Engineering Rubisco activase from thermophilic cyanobacteria into high-temperature sensitive plants

Synergizing biotechnology and natural farming: pioneering agricultural sustainability through innovative interventions

The world has undergone a remarkable transformation from the era of famines to an age of global food production that caters to an exponentially growing population. This transformation has been made possible by significant agricultural revolutions, marked by the intensification of agriculture through the infusion of mechanical, industrial, and economic inputs. However, this rapid advancement in agriculture has also brought about the proliferation of agricultural inputs such as pesticides, fertilizers, and irrigation, which have given rise to long-term environmental crises. Over the past two decades, we have witnessed a concerning plateau in crop production, the loss of arable land, and dramatic shifts in climatic conditions. These challenges have underscored the urgent need to protect our global commons, particularly the environment, through a participatory approach that involves countries worldwide, regardless of their developmental status. To achieve the goal of sustainability in agriculture, it is imperative to adopt multidisciplinary approaches that integrate fields such as biology, engineering, chemistry, economics, and community development. One noteworthy initiative in this regard is Zero Budget Natural Farming, which highlights the significance of leveraging the synergistic effects of both plant and animal products to enhance crop establishment, build soil fertility, and promote the proliferation of beneficial microorganisms. The ultimate aim is to create self-sustainable agro-ecosystems. This review advocates for the incorporation of biotechnological tools in natural farming to expedite the dynamism of such systems in an eco-friendly manner. By harnessing the power of biotechnology, we can increase the productivity of agro-ecology and generate abundant supplies of food, feed, fiber, and nutraceuticals to meet the needs of our ever-expanding global population.

Feeding the world: impacts of elevated [CO2] on nutrient content of greenhouse grown fruit crops and options for future yield gains

Several long-term studies have provided strong support demonstrating that growing crops under elevated [CO2] can increase photosynthesis and result in an increase in yield, flavour and nutritional content (including but not limited to Vitamins C, E and pro-vitamin A). In the case of tomato, increases in yield by as much as 80% are observed when plants are cultivated at 1000 ppm [CO2], which is consistent with current commercial greenhouse production methods in the tomato fruit industry. These results provide a clear demonstration of the potential for elevating [CO2] for improving yield and quality in greenhouse crops. The major focus of this review is to bring together 50 years of observations evaluating the impact of elevated [CO2] on fruit yield and fruit nutritional quality. In the final section, we consider the need to engineer improvements to photosynthesis and nitrogen assimilation to allow plants to take greater advantage of elevated CO2 growth conditions.

Photosynthesis and Salt Exclusion Are Key Physiological Processes Contributing to Salt Tolerance of Canola (Brassica napus L.): Evidence from Physiology and Transcriptome Analysis

Plant salt tolerance is controlled by various physiological processes such as water and ion homeostasis, photosynthesis, and cellular redox balance, which are in turn controlled by gene expression. In the present study, plants of six canola cultivars (DGL, Dunkled, Faisal Canola, Cyclone, Legend, and Oscar) were evaluated for salt tolerance by subjecting them to 0 or 200 mM NaCl stress. Based on growth, cultivars DGL, Dunkled, and Faisal Canola were ranked as salt tolerant, while cultivars Cyclone, Legend, and Oscar were ranked as salt-sensitive ones. Differential salt tolerance in these canola cultivars was found to be associated with a relatively lower accumulation of Na⁺ and greater accumulation of K⁺ in the leaves, lower oxidative damage (MDA), and better antioxidative defense system (Superoxide dismutase, SOD; peroxidase, POD, and catalase, CAT). Cultivar Oscar was the poorest to discriminate Na⁺ and K⁺ uptake and accumulation in leaves and had poor antioxidant potential to scavenge ROS. Salt stress did not affect the structural stability of photosystem-II (PSII) till three weeks, thereafter it caused a significant decrease. Salt stress increased the performance index (PI_ABS) by increasing the density of active reaction centers in Oscar. Salt stress decreased the antenna size thereby lowering the absorption and trapping energy flux, and maintaining the electron transport with an increase in heat dissipation. This may represent a potential mechanism to cope with salt stress. Transcriptome analysis of salt-sensitive cultivar Oscar further revealed that salt stress down-regulated DEGs related to hormonal signal transduction pathways, photosynthesis, and transcription factors, while DEGs related to the biosynthesis of amino acid and ion transport were up-regulated. In conclusion, salt tolerance in canola cultivars was associated with ion exclusion and maintenance of photosynthesis. Salt stress sensitivity in cultivar Oscar was mainly associated with poor control of ion homeostasis which caused oxidative stress and reduced photosynthetic efficiency.

