The impact of multifactorial stress combination on plant growth and survival

The Changes of Amino-Acid Metabolism between Wheat and Rice during Early Growth under Flooding Stress

Floods induce hypoxic stress and reduce wheat growth. On the other hand, rice is a semi-aquatic plant and usually grows even when partially submerged. To clarify the dynamic differences in the cellular mechanism between rice and wheat under flooding stress, morphological and biochemical analyses were performed. Although the growth of wheat in the early stage was significantly suppressed due to flooding stress, rice was hardly affected. Amino-acid analysis revealed significant changes in amino acids involved in the gamma-aminobutyric acid (GABA) shunt and anaerobic/aerobic metabolism. Flood stress significantly increased the contents of GABA and glutamate in wheat compared with rice, though the abundances of glutamate decarboxylase and succinyl semialdehyde dehydrogenase did not change. The abundance of alcohol dehydrogenase and pyruvate carboxylase increased in wheat and rice, respectively. The contents of aspartic acid and pyruvic acid increased in rice root but remained unchanged in wheat; however, the abundance of aspartate aminotransferase increased in wheat root. These results suggest that flooding stress significantly inhibits wheat growth through upregulating amino-acid metabolism and increasing the alcohol-fermentation system compared to rice. When plant growth is inhibited by flooding stress and the aerobic-metabolic system is activated, GABA content increases.

Complexity of responses to ionizing radiation in plants, and the impact on interacting biotic factors

In nature, plants are simultaneously exposed to different abiotic (e.g., heat, drought, and salinity) and biotic (e.g., bacteria, fungi, and insects) stresses. Climate change and anthropogenic pressure are expected to intensify the frequency of stress factors. Although plants are well equipped with unique and common defense systems protecting against stressors, they may compromise their growth and development for survival in such challenging environments. Ionizing radiation is a peculiar stress factor capable of causing clustered damage. Radionuclides are both naturally present on the planet and produced by human activities. Natural and artificial radioactivity affects plants on molecular, biochemical, cellular, physiological, populational, and transgenerational levels. Moreover, the fitness of pests, pathogens, and symbionts is concomitantly challenged in radiologically contaminated areas. Plant responses to artificial acute ionizing radiation exposure and laboratory-simulated or field chronic exposure are often discordant. Acute or chronic ionizing radiation exposure may occasionally prime the defense system of plants to better tolerate the biotic stress or could often exhaust their metabolic reserves, making plants more susceptible to pests and pathogens. Currently, these alternatives are only marginally explored. Our review summarizes the available literature on the responses of host plants, biotic factors, and their interaction to ionizing radiation exposure. Such systematic analysis contributes to improved risk assessment in radiologically contaminated areas.

Surviving a Double-Edged Sword: Response of Horticultural Crops to Multiple Abiotic Stressors

Climate change-induced weather events, such as extreme temperatures, prolonged drought spells, or flooding, pose an enormous risk to crop productivity. Studies on the implications of multiple stresses may vary from those on a single stress. Usually, these stresses coincide, amplifying the extent of collateral damage and contributing to significant financial losses. The breadth of investigations focusing on the response of horticultural crops to a single abiotic stress is immense. However, the tolerance mechanisms of horticultural crops to multiple abiotic stresses remain poorly understood. In this review, we described the most prevalent types of abiotic stresses that occur simultaneously and discussed them in in-depth detail regarding the physiological and molecular responses of horticultural crops. In particular, we discussed the transcriptional, posttranscriptional, and metabolic responses of horticultural crops to multiple abiotic stresses. Strategies to breed multi-stress-resilient lines have been presented. Our manuscript presents an interesting amount of proposed knowledge that could be valuable in generating resilient genotypes for multiple stressors.

The ascorbate-glutathione cycle coming of age

Concepts regarding the operation of the ascorbate-glutathione cycle and the associated water/water cycle in the processing of metabolically generated hydrogen peroxide and other forms of reactive oxygen species (ROS) are well established in the literature. However, our knowledge of the functions of these cycles and their component enzymes continues to grow and evolve. Recent insights include participation in the intrinsic environmental and developmental signalling pathways that regulate plant growth, development, and defence. In addition to ROS processing, the enzymes of the two cycles not only support the functions of ascorbate and glutathione, they also have 'moonlighting' functions. They are subject to post-translational modifications and have an extensive interactome, particularly with other signalling proteins. In this assessment of current knowledge, we highlight the central position of the ascorbate-glutathione cycle in the network of cellular redox systems that underpin the energy-sensitive communication within the different cellular compartments and integrate plant signalling pathways.

Resource allocation modeling for autonomous prediction of plant cell phenotypes

Predicting the plant cell response in complex environmental conditions is a challenge in plant biology. Here we developed a resource allocation model of cellular and molecular scale for the leaf photosynthetic cell of Arabidopsis thaliana, based on the Resource Balance Analysis (RBA) constraint-based modeling framework. The RBA model contains the metabolic network and the major macromolecular processes involved in the plant cell growth and survival and localized in cellular compartments. We simulated the model for varying environmental conditions of temperature, irradiance, partial pressure of CO2 and O2, and compared RBA predictions to known resource distributions and quantitative phenotypic traits such as the relative growth rate, the C:N ratio, and finally to the empirical characteristics of CO2 fixation given by the well-established Farquhar model. In comparison to other standard constraint-based modeling methods like Flux Balance Analysis, the RBA model makes accurate quantitative predictions without the need for empirical constraints. Altogether, we show that RBA significantly improves the autonomous prediction of plant cell phenotypes in complex environmental conditions, and provides mechanistic links between the genotype and the phenotype of the plant cell.

Functional trait correlation network and proteomic analysis reveal multifactorial adaptation mechanisms to a climatic gradient associated with high altitude in the Himalayan region

Globally occurring changes in environmental conditions necessitate extending our knowledge of the system-level mechanisms underlying plant adaptation to multifactorial stress conditions or stress combinations. This is crucial for designing new strategies to maintain plant performance under simultaneous abiotic pressure. Here, we conducted our study at Rohtang Pass and sampled Picrorhiza kurroa leaves along high-altitude gradient (3400, 3800 and 4100 meters above sea level) in the western Himalayas. The results showed the functional traits associated with morpho-anatomical structures and eco-physiological performances are highly variable. The air temperature and relative humidity represent dominant environmental factors among others that significantly regulate plant's physiological performance by adjusting the functional traits in altitude-specific manner. A trait coordination network is developed among significantly altered plant functional traits, which reveals high-altitude associated trait-based adaptation. Moreover, it reveals leaf area shows the highest degree, while photochemical quenching reflects the weighted degree of centrality in the network. Proteomic analysis reveals various stress-responsive proteins, including antioxidants were accumulated to deal with combined stress factors. Furthermore, a high-altitudinal protein interaction network unravels key players of alpine plant adaptation processes. Altogether, these systems demonstrate a complex molecular interaction web extending the current knowledge of high-altitudinal alpine plant adaptation, particularly in an endangered medicinal herb, P. kurroa.

Significance of phosphorus deficiency for the mitigation of mercury toxicity in the Robinia pseudoacacia L.- rhizobia symbiotic association

Nitrogen (N2)-fixing legumes can be used for phytoremediation of toxic heavy metal Mercury (Hg) contaminated soil, but N2-fixation highly relies on phosphorus (P) availability for nodule formation and functioning. Here, we characterized the significance of P deficiency for Hg accumulation and toxicity in woody legume plants. Consequences for foliar and root traits of rhizobia inoculation, Hg exposure (+Hg) and low P (-P) supply, individually and in combination were characterized at both the metabolite and transcriptome levels in seedlings of two Robinia pseudoacacia L. provenances originating from contrasting climate and soil backgrounds, i.e., GS in northwest and the DB in northeast China. Our results reveal that depleted P mitigates the toxicity of Hg at the transcriptional level. In leaves of Robinia depleted P reduced oxidative stress and improved the utilization strategy of C, N and P nutrition; in roots depleted P regulated the expression of genes scavenging oxidative stress and promoting cell membrane synthesis. Rhizobia inoculation significantly improved the performance of both Robinia provenances under individual and combined +Hg and -P by promoting photosynthesis, increasing foliar N and P content and reducing H2O2 and MDA accumulation despite enhanced Hg uptake. DB plants developed more nodules, had higher biomass and accumulated higher Hg amounts than GS plants and thus are suggested as the high potential Robinia provenance for future phytoremediation of Hg contaminated soils with P deficiency.

