)-and analysed photosynthesis and biomass at 25 and 40°C. Compared with the WT, the Rubisco activase content was 153% higher in oxRCA and 138% higher in oxRCA-RBCS, and the Rubisco content was 27% lower in oxRCA and similar in oxRCA-RBCS. The CO₂ assimilation rate (A) of WT was lower at 40°C than at 25°C, attributable to Rubisco deactivation by heat. On the other hand, that of oxRCA and oxRCA-RBCS was maintained at 40°C, resulting in higher A than WT. Notably, the dry weight of oxRCA-RBCS was 26% higher than that of WT at 40°C. These results show that increasing the Rubisco activase content without the reduction of Rubisco content could improve yield and sustainability in rice at high temperature.

The role of Cytochrome b6f in the control of steady-state photosynthesis: a conceptual and quantitative model

Here, we present a conceptual and quantitative model to describe the role of the Cytochrome [Formula: see text] complex in controlling steady-state electron transport in [Formula: see text] leaves. The model is based on new experimental methods to diagnose the maximum activity of Cyt [Formula: see text] in vivo, and to identify conditions under which photosynthetic control of Cyt [Formula: see text] is active or relaxed. With these approaches, we demonstrate that Cyt [Formula: see text] controls the trade-off between the speed and efficiency of electron transport under limiting light, and functions as a metabolic switch that transfers control to carbon metabolism under saturating light. We also present evidence that the onset of photosynthetic control of Cyt [Formula: see text] occurs within milliseconds of exposure to saturating light, much more quickly than the induction of non-photochemical quenching. We propose that photosynthetic control is the primary means of photoprotection and functions to manage excitation pressure, whereas non-photochemical quenching functions to manage excitation balance. We use these findings to extend the Farquhar et al. (Planta 149:78-90, 1980) model of [Formula: see text] photosynthesis to include a mechanistic description of the electron transport system. This framework relates the light captured by PS I and PS II to the energy and mass fluxes linking the photoacts with Cyt [Formula: see text], the ATP synthase, and Rubisco. It enables quantitative interpretation of pulse-amplitude modulated fluorometry and gas-exchange measurements, providing a new basis for analyzing how the electron transport system coordinates the supply of Fd, NADPH, and ATP with the dynamic demands of carbon metabolism, how efficient use of light is achieved under limiting light, and how photoprotection is achieved under saturating light. The model is designed to support forward as well as inverse applications. It can either be used in a stand-alone mode at the leaf-level or coupled to other models that resolve finer-scale or coarser-scale phenomena.

Proteomic analysis reveals the protective role of exogenous hydrogen sulfide against salt stress in rice seedlings

Hydrogen sulfide (H₂S) is an important gaseous signal molecule which participates in various abiotic stress responses. However, the underlying mechanism of H₂S associated salt tolerance remains elusive. In this study, sodium hydrosulfide (NaHS, donor of H₂S) was used to investigate the protective role of H₂S against salt stress at the biochemical and proteomic levels. Antioxidant activity and differentially expressed proteins (DEPs) of rice seedlings treated by NaCl or/and exogenous H₂S were investigated by the methods of biochemical approaches and comparative proteomic analysis. The protein-protein interaction (PPI) analysis was used for understanding the interaction networks of stress responsive proteins. In addition, relative mRNA levels of eight selected identified DEPs were analyzed by quantitative real-time PCR. The result showed that H₂S alleviated oxidative damage caused by salt stress in rice seedling. The activities of some antioxidant enzymes and glutathione metabolism were mediated by H₂S under salt stress. Proteomics analyses demonstrated that NaHS regulated antioxidant related proteins abundances and affected related enzyme activities under salt stress. Proteins related to light reaction system (PsbQ domain protein, plastocyanin oxidoreductase iron-sulfur protein), Calvin cycle (phosphoglycerate kinase, sedoheptulose-1,7-bisphosphatase precursor, ribulose-1,5-bisphosphate carboxylase/oxygenase) and chlorophyll biosynthesis (glutamate-1-semialdehyde 2,1-aminomutase, coproporphyrinogen III oxidase) are important for NaHS against salt stress. ATP synthesis related proteins, malate dehydrogenase and 2, 3-bisphosphoglycerate-independent phosphoglycerate mutase were up-regulated by NaHS under salt stress. Protein metabolism related proteins and cell structure related proteins were recovered or up-regulated by NaHS under salt stress. The PPI analysis further unraveled a complicated regulation network among above biological processes to enhance the tolerance of rice seedling to salt stress under H₂S treatment. Overall, our results demonstrated that H₂S takes protective roles in salt tolerance by mitigating oxidative stress, recovering photosynthetic capacity, improving primary and energy metabolism, strengthening protein metabolism and consolidating cell structure in rice seedlings.

