ROS and redox signalling in the response of plants to abiotic stress

Two faces of one coin: Beneficial and deleterious effects of reactive oxygen species during short-term acclimation to hypo-osmotic stress in a decapod crab

Exposure to environmental changes often results in the production of reactive oxygen species (ROS), which, if uncontrolled, leads to loss of cellular homeostasis and oxidative distress. However, at physiological levels these same ROS are known to be key players in cellular signaling and the regulation of key biological activities (oxidative eustress). While ROS are known to mediate salinity tolerance in plants, little is known for the animal kingdom. In this study, we use the Mediterranean crab Carcinus aestuarii, highly tolerant to salinity changes in its environment, as a model to test the healthy or pathological role of ROS due to exposure to diluted seawater (dSW). Crabs were injected either with an antioxidant [N-acetylcysteine (NAC), 150 mg·kg-1] or phosphate buffered saline (PBS). One hour after the first injection, animals were either maintained in seawater (SW) or transferred to dSW and injections were carried out at 12-h intervals. After ≈48 h of salinity change, all animals were sacrificed and gills dissected for analysis. NAC injections successfully inhibited ROS formation occurring due to dSW transfer. However, this induced 55% crab mortality, as well as an inhibition of the enhanced catalase defenses and mitochondrial biogenesis that occur with decreased salinity. Crab osmoregulatory capacity under dSW condition was not affected by NAC, although it induced in anterior (non-osmoregulatory) gills a 146-fold increase in Na+/K+/2Cl- expression levels, reaching values typically observed in osmoregulatory tissues. We discuss how ROS influences the physiology of anterior and posterior gills, which have two different physiological functions and strategies during hyper-osmoregulation in dSW.

The role of drought response genes and plant growth promoting bacteria on plant growth promotion under sustainable agriculture: A review

Drought is a major stressor that poses significant challenges for agricultural practices. It becomes difficult to meet the global demand for food crops and fodder. Plant physiology, physico-chemistry and morphology changes in plants like decreased photosynthesis and transpiration rate, overproduction of reactive oxygen species, repressed shoot and root shoot growth and modified stress signalling pathways by drought, lead to detrimental impacts on plant development and output. Coping with drought stress requires a variety of adaptations and mitigation techniques. Crop yields could be effectively increased by employing plant growth-promoting rhizobacteria (PGPR), which operate through many mechanisms. These vital microbes colonise the rhizosphere of crops and promote drought resistance by producing exopolysaccharides (EPS), 1-aminocyclopropane-1-carboxylate (ACC) deaminase and phytohormones including volatile compounds. The upregulation or downregulation of stress-responsive genes causes changes in root architecture due to acquiring drought resistance. Further, PGPR induces osmolyte and antioxidant accumulation. Another key feature of microbial communities associated with crops includes induced systemic tolerance and the production of free radical-scavenging enzymes. This review is focused on detailing the role of PGPR in assisting plants to adapt to drought stress.

Evaluating the phytotoxicological effects of bulk and nano forms of zinc oxide on cellular respiration-related indices and differential gene expression in Hordeum vulgare L

The increasing use of nanoparticles is driving the growth of research on their effects on living organisms. However, studies on the effects of nanoparticles on cellular respiration are still limited. The remodeling of cellular-respiration-related indices in plants induced by zinc oxide nanoparticles (nnZnO) and its bulk form (blZnO) was investigated for the first time. For this purpose, barley (Hordeum vulgare L.) seedlings were grown hydroponically for one week with the addition of test compounds at concentrations of 0, 0.3, 2, and 10 mg mL-1. The results showed that a low concentration (0.3 mg mL-1) of blZnO did not cause significant changes in the respiration efficiency, ATP content, and total reactive oxygen species (ROS) content in leaf tissues. Moreover, a dose of 0.3 mg mL-1 nnZnO increased respiration efficiency in both leaves (17 %) and roots (38 %). Under the influence of blZnO and nnZnO at medium (2 mg mL-1) and high (10 mg mL-1) concentrations, a dose-dependent decrease in respiration efficiency from 28 % to 87 % was observed. Moreover, the negative effect was greater under the influence of nnZnO. The gene transcription of the subunits of the mitochondria electron transport chain (ETC) changed mainly only under the influence of nnZnO in high concentration. Expression of the ATPase subunit gene, atp1, increased slightly (by 36 %) in leaf tissue under the influence of medium and high concentrations of test compounds, whereas in the root tissues, the atp1 mRNA level decreased significantly (1.6-2.9 times) in all treatments. A dramatic decrease (1.5-2.4 times) in ATP content was also detected in the roots. Against the background of overexpression of the AOX1d1 gene, an isoform of alternative oxidase (AOX), the total ROS content in leaves decreased (with the exception of 10 mg mL-1 nnZnO). However, in the roots, where the pressure of the stress factor is higher, there was a significant increase in ROS levels, with a maximum six-fold increase under 10 mg mL-1 nnZnO. A significant decrease in transcript levels of the pentose phosphate pathway and glycolytic enzymes was also shown in the root tissues compared to leaves. Thus, the disruption of oxidative phosphorylation leads to a decrease in ATP synthesis and an increase in ROS production; concomitantly reducing the efficiency of cellular respiration.

Melatonin-mediated low-temperature tolerance of cucumber seedlings requires Ca2+/CPKs signaling pathway

Melatonin (Mel) is recognized as a prominent plant growth regulator. This study investigated the alleviating effect of Mel pretreatment on growth inhibition caused by low-temperature (LT) stress (10 °C/6 °C) in cucumber seedlings and explored the role of the Ca2+/Calcium-dependent protein kinases (CPKs) signaling pathway in Mel-regulated LT tolerance. The main results are as follows: compared to LT treatment alone, 100 μM Mel increased both the content of Ca2+ (highest about 42.01%) and the expression levels of Ca2+ transporter and cyclic nucleotide-gated channel (CNGC) genes under LT. Similarly, Mel enhanced the content of CPKs (highest about 27.49%) and the expression levels of CPKs family genes in cucumber leaves under LT. Additionally, pretreatment with 100 μM Mel for three days strengthened the antioxidant defense and photosynthesis of seedlings under LT. Genes in the ICE-CBF-COR pathway and the MAPK cascade were upregulated by Mel, with maximum upregulations reaching approximately 2.5-fold and 1.9-fold, respectively, thus conferring LT tolerance to cucumber seedlings. However, the above beneficial effects of Mel were weakened by co-treatment with calcium signaling blockers (LaCl3 or EGTA) or CPKs inhibitors (TFP or W-7), suggesting that the Ca2+/CPKs pathway is involved in the Mel-mediated regulation of LT tolerance. In conclusion, this study revealed that Mel can alleviate growth inhibition in cucumber seedlings under LT stress and demonstrated that the Ca2+/CPKs signaling pathway is crucial for the Mel-mediated enhancement of LT tolerance. The findings hold promise for providing theoretical insights into the application of Mel in agricultural production and for investigating its underlying mechanisms of action.

Potassium may mitigate drought stress by increasing stem carbohydrates and their mobilization into grains

Potassium (K) deficiency occurs commonly in crop plants. Optimal K nutrition is particularly important when plants are exposed to stress conditions (especially drought and heat) because a cellular demand for K increases. Low K in plant tissues is known to aggravate the effects of drought stress by impairing the osmoregulation process and the photosynthetic carbon metabolism. However, despite numerous publications about the role of K in enhancing tolerance to drought stress in crop plants, our understanding of the major mechanisms underlying the stress-mitigating effects of K is still limited. This paper summarizes and appraises the current knowledge on the major protective effects of K under drought stress, and then proposes a new K-related drought stress-mitigating mechanism, whereby optimal K nutrition may promote partitioning of carbohydrates in stem tissues and subsequent mobilization of these carbohydrates into developing grain under drought stress. The importance of stem reserves of carbohydrates is based on limited photosynthetic capacity during the grain-filling period under drought conditions due to premature leaf senescence as well as due to impaired assimilate transport from leaves to the developing grains. Plants with a high capacity to store large amounts of soluble carbohydrates in stems before anthesis and mobilize them into grain post-anthesis have a high potential to yield well in dry and hot environments. In practice, particular attention needs to be paid to the K nutritional status of plants grown with limited water supply, especially during grain filling. Because K is the mineral nutrient deposited mainly in stem, a special consideration should be given to stems of crop plants in research dealing with the effects of K on yield formation and stress mitigation.

Heterologous Expression of Chrysanthemum TCP Transcription Factor CmTCP13 Enhances Salinity Tolerance in Arabidopsis

Plant-specific TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR (TCP) proteins play critical roles in plant development and stress responses; however, their functions in chrysanthemum (Chrysanthemum morifolium) have not been well-studied. In this study, we isolated and characterized the chrysanthemum TCP transcription factor family gene CmTCP13, a homolog of AtTCP13. This gene encoded a protein harboring a conserved basic helix-loop-helix motif, and its expression was induced by salinity stress in chrysanthemum plants. Subcellular localization experiments showed that CmTCP13 localized in the nucleus. Sequence analysis revealed the presence of multiple stress- and hormone-responsive cis-elements in the promoter region of CmTCP13. The heterologous expression of CmTCP13 in Arabidopsis plants enhanced their tolerance to salinity stress. Under salinity stress, CmTCP13 transgenic plants exhibited enhanced germination, root length, seedling growth, and chlorophyll content and reduced relative electrical conductivity compared with those exhibited by wild-type (WT) plants. Moreover, the expression levels of stress-related genes, including AtSOS3, AtP5CS2, AtRD22, AtRD29A, and AtDREB2A, were upregulated in CmTCP13 transgenic plants than in WT plants under salt stress. Taken together, our results demonstrate that CmTCP13 is a critical regulator of salt stress tolerance in plants.