Rhizobacteria isolated from xerophyte Haloxylon ammodendron manipulate root system architecture and enhance drought and salt tolerance in Arabidopsis thaliana

The objective of this study was to identify bacteria from the rhizosphere of the black saxaul (Haloxylon ammodendron) and test the possibility of using the bacteria for enhancement of drought and/or salt tolerance in the model plant, Arabidopsis thaliana. We collected rhizosphere and bulk soil samples from a natural habitat of H. ammodendron in Iran and identified 58 morphotypes of bacteria that were enriched in the rhizosphere. From this collection, we focused our further experiments on eight isolates. Microbiological analyses showed that these isolates have different levels of tolerance to heat, salt, and drought stresses, and showed different capabilities of auxin production and phosphorous solubilization. We first tested the effects of these bacteria on the salt tolerance of Arabidopsis on agar plate assays. The bacteria substantially influenced the root system architecture, but they were not effective in increasing salt tolerance significantly. Pot assays were then conducted to evaluate the effects of the bacteria on salt or drought tolerance of Arabidopsis on peat moss. Results showed that three of these bacteria (Pseudomonas spp. and Peribacillus sp.) effectively enhanced drought tolerance in Arabidopsis, so that while none of the mock-inoculated plants survived after 19 days of water withholding, the survival rate was 50-100% for the plants that were inoculated with these bacteria. The positive effects of the rhizobacteria on a phylogenetically-distant plant species imply that the desert rhizobacteria may be used to enhance abiotic stress in crops.

Systemic stomatal responses in plants: Coordinating development, stress, and pathogen defense under a changing climate

To successfully survive, develop, grow and reproduce, multicellular organisms must coordinate their molecular, physiological, developmental and metabolic responses among their different cells and tissues. This process is mediated by cell-to-cell, vascular and/or volatile communication, and involves electric, chemical and/or hydraulic signals. Within this context, stomata serve a dual role by coordinating their responses to the environment with their neighbouring cells at the epidermis, but also with other stomata present on other parts of the plant. As stomata represent one of the most important conduits between the plant and its above-ground environment, as well as directly affect photosynthesis, respiration and the hydraulic status of the plant by controlling its gas and vapour exchange with the atmosphere, coordinating the overall response of stomata within and between different leaves and tissues plays a cardinal role in plant growth, development and reproduction. Here, we discuss different examples of local and systemic stomatal coordination, the different signalling pathways that mediate them, and the importance of systemic stomatal coordination to our food supply, ecosystems and weather patterns, under our changing climate. We further discuss the potential biotechnological implications of regulating systemic stomatal responses for enhancing agricultural productivity in a warmer and CO2 -rich environment.

Dalbergia odorifera undergoes massive molecular shifts in response to waterlogging combined with salinity

Field and greenhouse studies attempting to describe the molecular responses of plant species under waterlogging (WL) combined with salinity (ST) are almost nonexistent. We integrated transcriptional, metabolic, and physiological responses involving several crucial transcripts and common differentially expressed genes and metabolites in fragrant rosewood (Dalbergia odorifera) leaflets to dissect plant-specific molecular responses and patterns under WL combined with ST (SWL). We discovered that the synergistic pattern of the transcriptional response of fragrant rosewood under SWL was exclusively characterized by the number of regulated transcripts. The response patterns under SWL based on transcriptome and metabolome regulation statuses revealed different patterns (additive, dominant, neutral, minor, unilateral, and antagonistic) of transcripts or metabolites that were commonly regulated or expressed uniquely under SWL. Under SWL, the synergistic transcriptional response of several functional gene subsets was positively associated with several metabolomic and physiological responses related to the shutdown of the photosynthetic apparatus and the extensive degradation of starch into saccharides through α-amylase, β-amylase, and α-glucosidase or plastoglobuli accumulation. The dissimilarity between the regulation status and number of transcripts in plants under combined stresses led to nonsynergistic responses in several physiological and phytohormonal traits. As inferred from the impressive synergistic transcriptional response to morpho-physiological changes, combined stresses exhibited a gradually decreasing effect on the changes observed at the molecular level compared to those in the morphological one. Here, by characterizing the molecular responses and patterns of plant species under SWL, our study considerably improves our understanding of the molecular mechanisms underlying combined stress.

Soil, rhizosphere, and root microbiome in kiwifruit vine decline, an emerging multifactorial disease

Kiwifruit vine decline syndrome (KVDS) is characterized by severe root system impairment, which leads to irreversible wilting of the canopy. Plants usually collapse rapidly from the appearance of the first aboveground symptoms, without recovery even in the following seasons. The syndrome has been negatively impacting kiwifruit yield in different areas of Italy, the main producing European country, since its first outbreak in 2012. To date, a unique, common causal factor has yet to be found, and the syndrome is referred to as multifactorial. In this article, we investigated the whole biotic community (fungi, bacteria, and oomycetes) associated with the development of KVDS in three different belowground matrices/compartments (soil, rhizosphere, and root). Sampling was performed at both healthy and affected sites located in the main kiwifruit-producing area of Northwestern Italy. To address the multifactorial nature of the syndrome and to investigate the potential roles of abiotic factors in shaping these communities, a physicochemical analysis of soils was also performed. This study investigates the associations among taxonomic groups composing the microbiome and also between biotic and abiotic factors. Dysbiosis was considered as a driving event in shaping KVDS microbial communities. The results obtained from this study highlight the role of the oomycete genus Phytopythium, which resulted predominantly in the oomycete community composition of diseased matrices, though it was also present in healthy ones. Both bacterial and fungal communities resulted in a high richness of genera and were highly correlated to the sampling site and matrix, underlining the importance of multiple location sampling both geographically and spatially. The rhizosphere community associated with KVDS was driven by a dysbiotic process. In addition, analysis of the association network in the diseased rhizosphere revealed the presence of potential cross-kingdom competition for plant-derived carbon between saprobes, oomycetes, and bacteria.

Gene pyramiding for boosted plant growth and broad abiotic stress tolerance

Abiotic stresses such as salinity, heat and drought seriously impair plant growth and development, causing a significant loss in crop yield and ornamental value. Biotechnology approaches manipulating specific genes prove to be effective strategies in crop trait modification. The Arabidopsis vacuolar pyrophosphatase gene AVP1, the rice SUMO E3 ligase gene OsSIZ1 and the cyanobacterium flavodoxin gene Fld have previously been implicated in regulating plant stress responses and conferring enhanced tolerance to different abiotic stresses when individually overexpressed in various plant species. We have explored the feasibility of combining multiple favourable traits brought by individual genes to acquire superior plant performance. To this end, we have simultaneously introduced AVP1, OsSIZ1 and Fld in creeping bentgrass. Transgenic (TG) plants overexpressing these three genes performed significantly better than wild type controls and the TGs expressing individual genes under both normal and various abiotic stress conditions, exhibited significantly enhanced plant growth and tolerance to drought, salinity and heat stresses as well as nitrogen and phosphate starvation, which were associated with altered physiological and biochemical characteristics and delicately fine-tuned expression of genes involved in plant stress responses. Our results suggest that AVP1, OsSIZ1 and Fld function synergistically to regulate plant development and plant stress response, leading to superior overall performance under both normal and adverse environments. The information obtained provides new insights into gene stacking as an effective approach for plant genetic engineering. A similar strategy can be extended for the use of other beneficial genes in various crop species for trait modifications, enhancing agricultural production.

'Against all floods': plant adaptation to flooding stress and combined abiotic stresses

Current climate change brings with it a higher frequency of environmental stresses, which occur in combination rather than individually leading to massive crop losses worldwide. In addition to, for example, drought stress (low water availability), also flooding (excessive water) can threaten the plant, causing, among others, an energy crisis due to hypoxia, which is responded to by extensive transcriptional, metabolic and growth-related adaptations. While signalling during flooding is relatively well understood, at least in model plants, the molecular mechanisms of combinatorial flooding stress responses, for example, flooding simultaneously with salinity, temperature stress and heavy metal stress or sequentially with drought stress, remain elusive. This represents a significant gap in knowledge due to the fact that dually stressed plants often show unique responses at multiple levels not observed under single stress. In this review, we (i) consider possible effects of stress combinations from a theoretical point of view, (ii) summarize the current state of knowledge on signal transduction under single flooding stress, (iii) describe plant adaptation responses to flooding stress combined with four other abiotic stresses and (iv) propose molecular components of combinatorial flooding (hypoxia) stress adaptation based on their reported dual roles in multiple stresses. This way, more future emphasis may be placed on deciphering molecular mechanisms of combinatorial flooding stress adaptation, thereby potentially stimulating development of molecular tools to improve plant resilience towards multi-stress scenarios.

