Hot topic: Thermosensing in plants

Soybean gene GmMLP34 regulates Arabidopsis negative response to high temperature stress

The functions of major latex proteins (MLPs) in plant defense and stress responses have been widely documented; however, their roles in HT stress response in soybeans have not been elucidated. This study investigated the role of GmMLP34, a member of the major latex protein (MLP) family, in the response of soybeans to HT stress. Transcriptome analysis of HT-resistant (JD21) and HT-sensitive (HD14) soybean leaves under HT stress (43.40 ± 1.70 °C) and field conditions revealed differential expression of GmMLP34. Further examination across different HT-resistant varieties showed that GmMLP34 was down-regulated in the leaves of 6 HT-resistant varieties (85.7 %) and up-regulated in the leaves of 6 HT-sensitive varieties (85.7 %) under the HT treatment (45 °C for 3 h). The results of this study indicate that ectopic expression of the GmMLP34 gene in Arabidopsis led to a significant decrease in the survival rate of seedling when compared to the wild type (WT) under HT stress conditions of 37/28 °C (day/night) for 5 d, Moreover, the results indicated a significant decrease in primary root length and lateral root number under 45 °C/3 h HT stress followed by 12 h room temperature recovery. Additionally, the levels of abscisic acid (ABA), and flavonoids, and the activity of the peroxidase (POD) enzyme in the antioxidant system was decreased, while the activity of the superoxide dismutase (SOD) enzyme increased in GmMLP34-overexpressing transgenic Arabidopsis thaliana. The expression levels of the HT-response genes AtCHS1 and AtCHI2-A, were significantly down-regulated, whereas that of AtGBP1 was significantly up-regulated. These results suggest that GmMLP34 negatively regulates the response of Arabidopsis thaliana to HT stress by modulating flavonoid synthesis, hormone synthesis, and the antioxidant enzyme system. These findings provide theoretical information for the genetic improvement of HT tolerance in soybean and contribute to the understanding of the molecular mechanisms underlying plant responses to abiotic stress.

Genome-wide characterization of RsHDAC gene members unravels a positive role of RsHDA9 in thermotolerance in radish (Raphanus sativus L.)

Radish is an economically important root vegetable crop worldwide. Histone deacetylases (HDACs), one of the most important epigenetic regulators, play prominent roles in plant growth and development as well as abiotic stress responses. Nevertheless, the systematical characterization and critical roles of HDAC gene members in thermogenesis remains elusive in radish. Herein, a total of 21 RsHDAC genes were identified from the radish genome. Among them, two RsSRTs, six RsHDTs and 13 RsHDAs were classified into the SIR2, HD2 and RPD3/HDA1subfamily, respectively. The RNA-seq analysis indicated that three RsHDAs (RsHDA6.1, RsHDA6.2 and RsHDA19) and five RsHDTs exhibited high expression in vascular cambium of radish taproot. Both the RsHDT3 and RsHDA9 showed dramatically up-regulated expression under heat, salt and three heavy metals treatments. Moreover, the transient LUC reporter assay revealed that the promoter activity of the nucleus-localized RsHDA9 was intensely induced by heat stress. Intriguingly, overexpression of RsHDA9 promoted thermotolerance via enhancing proline accumulation and scavenging of reactive oxygen species in radish cotyledons, whereas the supplement of trichostatin A (TSA) led to the opposite phenotype. Notably, RsWRKY26 bound to the RsHDA9 promoter and activated its transcription to achieve enhancing thermotolerance in radish. Collectively, these findings would facilitate deciphering molecular mechanism underlying RsHDA9-mediated regulatory network of thermogenesis in radish.

How Rice Responds to Temperature Changes and Defeats Heat Stress

With the intensification of the greenhouse effect, a series of natural phenomena, such as global warming, are gradually recognized; when the ambient temperature increases to the extent that it causes heat stress in plants, agricultural production will inevitably be affected. Therefore, several issues associated with heat stress in crops urgently need to be solved. Rice is one of the momentous food crops for humans, widely planted in tropical and subtropical monsoon regions. It is prone to high temperature stress in summer, leading to a decrease in yield and quality. Understanding how rice can tolerate heat stress through genetic effects is particularly vital. This article reviews how rice respond to rising temperature by integrating the molecular regulatory pathways and introduce its physiological mechanisms of tolerance to heat stress from the perspective of molecular biology. In addition, genome selection and genetic engineering for rice heat tolerance were emphasized to provide a theoretical basis for the sustainability and stability of crop yield-quality structures under high temperatures from the point of view of molecular breeding.

Unmasking complexities of combined stresses for creating climate-smart crops

Understanding the complex challenges that plants face from multiple stresses is key to developing climate-ready crops. We highlight the significance of the Stress Combinations and their Interactions in Plants database (SCIPdb) for studying the impact of stress combinations on plants and the importance of aligning thematic research programs to create crops aligned with achieving sustainable development goals.

