Photorespiration Research Articles

A Synthetic Facultative CAM-Like Shuttle in C3 Rice Plants.

Crassulacean acid metabolism (CAM) is one of the three major forms of photosynthesis, known for its efficient carbon sequestration mechanism. CAM plants store malate at night, which undergoes decarboxylation and promotes Rubisco carboxylation during the day. Despite its potential benefits, CAM engineering is not applied to C3 crops. This paper introduces a designed facultative CAM bypass (CBP) in rice by incorporating codon-optimized nocturnal carboxylation and decarboxylation modules, a malate transporter module, and a stomatal regulation module using the transgene stacking system. The CBP plants are correctly assembled by detection at the gene level, transcription level, protein level, and enzyme activity. Malate, CAM metabolism product, accumulated significantly at night in CBP plants. Metabolic analysis revealed that the malate is directed to the citric acid cycle and impacted carbon sequestration. The CBP plants showed a significant increase of ≈21% and ≈27% in photosynthetic rate and carboxylation efficiency, respectively. Additionally, CBP plants exhibited ≈20% increase in grain yield and biomass over the 2-year field trials. Unexpectedly, the water use efficiency and drought resistance do not improve in CBP plants. This study is the first to attempt CAM engineering in C3 and demonstrates the potential of facultative CAM carbon sequestration in rice.

Bundle sheath cell-dependent chloroplast movement in mesophyll cells of C4 plants analyzed using live leaf-section imaging

C4 plants have C4 photosynthetic cycle, a CO2-concentrating pump that functions across mesophyll (M) and bundle sheath (BS) cells. M chloroplasts aggregate toward BS cells in response to environmental stress, which would contribute to adjustment in C4 photosynthetic cycle. However, it remains unclear whether M chloroplast movement is an intercellular response mediated by BS cells. One major challenge to resolve this is the difficulty in observing chloroplast movement due to scattering and absorption of observation light in live-leaf tissues. We established a live leaf-section imaging technique that enables the long-term observation of sections of chemically unfixed leaf blades, with which we quantitatively analyzed M chloroplast movements. Another challenge in clarifying the contribution of BS cells to M chloroplast movement is the selective ablation of BS cells without impairing M cell function. To investigate the necessity of BS cells for M chloroplast movement, we developed a method to remove BS cells only based on differences in shape between M and BS cells. We also found that chloroplasts in M cells without adjacent BS cell contents did not show typical aggregative movement. This indicates that the M chloroplast aggregative movement occurs during communication with BS cells.

Global environmental change mediated response of wetland plants: Evidence from past decades.

Wetland ecosystems are critically affected by global environmental changes, yet understanding the impact of these changes on wetland plants remains a challenge. This review article employs a comprehensive approach, including bibliographic analysis, utilization of various climate models for historical data retrieval, and extensive literature survey, to investigate the response of wetland plants to environmental shifts over the past decades. The analysis conducted in this study uncovers a multitude of climatic parameters that exhibit an influence on the dynamics of wetland vegetation. Results indicated a significant positive trend in atmospheric CO2 concentration, leading to increased water use efficiency in some plant species, particularly C3 plants. However, C4 plants did not show the same positive response. Nitrous oxide growth rate showed a weaker, less consistent trend than CO2, highlighting the need for further investigation into the complex factors influencing Nitrous oxide emissions from wetlands. Methane growth rate and global mean sea level demonstrated a strong positive linear trend. Ocean pH exhibited a statistically significant downward trend (acidification), while sea surface temperature showed a moderate but statistically significant upward trend. Glacier mass balance revealed a significant negative trend. Although some plants may benefit from increased CO2 initially, but the combined effects of rising sea levels, ocean acidification, and temperature changes pose substantial threats to the overall health and diversity of wetland plant life.

Comprehensive two dimensional gas chromatography – Time of flight mass spectrometry (GC×GC-TOFMS) for the investigation of botanical origin of raw spirits

Comprehensive two dimensional gas chromatography - time of flight mass spectrometry (GC×GC-TOFMS) with sample introduction using headspace solid phase microextraction (HS-SPME) was used for the botanical classification of raw spirits obtained from C3 (corn and sorghum) and C4 (rye, wheat and potato) plants. 45spirit samples representing these raw materials (10 spirits produced from rye, corn, wheat and potato, and 5 from sorghum) were analyzed. Volatile compounds profiles were compared by PCA, and after removal of outliers samples were subjected to the classification model. OPLS-DA model was built (R2Y=0.924 Q2Y=0.895) that enabled clear separation of all tested spirits of different botanical origin. The model was validated with training and testing sets and 100% correct assignment was achieved. GC×GC-TOFMS proved to be a method that not only can be used as a tool for botanic origin of raw spirits, but also provides detailed information of volatile fermentation by-products, characteristic for particular spirit.