Specific ABA-independent tomato transcriptome reprogramming under abiotic stress combination

Crops often have to face several abiotic stresses simultaneously, and under these conditions, the plant's response significantly differs from that observed under a single stress. However, up to the present, most of the molecular markers identified for increasing plant stress tolerance have been characterized under single abiotic stresses, which explains the unexpected results found when plants are tested under real field conditions. One important regulator of the plant's responses to abiotic stresses is abscisic acid (ABA). The ABA signaling system engages many stress-responsive genes, but many others do not respond to ABA treatments. Thus, the ABA-independent pathway, which is still largely unknown, involves multiple signaling pathways and important molecular components necessary for the plant's adaptation to climate change. In the present study, ABA-deficient tomato mutants (flacca, flc) were subjected to salinity, heat, or their combination. An in-depth RNA-seq analysis revealed that the combination of salinity and heat led to a strong reprogramming of the tomato transcriptome. Thus, of the 685 genes that were specifically regulated under this combination in our flc mutants, 463 genes were regulated by ABA-independent systems. Among these genes, we identified six transcription factors (TFs) that were significantly regulated, belonging to the R2R3-MYB family. A protein-protein interaction network showed that the TFs SlMYB50 and SlMYB86 were directly involved in the upregulation of the flavonol biosynthetic pathway-related genes. One of the most novel findings of the study is the identification of the involvement of some important ABA-independent TFs in the specific plant response to abiotic stress combination. Considering that ABA levels dramatically change in response to environmental factors, the study of ABA-independent genes that are specifically regulated under stress combination may provide a remarkable tool for increasing plant resilience to climate change.

Synergistic regulation at physiological, transcriptional and metabolic levels in tomato plants subjected to a combination of salt and heat stress

With global warming and climate change, abiotic stresses often simultaneously occur. Combined salt and heat stress was a common phenomenon that was severe, particularly in arid/semi-arid lands. We aimed to reveal the systematic responsive mechanisms of tomato genotypes with different salt/heat susceptibilities to combined salt and heat stress. Morphological and physiological responses of salt-tolerant/sensitive and heat-tolerant/sensitive tomatoes at control, heat, salt and combined stress were investigated. Based on leaf Fv /Fm and H2 O2 content, samples from tolerant genotype at the four treatments for 36 h were taken for transcriptomics and metabolomics. We found that plant height, dry weight and net photosynthetic rate decreased while leaf Na+ concentration increased in all four genotypes under salt and combined stress than control. Changes in physiological indicators such as photosynthetic parameters and defence enzyme activities in tomato under combined stress were regulated by the expression of relevant genes and the accumulation of key metabolites. We screened five key pathways in tomato responding to a combination of salt and heat stress, such as oxidative phosphorylation (map00190). Synergistic regulation at morphological, physiological, transcriptional and metabolic levels in tomato plants was induced by combined stress. Heat stress was considered as a dominant stressor for tomato plants under the current combined stress. The oxidative phosphorylation pathway played a key role in tomato in response to combined stress, where tapped key genes (e.g. alternative oxidase, Aox1a) need further functional analysis. Our study will provide a valuable resource important for studying stress combination and improving tomato tolerance.

Factors of global change affecting plants act at different levels of the ecological hierarchy

Plants and ecosystems worldwide are exposed to a wide range of chemical, physical, and biological factors of global change, many of which act concurrently. As bringing order to the array of factors is required in order to generate an enhanced understanding of simultaneous impacts, classification schemes have been developed. One such classification scheme is dedicated to capturing the different targets of global change factors along the ecological hierarchy. We build on this pioneering work, and refine the conceptual framework in several ways, focusing on plants and terrestrial systems: (i) we more strictly define the target level of the hierarchy, such that every factor typically has just one target level, and not many; (ii) we include effects above the level of the community, that is, there are effects also at the ecosystem scale that cannot be reduced to any level below this; (iii) we introduce the level of the landscape to capture certain land use change effects while abandoning the level below the individual. We discuss how effects can propagate along the levels of the ecological hierarchy, upwards and downwards, presenting opportunities for explaining non-additivity of effects of multiple factors. We hope that this updated conceptual framework will help inform the next generation of plant-focused global change experiments, specifically aimed at non-additivity of effects at the confluence of many factors.

The impact of multifactorial stress combination on plants, crops, and ecosystems: how should we prepare for what comes next?

The complexity of environmental conditions encountered by plants in the field, or in nature, is gradually increasing due to anthropogenic activities that promote global warming, climate change, and increased levels of pollutants. While in the past it seemed sufficient to study how plants acclimate to one or even two different stresses affecting them simultaneously, the complex conditions developing on our planet necessitate a new approach of studying stress in plants: Acclimation to multiple stress conditions occurring concurrently or consecutively (termed, multifactorial stress combination [MFSC]). In an initial study of the plant response to MFSC, conducted with Arabidopsis thaliana seedlings subjected to an MFSC of six different abiotic stresses, it was found that with the increase in the number and complexity of different stresses simultaneously impacting a plant, plant growth and survival declined, even if the effects of each stress involved in such MFSC on the plant was minimal or insignificant. In three recent studies, conducted with different crop plants, MFSC was found to have similar effects on a commercial rice cultivar, a maize hybrid, tomato, and soybean, causing significant reductions in growth, biomass, physiological parameters, and/or yield traits. As the environmental conditions on our planet are gradually worsening, as well as becoming more complex, addressing MFSC and its effects on agriculture and ecosystems worldwide becomes a high priority. In this review, we address the effects of MFSC on plants, crops, agriculture, and different ecosystems worldwide, and highlight potential avenues to enhance the resilience of crops to MFSC.

The impact of multifactorial stress combination on reproductive tissues and grain yield of a crop plant

Global warming, climate change, and industrial pollution are altering our environment subjecting plants, microbiomes, and ecosystems to an increasing number and complexity of abiotic stress conditions, concurrently or sequentially. These conditions, termed, "multifactorial stress combination" (MFSC), can cause a significant decline in plant growth and survival. However, the impacts of MFSC on reproductive tissues and yield of major crop plants are largely unknown. We subjected soybean (Glycine max) plants to a MFSC of up to five different stresses (water deficit, salinity, low phosphate, acidity, and cadmium), in an increasing level of complexity, and conducted integrative transcriptomic-phenotypic analysis of their reproductive and vegetative tissues. We reveal that MFSC has a negative cumulative effect on soybean yield, that each set of MFSC condition elicits a unique transcriptomic response (that is different between flowers and leaves), and that selected genes expressed in leaves or flowers of soybean are linked to the effects of MFSC on different vegetative, physiological, and/or reproductive parameters. Our study identified networks and pathways associated with reactive oxygen species, ascorbic acid and aldarate, and iron/copper signaling/metabolism as promising targets for future biotechnological efforts to augment the resilience of reproductive tissues of major crop plants to MFSC. In addition, we provide unique phenotypic and transcriptomic datasets for dissecting the mechanistic effects of MFSC on the vegetative, physiological, and reproductive processes of a crop plant.

The effects of multifactorial stress combination on rice and maize

The complexity of environmental factors affecting crops in the field is gradually increasing due to climate change-associated weather events, such as droughts or floods combined with heat waves, coupled with the accumulation of different environmental and agricultural pollutants. The impact of multiple stress conditions on plants was recently termed "multifactorial stress combination" (MFSC) and defined as the occurrence of 3 or more stressors that impact plants simultaneously or sequentially. We recently reported that with the increased number and complexity of different MFSC stressors, the growth and survival of Arabidopsis (Arabidopsis thaliana) seedlings declines, even if the level of each individual stress is low enough to have no significant effect on plants. However, whether MFSC would impact commercial crop cultivars is largely unknown. Here, we reveal that a MFSC of 5 different low-level abiotic stresses (salinity, heat, the herbicide paraquat, phosphorus deficiency, and the heavy metal cadmium), applied in an increasing level of complexity, has a significant negative impact on the growth and biomass of a commercial rice (Oryza sativa) cultivar and a maize (Zea mays) hybrid. Proteomics, element content, and mixOmics analyses of MFSC in rice identified proteins that correlate with the impact of MFSC on rice seedlings, and analysis of 42 different rice genotypes subjected to MFSC revealed substantial genetic variability in responses to this unique state of stress combination. Taken together, our findings reveal that the impacts of MFSC on 2 different crop species are severe and that MFSC may substantially affect agricultural productivity.