Overexpression of Rhodiola crenulata glutathione peroxidase 5 increases cold tolerance and enhances the pharmaceutical value of the hairy roots

Rhodiola crenulata, a plant of great medicinal value found in cold high-altitude regions, has been excessively exploited due to the difficulty in cultivation. Understanding Rhodiola crenulata's adaptation mechanisms to cold environment can provide a theoretical basis for artificial breeding. Glutathione peroxidases (GPXs), critical enzymes found in plants, play essential roles in antioxidant defense through the ascorbate-glutathione cycle. However, it is unknown whether GPX5 contributes to Rhodiola crenulata's cold tolerance. In this study, we investigated the role of GPX5 in Rhodiola crenulata's cold tolerance mechanisms. By overexpressing Rhodiola crenulata GPX5 (RcGPX5) in yeast and Arabidopsis thaliana, we observed down-regulation of Arabidopsis thaliana GPX5 (AtGPX5) and increased cold tolerance in both organisms. Furthermore, the levels of antioxidants and enzyme activities in the ascorbate-glutathione cycle were elevated, and cold-responsive genes such as AtCBFs and AtCORs were induced. Additionally, RcGPX5 overexpressing lines showed insensitivity to exogenous abscisic acid (ABA), suggesting a negative regulation of the ABA pathway by RcGPX5. RcGPX5 also promoted the expression of several thioredoxin genes in Arabidopsis and interacted with two endogenous genes of Rhodiola crenulata, RcTrx2-3 and RcTrxo1, located in mitochondria and chloroplasts. These findings suggest a significantly different model in Rhodiola crenulata compared to Arabidopsis thaliana, highlighting a complex network involving the function of RcGPX5. Moreover, overexpressing RcGPX5 in Rhodiola crenulata hairy roots positively influenced the salidroside synthesis pathway, enhancing its pharmaceutical value for doxorubicin-induced cardiotoxicity. These results suggested that RcGPX5 might be a key component for Rhodiola crenulata to adapt to cold stress and overexpressing RcGPX5 could enhance the pharmaceutical value of the hairy roots.

PbGBF3 enhances salt response in pear by upregulating PbAPL2 and PbSDH1 and reducing ABA-mediated salt sensitivity

Pear is a widely cultivated fruit crop, but its distribution and sustainable production are significantly limited by salt stress. This study used RNA-Seq time-course analysis, WGCNA, and functional enrichment analysis to uncover the molecular mechanisms underlying salt stress tolerance in Pyrus ussuriensis. We identified an ABA-related regulatory module, PbGBF3-PbAPL2-PbSDH1, as crucial in this response. PbGBF3, a bZIP transcription factor, enhances salt tolerance by upregulating PbAPL2 and PbSDH1. Overexpression of PbGBF3 improved salt tolerance in Pyrus communis calli and Arabidopsis, while silencing it reduced tolerance in Pyrus betulifolia. Functional assays showed that PbGBF3 binds to the promoters of PbAPL2 and PbSDH1, increasing their expression. PbAPL2 and PbSDH1, key enzymes in starch synthesis and the sorbitol pathway, respectively, enhance salt tolerance by increasing AGPase activity, soluble sugar content, and SDH activity, improving ROS scavenging and ion balance. Our findings suggest that the PbGBF3-PbAPL2 and PbGBF3-PbSDH1 modules positively regulate salt tolerance by enhancing ABA signaling and reducing ABA-mediated growth inhibition. These insights provide a foundation for developing salt-tolerant pear cultivars.

Heat-stress-induced ROS in maize silks cause late pollen tube growth arrest and sterility

The reproductive phase of plants is highly sensitive to ambient temperature stresses. To investigate sensitivity of female reproductive organs in grass crops during the pollination phase, we exposed the elongated stigma (silk) of maize to ambient environment at the silking stage. Moderate heat stress causes cell death of silk hair cells but did not affect early pollen tube growth inside the silk. Late pollen tube growth arrest was observed, leading to sterility. Heat stress causes elevated levels of reactive oxygen species (ROS) in silks, whose levels can be reduced by scavengers partly restoring pollen tube growth and fertility. A number of biological processes including hydrogen peroxide catabolic processes and bHLH transcription factor genes are downregulated by heat stress, while some NAC transcription factor genes are strongly upregulated. In conclusion, this study now provides a basis to select genes for engineering heat-stress-tolerant grass crops during the pollination phase.

Natural soil biotin application activates soil beneficial microorganisms to improve the thermotolerance of Chinese cabbage

Chinese cabbage (Brassica campestris L. syn. B. rapa), a widely cultivated leafy vegetable, faces significant challenges in annual production due to high-temperature stress, which adversely affects plant weight and quality. The need for an effective solution to mitigate these impacts is imperative for sustainable horticulture. This study explored the effects of a novel biofertilizer, natural soil biotin (NSB), on Chinese cabbage under high-temperature conditions. NSB, rich in organic matter-degrading enzymes, was applied to assess its impact on crop yield, growth, nutrient use efficiency, product quality, and safety. The study also examined the soil microbial community response to NSB application, particularly the changes in the rhizosphere soil's fungal population. The application of NSB led to an increase in the abundance of Oleomycetes, which was associated with a decrease in the diversity and abundance of harmful fungi in the rhizosphere soil. This microbial shift promoted the growth of Chinese cabbage, enhancing both plant weight and quality by fostering a more favorable growth environment. Furthermore, NSB was found to reduce lipid peroxidation in Chinese cabbage leaves under high-temperature stress (40°C/30°C, 16 h/8 h, 24 h) by boosting antioxidant enzyme activity and osmoregulatory substance content. The findings suggest that the NSB application offers a promising approach to environmentally friendly cultivation of Chinese cabbage during high-temperature seasons. It contributes to improving the crop's adaptation to climate change and soil degradation, supporting the development of sustainable agricultural practices. The integration of NSB into agricultural practices presents a viable strategy for enhancing the resilience of Chinese cabbage to high-temperature stress, thereby potentially increasing yield and improving the quality of the produce, which is crucial for the advancement of sustainable horticulture.

Genome-Wide Identification and Expression Analysis of BrBASS Genes in Brassica rapa Reveals Their Potential Roles in Abiotic Stress Tolerance

The bile acid sodium symporter (BASS) family plays an important role in transporting substances and coordinating plants' salt tolerance. However, the function of BASS in Brassica rapa has not yet been elucidated. In this study, eight BrBASS genes distributed on five chromosomes were identified that belonged to four subfamilies. Expression profile analysis showed that BrBASS7 was highly expressed in roots, whereas BrBASS4 was highly expressed in flowers. The promoter element analysis also identified several typical homeopathic elements involved in abiotic stress tolerance and stress-related hormonal responses. Notably, under salt stress, the expression of BrBASS2 was significantly upregulated; under osmotic stress, that of BrBASS4 increased and then decreased; and under cold stress, that of BrBASS7 generally declined. The protein-protein interaction analysis revealed that the BrBASS2 homologous gene AtBASS2 interacted with Nhd1 (N-mediated heading date-1) to alleviate salt stress in plants, while the BrBASS4 homologous gene AtBASS3 interacted with BLOS1 (biogenesis of lysosome-related organelles complex 1 subunit 1) via co-regulation with SNX1 (sorting nexin 1) to mitigate an unfavorable growing environment for roots. Further, Bra-miR396 (Bra-microRNA396) targeting BrBASS4 and BrBASS7 played a role in the plant response to osmotic and cold stress conditions, respectively. This research demonstrates that BrBASS2, BrBASS4, and BrBASS7 harbor great potential for regulating abiotic stresses. The findings will help advance the study of the functions of the BrBASS gene family.

Modeling the reactive oxygen species (ROS) wave in Chlamydomonas reinhardtii colonies

Reactive oxygen species (ROS) play a crucial role as signaling molecules in both plant and animal cells, enabling rapid responses to various stimuli. Among the many cellular mechanisms used to generate and transduce ROS signals, ROS-induced-ROS release (RIRR) is emerging as an important pathway involved in the responses of various multicellular and unicellular organisms to environmental stresses. In RIRR, one cellular compartment, organelle, or cell generates or releases ROS, triggering an increased ROS production and release by another compartment, organelle, or cell, thereby giving rise to a fast propagating ROS wave. This RIRR-based signal relay has been demonstrated to facilitate mitochondria-to-mitochondria communication in animal cells and long-distance systemic signaling in plants in response to biotic and abiotic stresses. More recently, it has been discovered that different unicellular microorganism communities also exhibit a RIRR cell-to-cell signaling process triggered by a localized stress treatment. However, the precise mechanism underlying the propagation of the ROS signal among cells within these unicellular communities remained elusive. In this study, we employed a reaction-diffusion model incorporating the RIRR mechanism to analyze the propagation of ROS-mediated signals. By effectively balancing production and scavenging processes, our model successfully reproduces the experimental ROS signal velocities observed in unicellular green algae (Chlamydomonas reinhardtii) colonies grown on agar plates, furthering our understanding of intercellular ROS communication.

Sub1 QTL confers submergence tolerance in rice through nitro-oxidative regulation and phytohormonal signaling

Constant change in global climate has become the most important limiting factor to crop productivity. Asymmetrical precipitations are causing recurrent flood events around the world. Submergence is one of the most detrimental abiotic stresses for sustainable rice production in the rainfed ecosystems of Southeast Asia. Therefore, the development of submergence-tolerant rice is an essential requirement to encounter food security. Submergence tolerance in rice is governed by the major quantitative trait locus (QTL) designated as Submergence1 (Sub1) near the centromere of chromosome 9. The introduction of the Sub1 in high-yielding rice varieties producing near-isogenic lines (NILs) has shown extreme submergence tolerance. The present study aimed to understand the responses of rice genotype IR64 and its Sub1 NIL IR64 Sub1 following one week of complete submergence treatment. Submergence imposed severe nitro-oxidative stress in both the rice genotypes, consequently disrupting the cellular redox homeostasis. In this study, IR64 exhibited higher NADPH oxidase activity accompanied by increased reactive oxygen species, reactive nitrogen species, and malondialdehyde buildups and cell death under submergence. Higher accumulations of 1-Aminocyclopropane-1-carboxylic acid, gibberellic acid, and Indole-3-acetic acid were also observed in IR64 which accelerated the plant growth and root cortical aerenchyma development following submergence. In contrast, IR64 Sub1 had enhanced submergence tolerance associated with an improved antioxidant defense system with sustainable morpho-physiological activities and restricted root aerenchyma formation. The comprehensive analyses of the responses of rice genotypes with contrasting submergence tolerance may demonstrate the intricacies of rice under complete submergence and may potentially contribute to improving stress resilience by advancing our understanding of the mechanisms of submergence tolerance in rice.

