RuBisCo can conjugate and stabilize peonidin-3-O-p-coumaroylrutinoside-5-O-glucoside in isotonic sport models: Mechanisms from kinetics, multispectral, and libDock assays

The co-pigmentation behaviour of RuBisCo proteins (with different concentrations) on peonidin-3-O-p-coumaroylrutinoside-5-O-glucoside (P3C5G, extracted from Rosetta potato's peels) conjugates in isotonic sport drinks (ISD) was examined using multispectral, thermal stability kinetics, and libDock-based molecular docking approaches. The colorant effects of RuBisCo on P3C5G were also studied in spray-dried microencapsulated ISD-models. RuBisCo, especially at a concentration of 10 mg/mL in ISD, showed a co-pigmentation effect on the color of P3C5G, mostly owing to its superior hyperchromicity, pKH-levels, and thermal stability. Results from multispectral approaches also revealed that RuBisCo could noncovalently interact with P3C5G as confirmed by libDock findings, where P3C5G strongly bound with RuBisCo via H-bonding and π-π forces, thereby altering its secondary structure. RuBisCo also preserved color of P3C5G in ISD-powdered models. These detailed results imply that RuBisCo could be utilized in ISD-liquid and powder models that might industrially be applied as potential food colorants in products under different conditions.

Green Biomass-Based Protein for Sustainable Feed and Food Supply: An Overview of Current and Future Prospective

It is necessary to develop and deploy novel protein production to allow the establishment of a sustainable supply for both humans and animals, given the ongoing expansion of protein demand to meet the future needs of the increased world population and high living standards. In addition to plant seeds, green biomass from dedicated crops or green agricultural waste is also available as an alternative source to fulfill the protein and nutrient needs of humans and animals. The development of extraction and precipitation methods (such as microwave coagulation) for chloroplast and cytoplasmic proteins, which constitute the bulk of leaf protein, will allow the production of leaf protein concentrates (LPC) and protein isolates (LPI). Obtained LPC serves as a sustainable alternative source of animal-based protein besides being an important source of many vital phytochemicals, including vitamins and substances with nutritional and pharmacological effects. Along with it, the production of LPC, directly or indirectly, supports sustainability and circular economy concepts. However, the quantity and quality of LPC largely depend on several factors, including plant species, extraction and precipitation techniques, harvest time, and growing season. This paper provides an overview of the history of green biomass-derived protein from the early green fodder mill concept by Károly Ereky to the state-of-art of green-based protein utilization. It highlights potential approaches for enhancing LPC production, including dedicated plant species, associated extraction methods, selection of optimal technologies, and best combination approaches for improving leaf protein isolation.

A temporal gradient of cytonuclear coordination of chaperonins and chaperones during RuBisCo biogenesis in allopolyploid plants

Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo), consisting of subunits encoded by nuclear and cytoplasmic genes, is a model for cytonuclear evolution in plant allopolyploids. To date, coordinated cytonuclear evolutionary responses of auxiliary cofactors involved in RuBisCo biogenesis remain unexplored. This study characterized and compared genomic and transcriptional cytonuclear coevolutionary responses of chaperonin/chaperones in RuBisCo folding and assembly processes across different allopolyploids. We discovered significant cytonuclear evolutionary responses in folding cofactors, with diminishing or attenuated responses later during assembly. Our results have general significance for understanding the unrecognized cytonuclear evolution of chaperonin/chaperone genes, structural and functional features of intermediate complexes, and the functioning stage of the Raf2 cofactor. Generally, the results reveal a hitherto unexplored dimension of allopolyploidy in plants.

Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo) has long been studied from many perspectives. As a multisubunit (large subunits [LSUs] and small subunits[SSUs]) protein encoded by genes residing in the chloroplast (rbcL) and nuclear (rbcS) genomes, RuBisCo also is a model for cytonuclear coevolution following allopolyploid speciation in plants. Here, we studied the genomic and transcriptional cytonuclear coordination of auxiliary chaperonin and chaperones that facilitate RuBisCo biogenesis across multiple natural and artificially synthesized plant allopolyploids. We found similar genomic and transcriptional cytonuclear responses, including respective paternal-to-maternal conversions and maternal homeologous biased expression, in chaperonin/chaperon-assisted folding and assembly of RuBisCo in different allopolyploids. One observation is about the temporally attenuated genomic and transcriptional cytonuclear evolutionary responses during early folding and later assembly process of RuBisCo biogenesis, which were established by long-term evolution and immediate onset of allopolyploidy, respectively. Our study not only points to the potential widespread and hitherto unrecognized features of cytonuclear evolution but also bears implications for the structural interaction interface between LSU and Cpn60 chaperonin and the functioning stage of the Raf2 chaperone.