Overexpression of MdATG8i improves water use efficiency in transgenic apple by modulating photosynthesis, osmotic balance, and autophagic activity under moderate water deficit

Water deficit is one of the major limiting factors for apple (Malus domestica) production on the Loess Plateau, a major apple cultivation area in China. The identification of genes related to the regulation of water use efficiency (WUE) is a crucial aspect of crop breeding programs. As a conserved degradation and recycling mechanism in eukaryotes, autophagy has been reported to participate in various stress responses. However, the relationship between autophagy and WUE regulation has not been explored. We have shown that a crucial autophagy protein in apple, MdATG8i, plays a role in improving salt tolerance. Here, we explored its biological function in response to long-term moderate drought stress. The results showed that MdATG8i-overexpressing (MdATG8i-OE) apple plants exhibited higher WUE than wild-type (WT) plants under long-term moderate drought conditions. Plant WUE can be increased by improving photosynthetic efficiency. Osmoregulation plays a critical role in plant stress resistance and adaptation. Under long-term drought conditions, the photosynthetic capacity and accumulation of sugar and amino acids were higher in MdATG8i-OE plants than in WT plants. The increased photosynthetic capacity in the OE plants could be attributed to their ability to maintain optimal stomatal aperture, organized chloroplasts, and strong antioxidant activity. MdATG8i overexpression also promoted autophagic activity, which was likely related to the changes described above. In summary, our results demonstrate that MdATG8i-OE apple lines exhibited higher WUE than WT under long-term moderate drought conditions because they maintained robust photosynthesis, effective osmotic adjustment processes, and strong autophagic activity.

Overproduction of Chloroplast Glyceraldehyde-3-Phosphate Dehydrogenase Improves Photosynthesis Slightly under Elevated [CO2] Conditions in Rice

Chloroplast glyceraldehyde-3-phosphate dehydrogenase (GAPDH) limits the regeneration of ribulose 1,5-bisphosphate (RuBP) in the Calvin-Benson cycle. However, it does not always limit the rate of CO2 assimilation. In the present study, the effects of overproduction of GAPDH on the rate of CO2 assimilation under elevated [CO2] conditions, where the capacity for RuBP regeneration limits photosynthesis, were examined in transgenic rice (Oryza sativa). GAPDH activity was increased to 3.2- and 4.5-fold of the wild-type levels by co-overexpression of the GAPDH genes, GAPA and GAPB, respectively. In the transgenic rice plants, the rate of CO2 assimilation under elevated [CO2] conditions increased by approximately 10%, whereas that under normal and low [CO2] conditions was not affected. These results indicate that overproduction of GAPDH is effective in improving photosynthesis under elevated [CO2] conditions, although its magnitude is relatively small. By contrast, biomass production of the transgenic rice plants was not greater than that of wild-type plants under elevated [CO2] conditions, although starch content tended to increase marginally.

High temperature-mediated disturbance of carbohydrate metabolism and gene expressional regulation in rice: a review

Global warming has induced higher frequencies of excessively high-temperature weather episodes, which pose damage risk to rice growth and production. Past studies seldom specified how high temperature-induced carbohydrate metabolism disturbances from both source and sink affect rice fertilization and production. Here we discuss the mechanism of heat-triggered damage to rice quality and production through disturbance of carbohydrate generation and consumption under high temperatures. Furthermore, we provide strong evidence from past studies that rice varieties that maintain high photosynthesis and carbohydrate usage efficiencies under high temperatures will suffer less heat-induced damage during reproductive developmental stages. We also discuss the complexity of expressional regulation of rice genes in response to high temperatures, while highlighting the important roles of heat-inducible post-transcriptional regulations of gene expression. Lastly, we predict future directions in heat-tolerant rice breeding and also propose challenges that need to be conquered in the future.