Plant Thermosensors

Plants are exposed to temperature conditions that fluctuate over different time scales, including those inherent to global warming. In the face of these variations, plants sense temperature to adjust their functions and minimize the negative consequences. Transcriptome responses underlie changes in growth, development, and biochemistry (thermomorphogenesis and acclimation to extreme temperatures). We are only beginning to understand temperature sensation by plants. Multiple thermosensors convey complementary temperature information to a given signaling network to control gene expression. Temperature-induced changes in protein or transcript structure and/or in the dynamics of biomolecular condensates are the core sensing mechanisms of known thermosensors, but temperature impinges on their activities via additional indirect pathways. The diversity of plant responses to temperature anticipates that many new thermosensors and eventually novel sensing mechanisms will be uncovered soon.

Identification of heat stress-related genomic regions by genome-wide association study in Solanum tuberosum

The climate crisis impairs yield and quality of crucial crops like potatoes. We investigated the effects of heat stress on five morpho-physiological parameters in a diverse panel of 178 potato cultivars under glasshouse conditions. Overall, heat stress increased shoot elongation and green fresh weight, but reduced tuber yield, starch content and harvest index. Genomic information was obtained from 258 tetraploid and three diploid cultivars by a genotyping-by-sequencing approach using methylation-sensitive restriction enzymes. This resulted in an enrichment of sequences in gene-rich regions. Population structure analyses using genetic distances and hierarchical clustering revealed strong kinship but weak overall population structure cultivars. A genome-wide association study (GWAS) was conducted with a subset of 20 K stringently filtered SNPs to identify quantitative trait loci (QTL) linked to heat tolerance. We identified 67 QTL and established haploblock boundaries to narrow down the number of candidate genes. Additionally, GO-enrichment analyses provided insights into gene functions. Heritability and genomic prediction were conducted to assess the usability of the collected data for selecting breeding material. The detected QTL might be exploited in marker-assisted selection to develop heat-resilient potato cultivars.

Identification of a novel gene, Bryophyte Co-retained Gene 1, that has a positive role in desiccation tolerance in the moss Physcomitrium patens

The moss Physcomitrium patens is a model system for the evolutionary study of land plants, and as such, it may contain as yet unannotated genes with functions related to the adaptation to water deficiency that was required during the water-to-land transition. In this study, we identified a novel gene, Bryophyte Co-retained Gene 1 (BCG1), in P. patens that is responsive to dehydration and rehydration. Under de- and rehydration treatments, BCG1 was significantly co-expressed with DHNA, which encodes a dehydrin (DHN). Examination of previous microarray data revealed that BCG1 is highly expressed in spores, archegonia (female reproductive organ), and mature sporophytes. In addition, the bcg1 mutant showed reduced dehydration tolerance, and this was accompanied by a relatively low level of chlorophyll content during recovery. Comprehensive transcriptomics uncovered a detailed set of regulatory processes that were affected by the disruption to BCG1. Experimental evidence showed that BCG1 might function in antioxidant activity, the abscisic acid pathway, and in intracellular Ca2+ homeostasis to resist desiccation. Overall, our results provide insights into the role of a bryophyte co-retained gene in desiccation tolerance.

RETINOBLASTOMA-RELATED Has Both Canonical and Noncanonical Regulatory Functions During Thermo-Morphogenic Responses in Arabidopsis Seedlings

Warm temperatures accelerate plant growth, but the underlying molecular mechanism is not fully understood. Here, we show that increasing the temperature from 22°C to 28°C rapidly activates proliferation in the apical shoot and root meristems of wild-type Arabidopsis seedlings. We found that one of the central regulators of cell proliferation, the cell cycle inhibitor RETINOBLASTOMA-RELATED (RBR), is suppressed by warm temperatures. RBR became hyper-phosphorylated at a conserved CYCLIN-DEPENDENT KINASE (CDK) site in young seedlings growing at 28°C, in parallel with the stimulation of the expressions of the regulatory CYCLIN D/A subunits of CDK(s). Interestingly, while under warm temperatures ectopic RBR slowed down the acceleration of cell proliferation, it triggered elongation growth of post-mitotic cells in the hypocotyl. In agreement, the central regulatory genes of thermomorphogenic response, including PIF4 and PIF7, as well as their downstream auxin biosynthetic YUCCA genes (YUC1-2 and YUC8-9) were all up-regulated in the ectopic RBR expressing line but down-regulated in a mutant line with reduced RBR level. We suggest that RBR has both canonical and non-canonical functions under warm temperatures to control proliferative and elongation growth, respectively.