Dynamic and fluctuating generation of hydrogen peroxide via photorespiratory metabolic channeling in plants

The homeostasis of hydrogen peroxide (H₂ O₂ ), a key regulator of basic biological processes, is a result of the cooperation between its generation and scavenging. However, the mechanistic basis of this balance is not fully understood. We previously proposed that the interaction between glycolate oxidase (GLO) and catalase (CAT) may serve as a molecular switch that modulates H₂ O₂ levels in plants. In this study, we demonstrate that the GLO-CAT complex in plants exists in different states, which are dynamically interchangeable in response to various stimuli, typically salicylic acid (SA), at the whole-plant level. More crucially, changes in the state of the complex were found to be closely linked to peroxisomal H₂ O₂ fluctuations, which were independent of the membrane-associated NADPH oxidase. Furthermore, evidence suggested that H₂ O₂ channeling occurred even in vitro when GLO and CAT worked cooperatively. These results demonstrate that dynamic changes in H₂ O₂ levels are physically created via photorespiratory metabolic channeling in plants, and that such H₂ O₂ fluctuations may serve as signals that are mechanistically involved in the known functions of photorespiratory H₂ O₂ . In addition, our study also revealed a new way for SA to communicate with H₂ O₂ in plants.

Involvement of ethylene in melatonin-modified photosynthetic-N use efficiency and antioxidant activity to improve photosynthesis of salt grown wheat

The involvement of melatonin in the regulation of salt stress acclimation has been shown in plants in this present work. We found that the GOAL cultivar of wheat (Triticum aestivum L.) was the most salt-tolerant among the investigated cultivars, GOAL, HD-2967, PBW-17, PBW-343, PBW-550, and WH-1105 when screened for tolerance to 100 mM NaCl. The application of 100 μM melatonin maximally reduced oxidative stress and improved photosynthesis in the cv. GOAL. Melatonin supplementation reduced salt stress-induced oxidative stress by upregulating the activity of antioxidant enzymes, such as superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR), and reduced the glutathione (GSH) production. This resulted in increased membrane stability, photosynthetic-N use efficiency and photosynthesis in plants. The application of 50 μM of the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG) in the presence of melatonin and salt stress increased H₂ O₂ content but reduced GR activity and GSH, photosynthesis, and plant dry mass. This signifies that melatonin-mediated salt stress tolerance was related to ethylene synthesis as it improved antioxidant activity and photosynthesis of plants under salt stress. Thus, the interaction of melatonin and ethylene bears a prominent role in salt stress tolerance in wheat and can be used to develop salt tolerance in other crops.

Methyl Jasmonate Alleviated the Adverse Effects of Cadmium Stress in Pea (Pisum sativum L.): A Nexus of Photosystem II Activity and Dynamics of Redox Balance