Concurrent improvement of rice grain yield and abiotic stress tolerance by overexpression of cytokinin activating enzyme LONELY GUY (OsLOG)

Meristem activity is important for normal plant growth as well as adaptive plastic development under abiotic stresses. Cytokinin has been recognized to have a major role in regulating meristem function which is controlled by cytokinin activating enzymes by fine-tuning the concentrations and spatial distribution of its bioactive forms. It was previously reported that LONELY GUY (LOG) acts in the direct activation pathway of cytokinin in rice shoot meristems. LOG has a cytokinin specific phosphoribohydrolase activity, which transforms inactive cytokinin nucleotides into active free bases. Here, we explored the role of OsLOG in controlling meristem activity mediated by cytokinin and its effects on growth, development, and stress resilience of rice plants. Overexpression of OsLOG in rice led to significant alterations in cytokinin levels in the inflorescence meristem, leading to enhanced plant growth, biomass and grain yield under both non-stress as well as stress conditions such as drought and salinity. Moreover, our study provides insight into how overexpression of OsLOG improves the ability of plants to withstand stress. The OsLOG-overexpressing lines exhibit reduced accumulation of H2O2 along with elevated antioxidant enzyme activities, thereby maintaining better redox homeostasis under stress conditions. This ultimately reduces the negative impact of stresses on grain yield and improves harvest index, as evidenced by observations in the OsLOG-overexpressing lines. In summary, our study emphasizes the diverse role of OsLOG, not only in regulating plant growth and yield via cytokinin but also in enhancing adaptability to abiotic stresses. This highlights its potential to improve crop yield and promote sustainable agriculture.

Specificity and dynamics of H2O2 detoxification by the cytosolic redox regulatory network as revealed by in vitro reconstitution

The thiol redox state is a decisive functional characteristic of proteins in cell biology. Plasmatic cell compartments maintain a thiol-based redox regulatory network linked to the glutathione/glutathione disulfide couple (GSH/GSSG) and the NAD(P)H system. The basic network constituents are known and in vivo cell imaging with gene-encoded probes have revealed insight into the dynamics of the [GSH]2/[GSSG] redox potential, cellular H2O2 and NAD(P)H+H+ amounts in dependence on metabolic and environmental cues. Less understood is the contribution and interaction of the network components, also because of compensatory reactions in genetic approaches. Reconstituting the cytosolic network of Arabidopsis thaliana in vitro from fifteen recombinant proteins at in vivo concentrations, namely glutathione peroxidase-like (GPXL), peroxiredoxins (PRX), glutaredoxins (GRX), thioredoxins, NADPH-dependent thioredoxin reductase A and glutathione reductase and applying Grx1-roGFP2 or roGFP2-Orp1 as dynamic sensors, allowed for monitoring the response to a single H2O2 pulse. The major change in thiol oxidation as quantified by mass spectrometry-based proteomics occurred in relevant peptides of GPXL, and to a lesser extent of PRX, while other Cys-containing peptides only showed small changes in their redox state and protection. Titration of ascorbate peroxidase (APX) into the system together with dehydroascorbate reductase lowered the oxidation of the fluorescent sensors in the network but was unable to suppress it. The results demonstrate the power of the network to detoxify H2O2, the partially independent branches of electron flow with significance for specific cell signaling and the importance of APX to modulate the signaling without suppressing it and shifting the burden to glutathione oxidation.

Genome-wide association study for seedling heat tolerance under two temperature conditions in bread wheat (Triticum aestivum L.)

BACKGROUND

As the greenhouse effect intensifies, global temperatures are steadily increasing, posing a challenge to bread wheat (Triticum aestivum L.) production. It is imperative to comprehend the mechanism of high temperature tolerance in wheat and implement breeding programs to identify and develop heat-tolerant wheat germplasm and cultivars.

RESULTS

To identify quantitative trait loci (QTL) related to heat stress tolerance (HST) at seedling stage in wheat, a panel of 253 wheat accessions which were re-sequenced used to conduct genome-wide association studies (GWAS) using the factored spectrally transformed linear mixed models (FaST-LMM). For most accessions, the growth of seedlings was found to be inhibited under heat stress. Analysis of the phenotypic data revealed that under heat stress conditions, the main root length, total root length, and shoot length of seedlings decreased by 47.46%, 49.29%, and 15.19%, respectively, compared to those in normal conditions. However, 17 varieties were identified as heat stress tolerant germplasm. Through GWAS analysis, a total of 115 QTLs were detected under both heat stress and normal conditions. Furthermore, 15 stable QTL-clusters associated with heat response were identified. By combining gene expression, haplotype analysis, and gene annotation information within the physical intervals of the 15 QTL-clusters, two novel candidate genes, TraesCS4B03G0152700/TaWRKY74-B and TraesCS4B03G0501400/TaSnRK3.15-B, were responsive to temperature and identified as potential regulators of HST in wheat at the seedling stage.

CONCLUSIONS

This study conducted a detailed genetic analysis and successfully identified two genes potentially associated with HST in wheat at the seedling stage, laying a foundation to further dissect the regulatory mechanism underlying HST in wheat under high temperature conditions. Our finding could serve as genomic landmarks for wheat breeding aimed at improving adaptation to heat stress in the face of climate change.

Deleterious Effects of Heat Stress on the Tomato, Its Innate Responses, and Potential Preventive Strategies in the Realm of Emerging Technologies

The tomato is a fruit vegetable rich in nutritional and medicinal value grown in greenhouses and fields worldwide. It is severely sensitive to heat stress, which frequently occurs with rising global warming. Predictions indicate a 0.2 °C increase in average surface temperatures per decade for the next three decades, which underlines the threat of austere heat stress in the future. Previous studies have reported that heat stress adversely affects tomato growth, limits nutrient availability, hammers photosynthesis, disrupts reproduction, denatures proteins, upsets signaling pathways, and damages cell membranes. The overproduction of reactive oxygen species in response to heat stress is toxic to tomato plants. The negative consequences of heat stress on the tomato have been the focus of much investigation, resulting in the emergence of several therapeutic interventions. However, a considerable distance remains to be covered to develop tomato varieties that are tolerant to current heat stress and durable in the perspective of increasing global warming. This current review provides a critical analysis of the heat stress consequences on the tomato in the context of global warming, its innate response to heat stress, and the elucidation of domains characterized by a scarcity of knowledge, along with potential avenues for enhancing sustainable tolerance against heat stress through the involvement of diverse advanced technologies. The particular mechanism underlying thermotolerance remains indeterminate and requires further elucidatory investigation. The precise roles and interplay of signaling pathways in response to heat stress remain unresolved. The etiology of tomato plants' physiological and molecular responses against heat stress remains unexplained. Utilizing modern functional genomics techniques, including transcriptomics, proteomics, and metabolomics, can assist in identifying potential candidate proteins, metabolites, genes, gene networks, and signaling pathways contributing to tomato stress tolerance. Improving tomato tolerance against heat stress urges a comprehensive and combined strategy including modern techniques, the latest apparatuses, speedy breeding, physiology, and molecular markers to regulate their physiological, molecular, and biochemical reactions.

Alternative electron sinks in chloroplasts and mitochondria of halophytes as a safety valve for controlling ROS production during salinity

Electron flow through the electron transport chain (ETC) is essential for oxidative phosphorylation in mitochondria and photosynthesis in chloroplasts. Electron fluxes depend on environmental parameters, e.g., ionic and osmotic conditions and endogenous factors, and this may cause severe imbalances. Plants have evolved alternative sinks to balance the reductive load on the electron transport chains in order to avoid overreduction, generation of reactive oxygen species (ROS), and to cope with environmental stresses. These sinks act primarily as valves for electron drainage and secondarily as regulators of tolerance-related metabolism, utilizing the excess reductive energy. High salinity is an environmental stressor that stimulates the generation of ROS and oxidative stress, which affects growth and development by disrupting the redox homeostasis of plants. While glycophytic plants are sensitive to high salinity, halophytic plants tolerate, grow, and reproduce at high salinity. Various studies have examined the ETC systems of glycophytic plants, however, information about the state and regulation of ETCs in halophytes under non-saline and saline conditions is scarce. This review focuses on alternative electron sinks in chloroplasts and mitochondria of halophytic plants. In cases where information on halophytes is lacking, we examined the available knowledge on the relationship between alternative sinks and gradual salinity resilience of glycophytes. To this end, transcriptional responses of involved components of photosynthetic and respiratory ETCs were compared between the glycophyte Arabidopsis thaliana and the halophyte Schrenkiella parvula, and the time-courses of these transcripts were examined in A. thaliana. The observed regulatory patterns are discussed in the context of reactive molecular species formation in halophytes and glycophytes.