The OsSRO1c-OsDREB2B complex undergoes protein phase transition to enhance cold tolerance in rice

Cold stress is one of the major abiotic stress factors affecting rice growth and development, leading to significant yield loss in the context of global climate change. Exploring natural variants that confer cold resistance and the underlying molecular mechanism responsible for this is the major strategy to breed cold-tolerant rice varieties. Here, we show that natural variations of a SIMILAR to RCD ONE (SRO) gene, OsSRO1c, confer cold tolerance in rice at both seedling and booting stages. Our in vivo and in vitro experiments demonstrated that OsSRO1c possesses intrinsic liquid-liquid phase-separation ability and recruits OsDREB2B, an AP2/ERF transcription factor that functions as a positive regulator of cold stress, into its biomolecular condensates in the nucleus, resulting in elevated transcriptional activity of OsDREB2B. We found that the OsSRO1c-OsDREB2B complex directly responds to low temperature through dynamic phase transitions and regulates key cold-response genes, including COLD1. Furthermore, we showed that introgression of an elite haplotype of OsSRO1c into a cold-susceptible indica rice could significantly increase its cold resistance. Collectively, our work reveals a novel cold-tolerance regulatory module in rice and provides promising genetic targets for molecular breeding of cold-tolerant rice varieties.

Thermomorphogenesis of the Arabidopsis thaliana Root: Flexible Cell Division, Constrained Elongation and the Role of Cryptochrome

Understanding how plants respond to temperature is relevant for agriculture in a warming world. Responses to temperature in the shoot have been characterized more fully than those in the root. Previous work on thermomorphogenesis in roots established that for Arabidopsis thaliana (Columbia) seedlings grown continuously at a given temperature, the root meristem produces cells at the same rate at 15°C as at 25°C and the root's growth zone is the same length. To uncover the pathway(s) underlying this constancy, we screened 34 A. thaliana genotypes for parameters related to growth and division. No line failed to respond to temperature. Behavior was little affected by mutations in phytochrome or other genes that underly thermomorphogenesis in shoots. However, a mutant in cryptochrome 2 was disrupted substantially in both cell division and elongation, specifically at 15°C. Among the 34 lines, cell production rate varied extensively and was associated only weakly with root growth rate; in contrast, parameters relating to elongation were stable. Our data are consistent with models of root growth that invoke cell non-autonomous regulation for establishing boundaries between meristem, elongation zone and mature zone.

Genome editing prospects for heat stress tolerance in cereal crops

The world population is steadily growing, exerting increasing pressure to feed in the future, which would need additional production of major crops. Challenges associated with changing and unpredicted climate (such as heat waves) are causing global food security threats. Cereal crops are a staple food for a large portion of the world's population. They are mostly affected by these environmentally generated abiotic stresses. Therefore, it is imperative to develop climate-resilient cultivars to support the sustainable production of main cereal crops (Rice, wheat, and maize). Among these stresses, heat stress causes significant losses to major cereals. These issues can be solved by comprehending the molecular mechanisms of heat stress and creating heat-tolerant varieties. Different breeding and biotechnology techniques in the last decade have been employed to develop heat-stress-tolerant varieties. However, these time-consuming techniques often lack the pace required for varietal improvement in climate change scenarios. Genome editing technologies offer precise alteration in the crop genome for developing stress-resistant cultivars. CRISPR/Cas9 (Clustered regularly interspaced short palindromic repeat/Cas9), one such genome editing platform, recently got scientists' attention due to its easy procedures. It is a powerful tool for functional genomics as well as crop breeding. This review will focus on the molecular mechanism of heat stress and different targets that can be altered using CRISPR/Cas genome editing tools to generate climate-smart cereal crops. Further, heat stress signaling and essential players have been highlighted to provide a comprehensive overview of the topic.

Biomolecular condensates in plant cells: Mediating and integrating environmental signals and development

In response to the spatiotemporal coordination of various biochemical reactions and membrane-encapsulated organelles, plants appear to provide another effective mechanism for cellular organization by phase separation that allows the internal compartmentalization of cells to form a variety of membrane-less organelles. Most of the research on phase separation has centralized in various non-plant systems, such as yeast and animal systems. Recent studies have shown a remarkable correlation between the formation of condensates in plant systems and the formation of condensates in these systems. Moreover, the last decade has made new advances in phase separation research in the context of plant biology. Here, we provide an overview of the physicochemical forces and molecular factors that drive liquid-liquid phase separation in plant cells and the biochemical characterization of condensates. We then explore new developments in phase separation research specific to plants, discussing examples of condensates found in green plants and detailing their role in plant growth and development. We propose that phase separation may be a conserved organizational mechanism in plant evolution to help plants respond rapidly and effectively to various environmental stresses as sessile organisms.