The accumulation of cadmium (Cd) in leaves reduces photosynthetic capacity by degrading photosynthetic pigments, reducing photosystem II activity, and producing reactive oxygen species (ROS). Though it was demonstrated that the application of Methyl Jasmonate (MeJA) induces heavy metal (HM) stress tolerance in plants, its role in adjusting redox balance and photosynthetic machinery is unclear. In this study, the role of MeJA in modulating photosystem II (PSII) activity and antioxidant defense system was investigated to reduce the toxic effects of Cd on the growth of pea (Pisum sativum L.) cultivars. One-week-old seedlings of three pea varieties were subjected to Cd stress (0, 50, 100 μm), and MeJA (0, 1, 5, 10 μm) was applied as a foliar spray for 2 weeks. Cadmium stress reduced the growth of all three pea varieties. Cadmium stress decreased photosynthetic pigments [Chl a (58.15%), Chl b (48.97%), total Chl (51.9%) and carotenoids (44.01%)] and efficiency of photosystem II [Fv/Fm (19.52%) and Y(II; 67.67%)], while it substantially increased Cd accumulation along with an increase in ROS (79.09%) and lipid peroxidation (129.28%). However, such adverse effects of Cd stress varied in different pea varieties. Exogenous application of MeJA increased the activity of a battery of antioxidant enzymes [superoxide dismutase (33.68%), peroxidase (29.75%), and catalase (38.86%)], improved photosynthetic pigments and PSII efficiency. This led to improved growth of pea varieties under Cd stress, such as increased fresh and dry weights of shoots and roots. In addition, improvement in root biomass by MeJA was more significant than that of shoot biomass. Thus, the mitigating effect of MeJA was attributed to its role in cellular redox balance and photosynthetic machinery of pea plants when exposed to Cd stress.

Regulation of Calvin-Benson cycle enzymes under high temperature stress

The Calvin-Benson cycle (CBC) consists of three critical processes, including fixation of CO₂ by Rubisco, reduction of 3-phosphoglycerate (3PGA) to triose phosphate (triose-P) with NADPH and ATP generated by the light reactions, and regeneration of ribulose 1,5-bisphosphate (RuBP) from triose-P. The activities of photosynthesis-related proteins, mainly from the CBC, were found more significantly affected and regulated in plants challenged with high temperature stress, including Rubisco, Rubisco activase (RCA) and the enzymes involved in RuBP regeneration, such as sedoheptulose-1,7-bisphosphatase (SBPase). Over the past years, the regulatory mechanism of CBC, especially for redox-regulation, has attracted major interest, because balancing flux at the various enzymatic reactions and maintaining metabolite levels in a range are of critical importance for the optimal operation of CBC under high temperature stress, providing insights into the genetic manipulation of photosynthesis. Here, we summarize recent progress regarding the identification of various layers of regulation point to the key enzymes of CBC for acclimation to environmental temperature changes along with open questions are also discussed.

Is Photoprotection of PSII One of the Key Mechanisms for Drought Tolerance in Maize?

Drought is one of the most important abiotic stress factors limiting maize production worldwide. The objective of this study was to investigate whether photoprotection of PSII was associated with the degree of drought tolerance and yield in three maize hybrids (30Y87, 31R88, P3939). To do this, three maize hybrids were subjected to three cycles of drought, and we measured the activities of photosystem II (PSII) and photosystem I (PSI). In a second field experiment, three maize hybrids were subjected to drought by withholding irrigation, and plant water status, yield and yield attributes were measured. Drought stress decreased leaf water potential (Ψ_L) in three maize hybrids, and this reduction was more pronounced in hybrid P3939 (−40%) compared to that of 30Y87 (−30%). Yield and yield attributes of three maize hybrids were adversely affected by drought. The number of kernels and 100-kernel weight was the highest in maize hybrid 30Y87 (−56%, −6%), whereas these were lowest in hybrid P3939 (−88%, −23%). Drought stress reduced the quantum yield of PSII [Y(II)], photochemical quenching (qP), electron transport rate through PSII [ETR(II)] and NPQ, except in P3939. Among the components of NPQ, drought increased the Y(NPQ) with concomitant decrease in Y(NO) only in P3939, whereas Y(NO) increased in drought-stressed plants of hybrid 30Y87 and 31R88. However, an increase in cyclic electron flow (CEF) around PSI and Y(NPQ) in P3939 might have protected the photosynthetic machinery but it did not translate in yield. However, drought-stressed plants of 30Y87 might have sufficiently downregulated PSII to match the energy consumption in downstream biochemical processes. Thus, changes in PSII and PSI activity and development of NPQ through CEF are physiological mechanisms to protect the photosynthetic apparatus, but an appropriate balance between these physiological processes is required, without which plant productivity may decline.