Canopy height affects the allocation of photosynthetic carbon and nitrogen in two deciduous tree species under elevated CO2

Down-regulation of leaf N and Rubisco under elevated CO₂ (eCO₂) are accompanied by increased non-structural carbohydrates (NSC) due to the sink-source imbalance. Here, to investigate whether the canopy position affects the down-regulation of Rubisco, we measured leaf N, NSC and N allocation in two species with different heights at maturity [Fraxinus rhynchophylla (6.8 ± 0.3 m) and Sorbus alnifolia (3.6 ± 0.2 m)] from 2017 to 2019. Since 2009, both species were grown at three different CO₂ concentrations in open-top chambers: ambient CO₂ (400 ppm; aCO₂); ambient CO₂ × 1.4 (560 ppm; eCO₂1.4); and ambient CO₂ × 1.8 (720 ppm; eCO₂1.8). Leaf N per unit mass (N_mass) decreased under eCO₂, except under eCO₂1.8 in S. alnifolia and coincided with increased NSC. NSC increased under eCO₂ in F. rhynchophylla, but the increment of NSC was greater in the upper canopy of S. alnifolia. Conversely, Rubisco content per unit area was reduced under eCO₂ in S. alnifolia and there was no interaction between CO₂ and canopy position. In contrast, the reduction of Rubisco content per unit area was greater in the upper canopy of F. rhynchophylla, with a significant interaction between CO₂ and canopy position. Rubisco was negatively correlated with NSC only in the upper canopy of F. rhynchophylla, and at the same NSC, Rubisco was lower under eCO₂ than under aCO₂. Contrary to Rubisco, chlorophyll increased under eCO₂ in both species, although there was no interaction between CO₂ and canopy position. Finally, photosynthetic N content (Rubisco + chlorophyll + PSII) was reduced and consistent with down-regulation of Rubisco. Therefore, the observed N_mass reduction under eCO₂ was associated with dilution due to NSC accumulation. Moreover, down-regulation of Rubisco under eCO₂ was more sensitive to NSC accumulation in the upper canopy. Our findings emphasize the need for the modification of the canopy level model in the context of climate change.

How to resolve the enigma of diurnal malate remobilisation from the vacuole in plants with crassulacean acid metabolism?

Opening of stomata in plants with crassulacean acid metabolism (CAM) is mainly shifted to the night period when atmospheric CO₂ is fixed by phosphoenolpyruvate carboxylase and stored as malic acid in the vacuole. As such, CAM plants ameliorate transpirational water losses and display substantially higher water-use efficiency compared with C₃ and C₄ plants. In the past decade significant technical advances have allowed an unprecedented exploration of genomes, transcriptomes, proteomes and metabolomes of CAM plants and efforts are ongoing to engineer the CAM pathway in C₃ plants. Whilst research efforts have traditionally focused on nocturnal carboxylation, less information is known regarding the drivers behind diurnal malate remobilisation from the vacuole that liberates CO₂ to be fixed by RuBisCo behind closed stomata. To shed more light on this process, we provide a stoichiometric analysis to identify potentially rate-limiting steps underpinning diurnal malate mobilisation and help direct future research efforts. Within this remit we address three key questions: Q1 Does light-dependent assimilation of CO₂ via RuBisCo dictate the rate of malate mobilisation? Q2: Do the enzymes responsible for malate decarboxylation limit daytime mobilisation from the vacuole? Q3: Does malate efflux from the vacuole set the pace of decarboxylation?

Design and optimization of bioreactor to boost carbon dioxide assimilation in RuBisCo-equipped Escherichia coli

Global warming is a surging issue that has provoked the demand of green process to mitigate carbon dioxide. In this context, RuBisCo-equipped Escherichia coli has first developed and evaluated the CO₂-assimiliable capability based on the mass balance in three devices: Flask-based in CO₂ incubator (FIC), two-layered device (TLD) and CO₂ bubbling device (CBD) systematically. With the forced diffusion of 5% CO₂ in CBD, which confers an efficient attack of CO₂ to RuBisCo, the CO₂ assimilation increased from -5.03 to -2.63 g-CO₂/g-DCW. Furthermore, boosted CO₂ assimilation ability was observed by co-expression of GroELS chaperone with 71% reduction on CO₂ release. By DNA sequencing and tandem MS/MS analysis, the toxicity of RuBisCo and PRK was identified to interfere the sugar metabolism and energy producing, while the cell morphology was changed and observed in RuBisCo-equipped E. coli. Our study provides a new perspective of higher CO₂ assimilation for sustainable to eco-friendly green bioprocess.