PbHsfC1a-coordinates ABA biosynthesis and H2O2 signalling pathways to improve drought tolerance in Pyrus betulaefolia

Abiotic stresses have had a substantial impact on fruit crop output and quality. Plants have evolved an efficient immune system to combat abiotic stress, which employs reactive oxygen species (ROS) to activate the downstream defence response signals. Although an aquaporin protein encoded by PbPIP1;4 is identified from transcriptome analysis of Pyrus betulaefolia plants under drought treatments, little attention has been paid to the role of PIP and ROS in responding to abiotic stresses in pear plants. In this study, we discovered that overexpression of PbPIP1;4 in pear callus improved tolerance to oxidative and osmotic stresses by reconstructing redox homeostasis and ABA signal pathways. PbPIP1;4 overexpression enhanced the transport of H2O2 into pear and yeast cells. Overexpression of PbPIP1;4 in Arabidopsis plants mitigates the stress effects caused by adding ABA, including stomatal closure and reduction of seed germination and seedling growth. Overexpression of PbPIP1;4 in Arabidopsis plants decreases drought-induced leaf withering. The PbPIP1;4 promoter could be bound and activated by TF PbHsfC1a. Overexpression of PbHsfC1a in Arabidopsis plants rescued the leaf from wilting under drought stress. PbHsfC1a could bind to and activate AtNCED4 and PbNCED4 promoters, but the activation could be inhibited by adding ABA. Besides, PbNCED expression was up-regulated under H2O2 treatment but down-regulated under ABA treatment. In conclusion, this study revealed that PbHsfC1a is a positive regulator of abiotic stress, by targeting PbPIP1;4 and PbNCED4 promoters and activating their expression to mediate redox homeostasis and ABA biosynthesis. It provides valuable information for breeding drought-resistant pear cultivars through gene modification.

Fluoranthene biotreatment using prominent freshwater microalgae: physiological responses of microalgae and artificial neural network modeling of the bioremoval process

Due to the intensified industrial activities and other anthropogenic actions, contamination of polycyclic aromatic hydrocarbons (PAHs) has been growing at an alarming rate, turning in to a serious environmental concern. Bioremediation, as an eco-friendly and sustainable removal technology, can be used by organisms to reduce the resulting contaminations. In the present study, the ability of Tetradesmus obliquus to remove of fluoranthene (FLA) was evaluated. It was confirmed that FLA removal efficiency was managed by various environmental parameters and pH was found to be one of the most important influencial factors. The reusability of the algae in long-term repetitive operations confirmed the occurrence of biodegradation along with other natural attenuation and 10 intermediate compounds were identified in the FLA biodegradation pathway by GC-MS. As a result of physiological assays, induced antioxidant enzymes activities and augmentation of phenol and flavonoids contents, after the treatment of the microalgae by a high concentration of FLA, confirmed the ability of the microalgae to upregulate its antioxidant defense system in response to the toxic effects of FLA. An artificial neural network (ANN) model was then developed to predict FLA biodegradation efficiency and the appropriate predictive performance of ANN was confirmed by comparing the experimental FLA removal efficiency with its predicted amounts (R2 = 0.99).

Concurrent effect of drought and heat stress in rice (Oryza sativa L.): physio-biochemical and molecular approach

The present study was carried out to investigate the physio-biochemical and molecular responses of two rice genotypes (Noichi and N22) under drought, heat and combined drought/heat stress conditions. The antagonistic stomatal activity was found under the combined stress conditions; stomata were open under control and heat stress, conversely, stomata remained closed under drought and combined stress levels. Photosynthetic activity and chlorophyll content are decreased by the overproduction of reactive oxygen species and increased lipid peroxidation in both rice genotypes. To prevent oxidative damage, many antioxidant enzymes like catalase (CAT), ascorbate peroxidase (APX) and superoxide dismutase (SOD) are produced in both genotypes under these conditions. Under the single stress conditions, CAT activity were increased in N22, whereas combined stress levels, SOD and APX activity were higher for both genotypes. Proline accumulation was also increased under single as well as combined stress conditions for both genotypes to combat stress injuries. Pollen viability was lost under all stress levels but severe loss was found under combined stress levels, which causes spikelet sterility leading to yield losses for both genotypes. As evident from transcript levels, HSP71.18 and HSP71.10 expressions were higher under single and combined conditions, butHSP72.57 gene expression increased only by individual stress levels. WRKY11, WRKY 55, DREB 2A, LEA3 and DHN1 were positively expressed under all stress levels. Conversely, expression of DREB2B genes was higher only under single stress levels. In summary, these results suggest that the effect of combined stress is different from the single stress and it is more severe than the individual stress.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-03980-1.

Coping with salinity stress: segmental group 7 chromosome introgressions from halophytic Thinopyrum species greatly enhance tolerance of recipient durum wheat

Increased soil salinization, tightly related to global warming and drought and exacerbated by intensified irrigation supply, implies highly detrimental effects on staple food crops such as wheat. The situation is particularly alarming for durum wheat (DW), better adapted to arid/semi-arid environments yet more sensitive to salt stress than bread wheat (BW). To enhance DW salinity tolerance, we resorted to chromosomally engineered materials with introgressions from allied halophytic Thinopyrum species. "Primary" recombinant lines (RLs), having portions of their 7AL arms distally replaced by 7el1L Th. ponticum segments, and "secondary" RLs, harboring Th. elongatum 7EL insertions "nested" into 7el1L segments, in addition to near-isogenic lines lacking any alien segment (CLs), cv. Om Rabia (OR) as salt tolerant control, and BW introgression lines with either most of 7el1 or the complete 7E chromosome substitution as additional CLs, were subjected to moderate (100 mM) and intense (200 mM) salt (NaCl) stress at early growth stages. The applied stress altered cell cycle progression, determining a general increase of cells in G1 and a reduction in S phase. Assessment of morpho-physiological and biochemical traits overall showed that the presence of Thinopyrum spp. segments was associated with considerably increased salinity tolerance versus its absence. For relative water content, Na+ accumulation and K+ retention in roots and leaves, oxidative stress indicators (malondialdehyde and hydrogen peroxide) and antioxidant enzyme activities, the observed differences between stressed and unstressed RLs versus CLs was of similar magnitude in "primary" and "secondary" types, suggesting that tolerance factors might reside in defined 7el1L shared portion(s). Nonetheless, the incremental contribution of 7EL segments emerged in various instances, greatly mitigating the effects of salt stress on root and leaf growth and on the quantity of photosynthetic pigments, boosting accumulation of compatible solutes and minimizing the decrease of a powerful antioxidant like ascorbate. The seemingly synergistic effect of 7el1L + 7EL segments/genes made "secondary" RLs able to often exceed cv. OR and equal or better perform than BW lines. Thus, transfer of a suite of genes from halophytic germplasm by use of fine chromosome engineering strategies may well be the way forward to enhance salinity tolerance of glycophytes, even the sensitive DW.

Study of cabbage antioxidant system response on early infection stage of Xanthomonas campestris pv. campestris

Black rot, caused by Xanthomonas campestris pv. campestris (Xcc) significantly affects the production of cabbage and other cruciferous vegetables. Plant antioxidant system plays an important role in pathogen invasion and is one of the main mechanisms underlying resistance to biological stress. Therefore, it is important to study the resistance mechanisms of the cabbage antioxidant system during the early stages of Xcc. In this study, 108 CFU/mL (OD600 = 0.1) Xcc race1 was inoculated on "zhonggan 11" cabbage using the spraying method. The effects of Xcc infection on the antioxidant system before and after Xcc inoculation (0, 1, 3, and 5 d) were studied by physiological indexes determination, transcriptome and metabolome analyses. We concluded that early Xcc infection can destroy the balance of the active oxygen metabolism system, increase the generation of free radicals, and decrease the scavenging ability, leading to membrane lipid peroxidation, resulting in the destruction of the biofilm system and metabolic disorders. In response to Xcc infection, cabbage clears a series of reactive oxygen species (ROS) produced during Xcc infection via various antioxidant pathways. The activities of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) increased after Xcc infection, and the ROS scavenging rate increased. The biosynthesis of non-obligate antioxidants, such as ascorbic acid (AsA) and glutathione (GSH), is also enhanced after Xcc infection. Moreover, the alkaloid and vitamin contents increased significantly after Xcc infection. We concluded that cabbage could resist Xcc invasion by maintaining the stability of the cell membrane system and improving the biosynthesis of antioxidant substances and enzymes after infection by Xcc. Our results provide theoretical basis and data support for subsequent research on the cruciferous vegetables resistance mechanism and breeding to Xcc.

Sensitivity and responses of chloroplasts to salt stress in plants

Chloroplast, the site for photosynthesis and various biochemical reactions, is subject to many environmental stresses including salt stress, which affects chloroplast structure, photosynthetic processes, osmotic balance, ROS homeostasis, and so on. The maintenance of normal chloroplast function is essential for the survival of plants. Plants have developed different mechanisms to cope with salt-induced toxicity on chloroplasts to ensure the normal function of chloroplasts. The salt tolerance mechanism is complex and varies with plant species, so many aspects of these mechanisms are not entirely clear yet. In this review, we explore the effect of salinity on chloroplast structure and function, and discuss the adaptive mechanisms by which chloroplasts respond to salt stress. Understanding the sensitivity and responses of chloroplasts to salt stress will help us understand the important role of chloroplasts in plant salt stress adaptation and lay the foundation for enhancing plant salt tolerance.