A review on ubiquitin ligases: Orchestrators of plant resilience in adversity

Ubiquitin- proteasome system (UPS) is universally present in plants and animals, mediating many cellular processes needed for growth and development. Plants constantly defend themselves against endogenous and exogenous stimuli such as hormonal signaling, biotic stresses such as viruses, fungi, nematodes, and abiotic stresses like drought, heat, and salinity by developing complex regulatory mechanisms. Ubiquitination is a regulatory mechanism involving selective elimination and stabilization of regulatory proteins through the UPS system where E3 ligases play a central role; they can bind to the targets in a substrate-specific manner, followed by poly-ubiquitylation, and subsequent protein degradation by 26 S proteasome. Increasing evidence suggests different types of E3 ligases play important roles in plant development and stress adaptation. Herein, we summarize recent advances in understanding the regulatory roles of different E3 ligases and primarily focus on protein ubiquitination in plant-environment interactions. It also highlights the diversity and complexity of these metabolic pathways that enable plant to survive under challenging conditions. This reader-friendly review provides a comprehensive overview of E3 ligases and their substrates associated with abiotic and biotic stresses that could be utilized for future crop improvement.

Ozone stress-induced DNA methylation variations and their transgenerational inheritance in foxtail millet

Elevated near-surface ozone (O3) concentrations have surpassed the tolerance limits of plants, significantly impacting crop growth and yield. To mitigate ozone pollution, plants must evolve a rapid and effective defense mechanism to alleviate ozone-induced damage. DNA methylation, as one of the most crucial epigenetic modifications, plays a pivotal role in maintaining gene stability, regulating gene expression, and enhancing plant resilience to environmental stressors. However, the epigenetic response of plants to O3 stress, particularly DNA methylation variations and their intergenerational transmission, remains poorly understood. This study aims to explore the epigenetic mechanisms underlying plant responses to ozone stress across generations and to identify potential epigenetic modification sites or genes crucial in response to ozone stress. Using Open Top Chambers (OTCs), we simulated ozone conditions and subjected foxtail millet to continuous ozone stress at 200 nmol mol-1 for two consecutive generations (S0 and S1). Results revealed that under high-concentration ozone stress, foxtail millet leaves exhibited symptoms ranging from yellowing and curling to desiccation, but the damage in the S1 generation was not more severe than that in the S0 generation. Methylation Sensitive Amplified Polymorphism (MSAP) analysis of the two generations indicated that ozone stress-induced methylation variations ranging from 10.82% to 13.59%, with demethylation events ranged from 0.52% to 5.58%, while hypermethylation occurred between 0.35% and 2.76%. Reproductive growth stages were more sensitive to ozone than vegetative stages. Notably, the S1 generation exhibited widespread demethylation variations, primarily at CNG sites, compared to S0 under similar stress conditions. The inheritance pattern between S0 and S1 generations was mainly of the A-A-B-A type. By recovering and sequencing methylation variant bands, we identified six stress-related differential amplification sequences, implicating these variants in various biological processes. These findings underscore the potential significance of DNA methylation variations as a critical mechanism in plants' response to ozone stress, providing theoretical insights and references for a comprehensive understanding of plant adaptation mechanisms to ozone stress and the epigenetic role of DNA methylation in abiotic stress regulation.

Plant Phytochrome Interactions Decode Light and Temperature Signals

Plant phytochromes perceive red and far-red light to elicit adaptations to the changing environment. Downstream physiological responses revolve around red-light-induced interactions with phytochrome-interacting factors (PIF). Phytochromes double as thermoreceptors, owing to the pronounced temperature dependence of thermal reversion from the light-adapted Pfr to the dark-adapted Pr state. Here, we assess whether thermoreception may extend to the phytochrome:PIF interactions. While the association between Arabidopsis (Arabidopsis thaliana) PHYTOCHROME B (PhyB) and several PHYTOCHROME-INTERACTING FACTOR (PIF) variants moderately accelerates with temperature, the dissociation does more so, thus causing net destabilization of the phytochrome:PIF complex. Markedly different temperature profiles of PIF3 and PIF6 might underlie stratified temperature responses in plants. Accidentally, we identify a photoreception mechanism under strong continuous light, where the extent of phytochrome:PIF complexation decreases with red-light intensity rather than increases. Mathematical modeling rationalizes this attenuation mechanism and ties it to rapid red-light-driven Pr⇄Pfr interconversion and complex dissociation out of Pr. Varying phytochrome abundance, e.g., during diurnal and developmental cycles, and interaction dynamics, e.g., across different PIFs, modify the nature and extent of attenuation, thus permitting light-response profiles more malleable than possible for the phytochrome Pr⇄Pfr interconversion alone. Our data and analyses reveal a photoreception mechanism with implications for plant physiology, optogenetics, and biotechnological applications.