Chronic heat stress affects the photosynthetic apparatus of Solanum lycopersicum L. cv Micro-Tom

Tomato (Solanum lycopersicum L.) is one of the most widely cultivated crops in the world. Tomato is a plant model and the relationship between yield and biotic/abiotic stress has attracted increasing scientific interest. Tomato cultivation under sub-optimal conditions usually negatively impacts growth and development; in particular, heat stress affects several cellular and metabolic processes, such as respiration and photosynthesis. In this work, we studied the effects of chronic heat stress on various cytological and biochemical aspects using the Micro-Tom cultivar as a model. Photosynthetic efficiency decreased during heat stress while levels of post-photosynthetic sugars (sucrose, fructose, glucose and glucose 6-phosphate) oscillated during stress. Similarly, photosynthetic pigments (lutein, chlorophyll a, chlorophyll b and β-carotene) showed an oscillating downward trend with partial recovery during the stress-free phase. The energetic capacity of leaves (e.g. ATP and ADP) was altered, as well as the reactive oxygen species (ROS) profile; the latter increased during stress. Important effects were also found on the accumulation of Rubisco isoforms, which decreased in number. Heat stress also resulted in a decreased accumulation of lipids (oleic and linoleic acid). Photosynthetically alterations were accompanied by cytological changes in leaf structure, particularly in the number of lipid bodies and starch granules. Prolonged heat stress progressively compromised the photosynthetic efficiency of tomato leaves. The present study reports multi-approach information on metabolic and photosynthetic injuries and responses of tomato plants to chronic heat stress, highlighting the plant's ability to adapt to stress.

Augmenting the expression of accD and rbcL genes using optimized iron concentration to achieve higher biomass and biodiesel in Chlorella vulgaris

Chlorella vulgaris is a form of microalgae commonly employed as a biological source of oil for biodiesel production. Major algal cultivation strategies are focused on stimulating growth rate and lipid content. In the present study, the algal growth media was supplemented with iron (III) chloride (FeCl₃), as a stimulating factor for growth and lipid production, in three iron concentrations including 90, 200, and 500 µM. The turbidity of algal cells was measured on different days, to determine the growth rate. In optimum iron concentration, this measurement experienced a 2.1-fold increase. Next, the lipid content was extracted, and the amount of lipid produced in each treatment was calculated, which demonstrated a 4.57-fold increase in lipid productivity. The expression of genes corresponding to the metabolic enzymes (i.e. acetyl-CoA carboxylase (accD) and ribulose bisphosphate carboxylase large chain (rbcL)) was evaluated using real-time PCR under different initial iron feeds. As demonstrated in the results, the initial iron feed of 90 µM was an optimum concentration that obtained the highest growth rate, more cell density, and increased lipid production. In 90 µM initial iron concentration, the expression of accD and rbcL genes showed a 4.8- and 35-fold increase, respectively, compared to that of the control genes. Based on the results, this optimum iron concentration could satisfy the industrial interest in biodiesel production from C. vulgaris as a potential stimulating factor. However, higher levels of iron (e.g. 200 and 500 µM) failed to act as positive stress for increasing biodiesel production. Finally, in this paper, different mechanisms where iron affects acetyl-CoA carboxylase (ACCase) and 1,5-ribulose bisphosphate carboxylase/oxygenase (RuBisCo) are illustrated.

Interaction of potyvirus helper component-proteinase (HcPro) with RuBisCO and nucleosome in viral infections of plants

Bean common mosaic virus (BCMV) causes severe disease in Phaseolus vulgaris plants. One of its non structural protein, the helper-component proteinase (HcPro) involves in multiple roles in aphid transmission, RNA binding, suppression of gene silencing and protease activity. The multifunctional role of HcPro hint towards its regulation at multiple host cellular sites. The mechanisms of these regulatory activities are poorly understood. Therefore, it is very important to study the molecular level interaction of HcPro with different cellular components. In this study, we demonstrate that the HcPro interacts with RuBisCo, an enzyme of chloroplast origin which might plays a crucial role in virus infection. A further line of experiments were carried out with factors of nuclear origin. Due to nucleic acid binding activity of HcPro, it showed interaction with dsDNA of nucleosome, as ascertained through electrophoretic mobility shift assay (EMSA). Interestingly, HcPro interacts with host nucleoprotein histones, H3 and H4. The gel-overlay assay and native electrophoresis-western blot analysis (NEWeB) revealed a direct interaction of BCMV HcPro with host nucleosome and with histones. These findings suggest that the BCMV through HcPro, not only utilize the host cytoplasmic components but also use host nuclear factors for its propagation and disease development.

