Ribulose-1,5-bisphosphate regeneration in the Calvin-Benson-Bassham cycle: Focus on the last three enzymatic steps that allow the formation of Rubisco substrate

Closing the Loop in the Carbon Cycle: Enzymatic Reactions Housed in Metal-Organic Frameworks for CO2 Conversion to Methanol

The preparation of value-added chemicals from carbon dioxide (CO2) can act as a way of reducing the greenhouse gas from the atmosphere. Industrially significant C1 chemicals like methanol (CH3OH), formic acid (HCOOH), and formaldehyde (HCHO) can be formed from CO2. One sustainable way of achieving this is by connecting the reactions catalyzed by the enzymes formate dehydrogenase (FDH), formaldehyde dehydrogenase (FALDH), and alcohol dehydrogenase (ADH) into a single cascade reaction where CO2 is hydrogenated to CH3OH. For this to be adaptable for industrial use, the enzymes should be immobilized in materials that are extraordinarily protective of the enzymes, inexpensive, stable, and of ultra-large surface area. Metal-organic frameworks (MOFs) meet these criteria and are expected to usher in the much-awaited dispensation of industrial biocatalysis. Unfortunately, little is known about the molecular behaviour of MOF-immobilized FDH, FALDH, and ADH. It is also yet not known which MOFs are most promising for industrial enzyme-immobilization since the field of reticular chemistry is growing exponentially with millions of hypothetical and synthesized MOF structures reported at present. This review initially discusses the properties of the key enzymes required for CO2 hydrogenation to methanol including available cofactor regeneration strategies. Later, the characterization techniques of enzyme-MOF composites and the successes or lack thereof of enzyme-MOF-mediated CO2 conversion to CH3OH and intermediate products are discussed. We also discuss reported multi-enzyme-MOF systems for CO2 conversion cognizant of the fact that at present, these systems are the only chance of housing cascade-type biochemical reactions where strict substrate channelling and operational conditions are required. Finally, we delve into future perspectives.

An insight into heat stress response and adaptive mechanism in cotton

The growing worldwide population is driving up demand for cotton fibers, but production is hampered by unpredictable temperature rises caused by shifting climatic conditions. Numerous research based on breeding and genomics have been conducted to increase the production of cotton in environments with high and low-temperature stress. High temperature (HT) is a major environmental stressor with global consequences, influencing several aspects of cotton plant growth and metabolism. Heat stress-induced physiological and biochemical changes are research topics, and molecular techniques are used to improve cotton plants' heat tolerance. To preserve internal balance, heat stress activates various stress-responsive processes, including repairing damaged proteins and membranes, through various molecular networks. Recent research has investigated the diverse reactions of cotton cultivars to temperature stress, indicating that cotton plant adaptation mechanisms include the accumulation of sugars, proline, phenolics, flavonoids, and heat shock proteins. To overcome the obstacles caused by heat stress, it is crucial to develop and choose heat-tolerant cotton cultivars. Food security and sustainable agriculture depend on the application of genetic, agronomic, and, biotechnological methods to lessen the impacts of heat stress on cotton crops. Cotton producers and the textile industry both benefit from increased heat tolerance. Future studies should examine the developmental responses of cotton at different growth stages, emphasize the significance of breeding heat-tolerant cultivars, and assess the biochemical, physiological, and molecular pathways involved in seed germination under high temperatures. In a nutshell, a concentrated effort is required to raise cotton's heat tolerance due to the rising global temperatures and the rise in the frequency of extreme weather occurrences. Furthermore, emerging advances in sequencing technologies have made major progress toward successfully se sequencing the complex cotton genome.

Recent warming and increasing CO2 stimulate growth of dominant trees under no water limitation in South Korea

Increases in temperatures and atmospheric CO2 concentration influence the growth performance of trees worldwide. The direction and intensity of tree growth and physiological responses to changing climate do, however, vary according to environmental conditions. Here we present complex, long-term, tree-physiological responses to unprecedented temperature increase in East Asia. For this purpose, we studied radial growth and isotopic (δ13C and δ18O) variations using tree-ring data for the past 100 yr of dominant Quercus mongolica trees from the cool-temperate forests from Hallasan, South Korea. Overall, we found that tree stem basal area increment, intercellular CO2 concentration and intrinsic water-use efficiency significantly increased over the last century. We observed, however, short-term variability in the trends of these variables among four periods identified by change point analysis. In comparison, δ18O did not show significant changes over time, suggesting no major hydrological changes in this precipitation-rich area. The strength and direction of growth-climate relationships also varied during the past 100 yr. Basal area increment (BAI) did not show significant relationships with the climate over the 1924-1949 and 1975-1999 periods. However, over 1950-1974, BAI was negatively affected by both temperature and precipitation, while after 2000, a temperature stimulus was observed. Finally, over the past two decades, the increase in Q. mongolica tree growth accelerated and was associated with high spring-summer temperatures and atmospheric CO2 concentrations and decreasing intrinsic water-use efficiency, δ18O and vapour pressure deficit, suggesting that the photosynthetic rate continued increasing under no water limitations. Our results indicate that the performance of dominant trees of one of the most widely distributed species in East Asia has benefited from recent global changes, mainly over the past two decades. Such findings are essential for projections of forest dynamics and carbon sequestration under climate change.