Molecular mechanisms underlying the negative effects of transient heatwaves on crop fertility

Transient heatwaves occurring more frequently as the climate warms, yet their impacts on crop yield are severely underestimated and even overlooked. Heatwaves lasting only a few days or even hours during sensitive stages, such as microgametogenesis and flowering, can significantly reduce crop yield by disrupting plant reproduction. Recent advances in multi-omics and GWAS analysis have shed light on the specific organs (e.g., pollen, lodicule, style), key metabolic pathways (sugar and reactive oxygen species metabolism, Ca2+ homeostasis), and essential genes that are involved in crop responses to transient heatwaves during sensitive stages. This review therefore places particular emphasis on heat-sensitive stages, with pollen development, floret opening, pollination, and fertilization as the central narrative thread. The multifaceted effects of transient heatwaves and their molecular basis are systematically reviewed, with a focus on key structures such as the lodicule and tapetum. A number of heat-tolerance genes associated with these processes have been identified in major crops like maize and rice. The mechanisms and key heat-tolerance genes shared among different stages may facilitate the more precise improvement of heat-tolerant crops.

NAC transcription factor ATAF1 negatively modulates the PIF-regulated hypocotyl elongation under a short-day photoperiod

Day length modulates hypocotyl elongation in seedlings to optimize their overall fitness. Variations in cell growth-associated genes are regulated by several transcription factors. However, the specific transcription factors through which the plant clock increases plant fitness are still being elucidated. In this study, we identified the no apical meristem, Arabidopsis thaliana-activating factor (ATAF-1/2), and cup-shaped cotyledon (NAC) family transcription factor ATAF1 as a novel repressor of hypocotyl elongation under a short-day (SD) photoperiod. Variations in day length profoundly affected the transcriptional and protein levels of ATAF1. ATAF1-deficient mutant exhibited increased hypocotyl length and cell growth-promoting gene expression under SD conditions. Moreover, ATAF1 directly targeted and repressed the expression of the cycling Dof factor 1/5 (CDF1/5), two key transcription factors involved in hypocotyl elongation under SD conditions. Additionally, ATAF1 interacted with and negatively modulated the effects of phytochrome-interacting factor (PIF), thus inhibiting PIF-promoted gene expression and hypocotyl elongation. Taken together, our results revealed ATAF1-PIF as a crucial pair modulating the expression of key transcription factors to facilitate plant growth during day/night cycles under fluctuating light conditions.

Integrative phenotyping analyses reveal the relevance of the phyB-PIF4 pathway in Arabidopsis thaliana reproductive organs at high ambient temperature

BACKGROUND

The increasing ambient temperature significantly impacts plant growth, development, and reproduction. Uncovering the temperature-regulating mechanisms in plants is of high importance, for increasing our fundamental understanding of plant thermomorphogenesis, for its potential in applied science, and for aiding plant breeders in improving plant thermoresilience. Thermomorphogenesis, the developmental response to warm temperatures, has been primarily studied in seedlings and in the regulation of flowering time. PHYTOCHROME B and PHYTOCHROME-INTERACTING FACTORs (PIFs), particularly PIF4, are key components of this response. However, the thermoresponse of other adult vegetative tissues and reproductive structures has not been systematically evaluated, especially concerning the involvement of phyB and PIFs.

RESULTS

We screened the temperature responses of the wild type and several phyB-PIF4 pathway Arabidopsis mutant lines in combined and integrative phenotyping platforms for root growth in soil, shoot, inflorescence, and seed. Our findings demonstrate that phyB-PIF4 is generally involved in the relay of temperature signals throughout plant development, including the reproductive stage. Furthermore, we identified correlative responses to high ambient temperature between shoot and root tissues. This integrative and automated phenotyping was complemented by monitoring the changes in transcript levels in reproductive organs. Transcriptomic profiling of the pistils from plants grown under high ambient temperature identified key elements that may provide insight into the molecular mechanisms behind temperature-induced reduced fertilization rate. These include a downregulation of auxin metabolism, upregulation of genes involved auxin signalling, miRNA156 and miRNA160 pathways, and pollen tube attractants.

CONCLUSIONS

Our findings demonstrate that phyB-PIF4 involvement in the interpretation of temperature signals is pervasive throughout plant development, including processes directly linked to reproduction.