Enhancing crop yield by using Rubisco activase to improve photosynthesis under elevated temperatures

With the rapid growth of world population, it is essential to increase agricultural productivity to feed the growing population. Over the past decades, many methods have been used to increase crop yields. Despite the success in boosting the crop yield through these methods, global food production still needs to be increased to be on par with the increasing population and its dynamic consumption patterns. Additionally, given the prevailing environmental conditions pertaining to the global temperature increase, heat stress will likely be a critical factor that negatively affects plant biomass and crop yield. One of the key elements hindering photosynthesis and plant productivity under heat stress is the thermo-sensitivity of the Rubisco activase (RCA), a molecular chaperone that converts Rubisco back to active form after it becomes inactive. It would be an attractive and practical strategy to maintain photosynthetic activity under elevated temperatures by enhancing the thermo-stability of RCA. In this context, this review discusses the need to improve the thermo-tolerance of RCA under current climatic conditions and to further study RCA structure and regulation, and its limitations at elevated temperatures. This review summarizes successful results and provides a perspective on RCA research and its implication in improving crop yield under elevated temperature conditions in the future.

Linking changes in chlorophyll a fluorescence with drought stress susceptibility in mung bean [Vigna radiata (L.) Wilczek]

In the present study, the mung bean cv. NM-13-1^Tol was selected as drought-tolerant and NM-54^Sens as drought-sensitive. The effects of progressive drought (16 days) on the photosystem II (PSII) activity was assessed using OJIP and JIP-test in the selected two mung bean cultivars differing in drought tolerance. Drought stress reduced the relative water content to 70% (at threshold) and 62% (below the threshold) in cv.NM-13-1^Tol and NM-54^sens , respectively. The greater reduction in quantum yield of PSII in cv.NM-54^sens due to drought stress was due to PSII photodamage. Raw OJIP induction curves and F_o and F_m normalised curves showed that significant changes in fluorescence occurred at the O, J, I and P steps only in cv. NM-54^sens . Double normalised differential kinetics indicated adverse effects at the antennae, oxygen-evolving complex and intersystem electron acceptors in cv.NM54^sens . Moreover, JIP-test analysis showed that drought stress caused a greater decrease in performance index (PI_ABS ) in cv.NM-54^sens as compared to that in cv. NM-13-1^Tol , which is associated with an increase in V_j , rate of accumulation of closed reaction centres (M_o ), energy fluxes for absorption (ABS/RC), trapping (TR_o /RC), electron transport (ET_o /RC), and dissipation of absorbed energy as heat (DI_o /RC). In conclusion, two-week drought stress reduced the RWC below the threshold in cv.NM54^sens , which resulted in damages at the donor and acceptor sides of PSII. However, cv.NM-13-1^Tol somehow maintained the RWC around the threshold and thus protected PSII. Of various JIP-test parameters, PI_ABS , F_v /F_m , V_j and M_o are key indicators of drought stress tolerance in mung bean cultivars.

A perspective on biotechnological applications of thermophilic microalgae and cyanobacteria

The importance of expanding our knowledge on microorganisms derived from extreme environments stems from the development of novel and sustainable technologies for our health, food, and environment. Microalgae and cyanobacteria represent a group of diverse microorganisms that inhabit a wide range of environments, are capable of oxygenic photosynthesis, and form a thick microbial mat even at extreme environments. Studies of thermophilic microorganisms have shown a considerable biotechnological potential due to their optimum growth and metabolisms at high temperatures (≥50 °C), which is supported by their thermostable enzymes. Microalgal and cyanobacterial communities present in high-temperature ecosystems account for a large part of the total ecosystem biomass and productivity, and can be exploited to generate several value-added products of agricultural, pharmaceutical, nutraceutical, and industrial relevance. This review provides an overview on the current status of biotechnological applications of thermophilic microalgae and cyanobacteria, with an outlook on the challenges and future prospects.