Comparative transcriptome and coexpression network analysis revealed the regulatory mechanism of Astragalus cicer L. in response to salt stress

BACKGROUND

Astragalus cicer L. is a perennial rhizomatous legume forage known for its quality, high biomass yield, and strong tolerance to saline-alkaline soils. Soil salinization is a widespread environmental pressure. To use A. cicer L. more scientifically and environmentally in agriculture and ecosystems, it is highly important to study the molecular response mechanism of A. cicer L. to salt stress.

RESULTS

In this study, we used RNA-seq technology and weighted gene coexpression network analysis (WGCNA) were performed. The results showed 4 key modules were closely related to the physiological response of A. cicer. L. to salt stress. The differentially expressed genes (DEGs) of key modules were mapped into the KEGG database, and found that the most abundant pathways were the plant hormone signal transduction pathway and carbon metabolism pathway. The potential regulatory networks of the cytokinin signal transduction pathway, the ethylene signal transduction pathway, and carbon metabolism related pathways were constructed according to the expression pathways of the DEGs. Seven hub genes in the key modules were selected and distributed among these pathways. They may involved in the positive regulation of cytokinin signaling and carbon metabolism in plant leaves, but limited the positive expression of ethylene signaling. Thus endowing the plant with salt tolerance in the early stage of salt stress.

CONCLUSIONS

Based on the phenotypic and physiological responses of A. cicer L. to salt stress, this study constructed the gene coexpression network of potential regulation to salt stress in key modules, which provided a new reference for exploring the response mechanism of legumes to abiotic stress.

Photosynthesis: Genetic Strategies Adopted to Gain Higher Efficiency

The global challenge of feeding an ever-increasing population to maintain food security requires novel approaches to increase crop yields. Photosynthesis, the fundamental energy and material basis for plant life on Earth, is highly responsive to environmental conditions. Evaluating the operational status of the photosynthetic mechanism provides insights into plants' capacity to adapt to their surroundings. Despite immense effort, photosynthesis still falls short of its theoretical maximum efficiency, indicating significant potential for improvement. In this review, we provide background information on the various genetic aspects of photosynthesis, explain its complexity, and survey relevant genetic engineering approaches employed to improve the efficiency of photosynthesis. We discuss the latest success stories of gene-editing tools like CRISPR-Cas9 and synthetic biology in achieving precise refinements in targeted photosynthesis pathways, such as the Calvin-Benson cycle, electron transport chain, and photorespiration. We also discuss the genetic markers crucial for mitigating the impact of rapidly changing environmental conditions, such as extreme temperatures or drought, on photosynthesis and growth. This review aims to pinpoint optimization opportunities for photosynthesis, discuss recent advancements, and address the challenges in improving this critical process, fostering a globally food-secure future through sustainable food crop production.

Global insights into intermediate metabolites: Signaling, metabolic divergence and stress response modulation in plants

Climate change-induced environmental stresses pose significant challenges to plant survival and agricultural productivity. In response, many plants undergo genetic reprogramming, resulting in profound alterations in metabolic pathways and the production of diverse secondary metabolites. As a critical molecular junction, intermediate metabolites by targeted intensification or suppression of subpathways channel cell resources into a multifaceted array of functions such as cell signals, photosynthesis, energy metabolism, ROS homeostasis, producing defensive and protective molecules, epigenetic regulation and stress memory, phytohormones biosynthesis and cell wall architecture under stress conditions. Unlike the well-established functions of end products, intermediate metabolites are context-dependent and produce enigmatic alternatives during stress. As key components of signal transduction pathways, intermediate metabolites with relay and integration of stress signals ensure responses to stress combinations. Investigating efficient metabolic network pathways and their role in regulating unpredictable paths from upstream to downstream levels can unlock their full potential to shape the future of agriculture and ensure global food security. Here, we summarized the activity of some intermediate metabolites, from the perception step to tolerance responses to stress factors.