Molecular investigation of how drought stress affects chlorophyll metabolism and photosynthesis in leaves of C3 and C4 plant species: A transcriptome meta-analysis

Molecular investigation of how drought stress affects chlorophyll metabolism and photosynthesis in leaves of C3 and C4 plant species: A transcriptome meta-analysis

Steppe development and mammalian adaptation in the middle Miocene, North Junggar Basin, Central Asia

Steppe development and mammalian adaptation in the middle Miocene, North Junggar Basin, Central Asia

Reduced C3 plants on the southeastern margin of the Tibetan Plateau during the Late Pleistocene and implications for human dispersal into southern China

Reduced C3 plants on the southeastern margin of the Tibetan Plateau during the Late Pleistocene and implications for human dispersal into southern China

Stable isotope ecology of Quaternary cervid and bovid species in Southeast Asia with implications for wildlife conservation

Southeast Asia, one of the major biodiversity hotspots, is experiencing substantial species loss, with predictions indicating that 13–85% of species are threatened to lose their original habitats. As herbivores play a crucial role in shaping the structure of environments and the ecosystem dynamics of the region, it is crucial to protect these endangered species. Here we measure stable carbon isotopic ratios (δ13C) of tooth enamel samples of eight extant Southeast Asian cervid and bovid taxa, mostly listed as either endangered or vulnerable species by the IUCN and compare the results with their Pleistocene counterparts, in order to investigate their dietary and preferred habitat changes through time. As a result, three distinct categories of ecological patterns among these ruminant taxa are observed: (1) species with dietary and habitat changes through time (i.e. Axis axis, Rucervus eldii, Bos javanicus, and Bos gaurus), (2) those with more restricted diets and habitats today than in the past (i.e. Rusa unicolor and Bubalus arnee), and (3) those with unchanged diets and habitats over time (i.e. Axis porcinus and Muntiacus muntjak). In the case of species with dietary and habitat changes, the Pleistocene C4-grazer enamel isotopes showed a shift towards greater reliance on C3 plants or more closed environments during the Holocene. The isotopic evidence raises the question of whether climatic and environmental changes and/or anthropogenic pressure have significantly driven the population decline of threatened species and can contribute to the understanding of future conservation outlooks of existing wildlife populations in Southeast Asia.

Isotope analysis of birds’ eye lens provides early-life information

Early-life environment has a long-lasting effect on later life, though its estimation is often prevented in the wild because of a lack of available methods. Recently, isotope analysis of eye lenses has attracted considerable interest as a means to reconstruct the environmental conditions experienced by animals during the developmental period. This analysis has mostly been confined to fish for practical reasons and remains to be resolved for application to other animals. In this study, we broadened its applicability by developing a novel approach and verifying its usability for the reconstruction of early-life environments. We performed a feeding experiment using Japanese quail (Coturnix japonica), in which we administered two diets: one composed mainly of C3 plants (low δ13C and high δ15N) and the other of C4 plants (high δ13C and low δ15N). Quails in the control group were continuously fed a C3-based diet from hatching until 200 days old, whereas those in the treatment groups (T10, T15, T20, and T40) were switched from the C3 to the C4-based diet at 10, 15, 20, and 40 days after hatching, respectively. We found that the δ13C in the eye lenses of the treatment groups decreased from the center layer to the middle layer of the lens and then increased toward the outer layer, thus reflecting the diet change. In contrast, those of the control group exhibited a decreasing trend and equilibrated at the middle layer of the eye lens, with no increase thereafter. This novel approach revealed the postnatal feeding histories of the diet-shift experiment. The high δ13C values observed in the center of the eye lenses would reflect the prenatal feeding environment, i.e., the C4-based diet consumed by their mothers, which is further reinforced by higher δ15N values at this position due to the consumption of egg yolk-derived nutrition. These results indicate that the avian eye lens can be used as an “isotopic chronicle,” which is a useful tool for reconstructing chronological isotopic information about their early-life history.

