Martijn van Zanten

Summary: Stomata, the micropores on plant epidermal surfaces, balance the gain of inorganic carbon with evaporative loss of water. Stomata consist of two specialised guard cells that regulate aperture in a turgor‐driven manner. Stomatal development (number and size) and dynamics (opening and closing) are both factors determining performance and survival under stressful conditions. Understanding the regulatory mechanisms of stomatal development and dynamics is thus key for developing crops that are resilient to climate warming. This Tansley insight summarises the current knowledge of how temperature cues control stomatal dynamics for rapid responses and feed into stomatal developmental programmes for long‐term adaptation.

Arabidopsis thaliana naturally occurs across a wide geographic range and displays extensive natural variation in several traits including adaptive responses to the abiotic environment (e.g. temperature, drought, salt). Quantitative techniques like Genome Wide Association Studies (GWAS) enable mapping the genetic basis of such environmental responses and benefits from extensive genetic variation, but the size of the chosen diversity panel is often limited by phenotyping capacity. Most studies therefore use subpanels, often based on maximization of genetic diversity. However, this type of selection may overrepresent cosmopolitan alleles and underrepresent rare environment-specific alleles. Here, we demonstrate that the genetic variation in a GWAS subpanel of Arabidopsis thaliana accessions depends almost entirely on the number of accessions in the panel and very little on the composition of the panel. We present the EcoCore panel designed by grouping accessions of the 1001 genomes (1001G; 1135 accessions) collection, based on their native collection environment and selecting an equal number of accessions from each environment. We assessed hypocotyl lengths of plants grown at control and ambient high temperatures (20°C and 28°C) for 913 accessions of the 1001G and mapped these traits with the full 1001G panel versus the EcoCore panel. The EcoCore panel revealed novel genetic associations with hypocotyl length which is attributed to enrichment of alleles from rare environments. We present the EcoCore panel as a manageable resource for studying phenotypic plasticity and the genetic basis of plant–environment interactions.

Climate change forces species to adapt rapidly to avoid extinction. To directly observe rapid adaptation and extinction, we conducted synchronized evolution experiments with Arabidopsis thaliana in 30 locations across Western Europe, the Mediterranean, the Levant, and North America. Whole-genome pooled sequencing of ~70,000 surviving plants revealed repeatable allele frequency shifts in similar climates but divergent shifts across contrasting ones, indicating evolutionary adaptation. We identified genetic variants linked to climate adaptation, including genes involved in processes ranging from thermal-stress sensing to spring-flowering timing. Evolutionary trends were often predictable, but variable, across environments. In warmer climates, evolutionary predictability correlated with population survival over 5 years, whereas erratic changes preceded extinction. These results show that rapid climate adaptation is possible, but understanding its limits will be crucial for biodiversity forecasting.

Climate change drastically impacts the development, physiology, and phenology of plants. Conducting experiments to elucidate plant responses to high temperatures is essential to understanding and mitigating the impact of global warming. Typically, empirical research assessing the impact of (high) temperatures is conducted in climate-controlled growth chambers, cabinets, or greenhouses. Although informative, such experiments ignore the effects that seasonal, daily, and minute-scale changes in environmental parameters can have on temperature responsiveness. Semi-controlled field warming setups are therefore required in which average temperatures are consistently raised whereas other environmental parameters, such as diurnal fluctuations in temperature, rainfall, changes in light intensity, and photoperiod, remain reasonably unaffected. Here, we present a low-cost, low-input (in terms of construction materials and energy expenditure), field warming setup in which heating cables were combined with a PMMA/acrylic Open Top Chamber (OTC) and show that this setup can effectively raise internal temperatures by ~3 °C-5°C above ambient in field conditions. Assessing shoot phenotypes of cold-tolerant common snowdrops (Galanthus nivalis), Arabidopsis thaliana natural accessions, and tomato (Solanum lycopersicum) confirmed that the OTC setup can be used to study shoot responsiveness to high temperatures in the context of the stochastic outdoor environment. The low-cost materials used, combined with provided construction details and software code, should encourage the swift development of warmed OTCs by researchers worldwide.

Plants frequently encounter a range of abiotic stresses and their combinations. Even though stresses rarely occur in isolation, research on plant stress resilience typically focuses on single environmental stressors. Plant responses to abiotic stress combinations are often distinct from corresponding individual stresses. Factors determining the outcomes of combined stresses are complex and multifaceted. In this review, we summarize advancements in our understanding of the mechanisms underlying plant responses to co-occurring (combined and sequential) abiotic stresses, focusing on morphological, physiological, developmental, and molecular aspects. Comprehensive understanding of plant acclimation, including the signaling and response mechanisms to combined and individual stresses, can contribute to the development of strategies for enhancing plant resilience in dynamic environments.

Plants continuously respond to changing environmental conditions to prevent damage and maintain optimal performance. To regulate gas exchange with the environment and to control abiotic stress relief, plants have pores in their leaf epidermis, called stomata. Multiple environmental signals affect the opening and closing of these stomata. High temperatures promote stomatal opening (to cool down), and drought induces stomatal closing (to prevent water loss). Coinciding stress conditions may evoke conflicting stomatal responses, but the cellular mechanisms to resolve these conflicts are unknown. Here we demonstrate that the high-temperature-associated kinase TARGET OF TEMPERATURE 3 directly controls the activity of plasma membrane H⁺-ATPases to induce stomatal opening. OPEN STOMATA 1, which regulates stomatal closure to prevent water loss during drought stress, directly inactivates TARGET OF TEMPERATURE 3 through phosphorylation. Taken together, this signalling axis harmonizes stomatal opening and closing under high temperatures and/or drought. In the context of global climate change, understanding how different stress signals converge on stomatal regulation allows the development of climate-change-ready crops.