Exogenous application of ascorbic acid improves physiological and productive traits of Nigella sativa

For thousands of years, plants have been utilized for medicinal purposes. For its naturally existing antibacterial properties, Nigella sativa is one of the most researched herbs. A study was conducted during rabi 2020-21 at The University of Haripur in order to evaluate the potential of ascorbic acid as plant growth enhancer. Two concentrations of ascorbic acid i-e 350 μm and 400 μm were sprayed along with control and water only spray on Nigella sativa crop. The study was arranged in RCBD two factor factorial arrangement. Factor A: ascorbic acid concentrations along with control and water spray, factor B: Growth stages (Stage1 = 40 days after sowing, Stage 2 = 80 DAS, Stage 3 = 120 DAS, Stage 4 = 40 + 80 DAS, Stage 5 = 40 + 120 DAS, Stage 6 = 80 + 120 DAS, Stage 7 = 40 + 80 + 120 DAS). Crop was sown in first week of November. Results reviled that chlorophyll b content, fixed oil content, 1000 seed weight, grain yield, Photosynthetic rate (μ mole m-2s-1), Transpiration rate (mmole m-2s-1), photosynthetic water use efficiency, Internal CO2 concentration (Ci) of leaf tissue and Stomatal conductance (mmole m-2s-1) were significantly affected by ascorbic acid concentrations and stage of application. Crop growth rate increased by 19.88% and 17.29%, chlorophyll b by 12.3% and 11.2%, fixed oil by 11.7% and 9%, grain yield by 10.29% and 9.8%, harvest index by 4% and 5.7% photosynthetic rate by 33%, 20% and stomatal conductance by 24.24% and 24.25 with application of ascorbic acid @ 350 μm, over control and water spray respectively. On the basis of these results it is concluded that application of ascorbic acid at the rate of 350 μm, followed by ascorbic acid at the rate of 400 μm significantly improves black cumin (Nigella sativa) yield and production. Hence it is recommended to apply ascorbic acid at the rate of 350 μm at 40 + 80+120 days after sowing of Nigella sativa crop for obtaining maximum results.

ATP homeostasis and signaling in plants

ATP is the primary form of energy for plants, and a shortage of cellular ATP is generally acknowledged to pose a threat to plant growth and development, stress resistance, and crop quality. The overall metabolic processes that contribute to the ATP pool, from production, dissipation, and transport to elimination, have been studied extensively. Considerable evidence has revealed that in addition to its role in energy supply, ATP also acts as a regulatory signaling molecule to activate global metabolic responses. Identification of the eATP receptor DORN1 contributed to a better understanding of how plants cope with disruption of ATP homeostasis and of the key points at which ATP signaling pathways intersect in cells or whole organisms. The functions of SnRK1α, the master regulator of the energy management network, in restoring the equilibrium of the ATP pool have been demonstrated, and the vast and complex metabolic network mediated by SnRK1α to adapt to fluctuating environments has been characterized. This paper reviews recent advances in understanding the regulatory control of the cellular ATP pool and discusses possible interactions among key regulators of ATP-pool homeostasis and crosstalk between iATP/eATP signaling pathways. Perception of ATP deficit and modulation of cellular ATP homeostasis mediated by SnRK1α in plants are discussed at the physiological and molecular levels. Finally, we suggest future research directions for modulation of plant cellular ATP homeostasis.

CbMYB108 integrates the regulation of diterpene biosynthesis and trichome development in Conyza blinii against UV-B

Plants synthesize abundant terpenes through glandular trichomes (GTs), thereby protecting themselves from environmental stresses and increasing the economic value in some medicinal plants. However, the potential mechanisms for simultaneously regulating terpenes synthesis and GTs development remain unclear. Here, we showed that terpenes in Conyza blinii could be synthesized through capitate GTs. By treating with appropriate intensity of UV-B, the density of capitate GTs and diterpene content can be increased. Through analyzing corresponding transcriptome, we identified a MYB transcription factor CbMYB108 as a positive regulator of both diterpene synthesis and capitate GT density. Transiently overexpressing/silencing CbMYB108 on C. blinii leaves could increase diterpene synthesis and capitate GT density. Further verification showed that CbMYB108 upregulated CbDXS and CbGGPPS expression in diterpene synthesis pathway. Moreover, CbMYB108 could also upregulated the expression of CbTTG1, key WD40 protein confirmed in this study to promote GT development, rather than through interaction between CbMYB108 and CbTTG1 proteins. Thus, results showed that the UV-B-induced CbMYB108 owned dual-function of simultaneously improving diterpene synthesis and GT development. Our research lays a theoretical foundation for cultivating C. blinii with high terpene content, and broadens the understanding of the integrated mechanism on terpene synthesis and GT development in plants.

Two gene clusters and their positive regulator SlMYB13 that have undergone domestication-associated negative selection control phenolamide accumulation and drought tolerance in tomato

Among plant metabolites, phenolamides, which are conjugates of hydroxycinnamic acid derivatives and polyamines, play important roles in plant adaptation to abiotic and biotic stresses. However, the molecular mechanisms underlying phenolamide metabolism and regulation as well as the effects of domestication and breeding on phenolamide diversity in tomato remain largely unclear. In this study, we performed a metabolite-based genome-wide association study and identified two biosynthetic gene clusters (BGC7 and BGC11) containing 12 genes involved in phenolamide metabolism, including four biosynthesis genes (two 4CL genes, one C3H gene, and one CPA gene), seven decoration genes (five AT genes and two UGT genes), and one transport protein gene (DTX29). Using gene co-expression network analysis we further discovered that SlMYB13 positively regulates the expression of two gene clusters, thereby promoting phenolamide accumulation. Genetic and physiological analyses showed that BGC7, BGC11 and SlMYB13 enhance drought tolerance by enhancing scavenging of reactive oxygen species and increasing abscisic acid content in tomato. Natural variation analysis suggested that BGC7, BGC11 and SlMYB13 were negatively selected during tomato domestication and improvement, leading to reduced phenolamide content and drought tolerance of cultivated tomato. Collectively, our study discovers a key mechanism of phenolamide biosynthesis and regulation in tomato and reveals that crop domestication and improvement shapes metabolic diversity to affect plant environmental adaptation.

Evolutionary expansion, functional diversification, and transcript profiling of plant Glutathione Peroxidases

Glutathione peroxidases (GPXs) play a crucial role in combating activated oxygen species and have been widely studied for their involvement in stress responses. In addition to their stress-related functions, GPXs exhibit diverse roles such as immunological response, and involvement in growth and development. These enzymes are found in both animals and plants, with multiple families identified in the evolutionarily diverse species. These families consist of conserved genes as well as unique members, highlighting the evolutionary diversification of GPX members. While animals have eight GPX families, plants possess five families. Notably, plant genomes undergo duplication and expansion events, leading to an increase in the number of GPX genes and the overall size of the GPX superfamily. This expansion suggests a wide range of functional roles for GPX. In this study, the evolutionary diversification, family expansion, and diverse functional roles of GPX enzymes have been investigated. Additionally, the expression profile of Arabidopsis and Oryza sativa GPX genes were analyzed in different developmental stages, tissues, and abiotic stress conditions. Further extensive research has been required to unravel the intricate interplay between GPX and other proteins, to gain the comprehensive mechanism governing the physiological and developmental roles of GPX.

NADPH oxidase-mediated reactive oxygen species, antioxidant isozymes, and redox homeostasis regulate salt sensitivity in maize genotypes

The aim of the study is to examine the relationship between oxidative bursts, their regulation with ion homeostasis, and NADPH oxidase (NOX) in different salt-sensitive maize genotypes. For this, in the first study, four differently salt-sensitive maize genotypes (BIL214 × BIL218 as tolerant, BHM-5 as sensitive, and BHM-7 and BHM-9 as moderate-tolerant) were selected on the basis of phenotype, histochemical detection of reactive oxygen species (ROS), malondialdehyde (MDA) content, and specific and in-gel activity of NOX. In the next experiment, these genotypes were further examined in 200 mM NaCl solution in half-strength Hoagland media for nine days to study salt-induced changes in NOX activity, ROS accumulation, ion and redox homeostasis, the activity of antioxidants and their isozyme responses, and to find out potential relationships among the traits. Methylglyoxal (MG) and glyoxalse enzymes (Gly I and II) were also evaluated. Fully expanded leaf samplings were collected at 0 (control), 3, 6, 9-day, and after 7 days of recovery to assay different parameters. Na+/K+, NOX, ROS, and MDA contents increased significantly with the progression of stress duration in all maize genotypes, with a significantly higher value in BHM-5 as compared to tolerant and moderate-tolerant genotypes. A continual induction of Cu/Zn-SOD was observed in BIL214 × BIL218 due to salt stress. Substantial decreases in CAT2 and CAT3 isozymes in BHM-5 might be critical for the highest H2O2 burst in that sensitive genotype under salt stress. The highest intensified POD isozymes were visualized in BHM-5, BHM-7, and BHM-9, whereas BIL214 × BIL218 showed a continual induction of POD isozymes, although GPX activity decreased in all the genotypes at 9 days. Under salt stress, the tolerant genotype BIL214 × BIL218 showed superior ASA- and GSH-redox homeostasis by keeping GR and MDHAR activity high. This genotype also had a stronger MG detoxification system by having higher glyoxalase activity. Correlation, comparative heatmap, and PCA analyses revealed positive correlations among Na+/K+, NOX, O2•-, H2O2, MG, proline, GR, GST, and Gly I activities. Importantly, the relationship depends on the salt sensitivity of the genotypes. The reduced CAT activity as well as redox homeostasis were critical to the survival of the sensitive genotype.

Plant secondary metabolites involved in the stress tolerance of long-lived trees

Ancient trees are natural wonders because of their longevity, having lived for hundreds or thousands of years, and their ability to withstand changing environments and a variety of stresses. These long-lived trees have sophisticated defense mechanisms, such as the production of specialized plant metabolites (SPMs). In this review, we provide an overview of the major biotic and abiotic stresses that long-lived trees often face, as well as an analysis of renowned ancient tree species and their unique protective SPMs against environmental stressors. We also discuss the synthesis and accumulation of defensive SPMs induced by environmental factors and endophytes in these trees. Furthermore, we conducted a comparative genomic analysis of 17 long-lived tree species and discovered significant expansions of SPM biosynthesis gene families in these species. Our comprehensive review reveals the crucial role of SPMs in high resistance in long-lived trees, providing a novel natural resource for plant defense, crop improvement and even the pharmaceutical industry.