Machine learning the abiotic stressor impacts on nitrogen availability and photo energy use in dryland forage systems under different tillage and green manuring practices

Background and aimSorghum sudangrass (SSG), a vigorous hybrid C4 plant grown as forage or bioenergy crop during the summer has deeply distributed fibrous root system beneficial to dryland agriculture. Despite these advantages, the crop faces challenges from abiotic stressors, particularly during severe drought seasons. Thus, the goal of planting SSG as a forage is to generate ample biomass with minimal inputs, minimize toxicity, identify stress factors, and implement suitable management strategies with negligible environmental impact. This study focused on machine learning the intricate soil–plant-water-atmosphere relationships associated with abiotic stresses and agroenvironmental variables to enhance energy-efficiency and alleviate nitrogen (N) stress.MethodsA long-term simulation study involving SSG with four N treatments (spring-fallow and N fertilization, and three spring-time cover with 100% residue addition as green manures) under no-till (NT) and conventional (CT) tillage systems was unsuccessful to provide distinct effects of N strategies. Machine learning (ML) was employed to determine how abiotic-stress factors were varied, specifically under influence of green manures such as oat (OG), field peas (FP) and grass peas (GP) under conventional and conservation systems.ResultsResults indicated significantly higher use-efficiency of photosynthetically-active radiation (PAR) and the lowest N stress in NT + FP contrasting with the lowest PAR and the highest N-stress in conventional system. ML Regression models highlighted significant impact of average daily temperatures on water (R2 of 78%) and N-stress (R2 of 79%). Multi-regression ML models, incorporating various agro-environmental variables identified tillage as the most influential factor during wet seasons, water-stress during normal seasons, and temperature as the predominant factor during drought seasons influencing N stress in SSG forage-system.ConclusionConspicuously, drought exhibited a more pronounced influence from green manuring compared to wet or normal seasons in our study. Thus, farmers should be encouraged to adapt the practice of using cover and green-manures despite the concerns about water reserves for summertime cash crops.

The metabolite transporters of C4 photosynthesis.

C4 photosynthesis is a highly efficient form of photosynthesis that utilises a biochemical pump to concentrate CO2 around rubisco. Although variation in the implementation of this biochemical pump exists between species, each variant of the C4 pathway is critically dependent on metabolite transport between organelles and between cells. Here we review our understanding of metabolite transport in C4 photosynthesis. We discuss how the majority of our knowledge of the metabolite transporters co-opted for use in C4 photosynthesis has been obtained from studying C3 plants, and how there is a pressing need for in planta validation of transporter function in C4 species. We further explore the diversity of transport pathways present in disparate C4 lineages and highlight the important gaps in our understanding of metabolite transport in C4 plants. Finally, through integration of functional and transcriptional data from multiple C3 and C4 plants we propose a molecular blueprint for metabolite transport for NAD-ME photosynthesis.

Effect of plant growth regulators for yield enhancement in finger millet under drought stress

Finger millet (Ragi) is considered as wonder millet because of its high nutritive and therapeutic values. Drought is a major abiotic stress which limits the crop production and yield potential of finger millet. Considering the yield losses faced by the farmers during drought condition, foliar application of plant growth regulators (PGRs) is widely used to improve the physiological response that might lead to rapid changes in phenotype of the plant and enhancing the production of crops. Finger millet is less efficient in partitioning of assimilates and has low actual yield potential even as a C4 crop. To address these issues, experiments were conducted for improving the partitioning efficiency and yield. Hence, an experiment was conducted to mitigate the drought in finger millet through PGRs. The stress was imposed during flowering stage in the finger millet variety CO15 where different kinds of PGRs viz., Brassinosteroid, Salicylic acid and Chlormequat chloride were used in this experiment. After imposing the treatments, physiological, biochemical and yield traits were recorded. Foliar spray of 0.3 ppm brassinosteroid and 100 ppm salicylic acid exhibited superior performance for improving the osmotic potential, reduces the membrane lipid damage, better chlorophyll pigments, nitrate reductase activity and improved antioxidant system which leads to mitigate the negative impacts of drought in finger millet.