Plants are frequently exposed to environmental challenges. Responses to sub-lethal abiotic stress combinations are complex and often distinct from responses to individual stresses and remain poorly understood. Investigating traits and molecular factors mediating acclimation to stress combinations is essential for the development of climate change-resilient field crops. Here, we studied the morphological, physiological, and molecular responses of Arabidopsis thaliana to i) co-occurring high temperature and drought and ii) flooding followed by drought, both of which have increased in frequency due to climate change, and the individual component stresses: high temperature, drought and flooding. A set of 15 physiological and morphological traits were assessed during single and combined stresses. By combining these comprehensive trait analyses with transcriptome characterization, we established the generally additive negative effects of simultaneous or sequential stresses on plant morphology and physiology compared to the corresponding individual stresses. Although drought had a mild effect on various growth, morphological and physiological traits in both stress combinations, a unique transcriptome signature emerged upon combination with high temperature simultaneously or flooding sequentially. Molecular processes identified as important for multi-stress resilience included plastid-nucleus communication, ABA signaling and photo-acclimation. Based on the RNA-seq data, a set of 39 genes was identified as potential multi-stress response regulators. Mutants were tested to validate the contribution of these genes to plant survival and phenotypic acclimation under combined stress. We confirmed the involvement of several genes in regulating phenotypic acclimation traits. Among the identified factors were EARLY FLOWERING 6 (ELF6) and ARABIDOPSIS TÓXICOS EN LEVADURA 80 (ATL80), with substantial effects on plant growth, leaf development and plant survival (wilting) during high-temperature drought and post-submergence drought, respectively.

Plants must cope with ever-changing temperature conditions in their environment. In many plant species, suboptimal high and low temperatures can induce adaptive mechanisms that allow optimal performance. Thermomorphogenesis is the acclimation to high ambient temperature, whereas cold acclimation refers to the acquisition of cold tolerance following a period of low temperatures. The molecular mechanisms underlying thermomorphogenesis and cold acclimation are increasingly well understood but neither signalling components that have an apparent role in acclimation to both cold and warmth, nor factors determining dose-responsiveness, are currently well defined. This can be explained in part by practical limitations, as applying temperature gradients requires the use of multiple growth conditions simultaneously, usually unavailable in research laboratories. Here we demonstrate that commercially available thermal gradient tables can be used to grow and assess plants over a defined and adjustable steep temperature gradient within one experiment. We describe technical and thermodynamic aspects and provide considerations for plant growth and treatment. We show that plants display the expected morphological, physiological, developmental and molecular responses that are typically associated with high temperature and cold acclimation. This includes temperature dose-response effects on seed germination, hypocotyl elongation, leaf development, hyponasty, rosette growth, temperature marker gene expression, stomatal conductance, chlorophyll content, ion leakage and hydrogen peroxide levels. In conclusion, thermal gradient table systems enable standardized and predictable environments to study plant responses to varying temperature regimes and can be swiftly implemented in research on temperature signalling and response.

Plants are frequently exposed to environmental challenges. Responses to sub-lethal abiotic stress combinations are complex and often distinct from responses to individual stresses and remain poorly understood. Investigating traits and molecular factors mediating acclimation to stress combinations is essential for the development of climate change-resilient field crops. Here, we studied the morphological, physiological, and molecular responses of Arabidopsis thaliana to i) co-occurring high temperature and drought and ii) flooding sequentially followed by drought, both of which have increased in frequency due to climate change. A set of 15 physiological and morphological traits were assessed during single and combined stresses. By combining these comprehensive trait analyses with transcriptome characterization, we established the generally additive effects of simultaneous or sequential stresses on plant morphology and physiology compared to the corresponding individual stresses. Although drought had a mild effect in both stress combinations, a unique transcriptome signature emerged upon combination with high temperature simultaneously or flooding sequentially. Molecular processes identified as important for multi-stress resilience included plastid-nucleus communication, ABA signaling and photo-acclimation. Based on the RNA-seq data, a set of 39 genes was identified as potential multi-stress response regulators. Mutants were tested to validate their contribution to plant survival and phenotypic acclimation under combined stress. We confirmed the involvement of several genes in regulating phenotypic acclimation traits. Among the novel identified factors are EARLY FLOWERING 6 (ELF6) and ARABIDOPSIS TÓXICOS EN LEVADURA (ATL80), with significant effects on plant growth, leaf development and plant survival (wilting) during high-temperature drought and post-submergence drought respectively.

Plants continuously respond to changing environmental conditions to prevent damage and maintain optimal performance. To regulate gas exchange with the environment and to control abiotic stress relief, plants have pores in their leaf epidermis, called stomata 1. Multiple environmental signals affect the opening and closing of these stomata 2. Heat promotes stomatal opening (to cool down) and drought induces stomatal closing (to prevent water loss). Coinciding stress conditions, however, may evoke conflicting stomatal responses, but the cellular mechanisms to resolve these conflicts are unknown. Here, we demonstrate that the high temperature-associated kinase TARGET OF TEMPERATURE 3 (TOT3) directly controls the activity of plasma membrane H+-ATPases to induce stomatal opening. This TOT3 activity is directly antagonized by OPEN STOMATA 1 (OST1), to prevent water loss during drought stress. This signaling axis harmonizes conflicting heat and drought signals to regulate stomatal aperture. In the context of global climate change, understanding how conflicting stress signals converge on stomatal regulation allows the development of climate change-ready crops.