Remediation of soda-saline-alkali soil through soil amendments: Microbially mediated carbon and nitrogen cycles and remediation mechanisms

Due to the high salt content and pH value, the structure of saline-sodic soil was deteriorated, resulting in decreased soil fertility and inhibited soil element cycling. This, in turn, caused significant negative impacts on crop growth, posing a major challenge to global agriculture and food security. Despite numerous studies aimed at reducing the loss of plant productivity in saline-sodic soils, the knowledge regarding shifts in soil microbial communities and carbon/nitrogen cycling during saline-sodic soil improvement remains incomplete. Consequently, we developed a composite soil amendment to explore its potential to alleviate salt stress and enhance soil quality. Our findings demonstrated that the application of this composite soil amendment effectively enhanced microbial salinity resistance, promotes soil carbon fixation and nitrogen cycling, thereby reducing HCO3- concentration and greenhouse gas emissions while improving physicochemical properties and enzyme activity in the soil. Additionally, the presence of CaSO4 contributed to a decrease in water-soluble Na+ content, resulting in reduced soil ESP and pH by 14.64 % and 7.42, respectively. Our research presents an innovative approach to rehabilitate saline-sodic soil and promote ecological restoration through the perspective of elements cycles.

Characterization of chloroplast ribulose-5-phosphate-3-epimerase from the microalga Chlamydomonas reinhardtii

Carbon fixation relies on Rubisco and 10 additional enzymes in the Calvin-Benson-Bassham cycle. Epimerization of xylulose-5-phosphate (Xu5P) into ribulose-5-phosphate (Ru5P) contributes to the regeneration of ribulose-1,5-bisphosphate, the substrate of Rubisco. Ribulose-5-phosphate-3-epimerase (RPE, EC 5.1.3.1) catalyzes the formation of Ru5P, but it can also operate in the pentose-phosphate pathway by catalyzing the reverse reaction. Here, we describe the structural and biochemical properties of the recombinant RPE isoform 1 from Chlamydomonas (Chlamydomonas reinhardtii) (CrRPE1). The enzyme is a homo-hexamer that contains a zinc ion in the active site and exposes a catalytic pocket on the top of an α8β8 triose isomerase-type barrel as observed in structurally solved RPE isoforms from both plant and non-plant sources. By optimizing and developing enzyme assays to monitor the reversible epimerization of Ru5P to Xu5P and vice versa, we determined the catalytic parameters that differ from those of other plant paralogs. Despite being identified as a putative target of multiple thiol-based redox modifications, CrRPE1 activity is not affected by both reductive and oxidative treatments, indicating that enzyme catalysis is insensitive to possible redox alterations of cysteine residues. We mapped phosphorylation sites on the crystal structure, and the specific location at the entrance of the catalytic cleft supports a phosphorylation-based regulatory mechanism. This work provides an accurate description of the structural features of CrRPE1 and an in-depth examination of its catalytic and regulatory properties highlighting the physiological relevance of this enzyme in the context of photosynthetic carbon fixation.

Phosphoribulokinase abundance is not limiting the Calvin-Benson-Bassham cycle in Chlamydomonas reinhardtii

Improving photosynthetic efficiency in plants and microalgae is of utmost importance to support the growing world population and to enable the bioproduction of energy and chemicals. Limitations in photosynthetic light conversion efficiency can be directly attributed to kinetic bottlenecks within the Calvin-Benson-Bassham cycle (CBBC) responsible for carbon fixation. A better understanding of these bottlenecks in vivo is crucial to overcome these limiting factors through bio-engineering. The present study is focused on the analysis of phosphoribulokinase (PRK) in the unicellular green alga Chlamydomonas reinhardtii. We have characterized a PRK knock-out mutant strain and showed that in the absence of PRK, Chlamydomonas cannot grow photoautotrophically while functional complementation with a synthetic construct allowed restoration of photoautotrophy. Nevertheless, using standard genetic elements, the expression of PRK was limited to 40% of the reference level in complemented strains and could not restore normal growth in photoautotrophic conditions suggesting that the CBBC is limited. We were subsequently able to overcome this initial limitation by improving the design of the transcriptional unit expressing PRK using diverse combinations of DNA parts including PRK endogenous promoter and introns. This enabled us to obtain strains with PRK levels comparable to the reference strain and even overexpressing strains. A collection of strains with PRK levels between 16% and 250% of WT PRK levels was generated and characterized. Immunoblot and growth assays revealed that a PRK content of ≈86% is sufficient to fully restore photoautotrophic growth. This result suggests that PRK is present in moderate excess in Chlamydomonas. Consistently, the overexpression of PRK did not increase photosynthetic growth indicating that that the endogenous level of PRK in Chlamydomonas is not limiting the Calvin-Benson-Bassham cycle under optimal conditions.