Expression of a Small Ubiquitin-Like Modifier Protease Increases Drought Tolerance in Wheat (Triticum aestivum L.)

Post-translation modification of proteins plays a critical role in cellular signaling processes. In recent years, the SUMO (Small Ubiquitin-Like Modifier) class of molecules has emerged as an influential mechanism for target protein management. SUMO proteases play a vital role in regulating pathway flux and are therefore ideal targets for manipulating stress-responses. In the present study, the expression of an Arabidopsis thaliana cysteine protease (OVERLY TOLERANT TO SALT-1, OTS1) in wheat (Triticum aestivum L.) has led to improved plant growth under water stress conditions. Transformed wheat (pUBI-OTS1) displayed enhanced growth and delayed senescence under water deficit when compared with untransformed Gamtoos-R genotype or plants carrying an empty vector. Transformed pUBI-OTS1 plants also maintained a high relative moisture content (RMC), had a higher photosynthesis rate, and also had a higher total chlorophyll content when compared to untransformed plants or plants carrying an empty vector. SUMOylation of total protein also increased in untransformed plants but not in the AtOTS1 transformed plants. Our results suggest that SUMO-proteases may influence an array of mechanisms in wheat to the advantage of the crop to be more tolerant to water stress caused by drought. This is the first report to elucidate SUMOylation effects in the hexaploid crop wheat (T. aestivum L.).

Learning RuBisCO's birth and subsequent environmental adaptation

It is believed that organisms that first appeared after the formation of the earth lived in a very limited environment, making full use of the limited number of genes. From these early organisms' genes, more were created by replication, mutation, recombination, translocation, and transmission of other organisms' DNA; thus, it became possible for ancient organisms to grow in various environments. The photosynthetic CO₂-fixing enzyme RuBisCO (ribulose 1,5-bisphosphate carboxylase/oxygenase) began to function in primitive methanogenic archaea and has been evolved as a central CO₂-fixing enzyme in response to the large changes in CO₂ and O₂ concentrations that occurred in the subsequent 4 billion years. In this review, the processes of its adaptation to be specialized for CO₂ fixation will be presented from the viewpoint of functions and structures of RuBisCO.

Quantitative proteomic analysis reveals novel stress-associated active proteins (SAAPs) and pathways involved in modulating tolerance of wheat under terminal heat

Terminal heat stress has detrimental effect on the growth and yield of wheat. Very limited information is available on heat stress-associated active proteins (SAAPs) in wheat. Here, we have identified 159 protein groups with 4271 SAAPs in control (22 ± 3 °C) and HS-treated (38 °C, 2 h) wheat cvs. HD2985 and HD2329 using iTRAQ. We identified 3600 proteins to be upregulated and 5825 proteins to be downregulated in both the wheat cvs. under HS. We observed 60.3% of the common SAAPs showing upregulation in HD2985 (thermotolerant) and downregulation in HD2329 (thermosusceptible) under HS. GO analysis showed proton transport (molecular), photosynthesis (biological), and ATP binding (cellular) to be most altered under HS. Most of the SAAPs identified were observed to be chloroplast localized and involved in photosynthesis. Carboxylase enzyme was observed most abundant active enzymes in wheat under HS. An increase in the degradative isoenzymes (α/β-amylases) was observed, as compared to biosynthesis enzymes (ADP-glucophosphorylase, soluble starch synthase, etc.) under HS. Transcript profiling showed very high relative fold expression of HSP17, CDPK, Cu/Zn SOD, whereas downregulation of AGPase, SSS under HS. The identified SAAPs can be used for targeted protein-based precision wheat-breeding program for the development of 'climate-smart' wheat.