Climate Change-The Rise of Climate-Resilient Crops

Climate change disrupts food production in many regions of the world. The accompanying extreme weather events, such as droughts, floods, heat waves, and cold snaps, pose threats to crops. The concentration of carbon dioxide also increases in the atmosphere. The United Nations is implementing the climate-smart agriculture initiative to ensure food security. An element of this project involves the breeding of climate-resilient crops or plant cultivars with enhanced resistance to unfavorable environmental conditions. Modern agriculture, which is currently homogeneous, needs to diversify the species and cultivars of cultivated plants. Plant breeding programs should extensively incorporate new molecular technologies, supported by the development of field phenotyping techniques. Breeders should closely cooperate with scientists from various fields of science.

Research Progress on Plant Responses to Stress Combinations in the Context of Climate Change

In the context of climate change, the frequency and intensity of extreme weather events are increasing, environmental pollution and global warming are exacerbated by anthropogenic activities, and plants will experience a more complex and variable environment of stress combinations. Research on plant responses to stress combinations is crucial for the development and utilization of climate-adaptive plants. Recently, the concept of stress combinations has been expanded from simple to multifactorial stress combinations (MFSCs). Researchers have realized the complexity and necessity of stress combination research and have extensively employed composite gradient methods, multi-omics techniques, and interdisciplinary approaches to integrate laboratory and field experiments. Researchers have studied the response mechanisms of plant reactive oxygen species (ROS), phytohormones, transcription factors (TFs), and other response mechanisms under stress combinations and reached some generalized conclusions. In this article, we focus on the research progress and methodological dynamics of plant responses to stress combinations and propose key scientific questions that are crucial to address, in the context of plant responses to stress assemblages, conserving biodiversity, and ensuring food security. We can enhance the search for universal pathways, identify targets for stress combinations, explore adaptive genetic responses, and leverage high-technology research. This is in pursuit of cultivating plants with greater tolerance to stress combinations and enabling their adaptation to and mitigation of the impacts of climate change.

Antagonistic effect of mercury and excess nitrogen exposure reveals provenance-specific phytoremediation potential of black locust-rhizobia symbiosis

Interaction of different environmental constrains pose severe threats to plants that cannot be predicted from individual stress exposure. In this context, mercury (Hg), as a typical toxic and hazardous heavy metal, has recently attracted particular attention. Nitrogen (N2)-fixing legumes can be used for phytoremediation of Hg accumulation, whereas N availability could greatly affect its N2-fixation efficiency. However, information on the physiological responses to combined Hg exposure and excess N supply of woody legume species is still lacking. Here, we investigated the interactive effects of rhizobia inoculation, Hg exposure (+Hg), and high N (+N) supply, individually and in combination (+N*Hg), on photosynthesis and biochemical traits in Robinia pseudoacacia L. seedlings of two provenances, one from Northeast (DB) and one from Northwest (GS) China. Our results showed antagonistic effects of combined + N*Hg exposure compared to the individual treatments that were provenance-specific. Compared to individual Hg exposure, combined + N*Hg stress significantly increased foliar photosynthesis (+50.6%) of inoculated DB seedlings and resulted in more negative (-137.4%) δ15N abundance in the roots. Furthermore, combined + N*Hg stress showed 47.7% increase in amino acid N content, 39.4% increase in NR activity, and 14.8% decrease in MDA content in roots of inoculated GS seedlings. Inoculation with rhizobia significantly promoted Hg uptake in both provenances, reduced MDA contents of leaves and roots, enhanced photosynthesis and maintained the nutrient balance of Robinia. Among the two Robinia provenances investigated, DB seedlings formed more nodules, had higher biomass and Hg accumulation than GS seedlings. For example, total Hg concentrations in leaves and roots and total biomass of inoculated DB seedlings were 1.3,1.9 and 3.4 times higher than in inoculated GS seedlings under combined + N*Hg stress, respectively. Therefore, the DB provenance is considered to possess a higher potential for phytoremediation of Hg contamination compared to the GS provenance in environments subjected to N deposition.

Salicylic acid alleviates the effects of cadmium and drought stress by regulating water status, ions, and antioxidant defense in Pterocarya fraxinifolia

Introduction

Pterocarya fraxinifolia (Poiret) Spach (Caucasian wingnut, Juglandaceae) is a relict tree species, and little is known about its tolerance to abiotic stress factors, including drought stress and heavy metal toxicity. In addition, salicylic acid (SA) has been shown to have a pivotal role in plant responses to biotic and abiotic stresses.

Methods

The current study is focused on evaluating the impact of foliar application of SA in mediating Caucasian wingnut physiological and biochemical responses, including growth, relative water content (RWC), osmotic potential (Ψs), quantum yield (Fv/Fm), electrolyte leakage, lipid peroxidation, hydrogen peroxide, and antioxidant enzymes, to cadmium (Cd; 100 µM) and drought stress, as well as their interaction. Moreover, the antioxidant activity (e.g., ascorbate peroxidase, catalase, glutathione reductase, peroxidase, and superoxide dismutase activities) of the stressed trees was investigated. The study was conducted on 6-month-old seedlings under controlled environmental conditions in a greenhouse for 3 weeks.

Results and discussion

Leaf length, RWC, Ψs, and Fv/Fm were decreased under all treatments, although the effect of drought stress was the most pronounced. An efficient antioxidant defense mechanism was detected in Caucasian wingnut. Moreover, SA-treated Caucasian wingnut plants had lower lipid peroxidation, as one of the indicators of oxidative stress, when compared to non-SA-treated groups, suggesting the tolerance of this plant to Cd stress, drought stress, and their combination. Cadmium and drought stress also changed the ion concentrations in Caucasian wingnut, causing excessive accumulation of Cd in leaves. These results highlight the beneficial function of SA in reducing the negative effects of Cd and drought stress on Caucasian wingnut plants.

Ecophysiological response of Populus alba L. to multiple stress factors during the revitalisation of coal fly ash lagoons at different stages of weathering

The enormous quantities of fly ash (FA) produced by thermal power plants is a global problem and safe, sustainable approaches to reduce the amount and its toxic effects are still being sought. Vegetation cover comprising long-living species can help reduce FA dump-related environmental health issues. However, the synergistic effect of multiple abiotic factors, like drought, low organic matter content, a deficit of essential nutrients, alkaline pH, and phytotoxicity due to high potentially toxic element (PTE) and soluble salt content, limits the number of species that can grow under such stressful conditions. Thus, we hypothesised that Populus alba L., which spontaneously colonised two FA disposal lagoons at the 'Nikola Tesla A' thermal power plant (Obrenovac, Serbia) 3 years (L3) and 11 years (L11) ago, has high restoration potential thanks to its stress tolerance. We analysed the basic physical and chemical properties of FA at different weathering stages, while the ecophysiological response of P. alba to multiple stresses was determined through biological indicators [the bioconcentration factor (BCF) and translocation factor (TF) for PTEs (As, B, Cr, Cu, Mn, Ni, Se, and Zn)] and by measuring the following parameters: photosynthetic efficiency and chlorophyll concentration, non-enzymatic antioxidant defence (carotenoids, anthocyanins, and phenols), oxidative stress (malondialdehyde (MDA) concentrations), and total antioxidant capacity (IC50) to neutralise DPPH free radical activity. Unlike at L3, toxic As, B, and Zn concentrations in leaves induced oxidative stress in P. alba at L11, shown by the higher MDA levels, lower vitality, and reduced synthesis of chlorophyll, carotenoids, and total antioxidant activity, suggesting its stress tolerance decreases with long-term exposure to adverse abiotic factors. Although P. alba is a fast-growing species with good metal accumulation ability and high stress tolerance, it has poor stabilisation potential for substrates with high As and B concentrations, making it highly unsuitable for revitalising such habitats.