Types of Membrane Transporters and the Mechanisms of Interaction between Them and Reactive Oxygen Species in Plants

Membrane transporters are proteins that mediate the entry and exit of substances through the plasma membrane and organellar membranes and are capable of recognizing and binding to specific substances, thereby facilitating substance transport. Membrane transporters are divided into different types, e.g., ion transporters, sugar transporters, amino acid transporters, and aquaporins, based on the substances they transport. These membrane transporters inhibit reactive oxygen species (ROS) generation through ion regulation, sugar and amino acid transport, hormone induction, and other mechanisms. They can also promote enzymatic and nonenzymatic reactions in plants, activate antioxidant enzyme activity, and promote ROS scavenging. Moreover, membrane transporters can transport plant growth regulators, solute proteins, redox potential regulators, and other substances involved in ROS metabolism through corresponding metabolic pathways, ultimately achieving ROS homeostasis in plants. In turn, ROS, as signaling molecules, can affect the activity of membrane transporters under abiotic stress through collaboration with ions and involvement in hormone metabolic pathways. The research described in this review provides a theoretical basis for improving plant stress resistance, promoting plant growth and development, and breeding high-quality plant varieties.

Regulation of chloroplast biogenesis, development, and signaling by endogenous and exogenous cues

Chloroplasts are one of the defining features in most plants, primarily known for their unique property to carry out photosynthesis. Besides this, chloroplasts are also associated with hormone and metabolite productions. For this, biogenesis and development of chloroplast are required to be synchronized with the seedling growth to corroborate the maximum rate of photosynthesis following the emergence of seedlings. Chloroplast biogenesis and development are dependent on the signaling to and from the chloroplast, which are in turn regulated by several endogenous and exogenous cues. Light and hormones play a crucial role in chloroplast maturation and development. Chloroplast signaling involves a coordinated two-way connection between the chloroplast and nucleus, termed retrograde and anterograde signaling, respectively. Anterograde and retrograde signaling are involved in regulation at the transcriptional level and downstream modifications and are modulated by several metabolic and external cues. The communication between chloroplast and nucleus is essential for plants to develop strategies to cope with various stresses including high light or high heat. In this review, we have summarized several aspects of chloroplast development and its regulation through the interplay of various external and internal factors. We have also discussed the involvement of chloroplasts as sensors of various external environment stress factors including high light and temperature, and communicate via a series of retrograde signals to the nucleus, thus playing an essential role in plants' abiotic stress response.

Unveiling differential expression profiles of the wheat DOG1 gene family and functional analysis of the association between TaDOG1-1 and heat stress tolerance in transgenic Arabidopsis

High temperatures can significantly impact wheat growth and grain yields during the grain-filling stage. In this study, we identified genes that respond to high-temperature stress during the grain-filling stage. We also identified and characterized 24 novel genes of the DOG1 gene family in hexaploid wheat. Motif analysis and conserved domain search revealed substantial similarities among TaDOG1 family members. Phylogenetic analysis demonstrated the evolutionary conservation of the TaDOG1 family across various plant species. Tissue-specific expression profiling indicated consistent patterns, with TaDOG1 genes predominantly expressed in stem tissues. Only TaDOG1-1 exhibited enhanced expression, particularly during hard dough and ripening stages. TaDOG1-1 and TaDOG1-7 exhibited increased expression under heat stress during the grain-filling stage, indicating their heat-responsive nature. Cis-element analysis revealed potential regulatory motifs, suggesting the involvement of TaDOG1-1 and TaDOG1-7 in stress tolerance mechanisms. Yeast two-hybrid screening revealed interacting proteins, including stress-responsive and grain development-associated proteins. To understand the biological function, we overexpressed TaDOG1-1 in Arabidopsis plants and observed enhanced thermotolerance under basal heat stress. Under heat stress, the transgenic plants exhibited increased biomass and elevated expression levels of heat-responsive genes. Furthermore, TaDOG1-1-overexpressing plants showed improved survival rates under soil heat stress, along with a greater accumulation of antioxidant enzymes in leaves. In this study, the identification and functions of the DOG1 gene family provide valuable insights for developing genetic engineering strategies aimed at improving wheat yield under high-temperature stress.

MdbHLH160 is stabilized via reduced MdBT2-mediated degradation to promote MdSOD1 and MdDREB2A-like expression for apple drought tolerance

Drought stress is a key environmental factor limiting the productivity, quality, and geographic distribution of crops worldwide. Abscisic acid (ABA) plays an important role in plant drought stress responses, but the molecular mechanisms remain unclear. Here, we report an ABA-responsive bHLH transcription factor, MdbHLH160, which promotes drought tolerance in Arabidopsis (Arabidopsis thaliana) and apple (Malus domestica). Under drought conditions, MdbHLH160 is directly bound to the MdSOD1 (superoxide dismutase 1) promoter and activated its transcription, thereby triggering reactive oxygen species (ROS) scavenging and enhancing apple drought tolerance. MdbHLH160 also promoted MdSOD1 enzyme activity and accumulation in the nucleus through direct protein interactions, thus inhibiting excessive nuclear ROS levels. Moreover, MdbHLH160 directly upregulated the expression of MdDREB2A-like, a DREB (dehydration-responsive element binding factor) family gene that promotes apple drought tolerance. Protein degradation and ubiquitination assays showed that drought and ABA treatment stabilized MdbHLH160. The BTB protein MdBT2 was identified as an MdbHLH160-interacting protein that promoted MdbHLH160 ubiquitination and degradation, and ABA treatment substantially inhibited this process. Overall, our findings provide insights into the molecular mechanisms of ABA-modulated drought tolerance at both the transcriptional and post-translational levels via the ABA-MdBT2-MdbHLH160-MdSOD1/MdDREB2A-like cascade.

Impact of induced mutation-derived genetic variability, genotype and varieties for quantitative and qualitative traits in Mentha species

PURPOSE

The genus Mentha spp. is an aromatic herb from the family 'Lamiaceae'. It is extensively predominant in temperate and sub-temperate regions of the world. The essential oil of this species is enriched with broad aroma constituents extensively utilized in food, beverages, flavor, cosmetics, perfumery, and pharmaceutical enterprises. With the global menthol market size estimated to be worth USD 765 million in 2022, India (accompanied by China and Brazil) is the world's primary manufacturer, consumer, and exporter of Mentha oil. Despite prominent global demand, the crucial bottleneck in mint cultivation is the need for more superior commercial cultivars. Predominant vegetative propagation mode with difficulties in manual emasculation, differential blooming times, sterile/sub-sterile hybrids, and low seed viability are the primary containment in creating genetic variability by classical breeding approaches. Therefore, genetic complications encountered in conventional breeding have led the breeders to apply mutation breeding as an alternative crop improvement approach in Mentha spp. These attempts at mutation breeding have produced some distinctive mutants as genetic pools for plant breeding programs, and some novel mutant mint cultivars have been made available for commercial cultivation.

CONCLUSIONS

The prime strategy in mutation-based breeding has proven an adept means of encouraging the expression of recessive genes and producing new genetic variations. The present review comprises a significant contribution of mutation breeding approaches in the development of mutant mint species and its effects on physiological variation, photosynthetic pigment, essential oil content and composition, phytochemical-mediated defense response, pathogen resistivity, and differential expression of genes related to terpenoid biogenesis. Development and diversification have led to the release of varieties, namely Todd's Mitcham, Murray Mitcham, Pranjal, Tushar, and Kukrail in M. piperita L., Mukta, and Pratik in M. cardiaca Baker, Neera in M. spicata L., Kiran in M. citrata Ehrh., and Rose mint in M. arvensis L. that have revolutionized and uplifted mint cultivation leading to economic gain by the farmers and entrepreneurs.

Metabolic Adaptations in Rapeseed: Hemin-Induced Resilience to NaCl Stress by Enhancing Growth, Photosynthesis, and Cellular Defense Ability

This study aimed to investigate whether presoaking with hemin (5 μmol·L-1) could alleviate NaCl stress during rapeseed seedlings' growth and its role in the regulation of photosynthesis. In this experiment, 'HUAYOUZA 62 (HYZ 62)' and 'HUAYOUZA 158R (158R)' were used as materials for pot experiments to study the morphology, photosynthetic characteristics, antioxidant activity, and osmoregulatory factors of seedlings under different salt concentrations, as well as the regulatory effects of hemin-presoaked seeds. Our findings revealed that, compared the control, NaCl stress inhibited the growth of two rapeseed varieties, decreased the seedling emergence rate, and increased the content of malondialdehyde (MDA), the electrolyte leakage rate (EL) and antioxidant enzyme activity. Hemin soaking alleviated the adverse effects of salt stress and increased plant height, root elongation and dry matter accumulation. Compared with all NaCl treatments, hemin significantly enhanced photosynthetic indexes, including a percent increase of 12.99-24.36% and 5.39-16.52% in net photosynthetic rate (Pn), 17.86-48.08% and 8.6-23.44% in stomatal conductivity (Gs), and 15.42-37.94% and 11.09-19.08% in transpiration rate (Tr) for HYZ62 and 158R, respectively. Moreover, hemin soaking also increased antioxidant enzyme activities, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX), reducing the malondialdehyde, and thus resulting in the alleviation of oxidative damage caused by NaCl stress. Furthermore, hemin stimulated the formation of soluble protein, which effectively regulated the osmo-protective qualities. The current findings strongly elucidate that hemin soaking could effectively alleviate the negative impacts of NaCl stress by regulating the morphological, photosynthetic, and antioxidant traits. This study provides a new idea regarding the effect of Hemin on the salt tolerance of rapeseed, and provides a basis for the practical application of Hemin in saline-alkali soil to improve the salt tolerance of cultivated rapeseed.