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

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

Multi-scale analysis of heat stress acclimation in Arabidopsis seedlings highlights the primordial contribution of energy-transducing organelles

Much progress has been made in understanding the molecular mechanisms of plant adaptation to heat stress. However, the great diversity of models and stress conditions, and the fact that analyses are often limited to a small number of approaches, complicate the picture. We took advantage of a liquid culture system in which Arabidopsis seedlings are arrested in their development, thus avoiding interference with development and drought stress responses, to investigate through an integrative approach seedlings' global response to heat stress and acclimation. Seedlings perfectly tolerate a noxious heat shock (43°C) when subjected to a heat priming treatment at a lower temperature (38°C) the day before, displaying a thermotolerance comparable to that previously observed for Arabidopsis. A major effect of the pre-treatment was to partially protect energy metabolism under heat shock and favor its subsequent rapid recovery, which was correlated with the survival of seedlings. Rapid recovery of actin cytoskeleton and mitochondrial dynamics were another landmark of heat shock tolerance. The omics confirmed the role of the ubiquitous heat shock response actors but also revealed specific or overlapping responses to priming, heat shock, and their combination. Since only a few components or functions of chloroplast and mitochondria were highlighted in these analyses, the preservation and rapid recovery of their bioenergetic roles upon acute heat stress do not require extensive remodeling of the organelles. Protection of these organelles is rather integrated into the overall heat shock response, thus allowing them to provide the energy required to elaborate other cellular responses toward acclimation.

Bridging the Gap: From Photoperception to the Transcription Control of Genes Related to the Production of Phenolic Compounds

Phenolic compounds are a group of secondary metabolites responsible for several processes in plants-these compounds are involved in plant-environment interactions (attraction of pollinators, repelling of herbivores, or chemotaxis of microbiota in soil), but also have antioxidative properties and are capable of binding heavy metals or screening ultraviolet radiation. Therefore, the accumulation of these compounds has to be precisely driven, which is ensured on several levels, but the most important aspect seems to be the control of the gene expression. Such transcriptional control requires the presence and activity of transcription factors (TFs) that are driven based on the current requirements of the plant. Two environmental factors mainly affect the accumulation of phenolic compounds-light and temperature. Because it is known that light perception occurs via the specialized sensors (photoreceptors) we decided to combine the biophysical knowledge about light perception in plants with the molecular biology-based knowledge about the transcription control of specific genes to bridge the gap between them. Our review offers insights into the regulation of genes related to phenolic compound production, strengthens understanding of plant responses to environmental cues, and opens avenues for manipulation of the total content and profile of phenolic compounds with potential applications in horticulture and food production.

The LOV-domain blue-light receptor LreA of the fungus Alternaria alternata binds predominantly FAD as chromophore and acts as a light and temperature sensor

Light and temperature sensing are important features of many organisms. Light may provide energy but may also be used by non-photosynthetic organisms for orientation in the environment. Recent evidence suggests that plant and fungal phytochrome and plant phototropin serve dual functions as light and temperature sensors. Here we characterized the fungal LOV-domain blue-light receptor LreA of Alternaria alternata and show that it predominantly contains FAD as chromophore. Blue-light illumination induced ROS production followed by protein agglomeration in vitro. In vivo ROS may control LreA activity. LreA acts as a blue-light photoreceptor but also triggers temperature-shift-induced gene expression. Both responses required the conserved amino acid cysteine 421. We therefore propose that temperature mimics the photoresponse, which could be the ancient function of the chromoprotein. Temperature-dependent gene expression control with LreA was distinct from the response with phytochrome suggesting fine-tuned, photoreceptor-specific gene regulation.

CaSTH2 disables CaWRKY40 from activating pepper thermotolerance and immunity against Ralstonia solanacearum via physical interaction

CaWRKY40 coordinately activates pepper immunity against Ralstonia solanacearum infection (RSI) and high temperature stress (HTS), forms positive feedback loops with other positive regulators and is promoted by CaWRKY27b/CaWRKY28 through physical interactions; however, whether and how it is regulated by negative regulators to function appropriately remain unclear. Herein, we provide evidence that CaWRKY40 is repressed by a SALT TOLERANCE HOMOLOG2 in pepper (CaSTH2). Our data from gene silencing and transient overexpression in pepper and epoptic overexpression in Nicotiana benthamiana plants showed that CaSTH2 acted as negative regulator in immunity against RSI and thermotolerance. Our data from BiFC, CoIP, pull down, and MST indicate that CaSTH2 interacted with CaWRKY40, by which CaWRKY40 was prevented from activating immunity or thermotolerance-related genes. It was also found that CaSTH2 repressed CaWRKY40 at least partially through blocking interaction of CaWRKY40 with CaWRKY27b/CaWRKY28, but not through directly repressing binding of CaWRKY40 to its target genes. The results of study provide new insight into the mechanisms underlying the coordination of pepper immunity and thermotolerance.