Uncovering the wide protective responses in Coffea spp. leaves to single and superimposed exposure of warming and severe water deficit

Climate changes boosted the frequency and severity of drought and heat events, with aggravated when these stresses occur simultaneously, turning crucial to unveil the plant response mechanisms to such harsh conditions. Therefore, plant responses/resilience to single and combined exposure to severe water deficit (SWD) and heat were assessed in two cultivars of the main coffee-producing species: Coffea arabica cv. Icatu and C. canephora cv. Conilon Clone 153 (CL153). Well-watered plants (WW) were exposed to SWD under an adequate temperature of 25/20°C (day/night), and thereafter submitted to a gradual increase up to 42/30°C, and a 14-d recovery period (Rec14). Greater protective response was found to single SWD than to single 37/28°C and/or 42/30°C (except for HSP70) in both cultivars, but CL153-SWD plants showed the larger variations of leaf thermal imaging crop water stress index (CWSI, 85% rise at 37/28°C) and stomatal conductance index (IG, 66% decline at 25/20°C). Both cultivars revealed great resilience to SWD and/or 37/28°C, but a tolerance limit was surpassed at 42/30°C. Under stress combination, Icatu usually displayed lower impacts on membrane permeability, and PSII function, likely associated with various responses, usually mostly driven by drought (but often kept or even strengthened under SWD and 42/30°C). These included the photoprotective zeaxanthin and lutein, antioxidant enzymes (superoxide dismutase, Cu,Zn-SOD; ascorbate peroxidase, APX), HSP70, arabinose and mannitol (involving de novo sugar synthesis), contributing to constrain lipoperoxidation. Also, only Icatu showed a strong reinforcement of glutathione reductase activity under stress combination. In general, the activities of antioxidative enzymes declined at 42/30°C (except Cu,Zn-SOD in Icatu and CAT in CL153), but HSP70 and raffinose were maintained higher in Icatu, whereas mannitol and arabinose markedly increased in CL153. Overall, a great leaf plasticity was found, especially in Icatu that revealed greater responsiveness of coordinated protection under all experimental conditions, justifying low PIChr and absence of lipoperoxidation increase at 42/30°C. Despite a clear recovery by Rec14, some aftereffects persisted especially in SWD plants (e.g., membranes), relevant in terms of repeated stress exposure and full plant recovery to stresses.

Assembly of typical steppe community and functional groups along the precipitation gradient from 1985 to 2022

Long-term observations have shown that structure and function of grasslands have changed due to climate change over the past decades. However, little is known about how grasslands respond to climate change along the precipitation gradient, and potential mechanisms remain elusive. Here, we utilize a long-term experiment in typical steppe to explore universal and differential mechanisms of community and functional groups assembly along the precipitation gradient. Our results indicated that the sensitivity of community and functional groups assembly to climate change was related to local precipitation. The strength of the positive effects of climate change on aboveground biomass, species richness, and their relationship of community decreased modestly with local precipitation. The mechanism behind this was the change in plant community composition of the precipitation-induced, annuals that was more responsive to climate change decreased as increased local precipitation. Furthermore, current and past climate both drove community and functional group assembly, and the role of past climate diminished with increasing local precipitation. Among them, climate fluctuation, average climate and current climate were the most critical climate indicators affecting community and functional groups assembly in low, medium and high precipitation sites, respectively. In conclusion, climatic change do not always exert identical effects on grasslands along the precipitation gradient. This could be critical importance for improving our ability to predict future changes in grassland ecosystems.

Functional Trait Responses of Sophora alopecuroides L. Seedlings to Diverse Environmental Stresses in the Desert Steppe of Ningxia, China

The seedling stage of plants is a crucial and vulnerable period in population and community dynamics. Despite this, studies on how plant traits respond to different environmental stresses often tend to overlook this early stage. Our study focused on Sophora alopecuroides L. seedlings in Ningxia Yanchi desert steppe, analyzing the effects of sand burial, salinity, and drought on their key aboveground and belowground traits. The results showed that sand burial significantly negatively affected stem biomass (SB), leaf biomass (LB), stem diameter (SD), leaf length (LL), leaf width (LW), leaf area (LA), and total root volume (RV), but positively influenced total root length (RL). As sand burial depth increased, SB, LB, SD, LL, LW, LA, RV, root biomass (RB), RV, and lateral root numbers (LRN) significantly decreased. Salinity stress negatively affected SB, LB, SD, LL, LW, LA, RB, RL, and RV, with these traits declining as the stress concentration increased. Drought stress had a positive effect on SD and LL, with both traits showing an increase as the intensity of the drought stress intensified; however, it adversely affected RL. In Ningxia Yanchi desert steppe, salinity stress had the most significant effect on the traits of S. alopecuroides seedlings, followed by sand burial, with drought having the least significant effect. This study provides essential theoretical support for understanding how S. alopecuroides seedlings cope with environmental stresses in their early life stages.

Effects of long-term blue light irradiation on carotenoid biosynthesis and antioxidant activities in Chinese cabbage (Brassica rapa L. ssp. pekinensis)

The aim of this study was to investigate the impact of long-term exposure to blue light-emitting diodes (LEDs) on the accumulation of indolic glucosinolates and carotenoids, as well as the plant growth and antioxidant activities in both orange and common Chinese cabbage (Brassica rapa L. ssp. pekinensis). Blue light treatment also induced higher ferric-reducing antioxidant power and 2,2-diphenyl-1-picrylhydrazyl by 20.66 % and 30.82 % and antioxidant enzyme activities catalase, peroxidase, superoxide dismutase, and the accumulation of non-enzymatic antioxidant substances (total phenols and total flavonoids) in the orange Chinese cabbage. Furthermore, long-term exposure to blue light had negative effects on the net photosynthetic rate and chlorophyll fluorescence levels. Meanwhile, blue light promoted accumulation of Indol-3-ylmethyl glucosinolate (I3M), β-carotene, lutein and zeaxanthin due to the high expression of regulatory and biosynthetic genes of the above metabolic pathways. In particular, lycopene and β-carotene content in orange Chinese cabbage increased by 60.14 % and 65.33 % compared to the ones in common line. The accumulation of carotenoid and increasing antioxidant levels in the orange cabbage line was influenced by long-term blue light irradiation, leading to better tolerance to low temperature and drought stresses. The up-regulation of transcription factors such as BrHY5-2, BrPIF4 and BrMYB12 may also contribute to the increased tolerance in orange Chinese cabbage to extreme environmental stresses. The BrHY5-2 gene could activate carotenoid biosynthetic genes and induce the accumulation of carotenoids. These findings suggested that long-term blue light irradiation could be a promising technique for increasing the nutrition value and enhancing tolerance to low temperature and drought stresses in Chinese cabbage.

Meta-Analysis of Antioxidant Mutants Reveals Common Alarm Signals for Shaping Abiotic Stress-Induced Transcriptome in Plants

Aims: Reactive oxygen species (ROS) are key regulators of plant growth, development, and stress tolerance. Stress-induced changes in ROS levels trigger multilevel signaling. However, the precise mechanisms by which ROS signals are translated into changes in gene expression remain poorly defined. Focusing on six key antioxidant enzymes, we performed a meta-analysis of transcriptome data available in public databases to analyze ROS-mediated control of nuclear gene expression. Results: An information-guided pipeline was developed, which identified 19 putative transcription factors (TFs), as components in a "common alarm signal cascade" pathway following perception of changes in ROS levels. Crucially, 30%-35% of the abiotic stress transcriptome signatures had binding sites for common alarm signal-transcription factors (CAS-TFs) in their promoter regions. Furthermore, Phloem Early Dof 2 (PEAR2), DNA binding with one finger 5.8 (DOF5.8), and Obf-Binding Protein 3 (OBP3) were identified as top-ranked TFs on the basis of a cumulative DAPseq (DNA-affinity purification sequencing) score on the promoters of selected genes regulating core pathways of salt, drought, heat, and cold stress tolerance. Innovation: This study identifies a set of CAS-TFs that may play a major role in shaping the transcriptome of abiotic stress-induced ROS signaling. Ranking analysis identified PEAR2, DOF5.8, and OBP3 as the top-ranked CAS-TFs that regulated known markers of abiotic stress tolerance. Conclusion: The current findings suggest a major role of ROS in the abiotic stress signaling and also identify a set of TFs that take part in the signaling. Taken together, these findings suggested that the common alarm signal cascade underpins broad-range tolerance against multistress conditions. The identification of associated ROS-responsive CAS-TFs may provide novel targets for crop improvement.

Barley shows reduced Fusarium head blight under drought and modular expression of differentially expressed genes under combined stress

Plants often face simultaneous abiotic and biotic stress conditions; however, physiological and transcriptional responses under such combined stress conditions are still not fully understood. Spring barley (Hordeum vulgare) is susceptible to Fusarium head blight (FHB), which is strongly affected by weather conditions. We therefore studied the potential influence of drought on FHB severity and plant responses in three varieties of different susceptibility. We found strongly reduced FHB severity in susceptible varieties under drought. The number of differentially expressed genes (DEGs) and strength of transcriptomic regulation reflected the concentrations of physiological stress markers such as abscisic acid or fungal DNA contents. Infection-related gene expression was associated with susceptibility rather than resistance. Weighted gene co-expression network analysis revealed 18 modules of co-expressed genes that reflected the pathogen- or drought-response in the three varieties. A generally infection-related module contained co-expressed genes for defence, programmed cell death, and mycotoxin detoxification, indicating that the diverse genotypes used a similar defence strategy towards FHB, albeit with different degrees of success. Further, DEGs showed co-expression in drought- or genotype-associated modules that correlated with measured phytohormones or the osmolyte proline. The combination of drought stress with infection led to the highest numbers of DEGs and resulted in a modular composition of the single-stress responses rather than a specific transcriptional output.