Knocking out NEGATIVE REGULATOR OF PHOTOSYNTHESIS 1 increases rice leaf photosynthesis and biomass production in the field

Improving photosynthesis is a major approach to increasing crop yield potential. Here we identify a transcription factor as a negative regulator of photosynthesis, which can be manipulated to increase rice photosynthesis and plant biomass in the field. This transcription factor, named negative regulator of photosynthesis 1 (NRP1; Os07g0471900), was identified through a co-expression analysis using rice leaf RNA sequencing data. NRP1 expression showed significantly negative correlation with the expression of many genes involved in photosynthesis. Knocking out NRP1 led to greater photosynthesis and increased biomass in the field, while overexpression of NRP1 decreased photosynthesis and biomass. Transcriptomic data analysis shows that NRP1 can negatively regulate the expression of photosynthetic genes. Protein transactivation experiments show that NRP1 is a transcription activator, implying that NRP1 may indirectly regulate photosynthetic gene expression through an unknown regulator. This study shows that combination of bioinformatics analysis with transgenic testing can be used to identify new regulators to improve photosynthetic efficiency in crops.

Changes in excitation relaxation of diatoms in response to fluctuating light, probed by fluorescence spectroscopies

A marine pennate diatom Phaeodactylum tricornutum (Pt) and a marine centric diatom Chaetoceros gracilis (Cg) possess unique light-harvesting complexes, fucoxanthin chlorophyll a/c-binding proteins (FCPs). FCPs have dual functions: light harvesting in the blue to green regions and quenching of excess energy. So far, excitation dynamics including FCPs have been studied by altering continuous light conditions. In the present study, we examined responses of the diatom cells to fluctuating light (FL) conditions. Excitation dynamics in the cells incubated under the FL conditions were analyzed by time-resolved fluorescence measurements followed by global analysis. As responses common to the Pt and Cg cells, quenching behaviors were observed in photosystem (PS) II with time constants of hundreds of picoseconds. The PSII → PSI energy transfer was modified only in the Pt cells, whereas quenching in FCPs was suggested only in the Cg cells, indicating different strategy for the dissipation of excess energy under the FL conditions.

The Light Dependence of Mesophyll Conductance and Relative Limitations on Photosynthesis in Evergreen Sclerophyllous Rhododendron Species

Mesophyll conductance (g_m) limits CO₂ diffusion from sub-stomatal internal cavities to the sites of RuBP carboxylation. However, the response of g_m to light intensity remains controversial. Furthermore, little is known about the light response of relative mesophyll conductance limitation (l_m) and its effect on photosynthesis. In this study, we measured chlorophyll fluorescence and gas exchange in nine evergreen sclerophyllous Rhododendron species. g_m was maintained stable across light intensities from 300 to 1500 μmol photons m^-2 s^-1 in all these species, indicating that g_m did not respond to the change in illumination in them. With an increase in light intensity, l_m gradually increased, making g_m the major limiting factor for area-based photosynthesis (A_N) under saturating light. A strong negative relationship between l_m and A_N was found at 300 μmol photons m^-2 s^-1 but disappeared at 1500 μmol photons m^-2 s^-1, suggesting an important role for l_m in determining A_N at sub-saturating light. Furthermore, the light-dependent increase in l_m led to a decrease in chloroplast CO₂ concentration (C_c), inducing the gradual increase of photorespiration. A higher l_m under saturating light made A_N more limited by RuBP carboxylation. These results indicate that the light response of l_m plays significant roles in determining C_c, photorespiration, and the rate-limiting step of A_N.

Is the Kok effect a respiratory phenomenon? Metabolic insight using 13 C labeling in Helianthus annuus leaves

The Kok effect is a well-known phenomenon in which the quantum yield of photosynthesis changes abruptly at low light. This effect has often been interpreted as a shift in leaf respiratory metabolism and thus used widely to measure day respiration. However, there is still no formal evidence that the Kok effect has a respiratory origin. Here, both gas exchange and isotopic labeling were carried out on sunflower leaves, using glucose that was ¹³ C-enriched at specific C-atom positions. Position-specific decarboxylation measurements and NMR analysis of metabolites were used to trace the fate of C-atoms in metabolism. Decarboxylation rates were significant at low light (including above the Kok break point) and increased with decreasing irradiance below 100 µmol photons m^-2  s^-1 . The variation in several metabolite pools such as malate, fumarate or citrate, and flux calculations suggest the involvement of several decarboxylating pathways in the Kok effect, including the malic enzyme. Our results show that day respiratory CO₂ evolution plays an important role in the Kok effect. However, the increase in the apparent quantum yield of photosynthesis below the Kok break point is also probably related to malate metabolism, which participates in maintaining photosynthetic linear electron flow.