Small Antisense RNA RblR Positively Regulates RuBisCo in Synechocystis sp. PCC 6803

Small regulatory RNAs (sRNAs) function as transcriptional and post-transcriptional regulators of gene expression in organisms from all domains of life. Cyanobacteria are thought to have developed a complex RNA-based regulatory mechanism. In the current study, by genome-wide analysis of differentially expressed small RNAs in Synechocystis sp. PCC 6803 under high light conditions, we discovered an asRNA (RblR) that is 113nt in length and completely complementary to its target gene rbcL, which encodes the large chain of RuBisCO, the enzyme that catalyzes carbon fixation. Further analysis of the RblR(+)/(−) mutants revealed that RblR acts as a positive regulator of rbcL under various stress conditions; Suppressing RblR adversely affects carbon assimilation and thus the yield, and those phenotypes of both the wild type and the overexpressor could be downgraded to the suppressor level by carbonate depletion, indicated a regulatory role of RblR in CO₂ assimilation. In addition, a real-time expression platform in Escherichia coli was setup and which confirmed that RblR promoted the translation of the rbcL mRNA into the RbcL protein. The present study is the first report of a regulatory RNA that targets RbcL in Synechocystis sp. PCC 6803, and provides strong evidence that RblR regulates photosynthesis by positively modulating rbcL expression in Synechocystis.

Identification of Putative RuBisCo Activase (TaRca1)-The Catalytic Chaperone Regulating Carbon Assimilatory Pathway in Wheat (Triticum aestivum) under the Heat Stress

RuBisCo activase (Rca) is a catalytic chaperone involved in modulating the activity of RuBisCo (key enzyme of photosynthetic pathway). Here, we identified eight novel transcripts from wheat through data mining predicted to be Rca and cloned a transcript of 1.4 kb from cv. HD2985, named as TaRca1 (GenBank acc. no. KC776912). Single copy number of TaRca1 was observed in wheat genome. Expression analysis in diverse wheat genotypes (HD2985, Halna, PBW621, and HD2329) showed very high relative expression of TaRca1 in Halna under control and HS-treated, as compared to other cultivars at different stages of growth. TaRca1 protein was predicted to be chloroplast-localized with numerous potential phosphorylation sites. Northern blot analysis showed maximum accumulation of TaRca1 transcript in thermotolerant cv. during mealy-ripe stage, as compared to thermosusceptible. Decrease in the photosynthetic parameters was observed in all the cultivars, except PBW621 in response to HS. We observed significant increase in the Rca activity in all the cultivars under HS at different stages of growth. HS causes decrease in the RuBisCo activity; maximum reduction was observed during pollination stage in thermosusceptible cvs. as validated through immunoblotting. We observed uniform carbon distribution in different tissues of thermotolerant cvs., as compared to thermosusceptible. Similarly, tolerance level of leaf was observed maximum in Halna having high Rca activity under HS. A positive correlation was observed between the transcript and activity of TaRca1 in HS-treated Halna. Similarly, TaRca1 enzyme showed positive correlation with the activity of RuBisCo. There is, however, need to manipulate the thermal stability of TaRca1 enzyme through protein engineering for sustaining the photosynthetic rate under HS-a novel approach toward development of "climate-smart" crop.

Lipoic acid mitigates oxidative stress and recovers metabolic distortions in salt-stressed wheat seedlings by modulating ion homeostasis, the osmo-regulator level and antioxidant system

BACKROUND

Soil salinity is one of the most detrimental environmental factors affecting the growth of plants and limiting their agricultural productivity. This study investigated whether exogenous lipoic acid (LA) pretreatment plays a role in promoting salt tolerance in wheat seedlings. The seedlings were treated with LA (1.75 mmol L(-1)) and salt (100 mmol L(-1) NaCl) separately and a combination of them.

RESULTS

Salt stress significantly reduced relative water content, leaf surface area, ribulose bisphosphate carboxylase expression, and chlorophyll content but increased the content of osmo-regulator protein, carbohydrates and proline. In addition, salinity led to an imbalance in the inorganic composition of wheat leaves. While it elevated Na(+) content compared to control, Ca content and K(+)/Na(+) ratio were reduced. Under saline conditions, despite increases in antioxidant enzyme activity and levels of antioxidant compounds (ascorbate and glutathione), the content of reactive oxygen species (superoxide anion, hydrogen peroxide) and malondialdehyde were higher than in control seedlings. LA significantly promoted osmo-regulator level and antioxidant enzyme activities compared to stressed seedlings alone. Also, it both increased levels of ascorbate and glutathione and regenerated their oxidised forms, thus contributing to maintaining cellular redox status. Similarly, LA prevented excessive accumulation of Na(+) and promoted K(+)/Na(+) ratio and Ca content. Reactive oxygen species content was significantly reduced, and the inhibitions in the above parameters markedly recovered.

CONCLUSION

LA reduced salinity-induced oxidative damage and thus contributed to the growth and development of plants in saline soils by modulating ion homeostasis between plant and soil as well as in osmo-regulator content and antioxidant system.