A review of plants strategies to resist biotic and abiotic environmental stressors

Plants exposed to a variety of abiotic and biotic stressors including environmental pollution and global warming pose significant threats to biodiversity and ecosystem services. Despite substantial literature documenting how plants adapt to distinct stressors, there still is a lack of knowledge regarding responses to multiple stressors and how these affects growth and development. Exposure of plants to concurrent biotic and abiotic stressors such as cadmium and drought, leads to pronounced inhibition in above ground biomass, imbalance in oxidative homeostasis, nutrient assimilation and stunted root growth, elucidating the synergistic interactions of multiple stressors culminating in adverse physiological outcomes. Impact of elevated heavy metal and water deficit exposure extends beyond growth and development, influencing the biodiversity of the microenvironment including the rhizosphere nutrient profile and microbiome. These findings have significant implications for plant-stress interactions and ecosystem functioning that prompt immediate action in order to eliminate effect of pollution and address global environmental issues to promote sustainable tolerance for multiple stress combinations in plants. Here, we review plant tolerance against stress combinations, highlighting the need for interdisciplinary approaches and advanced technologies, such as omics and molecular tools, to achieve a comprehensive understanding of underlying stress tolerance mechanisms. To accelerate progress towards developing stress-tolerance in plants against multiple environmental stressors, future research in plant stress tolerance should adopt a collaborative approach, involving researchers from multiple disciplines with diverse expertise and resources.

Suppression of SlDREB3 increases leaf ABA responses and promotes drought tolerance in transgenic tomato plants

Drought susceptibility is a major yield limiting factor in agricultural crops especially in hybrids/varieties that have been bred for high yields. We show that manipulation of the SlDREB3 gene in tomato alters ABA responses and thereby sensitivity of stomatal closure to ABA. SlDREB3 suppression lines show ABA hypersensitivity and rapid stomatal closure in response to ABA while over-expression lines show reduced sensitivity to ABA and open stomata even at high ABA levels with rapid water loss after 10 days of water stress. This is accompanied with high ROS levels and increased membrane damage due to senescence of leaves and drastically reduced survival in drought. The relative water content (RWC) of OEx lines is much reduced even when grown under well-watered conditions. In contrast, suppression lines show greater tolerance to water stress and almost complete survival to 10-day water stress. They show much reduced ROS levels, reduced membrane damage, higher RWC and reduced leaf water loss. These changes are associated with higher expression of ABA signalling pathway genes in suppression lines while these are highly reduced in OEx lines. The studies suggest that control of ABA signalling by SlDREB3 can help in withstanding severe drought.

Grassland stability decreases with increasing number of global change factors: A meta-analysis

Experiments manipulating a single global change factor (GCF) have provided increasing evidence that global environmental changes, such as eutrophication, precipitation change, and warming, generally affect the temporal stability of grassland productivity. Whether the combined impact of global changes on grassland stability increases as the number of global changes increases remains unknown. Using a meta-analysis of 673 observations from 143 sites worldwide, including 7 different GCFs, we examined the responses of grassland temporal stability of productivity to increasing numbers of GCFs. We quantified the links between community stability, biotic factors (i.e., species richness, species stability, and species asynchrony), and abiotic factors (i.e., aridity index, experimental duration, and experimental intensity). Although inconsistent responses of community stability were found with different GCF types and combinations, when integrating existing GCFs studies and ignoring the identity of GCFs, we found a general decrease in community stability as the number of GCFs increases, but the main drivers of community stability varied with the numbers of GCFs. Specifically, one GCF mainly reduced species stability through species richness and thus weakened community stability. Two GCFs weakened community stability via independently weakening species stability and species asynchrony. Three GCFs reduce community stability mainly via independently weakening species asynchrony. Moreover, for single factor, the impact of GCFs on community stability was weaker under dryer conditions, but stronger when two or three factors were manipulated. In addition, the negative effect of GCFs on community stability was weaker with increasing experimental duration. Our study reveals that reduced community stability with increasing numbers of GCFs is caused by a shift from reduced species stability to reduced species asynchrony, suggesting that persistent global changes will destabilize grassland productivity by reducing asynchronous dynamics among species in response to natural environmental fluctuations.

Stress combinations and their interactions in plants database: a one-stop resource on combined stress responses in plants

We have developed a compendium and interactive platform, named Stress Combinations and their Interactions in Plants Database (SCIPDb; http://www.nipgr.ac.in/scipdb.php), which offers information on morpho-physio-biochemical (phenome) and molecular (transcriptome and metabolome) responses of plants to different stress combinations. SCIPDb is a plant stress informatics hub for data mining on phenome, transcriptome, trait-gene ontology, and data-driven research for advancing mechanistic understanding of combined stress biology. We analyzed global phenome data from 939 studies to delineate the effects of various stress combinations on yield in major crops and found that yield was substantially affected under abiotic-abiotic stresses. Transcriptome datasets from 36 studies hosted in SCIPDb identified novel genes, whose roles have not been earlier established in combined stress. Integretome analysis under combined drought-heat stress pinpointed carbohydrate, amino acid, and energy metabolism pathways as the crucial metabolic, proteomic, and transcriptional components in plant tolerance to combined stress. These examples illustrate the application of SCIPDb in identifying novel genes and pathways involved in combined stress tolerance. Further, we showed the application of this database in identifying novel candidate genes and pathways for combined drought and pathogen stress tolerance. To our knowledge, SCIPDb is the only publicly available platform offering combined stress-specific omics big data visualization tools, such as an interactive scrollbar, stress matrix, radial tree, global distribution map, meta-phenome analysis, search, BLAST, transcript expression pattern table, Manhattan plot, and co-expression network. These tools facilitate a better understanding of the mechanisms underlying plant responses to combined stresses.

Rapid systemic responses of Arabidopsis to waterlogging stress

Waterlogging stress (WLS) negatively impacts the growth and yield of crops resulting in heavy losses to agricultural production. Previous studies have revealed that WLS induces a systemic response in shoots that is partially dependent on the plant hormones ethylene and abscisic acid. However, the role of rapid cell-to-cell signaling pathways, such as the reactive oxygen species (ROS) and calcium waves, in systemic responses of plants to WLS is unknown at present. Here, we reveal that an abrupt WLS treatment of Arabidopsis (Arabidopsis thaliana) plants growing in peat moss triggers systemic ROS and calcium wave responses and that the WLS-triggered ROS wave response of Arabidopsis is dependent on the ROS-generating RESPIRATORY BURST OXIDASE HOMOLOG D (RBOHD), calcium-permeable channels GLUTAMATE-LIKE RECEPTOR 3.3 and 3.6 (GLR3.3 and GLR3.6), and aquaporin PLASMA MEMBRANE INTRINSIC PROTEIN 2;1 (PIP2;1) proteins. We further show that WLS is accompanied by a rapid systemic transcriptomic response that is evident as early as 10 min following waterlogging initiation, includes many hypoxia-response transcripts, and is partially dependent on RBOHD. Interestingly, the abrupt WLS of Arabidopsis resulted in the triggering of a rapid hydraulic wave response and the transient opening of stomata on leaves. In addition, it induced in plants a heightened state of tolerance to a subsequent submergence stress. Taken together, our findings reveal that the initiation of WLS in plants is accompanied by rapid systemic physiological and transcriptomic responses that involve the ROS, calcium, and hydraulic waves, as well as the induction of hypoxia acclimation mechanisms in systemic tissues.

Genetic and molecular exploration of maize environmental stress resilience: Toward sustainable agriculture

Global climate change exacerbates the effects of environmental stressors, such as drought, flooding, extreme temperatures, salinity, and alkalinity, on crop growth and grain yield, threatening the sustainability of the food supply. Maize (Zea mays) is one of the most widely cultivated crops and the most abundant grain crop in production worldwide. However, the stability of maize yield is highly dependent on environmental conditions. Recently, great progress has been made in understanding the molecular mechanisms underlying maize responses to environmental stresses and in developing stress-resilient varieties due to advances in high-throughput sequencing technologies, multi-omics analysis platforms, and automated phenotyping facilities. In this review, we summarize recent advances in dissecting the genetic factors and networks that contribute to maize abiotic stress tolerance through diverse strategies. We also discuss future challenges and opportunities for the development of climate-resilient maize varieties.