Early signaling enhance heat tolerance in Arabidopsis through modulating jasmonic acid synthesis mediated by HSFA2

Given the detrimental impact of global warming on crop production, it is particularly important to understand how plants respond and adapt to higher temperatures. Using the non-invasive micro-test technique and laser confocal microscopy, we found that the cascade process of early signals (K+, H2O2, H+, and Ca2+) ultimately resulted in an increase in the cytoplasmic Ca2+ concentration when Arabidopsis was exposed to heat stress. Quantitative real-time PCR demonstrated that heat stress significantly up-regulated the expression of CAM1, CAM3 and HSFA2; however, after CAM1 and CAM3 mutation, the upregulation of HSFA2 was reduced. In addition, heat stress affected the expression of LOX3 and OPR3, which was not observed when HSFA2 was mutated. Luciferase reporter gene expression assay and electrophoretic mobility shift assay showed that HSFA2 regulated the expression of both genes. Determination of jasmonic acid (JA) content showed that JA synthesis was promoted by heat stress, but was damaged when HSFA2 and OPR3 were mutated. Finally, physiological experiments showed that JA reduced the relative electrical conductivity of leaves, enhanced chlorophyll content and relative water content, and improved the survival rate of Arabidopsis under heat stress. Together, our results reveal a new pathway for Arabidopsis to sense and transmit heat signals; HSFA2 is involved in the JA synthesis, which can act as a defensive compound improving Arabidopsis heat tolerance.

The temperature sensor TWA1 is required for thermotolerance in Arabidopsis

Plants exposed to incidences of excessive temperatures activate heat-stress responses to cope with the physiological challenge and stimulate long-term acclimation1,2. The mechanism that senses cellular temperature for inducing thermotolerance is still unclear3. Here we show that TWA1 is a temperature-sensing transcriptional co-regulator that is needed for basal and acquired thermotolerance in Arabidopsis thaliana. At elevated temperatures, TWA1 changes its conformation and allows physical interaction with JASMONATE-ASSOCIATED MYC-LIKE (JAM) transcription factors and TOPLESS (TPL) and TOPLESS-RELATED (TPR) proteins for repressor complex assembly. TWA1 is a predicted intrinsically disordered protein that has a key thermosensory role functioning through an amino-terminal highly variable region. At elevated temperatures, TWA1 accumulates in nuclear subdomains, and physical interactions with JAM2 and TPL appear to be restricted to these nuclear subdomains. The transcriptional upregulation of the heat shock transcription factor A2 (HSFA2) and heat shock proteins depended on TWA1, and TWA1 orthologues provided different temperature thresholds, consistent with the sensor function in early signalling of heat stress. The identification of the plant thermosensors offers a molecular tool for adjusting thermal acclimation responses of crops by breeding and biotechnology, and a sensitive temperature switch for thermogenetics.

Plant thermosensors

Plants dynamically regulate their genes expression and physiological outputs to adapt to changing temperatures. The underlying molecular mechanisms have been extensively studied in diverse plants and in multiple dimensions. However, the question of exactly how temperature is detected at molecular level to transform the physical information into recognizable intracellular signals remains continues to be one of the undetermined occurrences in plant science. Recent studies have provided the physical and biochemical mechanistic breakthrough of how temperature changes can influence molecular thermodynamically stability, thus changing molecular structures, activities, interaction and signaling transduction. In this review, we focus on the thermosensing mechanisms of recognized and potential plant thermosensors, to describe the multi-level thermal input system in plants. We also consider the attributes of a thermosensor on the basis of thermal-triggered changes in function, structure, and physical parameters. This study thus provides a reference for discovering more plant thermosensors and elucidating plant thermal adaptive mechanisms.

Transcription factor CaHDZ15 promotes pepper basal thermotolerance by activating HEAT SHOCK FACTORA6a

High temperature stress (HTS) is a serious threat to plant growth and development and to crop production in the context of global warming, and plant response to HTS is largely regulated at the transcriptional level by the actions of various transcription factors (TFs). However, whether and how homeodomain-leucine zipper (HD-Zip) TFs are involved in thermotolerance are unclear. Herein, we functionally characterized a pepper (Capsicum annuum) HD-Zip I TF CaHDZ15. CaHDZ15 expression was upregulated by HTS and abscisic acid in basal thermotolerance via loss- and gain-of-function assays by virus-induced gene silencing in pepper and overexpression in Nicotiana benthamiana plants. CaHDZ15 acted positively in pepper basal thermotolerance by directly targeting and activating HEAT SHOCK FACTORA6a (HSFA6a), which further activated CaHSFA2. In addition, CaHDZ15 interacted with HEAT SHOCK PROTEIN 70-2 (CaHsp70-2) and glyceraldehyde-3-phosphate dehydrogenase1 (CaGAPC1), both of which positively affected pepper thermotolerance. CaHsp70-2 and CaGAPC1 promoted CaHDZ15 binding to the promoter of CaHSFA6a, thus enhancing its transcription. Furthermore, CaHDZ15 and CaGAPC1 were protected from 26S proteasome-mediated degradation by CaHsp70-2 via physical interaction. These results collectively indicate that CaHDZ15, modulated by the interacting partners CaGAPC1 and CaHsp70-2, promotes basal thermotolerance by directly activating the transcript of CaHSFA6a. Thus, a molecular linkage is established among CaHsp70-2, CaGAPC1, and CaHDZ15 to transcriptionally modulate CaHSFA6a in pepper thermotolerance.