The Role of Sugarcane Trash in Soil Fertility and Plant Growth: A Review

Sugarcane needs a hot and humid climate and can be grown on a variety of soils that can retain moisture. Owing to its long life cycle it heavily depletes soil nutrients during its growth period. Sugarcane, being a heavy feeder requires nearly 208 kg N, 53 kg P2O5, and 280 kg K2O from the soil to produce 100 t ha-1 sugarcane. Sugarcane, being a C4 plant, produces a large quantity of biomass. Approximately 10-15 t of trash, constituting 10-12% weight of cane harvested, is produced by the sugarcane crop. Generally, cane trash contains 68% organic matter, 0.42% N, 0.15% P, 0.57% K, 0.48% Ca, and 0.12% Mg, besides 25.7, 20.45, 236.4, and 16.8 ppm Zn, Fe, Mn and Ca, respectively. Trash conserves soil moisture, C, and N in the soil and provides energy to increase the yield. The trash application conserves the nutrients in the soil, also aids their availability to the plant, and reduces the fertilizer requirements through recycling nutrients in the soil from residue. Organic mulches also create a better physical, chemical, and biological environment of soils and in turn, improve crop productivity. Burning of trash deteriorate the fertility as well as soil health. It also reduces the soil microbial activity and destabilize of soil aggregates. Significant N losses from residues can occur during burning by high temperature volatilization. In the burnt system, >70% of the organic matter and nutrients in the trash are lost to the atmosphere.

Characterization, Phylogenetic Analyses, and Pathogenicity of Eutiarosporella dactylidis on Sorghum in China.

Sorghum, the fifth-largest cereal crop globally and a C4 crop, mainly grows in arid and semiarid areas. In 2021 to 2023, a new foliar disease of sorghum occurred in China. The diseased leaves showed water-soaked symptoms in the leaf tip and margins, resulting in half- and full-leaf desiccation and necrosis, thus affecting plant photosynthesis. A total of 24 Eutiarosporella strains were isolated from symptomatic leaves. Based on morphological characteristics, multilocus phylogenetic analysis involving ITS, LSU, and EF1-α sequences, and the pathogenicity test, the pathogen of sorghum causing leaf blight in China was identified as Eutiarosporella dactylidis. The virulence of all E. dactylidis strains was evaluated using the spray-mycelium method. Different strains showed significantly different pathogenicities toward a susceptible cultivar, Longza 10, with disease indexes ranging from 23.76 to 60.37. This study first reported leaf blight of sorghum caused by E. dactylidis and named it "Eutiarosporella leaf blight," which provides a theoretical basis for farmers in disease management.

A C4 plant K+ channel accelerates stomata to enhance C3 photosynthesis and water use efficiency.

Accelerating stomatal kinetics through synthetic optogenetics and mutations that enhance guard cell K+ flux has proven a viable strategy to improve water use efficiency and biomass production. Stomata of the model C4 species Gynandropsis gynandra, a relative of the C3 plant Arabidopsis thaliana, are similarly fast to open and close. We identified and cloned the guard cell rectifying outward K+ channel (GROK) of Gynandropsis and showed that GROK is preferentially expressed in stomatal guard cells. GROK is homologous to the Arabidopsis guard cell K+ channel GORK and, expressed in oocytes, yields a K+ current consistent with that of Gynandropsis guard cells. Complementing the Arabidopsis gork mutant with GROK promoted K+ channel gating and K+ flux, increasing stomatal kinetics and yielding gains in water use efficiency and biomass with varying light, especially under water limitation. Our findings demonstrate the potential for engineering a C4 K+ channel into guard cells of a C3 species and they speak to the puzzle of how C4 species have evolved mechanisms that enhance water use efficiency and growth under stress.

Higher PEPC activity and vein density contribute to improve cotton leaf water use efficiency under water stress.

Plants with the C4 photosynthetic pathway can withstand water stress better than plants with C3 metabolism. However, it is unclear whether C4 photosynthesis can be preliminarily activated in droughted cotton leaves, and if this contributes to increase in water use efficiency (WUE). An upland cotton (Gossypium hirsutum L., Xinluzao45) was used to determine gas exchange, stomatal and vein anatomy, phosphoenolpyruvate carboxykinase (PEPC) and Rubisco enzyme activity, and carbon isotope composition (δ13C) under well-watered, mild or moderate water stress. Water stress triggered reduced photosynthesis, stomatal conductance, and Rubisco activity, but higher vein density (VD), PEPC activity, and WUE. The correlations between δ13C and each of VD and PEPC activity implied that these coordinately contributed to higher leaf WUE via a preliminary induction of C4 photosynthetic pathway. Preliminary C4 photosynthesis indicated by more PEPC enzyme and veins offers an effective way to improve leaf WUE and potentially aids in acclimation to adverse growing conditions.