FERONIA, the kinase that phosphorylates PhyB

The phosphorylation status of phyB changes dynamically in response to environmental conditions and critically governs the corresponding plant's responses. However, the kinase(s) that phosphorylates phyB is/are still unknown. Liu et al. have not only identified the kinase that phosphorylates phyB but also revealed its biological implications during salt stress.

Metabolic pathways engineering for drought or/and heat tolerance in cereals

Drought (D) and heat (H) are the two major abiotic stresses hindering cereal crop growth and productivity, either singly or in combination (D/+H), by imposing various negative impacts on plant physiological and biochemical processes. Consequently, this decreases overall cereal crop production and impacts global food availability and human nutrition. To achieve global food and nutrition security vis-a-vis global climate change, deployment of new strategies for enhancing crop D/+H stress tolerance and higher nutritive value in cereals is imperative. This depends on first gaining a mechanistic understanding of the mechanisms underlying D/+H stress response. Meanwhile, functional genomics has revealed several stress-related genes that have been successfully used in target-gene approach to generate stress-tolerant cultivars and sustain crop productivity over the past decades. However, the fast-changing climate, coupled with the complexity and multigenic nature of D/+H tolerance suggest that single-gene/trait targeting may not suffice in improving such traits. Hence, in this review-cum-perspective, we advance that targeted multiple-gene or metabolic pathway manipulation could represent the most effective approach for improving D/+H stress tolerance. First, we highlight the impact of D/+H stress on cereal crops, and the elaborate plant physiological and molecular responses. We then discuss how key primary metabolism- and secondary metabolism-related metabolic pathways, including carbon metabolism, starch metabolism, phenylpropanoid biosynthesis, γ-aminobutyric acid (GABA) biosynthesis, and phytohormone biosynthesis and signaling can be modified using modern molecular biotechnology approaches such as CRISPR-Cas9 system and synthetic biology (Synbio) to enhance D/+H tolerance in cereal crops. Understandably, several bottlenecks hinder metabolic pathway modification, including those related to feedback regulation, gene functional annotation, complex crosstalk between pathways, and metabolomics data and spatiotemporal gene expressions analyses. Nonetheless, recent advances in molecular biotechnology, genome-editing, single-cell metabolomics, and data annotation and analysis approaches, when integrated, offer unprecedented opportunities for pathway engineering for enhancing crop D/+H stress tolerance and improved yield. Especially, Synbio-based strategies will accelerate the development of climate resilient and nutrient-dense cereals, critical for achieving global food security and combating malnutrition.

Early growth, development and allometry of glyphosate-resistant and susceptible Amaranthus palmeri in response to current and elevated temperature and CO2

This study aimed to evaluate the influence of CO2 and temperature on glyphosate-resistant and susceptible biotypes of Amaranthus palmeri (Palmer amaranth) in terms of morphological development. Height (cm), stem diameter (cm), leaf area (cm2), number of leaves, leaf, stem, and root dry matter, plant volume (m3), as well as shoot-to-root allometry were evaluated. The Palmer amaranth biotypes were grown under four different scenarios: 1-low temperature (23/33 °C) and CO2 (410 ± 25 ppm); 2-low temperature (23/33 °C) and high CO2 (750 ± 25 ppm); 3-high temperature (26/36 °C) and low CO2 (410 ± 25 ppm); and 4-high temperature (26/36 °C) and CO2 (750 ± 25 ppm). Between CO2 and temperature, the majority of differences observed were driven by CO2 levels. Palmer amaranth grown under 750 ppm of CO2 was 15.5% taller, displayed 10% more leaf area (cm2), 18% more stem dry matter, and had a 28.4% increase in volume (m3) compared to 410 ppm of CO2. GA2017 and GA2020 were 18% and 15.5% shorter, respectively. The number of leaves was 27% greater for GA2005. Plant volume decreased in GA2017 (35.6%) and GA2020 (23.8%). The shoot-to-root ratio was isomeric, except at 14 and 21 DAT, where an allometric growth towards shoot development was significant. Palmer amaranth biotypes responded differently to elevated CO2, and the impacts of temperature need further investigation on weed physiology. Thus, environmental and genetic background may affect the response of glyphosate-resistant and susceptible populations to climate change scenarios.

From stressor to protector, UV-induced abiotic stress resistance

Plants are continuously exposed to combinations of abiotic and biotic stressors. While much is known about responses to individual stressors, understanding of plant responses to combinations of stressors is limited. The effects of combined exposure to drought and UV radiation are particularly relevant in the context of climate change. In this study it was explored whether UV-exposure can be used as a tool to prime stress-resistance in plants grown under highly protected culture conditions. It was hypothesised that priming mint plantlets (Mentha spicata L.) with a low-dose of UV irradiance can alleviate the drought effect caused by a change in humidity upon transplanting. Plants were grown for 30 days on agar in sealed tissue culture containers. During this period, plants were exposed to ~ 0.22 W m-2 UV-B for 8 days, using either UV-blocking or UV- transmitting filters. Plants were then transplanted to soil and monitored for a further 7 days. It was found that non-UV exposed mint plants developed necrotic spots on leaves, following transfer to soil, but this was not the case for plants primed with UV. Results showed that UV induced stress resistance is associated with an increase in antioxidant capacity, as well as a decrease in leaf area. UV-induced stress resistance can be beneficial in a horticultural setting, where priming plants with UV-B can be used as a tool in the production of commercial crops.

Comparison of metabolomic reconfiguration between Columbia and Landsberg ecotypes subjected to the combination of high salinity and increased irradiance

BACKGROUND

Plants growing in the field are subjected to combinations of abiotic stresses. These conditions pose a devastating threat to crops, decreasing their yield and causing a negative economic impact on agricultural production. Metabolic responses play a key role in plant acclimation to stress and natural variation for these metabolic changes could be key for plant adaptation to fluctuating environmental conditions.

RESULTS

Here we studied the metabolomic response of two Arabidopsis ecotypes (Columbia-0 [Col] and Landsberg erecta-0 [Ler]), widely used as genetic background for Arabidopsis mutant collections, subjected to the combination of high salinity and increased irradiance. Our findings demonstrate that this stress combination results in a specific metabolic response, different than that of the individual stresses. Although both ecotypes displayed reduced growth and quantum yield of photosystem II, as well as increased foliar damage and malondialdehyde accumulation, different mechanisms to tolerate the stress combination were observed. These included a relocation of amino acids and sugars to act as potential osmoprotectants, and the accumulation of different stress-protective compounds such as polyamines or secondary metabolites.

CONCLUSIONS

Our findings reflect an initial identification of metabolic pathways that differentially change under stress combination that could be considered in studies of stress combination of Arabidopsis mutants that include Col or Ler as genetic backgrounds.

Population divergence in heat and drought responses of a coastal plant: from metabolic phenotypes to plant morphology and growth

Studying intraspecific variation in multistress responses is central for predicting and managing the population dynamics of wild plant species under rapid global change. Yet, it remains a challenging goal in this field to integrate knowledge on the complex biochemical underpinnings for the targeted 'non-model' species. Here, we studied divergence in combined drought and heat responses among Northern and Southern European populations of the dune plant Cakile maritima, by combining comprehensive plant phenotyping with metabolic profiling via FT-ICR-MS and UPLC-TQ-MS/MS. We observed pronounced constitutive divergence in growth phenology, leaf functional traits, and defence chemistry (glucosinolates and alkaloids) among population origins. Most importantly, the magnitude of growth reduction under drought was partly weaker in southern plants and associated with divergence in plastic growth responses (leaf abscission) and the modulation of primary and specialized metabolites with known central functions not only in plant abiotic but also in biotic stress responses. Our study indicates that divergent selection has shaped the constitutive and drought-/heat-induced expression of numerous morphological and biochemical functional traits to mediate higher abiotic stress resistance in southern Cakile populations, and highlights that metabolomics can be a powerful tool to explore the underlying mechanisms of local adaptation in 'non-model' species.