A novel R2R3-MYB transcription factor PbMYB1L of Pyrus bretschneideri regulates cold tolerance and anthocyanin accumulation

KEY MESSAGE

PbMYB1L enhances the cold tolerance and anthocyanin accumulation of transgenic Arabidopsis by regulating the expression of genes related to the cold-responsive genes pathway and anthocyanin synthesis pathway. MYB transcription factors (TFs) have been demonstrated to play diverse roles in plant growth and development. In the present study, we identified a novel R2R3-MYB transcription factor, PbMYB1L, from the peel of 'Red Zaosu' pear (Pyrus bretschneideri), which was induced by cold stress and acted as a positive regulator in anthocyanin biosynthesis. Notably, the transgenic Arabidopsis lines exhibited enhanced tolerance to cold stress. Compared to the Arabidopsis wild-type plants, the transgenic lines displayed longer primary roots and reduced reactive oxygen species (ROS) levels including O2-, hydrogen peroxide (H2O2), and malondialdehyde (MDA). Furthermore, significant upregulation of key cold-responsive genes AtCBF1, AtCBF2, AtCBF3, AtCBF4, and AtKIN1 was observed in the transgenic plants under cold stress conditions compared to wild type. Arabidopsis plants overexpressing PbMYB1L had significant anthocyanin accumulation in leaves after cold treatment with quantitative results indicating higher expression of anthocyanin structural genes compared to wild type. These findings suggest that PbMYB1L not only plays a vital role in conferring cold tolerance but also acts as a crucial regulator of anthocyanin biosynthesis.

Adaptive responses of eelgrass (Zostera marina L.) to ocean warming and acidification

Ocean warming (OW) and ocean acidification (OA), driven by rapid global warming accelerating at unprecedented rates, are profoundly impacting the stability of seagrass ecosystems. Yet, our current understanding of the effects of OW and OA on seagrass remains constrained. Herein, we investigated the response of eelgrass (Zostera marina L.), a representative seagrass species, to OW and OA through comprehensive transcriptomic and metabolomic analyses. The results showed notable variations in plant performance under varying conditions: OW, OA, and OWA (a combination of both conditions). Specifically, under average oceanic temperature conditions for eelgrass growth over the past 20 years -from May to November-OA promoted the production of differentially expressed genes and metabolites associated with alanine, aspartate, and glutamate metabolism, as well as starch and sucrose metabolism. Under warming condition, eelgrass was resistant to OA by accelerating galactose metabolism, along with glycine, serine, and threonine metabolism, as well as the tricarboxylic acid (TCA) cycle. Under the combined OW and OA condition, eelgrass stimulated fructose and mannose metabolism, glycolysis, and carbon fixation, in addition to galactose metabolism and the TCA cycle to face the interplay. Our findings suggest that eelgrass exhibits adaptive capacity by inducing different metabolites and associated genes, primarily connected with carbon and nitrogen metabolism, in response to varying degrees of OW and OA. The data generated here support the exploration of mechanisms underlying seagrass responses to environmental fluctuations, which hold critical significance for the future conservation and management of these ecosystems.

Peroxisome dynamics determines host-derived ROS accumulation and infectious growth of the rice blast fungus

IMPORTANCE

The interplay between plant and pathogen is a dynamic process, with the host's innate defense mechanisms serving a crucial role in preventing infection. In response to many plant pathogen infections, host cells generate the key regulatory molecule, reactive oxygen species (ROS), to limit the spread of the invading organism. In this study, we reveal the effects of fungal peroxisome dynamics on host ROS homeostasis, during the rice blast fungus Magnaporthe oryzae infection. The elongation of the peroxisome appears contingent upon ROS and links to the accumulation of ROS within the host and the infectious growth of the pathogen. Importantly, we identify a peroxisomal 3-ketoacyl-CoA thiolase, MoKat2, responsible for the elongation of the peroxisome during the infection. In response to host-derived ROS, the homodimer of MoKat2 undergoes dissociation to bind peroxisome membranes for peroxisome elongation. This process, in turn, inhibits the accumulation of host ROS, which is necessary for successful infection. Overall, our study is the first to highlight the intricate relationship between fungal organelle dynamics and ROS-mediated host immunity, extending the fundamental knowledge of pathogen-host interaction.

Function identification of miR159a, a positive regulator during poplar resistance to drought stress

Drought seriously affects the growth and development of plants. MiR159 is a highly conserved and abundant microRNA family that plays a crucial role in plant growth and stress responses. However, studies of its function in woody plants are still lacking. Here, the expression of miR159a was significantly upregulated after drought treatment in poplar, and the overexpression of miR159a (OX159a) significantly reduced the open area of the stomata and improved water-use efficiency in poplar. After drought treatment, OX159a lines had better scavenging ability of reactive oxygen species and damage of the membrane system was less than that in wild-type lines. MYB was the target gene of miR159a, as verified by psRNATarget prediction, RT-qPCR, degradome sequencing, and 5' rapid amplification of cDNA ends (5' RACE). Additionally, miR159a-short tandem target mimic suppression (STTM) poplar lines showed increased sensitivity to drought stress. Transcriptomic analysis comparing OX159a lines with wild-type lines revealed upregulation of a series of genes related to response to water deprivation and metabolite synthesis. Moreover, drought-responsive miR172d and miR398 were significantly upregulated and downregulated respectively in OX159a lines. This investigation demonstrated that miR159a played a key role in the tolerance of poplar to drought by reducing stomata open area, increasing the number and total area of xylem vessels, and enhancing water-use efficiency, and provided new insights into the role of plant miR159a and crucial candidate genes for the molecular breeding of trees with tolerance to drought stress.

EMS-induced mutagenesis in Choy sum (Brassica chinensis var. parachinensis) and selection for low light tolerance using abiotic stress indices

BACKGROUND

Choy Sum (Brassica rapa ssp. chinensis var. parachinensis), grown in a controlled environment, is vulnerable to changes in indoor light quality and displays distinct photo-morphogenesis responses. The scarcity of Choy Sum germplasm for indoor cultivation necessitates the development of new cultivars. Hence, this study attempted to develop mutants through chemical mutagenesis and select low-light-tolerant mutants by using abiotic stress tolerance indices.

RESULTS

A mutant population of Choy Sum created using 1.5% ethyl methane sulfonate (EMS) at 4 h was manually pollinated to obtain the M2 generation. 154 mutants with reduced hypocotyl length were initially isolated from 3600 M2 seedlings screened under low light (R: FR = 0.5). Five mutants that showed reduced plant height at mature stages were selected and screened directly for shade tolerance in the M3 generation. Principal component analysis based on phenotypic data distinguished the M3 mutants from the wild type. Abiotic stress tolerance indices such as relative stress index (RSI), stress tolerance index (STI), geometric mean productivity (GMP), yield stability index (YSI), and stress resistance index (SRI) showed significant (P < 0.05), and positive associations with leaf yield under shade. M3-12-2 was selected as a shade-tolerant mutant based on high values of STI, YSI, and SRI with low values for tolerance (TOL) and stress susceptibility index (SSI).

CONCLUSIONS

The results demonstrate that mutation breeding can be used to create dominant mutants in Choy Sum. Furthermore, we show that screening for low light and selection based on abiotic tolerance indices allowed the identification of mutants with high resilience under shade. This method should apply to developing new cultivars in other crop plants that can be suitable for controlled environments with stable yield performance.

HSF and Hsp Gene Families in sunflower: a comprehensive genome-wide determination survey and expression patterns under abiotic stress conditions

Sunflowers belong to the Asteraceae family, which comprises nutrimental and economic oilseed plants. Heat shock proteins (Hsps) are protein families vital for all organisms' growth and survival. Besides the ordinary conditions, the expression of these proteins ascends during abiotic stress factors such as high temperature, salinity, and drought. Using bioinformatics approaches, the current study identified and analyzed HSF and Hsp gene family members in the sunflower (Helianthus annuus L.) plant. HSF, sHsp, Hsp40, Hsp60, Hsp70, Hsp90, and Hsp100 domains were analyzed in the sunflower genome, and 88, 72, 192, 52, 85, 49, and 148 genes were identified, respectively. The motif structures of the proteins in the same phylogenetic tree were similar, and the α-helical form was dominant in all the protein families except for sHsp. The estimated three-dimensional structure of 28 sHsp proteins was determined as β-sheets. Considering protein-protein interactions, the Hsp60-09 protein (38 interactions) was found to be the most interacting protein. The most orthologous gene pairs (58 genes) were identified between Hsp70 genes and Arabidopsis genes. The expression analysis of selected genes was performed under high temperature, drought, and high temperature-drought combined stress conditions in two sunflower cultivars. In stress conditions, gene expressions were upregulated for almost all genes in the first half and first hours at large. The expressions of HanHSF-45 and HanHsp70-29 genes were raised in two cultivars under high temperature and high temperature-drought combined stress conditions. This study presents a blueprint for subsequent research and delivers comprehensive knowledge of this vital protein domain.

Negative regulation of tobacco cold stress tolerance by NtPhyA

Cold stress is a non-biological stressor that adversely affects tobacco yield and leaf quality. Plant photoreceptor proteins, which function as dual light-temperature sensors, play a vital role in temperature changes, making them crucial for responses to non-biological stressors. However, the regulatory mechanisms of PhyA in tobacco remain poorly understood. Therefore, in this study, we aimed to clone the NtPhyA gene from tobacco and generate overexpression (OE-NtPhyA) and mutant (KO-NtPhyA) constructs of NtPhyA. By assessing the physiological and biochemical responses of the mutants under cold stress and performing transcriptome sequencing, we determined the signalling mechanism of NtPhyA under cold stress. Comparative analysis with wild-type (WT) NtPhyA revealed that KO-NtPhyA exhibited increased seed germination rates and reduced wilting under cold stress. In additional, the degree of damage to leaf cells, cell membranes, and stomatal structures was mitigated, and the levels of reactive oxygen species (ROS) were significantly decreased. Antioxidant enzyme activity, net photosynthetic rate, and Fv/Fm were significantly enhanced in KO-NtPhyA, whereas the opposite effects were observed in OE-NtPhyA. These findings indicate that KO-NtPhyA augments tobacco tolerance to cold stress, implying a negative regulatory role of NtPhyA in tobacco during cold stress. Transcriptome analysis revealed that NtPhyA governs the expression of a cascade of genes involved in the response to oxygen-containing compounds, hydrogen peroxide (H2O2), ROS, temperature stimuli, photosystem II oxygen-evolving complex assembly, water channel activity, calcium channel activity, and carbohydrate transport. Collectively, our findings indicate that NtPhyA activates downstream gene expression to enhance the resilience of tobacco to cold stress.