Higher Stomatal Density Improves Photosynthetic Induction and Biomass Production in Arabidopsis Under Fluctuating Light

Stomatal density (SD) is closely associated with photosynthetic and growth characteristics in plants. In the field, light intensity can fluctuate drastically within a day. The objective of the present study is to examine how higher SD affects stomatal conductance (g s ) and CO2 assimilation rate (A) dynamics, biomass production and water use under fluctuating light. Here, we compared the photosynthetic and growth characteristics under constant and fluctuating light among three lines of Arabidopsis thaliana (L.): the wild type (WT), STOMAGEN/EPFL9-overexpressing line (ST-OX), and EPIDERMAL PATTERNING FACTOR 1 knockout line (epf1). ST-OX and epf1 showed 268.1 and 46.5% higher SD than WT (p < 0.05). Guard cell length of ST-OX was 10.0% lower than that of WT (p < 0.01). There were no significant variations in gas exchange parameters at steady state between WT and ST-OX or epf1, although these parameters tended to be higher in ST-OX and epf1 than WT. On the other hand, ST-OX and epf1 showed faster A induction than WT after step increase in light owing to the higher g s under initial dark condition. In addition, ST-OX and epf1 showed initially faster g s induction and, at the later phase, slower g s induction. Cumulative CO2 assimilation in ST-OX and epf1 was 57.6 and 78.8% higher than WT attributable to faster A induction with reduction of water use efficiency (WUE). epf1 yielded 25.6% higher biomass than WT under fluctuating light (p < 0.01). In the present study, higher SD resulted in faster photosynthetic induction owing to the higher initial g s . epf1, with a moderate increase in SD, achieved greater biomass production than WT under fluctuating light. These results suggest that higher SD can be beneficial to improve biomass production in plants under fluctuating light conditions.

Overexpression of maize transcription factor mEmBP-1 increases photosynthesis, biomass, and yield in rice

Identifying new options to improve photosynthetic capacity is a major approach to improve crop yield potential. Here we report that overexpression of the gene encoding the transcription factor mEmBP-1 led to simultaneously increased expression of many genes in photosynthesis, including genes encoding Chl a,b-binding proteins (Lhca and Lhcb), PSII (PsbR3 and PsbW) and PSI reaction center subunits (PsaK and PsaN), chloroplast ATP synthase subunit, electron transport reaction components (Fd1 and PC), and also major genes in the Calvin-Benson-Bassham cycle, including those encoding Rubisco, glyceraldehyde phosphate dehydrogenase, fructose bisphosphate aldolase, transketolase, and phosphoribulokinase. These increased expression of photosynthesis genes resulted in increased leaf chlorophyll pigment, photosynthetic rate, biomass growth, and grain yield both in the greenhouse and in the field. Using EMSA experiments, we showed that mEmBP-1a protein can directly bind to the promoter region of photosynthesis genes, suggesting that the direct binding of mEmBP-1a to the G-box domain of photosynthetic genes up-regulates expression of these genes. Altogether, our results show that mEmBP-1a is a major regulator of photosynthesis, which can be used to increase rice photosynthesis and yield in the field.