An ethylene-induced NAC transcription factor acts as a multiple abiotic stress responsor in conifer

The proper response to various abiotic stresses is essential for plants' survival to overcome their sessile nature, especially for perennial trees with very long-life cycles. However, in conifers, the molecular mechanisms that coordinate multiple abiotic stress responses remain elusive. Here, the transcriptome response to various abiotic stresses like salt, cold, drought, heat shock and osmotic were systematically detected in Pinus tabuliformis (P. tabuliformis) seedlings. We found that four transcription factors were commonly induced by all tested stress treatments, while PtNAC3 and PtZFP30 were highly up-regulated and co-expressed. Unexpectedly, the exogenous hormone treatment assays and the content of the endogenous hormone indicates that the upregulation of PtNAC3 and PtZFP30 are mediated by ethylene. Time-course assay showed that the treatment by ethylene immediate precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), activated the expression of PtNAC3 and PtZFP30 within 8 hours. We further confirm that the PtNAC3 can directly bind to the PtZFP30 promoter region and form a cascade. Overexpression of PtNAC3 enhanced unified abiotic stress tolerance without growth penalty in transgenic Arabidopsis and promoted reproductive success under abiotic stress by shortening the lifespan, suggesting it has great potential as a biological tool applied to plant breeding for abiotic stress tolerance. This study provides novel insights into the hub nodes of the abiotic stresses response network as well as the environmental adaptation mechanism in conifers, and provides a potential biofortification tool to enhance plant unified abiotic stress tolerance.

Molecular regulation of the salicylic acid hormone pathway in plants under changing environmental conditions

Salicylic acid (SA) is a central plant hormone mediating immunity, growth, and development. Recently, studies have highlighted the sensitivity of the SA pathway to changing climatic factors and the plant microbiome. Here we summarize organizing principles and themes in the regulation of SA biosynthesis, signaling, and metabolism by changing abiotic/biotic environments, focusing on molecular nodes governing SA pathway vulnerability or resilience. We especially highlight advances in the thermosensitive mechanisms underpinning SA-mediated immunity, including differential regulation of key transcription factors (e.g., CAMTAs, CBP60g, SARD1, bHLH059), selective protein-protein interactions of the SA receptor NPR1, and dynamic phase separation of the recently identified GBPL3 biomolecular condensates. Together, these nodes form a biochemical paradigm for how the external environment impinges on the SA pathway.

Sand Burial, Rather than Salinity or Drought, Is the Main Stress That Limits the Germination Ability of Sophora alopecuroides L. Seed in the Desert Steppe of Yanchi, Ningxia, China

Global change and environmental pollution have reawakened ecologists to the great threat of multi-stress interactions to different growth stages of plants. Sophora alopecuroides L., a dune plant, has been widely studied for its medicinal components and strong salinity tolerance. S. alopecuroides seeds, obtained from the desert steppe of Yanchi, Ningxia, China, were used to analyze the effects of sand burial, salinity, drought, and their interactions on seed germination (germination percentage, germination energy, and germination index). The results showed that sand burial and salinity stress had significant effects on the seed germination ability of S. alopecuroides, and drought stress had no significant effect, but the interaction of the three stresses had a significant effect. Under different drought-stress treatments, the interaction of no sand burial and a certain degree of salinity stress significantly improved the germination ability of S. alopecuroides, and the overall intensity of the effects of the three stresses showed that sand burial > salinity > drought. Considering the germination percentage, germination energy, and germination index of S. alopecuroides under various stress interactions, the treatment of no sand burial × 1% soil saline-alkali content × 18-20% soil water content was adopted to maximize the germination ability of S. alopecuroides. In the desert steppe area of Yanchi, Ningxia, sand burial stress was still the most limiting factor for seed germination of S. alopecuroides, and soil saline-alkali content should be increased moderately, and soil moisture should be ensured to obtain the best germination ability.

Omics analyses in citrus reveal a possible role of RNA translation pathways and Unfolded Protein Response regulators in the tolerance to combined drought, high irradiance, and heat stress

Environmental changes derived from global warming and human activities increase the intensity and frequency of stressful conditions for plants. Multiple abiotic factors acting simultaneously enhance stress pressure and drastically reduce plant growth, yield, and survival. Stress combination causes a specific stress situation that induces a particular plant response different to the sum of responses to the individual stresses. Here, by comparing transcriptomic and proteomic profiles to different abiotic stress combinations in two citrus genotypes, Carrizo citrange (Citrus sinensis × Poncirus trifoliata) and Cleopatra mandarin (Citrus reshni), with contrasting tolerance to different abiotic stresses, we revealed key responses to the triple combination of heat stress, high irradiance and drought. The specific transcriptomic response to this stress combination in Carrizo was directed to regulate RNA metabolic pathways and translation processes, potentially conferring an advantage with respect to Cleopatra. In addition, we found endoplasmic reticulum stress response as common to all individual and combined stress conditions in both genotypes and identified the accumulation of specific groups of heat shock proteins (HSPs), such as small HSPs and HSP70s, and regulators of the unfolded protein response, BiP2 and PDIL2-2, as possible factors involved in citrus tolerance to triple stress combination. Taken together, our findings provide new insights into the acclimation process of citrus plants to multiple stress combination, necessary for increasing crop tolerance to the changing climatic conditions.

Exogenous spermine alleviates the negative effects of combined salinity and paraquat in tomato plants by decreasing stress-induced oxidative damage

Plants are frequently exposed to different combinations of soil constraints including salinity and different herbicides. These abiotic conditions negatively affect photosynthesis, growth and plant development resulting in limitations in agriculture production. To respond to these conditions, plants accumulate different metabolites that restore cellular homeostasis and are key for stress acclimation processes. In this work, we analyzed the role of exogenous spermine (Spm), a polyamine involved in plant tolerance to abiotic stress, in tomato responses to the combination of salinity (S) and the herbicide paraquat (PQ). Our findings showed that application of Spm reduced leaf damage and enhanced survival, growth, photosystem II function and photosynthetic rate of tomato plants subjected to the combination of S and PQ. In addition, we revealed that exogenous Spm reduced H₂O₂ and malondialdehyde (MDA) accumulation in plants subjected to S+PQ, suggesting that the role of exogenous Spm in alleviating the negative effects of this stress combination could be attributed to a decrease in stress-induced oxidative damage in tomato plants. Taken together, our results identify a key role for Spm in improving plant tolerance to combined stress.

Nitrate supply decreases fermentation and alleviates oxidative and ionic stress in nitrogen-fixing soybean exposed to saline waterlogging

Nitrate (NO3 - ) nutrition is known to mitigate the damages caused by individual stresses of waterlogging and salinity. Here, we investigated the role of NO3 - in soybean plants exposed to these stresses in combination. Nodulated soybean cultivated under greenhouse conditions and daily fertilised with a nutrient solution without nitrogen were subjected to the following treatments: Water, NO3 - , NaCl, and NaCl+NO3 - . Then, plants were exposed to waterlogging (6days) and drainage (2days). Compared to plants exposed to isolated stress, the saline waterlogging resulted in higher concentrations of H2 O2 , O2 ˙- , and lipid peroxidation at the whole-plant level, mainly during drainage. Furthermore, saline waterlogging increased fermentation and the concentrations of Na+ and K+ in roots and leaves both during waterlogging and drainage. NO3 - supplementation led to augments in NO3 - and NO levels, and stimulated nitrate reductase activity in both organs. In addition, NO3 - nutrition alleviated oxidative stress and fermentation besides increasing the K+ /Na+ ratio in plants exposed to saline waterlogging. In conclusion, NO3 - supplementation is a useful strategy to help soybean plants overcome saline waterlogging stress. These findings are of high relevance for agriculture as soybean is an important commodity and has been cultivated in areas prone to saline waterlogging.

Interactive effects of changes in UV radiation and climate on terrestrial ecosystems, biogeochemical cycles, and feedbacks to the climate system

Terrestrial organisms and ecosystems are being exposed to new and rapidly changing combinations of solar UV radiation and other environmental factors because of ongoing changes in stratospheric ozone and climate. In this Quadrennial Assessment, we examine the interactive effects of changes in stratospheric ozone, UV radiation and climate on terrestrial ecosystems and biogeochemical cycles in the context of the Montreal Protocol. We specifically assess effects on terrestrial organisms, agriculture and food supply, biodiversity, ecosystem services and feedbacks to the climate system. Emphasis is placed on the role of extreme climate events in altering the exposure to UV radiation of organisms and ecosystems and the potential effects on biodiversity. We also address the responses of plants to increased temporal variability in solar UV radiation, the interactive effects of UV radiation and other climate change factors (e.g. drought, temperature) on crops, and the role of UV radiation in driving the breakdown of organic matter from dead plant material (i.e. litter) and biocides (pesticides and herbicides). Our assessment indicates that UV radiation and climate interact in various ways to affect the structure and function of terrestrial ecosystems, and that by protecting the ozone layer, the Montreal Protocol continues to play a vital role in maintaining healthy, diverse ecosystems on land that sustain life on Earth. Furthermore, the Montreal Protocol and its Kigali Amendment are mitigating some of the negative environmental consequences of climate change by limiting the emissions of greenhouse gases and protecting the carbon sequestration potential of vegetation and the terrestrial carbon pool.