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

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

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

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

Testing the kinetic tradeoff between bicarbonate versus phosphoenolpyruvate affinity and glucose-6 phosphate response of phosphoenolpyruvate carboxylase from two C4grasses.

Phosphoenolpyruvate (PEP) carboxylase (PEPC) has an anaplerotic role in central plant metabolism but also initiates the carbon concentrating mechanism during C4 photosynthesis. The C4 PEPC has different binding affinities (Km) for PEP (K0.5PEP) and HCO3- (K0.5HCO3), and allosteric regulation by glucose-6-phosphate (G6-P) compared to non-photosynthetic isoforms. These differences are linked to specific changes in amino acids within PEPC. For example, region II (residues 302-433, Zea mays numbering) has been identified as important for G6-P regulation and within this region residue 353 may be conserved in C4 PEPC enzymes. Additionally, residue 780 influences the C4 PEPC kinetic properties and may interact with region II as well as residue 353 to influence G6-P regulation. We test the hypothesis that variation within region II, including residue 353, and their interactions with residue 780 influence the kinetic and allosteric regulation by G6-P of two C4 PEPC isozymes from two C4 grasses. The data does not support a kinetic tradeoff between K0.5HCO3 and K0.5PEP in these PEPC isozymes. Additionally, these enzymes had different response to G6-P that was only partially attributed to region II, residue 353 and residue 780. This data provides new insights into factors influencing the kinetic variation of C4 PEPC isozymes.

First report of Curvularia chiangmaiensis causing leaf spot in elephant grass in Brazil.

Elephant grass, Cenchrus purpureus, exhibits high efficiency in sequesting atmospheric CO2 during photosynthesis, leading to significant biomass production. As a C4 plant, it holds immense potential for alternative biodiesel production and serves as fresh feed for cattle (Negawo et al. 2018). Field observations in commercial pastures planted with elephant grass, located in the Brazilian cerrado, revealed necrotic leaf spots with a brownish center and a yellowish halo, reaching a severity of 30 to 50% between 2022 and 2023 in Palmas (10°24'08"S 48°21'45" W) and Gurupi (11°46'21"S 49°02'08" W), municipalities located in the state of Tocantins, Brazil. In both years, the field incidence of the disease on young and mature leaves approached 100% during the rainy season. Affected leaves were collected, packed in a thermal box, and taken to the phytopathology laboratory. The 198 leaves were sanitised in 1% hypochlorite for 30 seconds and washed thrice in sterile water. Upon sanitisation, leaf tissues were cut and cultured on potato dextrose agar (PDA) medium and incubated in a controlled chamber (BOD) at 28°C with a 12-hour photoperiod. Colonies exhibited a greyish colour with whitish edges, and the top plate was brownish, growing to a diameter of 5 cm over seven days. The colonies obtained from monosporic cultures formed curved conidia, predominantly with three septa, of a brownish colour, with lengths ranging from (7 µm to 14 µm and widths from 5 µm to 7 µm. (N=-50, Fig 1) (Yasanthika et al. 2023). The UFTCC01 isolate's DNA was extracted using the extraction kit (PROMEGA ®), amplified for genes (ITS, Gapdh and Tefα1), sequenced (OR345316.1, OR344427.1 and OR344428.1) and compared in BLASTn at Gen Bank deposited sequences. Phylogenetic analysis using the parsimony method in MEGA X identified the isolate as Curvularia chiangmaiensis, showing 99.5% identity with reference sequences (MN215651.1, MN264085.1, and MN263942.1). Concatenated region comparison revealed 94% similarity to sequences (OP564987.1 and MF490814.1) in the phylogenetic tree, confirming the species. The pathogenicity test used 60 seedlings of 50-day-old elephant grass, 30 of which were inoculated with a spore suspension (3.0 × 106 spores/mL) and 30 with sterile water. The solutions were sprayed twice. Only plants inoculated with the spore suspension exhibited symptoms akin to those observed in the field. Then, the fungus was reisolated from the lesions and Koch's postulates were confirmed twice.Previous studies have documented the C. chiangmaiensis pathogenicity in other grasses, such as maise in Thailand (Marin et al. 2017). Our studies constitute the first report of C. chiangmaiensis causing leaf spots on elephant grass in the Brazil.