Increased stomatal conductance induces rapid changes to photosynthetic rate in response to naturally fluctuating light conditions in rice

A close correlation between stomatal conductance and the steady-state photosynthetic rate has been observed for diverse plant species under various environmental conditions. However, it remains unclear whether stomatal conductance is a major limiting factor for the photosynthetic rate under naturally fluctuating light conditions. We analysed a SLAC1 knockout rice line to examine the role of stomatal conductance in photosynthetic responses to fluctuating light. SLAC1 encodes a stomatal anion channel that regulates stomatal closure. Long exposures to weak light before treatments with strong light increased the photosynthetic induction time required for plants to reach a steady-state photosynthetic rate and also induced stomatal limitation of photosynthesis by restricting the diffusion of CO₂ into leaves. The slac1 mutant exhibited a significantly higher rate of stomatal opening after an increase in irradiance than wild-type plants, leading to a higher rate of photosynthetic induction. Under natural conditions, in which irradiance levels are highly variable, the stomata of the slac1 mutant remained open to ensure efficient photosynthetic reaction. These observations reveal that stomatal conductance is important for regulating photosynthesis in rice plants in the natural environment with fluctuating light.

Nuclear-encoded synthesis of the D1 subunit of photosystem II increases photosynthetic efficiency and crop yield

In photosynthetic organisms, the photosystem II (PSII) complex is the primary target of thermal damage. Plants have evolved a repair process to prevent the accumulation of damaged PSII. The repair of PSII largely involves de novo synthesis of proteins, particularly the D1 subunit protein encoded by the chloroplast gene psbA. Here we report that the allotropic expression of the psbA complementary DNA driven by a heat-responsive promoter in the nuclear genome sufficiently protects PSII from severe loss of D1 protein and dramatically enhances survival rates of the transgenic plants of Arabidopsis, tobacco and rice under heat stress. Unexpectedly, we found that the nuclear origin supplementation of the D1 protein significantly stimulates transgenic plant growth by enhancing net CO2 assimilation rates with increases in biomass and grain yield. These findings represent a breakthrough in bioengineering plants to achieve efficient photosynthesis and increase crop productivity under normal and heat-stress conditions.

Improved stomatal opening enhances photosynthetic rate and biomass production in fluctuating light

It has been reported that stomatal conductance often limits the steady-state photosynthetic rate. On the other hand, the stomatal limitation of photosynthesis in fluctuating light remains largely unknown, although in nature light fluctuates due to changes in sun position, cloud cover, and the overshadowing canopy. In this study, we analysed three mutant lines of Arabidopsis with increased stomatal conductance to examine to what extent stomatal opening limits photosynthesis in fluctuating light. The slac1 (slow anion channel-associated 1) and ost1 (open stomata 1) mutants with stay-open stomata, and the PATROL1 (proton ATPase translocation control 1) overexpression line with faster stomatal opening responses exhibited higher photosynthetic rates and plant growth in fluctuating light than the wild-type, whereas these four lines showed similar photosynthetic rates and plant growth in constant light. The slac1 and ost1 mutants tended to keep their stomata open in fluctuating light, resulting in lower water-use efficiency (WUE) than the wild-type. However, the PATROL1 overexpression line closed stomata when needed and opened stomata immediately upon irradiation, resulting in similar WUE to the wild-type. The present study clearly shows that there is room to optimize stomatal responses, leading to greater photosynthesis and biomass accumulation in fluctuating light in nature.

Enhanced Relative Electron Transport Rate Contributes to Increased Photosynthetic Capacity in Autotetraploid Pak Choi

Autopolyploids often show growth advantages over their diploid progenitors because of their increased photosynthetic activity; however, the underlying molecular basis of such mechanism remains elusive. In this study, we aimed to characterize autotetraploid pak choi (Brassica rapa ssp. chinensis) at the physiological, cellular and molecular levels. Autotetraploid pak choi has thicker leaves than its diploid counterparts, with relatively larger intercellular spaces and cell size and greater grana thylakoid height. Photosynthetic data showed that the relative electron transport rate (rETR) was markedly higher in autotetraploid than in diploid pak choi. Transcriptomic data revealed that the expressions of genes involved in 'photosynthesis' biological process and 'thylakoids' cellular component were mainly regulated in autotetraploids. Overall, our findings suggested that the increased rETR in the thylakoids contributed to the increased photosynthetic capacity of autotetraploid leaves. Furthermore, we found that the enhanced rETR is associated with increased BrPetC expression, which is likely altered by histone modification. The ectopic expression of BrPetC in Arabidopsis thaliana led to increased rETR and biomass, which were decreased in BrPetC-silenced pak choi. Autotetraploid pak choi also shows altered hormone levels, which was likely responsible for the increased drought resistance and the impaired powdery mildew resistance of this lineage. Our findings further our understanding on how autotetraploidy provides growth advantages to plants.