Dark septate endophyte inoculation enhances antioxidant activity in Astragalus membranaceus var. mongholicus under heat stress

The influence of dark septate endophytic (DSE) on the antioxidant activity of Astragalus membranaceus var. mongholicus under heat stress was investigated. A. membranaceus plants, with or without DSE inoculation, were grown at 28°C for 8 weeks in a greenhouse and subsequently subjected to heat stress conditions (42°C) in an artificial climate chamber. DSE inoculation significantly decreased the malondialdehyde (MDA) content during the initial three days of heat stress. The activities of superoxide dismutase (SOD) and peroxidase (POD) of A. membranaceus leaves were significantly enhanced by DSE inoculation under heat stress, with SOD activities being 63-81% higher than in other treatments. The glutathione (GSH) and putrescine (Put) contents accumulated significantly on the third day under heat stress with DSE inoculation. Additionally, the contents of soluble sugars and proline (Pro) exhibited significant increases on the seventh day of heat stress and were 33-55% and 81-83% higher than in other treatments, respectively. Three-way ANOVA shows that DSE inoculation under heat stress exerted a significant impact on MDA. Multivariate linear regression and structural equality modelling (SEM) further show that the interaction among these antioxidants significantly decreased MDA content and maintained the normal function of cell membranes. In conclusion, DSE inoculation enhanced the heat tolerance of A. membranaceus by boosting its antioxidant capacity and reducing MDA production. This study highlights the potential of utilizing DSE as a strategy to enhance plant heat tolerance.

Identification of ascorbate- and salicylate-responsive miRNAs and verification of the spectral control of miR395 in Arabidopsis

We assumed that miRNAs might regulate the physiological and biochemical processes in plants through their effects on the redox system and phytohormones. To check this hypothesis, the transcriptome profile of wild-type Arabidopsis and lines with decreased ascorbate (Asc), glutathione (GSH), or salicylate (Sal) levels were compared. GSH deficiency did not influence the miRNA expression, whereas lower levels of Asc and Sal reduced the accumulation of 9 and 44 miRNAs, respectively, but only four miRNAs were upregulated. Bioinformatics analysis revealed that their over-represented target genes are associated with the synthesis of nitrogen-containing and aromatic compounds, nucleic acids, and sulphate assimilation. Among them, the sulphate reduction-related miR395 - ATP-sulfurylase couple was selected to check the assumed modulating role of the light spectrum. A greater induction of the Asc- and Sal-responsive miR395 was observed under sulphur starvation in far-red light compared to white and blue light in wild-type and GSH-deficient Arabidopsis lines. Sal deficiency inhibited the induction of miR395 by sulphur starvation in blue light, whereas Asc deficiency greatly reduced it independently of the spectrum. Interestingly, sulphur starvation decreased only the level of ATP sulfurylase 4 among the miR395 target genes in far-red light. The expression level of ATP sulfurylase 3 was higher in far-red light than in blue light in wild-type and Asc-deficient lines. The results indicate the coordinated control of miRNAs by the redox and hormonal system since 11 miRNAs were affected by both Asc and Sal deficiency. This process can be modulated by light spectrum, as shown for miR395.

Deficiency in NDH-cyclic electron transport retards heat acclimation of photosynthesis in tobacco over day and night shift

In order to cope with the impact of global warming and frequent extreme weather, thermal acclimation ability is particularly important for plant development and growth, but the mechanism behind is still not fully understood. To investigate the role of NADH dehydrogenase-like complex (NDH) mediated cyclic electron flow (CEF) contributing to heat acclimation, wild type (WT) tobacco (Nicotiana tabacum) and its NDH-B or NDH-C, J, K subunits deficient mutants (ΔB or ΔCJK) were grown at 25/20°C before being shifted to a moderate heat stress environment (35/30°C). The photosynthetic performance of WT and ndh mutants could all eventually acclimate to the increased temperature, but the acclimation process of ndh mutants took longer. Transcriptome profiles revealed that ΔB mutant exhibited distinct photosynthetic-response patterns and stress-response genes compared to WT. Metabolite analysis suggested over-accumulated reducing power and production of more reactive oxygen species in ΔB mutant, which were likely associated with the non-parallel recovery of CO2 assimilation and light reactions shown in ΔB mutant during heat acclimation. Notably, in the warm night periods that could happen in the field, NDH pathway may link to the re-balance of excess reducing power accumulated during daytime. Thus, understanding the diurnal cycle contribution of NDH-mediated CEF for thermal acclimation is expected to facilitate efforts toward enhanced crop fitness and survival under future climates.

Overexpression of PsAMT1.2 in poplar enhances nitrogen utilization and resistance to drought stress

Ammonium is an important form of inorganic nitrogen, which is essential for plant growth and development, and the uptake of ammonium is mediated by different members of ammonium transporters (AMTs). It is reported that PsAMT1.2 is specially expressed in the root of poplar, and the overexpression of PsAMT1.2 could improve plant growth and the salt tolerance of poplar. However, the role of AMTs in plant drought and low nitrogen (LN) resistance remains unclear. To understand the role of PsAMT1.2 in drought and LN tolerance, the response of PsAMT1.2-overexpression poplar to polyethylene glycol (PEG)-simulated drought stress (5% PEG) under LN (0.001 mM NH4NO3) and moderate nitrogen (0.5 mM NH4NO3) conditions was investigated. The PsAMT1.2-overexpression poplar showed better growth with increased stem increment, net photosynthetic rate, chlorophyll content, root length, root area, average root diameter and root volume under drought and/or LN stress compared with the wild type (WT). Meanwhile, the content of malondialdehyde significantly decreased, and the activities of superoxide dismutase and catalase significantly increased in the roots and leaves of PsAMT1.2-overexpression poplar compared with WT. The content of NH4+ and NO2- in the roots and leaves of PsAMT1.2-overexpression poplar was increased, and nitrogen metabolism-related genes, such as GS1.3, GS2, Fd-GOGAT and NADH-GOGAT, were significantly upregulated in the roots and/or leaves of PsAMT1.2-overexpression poplar compared with WT under drought and LN stress. The result of this study would be helpful for understanding the function of PsAMT1.2 in plant drought and LN tolerance and also provides a new insight into improving the drought and LN tolerance of Populus at the molecular level.

Compartment-specific Ca2+ imaging in the green alga Chlamydomonas reinhardtii reveals high light-induced chloroplast Ca2+ signatures

To investigate the role of intracellular Ca2+ signaling in the perception and response mechanisms to light in unicellular microalgae, the genetically encoded ratiometric Ca2+ indicator Yellow Cameleon (YC3.6) was expressed in the model organism for green algae Chlamydomonas reinhardtii, targeted to cytosol, chloroplast, and mitochondria. Through in vivo single-cell confocal microscopy imaging, light-induced Ca2+ signaling was investigated in different conditions and different genotypes, including the photoreceptors mutants phot and acry. A genetically encoded H2 O2 sensor was also adopted to investigate the possible role of H2 O2 formation in light-dependent Ca2+ signaling. Light-dependent Ca2+ response was observed in Chlamydomonas reinhardtii cells only in the chloroplast as an organelle-autonomous response, influenced by light intensity and photosynthetic electron transport. The absence of blue and red-light photoreceptor aCRY strongly reduced the light-dependent chloroplast Ca2+ response, while the absence of the blue photoreceptor PHOT had no significant effects. A correlation between high light-induced chloroplast H2 O2 gradients and Ca2+ transients was drawn, supported by H2 O2 -induced chloroplast Ca2+ transients in the dark. In conclusion, different triggers are involved in the light-induced chloroplast Ca2+ signaling as saturation of the photosynthetic electron transport, H2 O2 formation, and aCRY-dependent light perception.

The protein phosphatase PC1 dephosphorylates and deactivates CatC to negatively regulate H2O2 homeostasis and salt tolerance in rice

Catalase (CAT) is often phosphorylated and activated by protein kinases to maintain hydrogen peroxide (H2O2) homeostasis and protect cells against stresses, but whether and how CAT is switched off by protein phosphatases remains inconclusive. Here, we identified a manganese (Mn2+)-dependent protein phosphatase, which we named PHOSPHATASE OF CATALASE 1 (PC1), from rice (Oryza sativa L.) that negatively regulates salt and oxidative stress tolerance. PC1 specifically dephosphorylates CatC at Ser-9 to inhibit its tetramerization and thus activity in the peroxisome. PC1 overexpressing lines exhibited hypersensitivity to salt and oxidative stresses with a lower phospho-serine level of CATs. Phosphatase activity and seminal root growth assays indicated that PC1 promotes growth and plays a vital role during the transition from salt stress to normal growth conditions. Our findings demonstrate that PC1 acts as a molecular switch to dephosphorylate and deactivate CatC and negatively regulate H2O2 homeostasis and salt tolerance in rice. Moreover, knockout of PC1 not only improved H2O2-scavenging capacity and salt tolerance but also limited rice grain yield loss under salt stress conditions. Together, these results shed light on the mechanisms that switch off CAT and provide a strategy for breeding highly salt-tolerant rice.