Flowering time control in rice by introducing Arabidopsis clock-associated PSEUDO-RESPONSE REGULATOR 5

Plants flower under appropriate day-length conditions by integrating temporal information provided by the circadian clock with light and dark information from the environment. A sub-group of plant specific circadian clock-associated PSEUDO-RESPONSE REGULATOR (PRR) genes (PRR7/PRR3 sub-group) controls flowering time both in long-day and short-day plants; however, flowering control by the other two PRR gene sub-groups has been reported only in Arabidopsis thaliana (Arabidopsis), a model long-day plant. Here, we show that an Arabidopsis PRR9/PRR5 sub-group gene can control flowering time (heading date) in rice, a short-day plant. Although PRR5 promotes flowering in Arabidopsis, transgenic rice overexpressing Arabidopsis PRR5 caused late flowering. Such transgenic rice plants produced significantly higher biomass, but not grain yield, due to the late flowering. Concomitantly, expression of Hd3a, a rice florigen gene, was reduced in the transgenic rice.Abbreviations: CCT: CONSTANS, CONSTANS-LIKE, and TOC1; HD: HEADING DATE; LHY: LATE ELONGATED HYPOCOTYL; Ppd: photoperiod; PR: pseudo-receiver; PRR: PSEUDO-RESPONSE REGULATOR; TOC1: TIMING OF CAB EXPRESSION 1; ZTL: ZEITLUPE.

High-yielding rice Takanari has superior photosynthetic response to a commercial rice Koshihikari under fluctuating light

Leaves within crop canopies experience variable light over the course of a day, which greatly affects photosynthesis and crop productivity. Little is known about the mechanisms of the photosynthetic response to fluctuating light and their genetic control. Here, we examined gas exchange, metabolite levels, and chlorophyll fluorescence during the photosynthetic induction response in an Oryza sativa indica cultivar with high yield (Takanari) and a japonica cultivar with lower yield (Koshihikari). Takanari had a faster induction response to sudden increases in light intensity than Koshihikari, as demonstrated by faster increases in net CO2 assimilation rate, stomatal conductance, and electron transport rate. In a simulated light regime that mimicked a typical summer day, the faster induction response in Takanari increased daily CO2 assimilation by 10%. The faster response of Takanari was explained in part by its maintenance of a larger pool of Calvin-Benson cycle metabolites. Together, the rapid responses of electron transport rate, metabolic flux, and stomatal conductance in Takanari contributed to the greater daily carbon gain under fluctuating light typical of natural environments.

Night Temperature Affects the Growth, Metabolism, and Photosynthetic Gene Expression in Astragalus membranaceus and Codonopsis lanceolata Plug Seedlings

Astragalus membranaceus and Codonopsis lanceolata are two important medical herbs used in traditional Oriental medicine for preventing cancer, obesity, and inflammation. Night temperature is an important factor that influences the plug seedling quality. However, little research has focused on how the night temperature affects the growth and development of plug seedlings of these two medicinal species. In this study, uniform plug seedlings were cultivated in three environmentally controlled chambers for four weeks under three sets of day/night temperatures (25/10 °C, 25/15 °C, or 25/20 °C), the same relative humidity (75%), photoperiod (12 h), and light intensity (150 μmol·m-2·s-1 PPFD) provided by white LEDs. The results showed that night temperature had a marked influence on the growth and development of both species. The night temperature of 15 °C notably enhanced the quality of plug seedlings evidenced by the increased shoot, root, and leaf dry weights, stem diameter, and Dickson's quality index. Moreover, a night temperature of 15 °C also stimulated and increased contents of primary and secondary metabolites, including soluble sugar, starch, total phenols and flavonoids. Furthermore, the 15 °C night temperature increased the chlorophyll content and stomatal conductance and decreased the hydrogen peroxide content. Analysis of the gene expression showed that granule-bound starch synthase (GBSS), ribulose bisphosphate carboxylase large chain (RBCL), and ferredoxin (FDX) were up-regulated when the night temperature was 15 °C. Taken together, the results suggested that 15 °C is the optimal night temperature for the growth and development of plug seedlings of A. membranaceus and C. lanceolata.