Small but mighty: Peptides regulating abiotic stress responses in plants

Throughout evolution, plants have developed strategies to confront and alleviate the detrimental impacts of abiotic stresses on their growth and development. The combat strategies involve intricate molecular networks and a spectrum of early and late stress-responsive pathways. Plant peptides, consisting of fewer than 100 amino acid residues, are at the forefront of these responses, serving as pivotal signalling molecules. These peptides, with roles similar to phytohormones, intricately regulate plant growth, development and facilitate essential cell-to-cell communications. Numerous studies underscore the significant role of these small peptides in coordinating diverse signalling events triggered by environmental challenges. Originating from the proteolytic processing of larger protein precursors or directly translated from small open reading frames, including microRNA (miRNA) encoded peptides from primary miRNA, these peptides exert their biological functions through binding with membrane-embedded receptor-like kinases. This interaction initiates downstream cellular signalling cascades, often involving major phytohormones or reactive oxygen species-mediated mechanisms. Despite these advances, the precise modes of action for numerous other small peptides remain to be fully elucidated. In this review, we delve into the dynamics of stress physiology, mainly focusing on the roles of major small signalling peptides, shedding light on their significance in the face of changing environmental conditions.

Molecular mechanisms underlying coordinated responses of plants to shade and environmental stresses

Shade avoidance syndrome (SAS) is triggered by a low ratio of red (R) to far-red (FR) light (R/FR ratio), which is caused by neighbor detection and/or canopy shade. In order to compete for the limited light, plants elongate hypocotyls and petioles by deactivating phytochrome B (phyB), a major R light photoreceptor, thus releasing its inhibition of the growth-promoting transcription factors PHYTOCHROME-INTERACTING FACTORs. Under natural conditions, plants must cope with abiotic stresses such as drought, soil salinity, and extreme temperatures, and biotic stresses such as pathogens and pests. Plants have evolved sophisticated mechanisms to simultaneously deal with multiple environmental stresses. In this review, we will summarize recent major advances in our understanding of how plants coordinately respond to shade and environmental stresses, and will also discuss the important questions for future research. A deep understanding of how plants synergistically respond to shade together with abiotic and biotic stresses will facilitate the design and breeding of new crop varieties with enhanced tolerance to high-density planting and environmental stresses.

Maize and heat stress: Physiological, genetic, and molecular insights

Global mean temperature is increasing at a rapid pace due to the rapid emission of greenhouse gases majorly from anthropogenic practices and predicted to rise up to 1.5°C above the pre-industrial level by the year 2050. The warming climate is affecting global crop production by altering biochemical, physiological, and metabolic processes resulting in poor growth, development, and reduced yield. Maize is susceptible to heat stress, particularly at the reproductive and early grain filling stages. Interestingly, heat stress impact on crops is closely regulated by associated environmental covariables such as humidity, vapor pressure deficit, soil moisture content, and solar radiation. Therefore, heat stress tolerance is considered as a complex trait, which requires multiple levels of regulations in plants. Exploring genetic diversity from landraces and wild accessions of maize is a promising approach to identify novel donors, traits, quantitative trait loci (QTLs), and genes, which can be introgressed into the elite cultivars. Indeed, genome wide association studies (GWAS) for mining of potential QTL(s) and dominant gene(s) is a major route of crop improvement. Conversely, mutation breeding is being utilized for generating variation in existing populations with narrow genetic background. Besides breeding approaches, augmented production of heat shock factors (HSFs) and heat shock proteins (HSPs) have been reported in transgenic maize to provide heat stress tolerance. Recent advancements in molecular techniques including clustered regularly interspaced short palindromic repeats (CRISPR) would expedite the process for developing thermotolerant maize genotypes.

A general concept of quantitative abiotic stress sensing

Plants often encounter stress in their environment. For appropriate responses to particular stressors, cells rely on sensory mechanisms that detect emerging stress. Considering sensor and signal amplification characteristics, a single sensor system hardly covers the entire stress range encountered by plants (e.g., salinity, drought, temperature stress). A dual system comprising stress-specific sensors and a general quantitative stress sensory system is proposed to enable the plant to optimize its response. The quantitative stress sensory system exploits the redox and reactive oxygen species (ROS) network by altering the oxidation and reduction rates of individual redox-active molecules under stress impact. The proposed mechanism of quantitative stress sensing also fits the requirement of dealing with multifactorial stress conditions.

HD-Zip I protein LlHOX6 antagonizes homeobox protein LlHB16 to attenuate basal thermotolerance in lily

Homeodomain-leucine zipper (HD-Zip) I transcription factors are crucial for plant responses to drought, salt, and cold stresses. However, how they are associated with thermotolerance remains mostly unknown. We previously demonstrated that lily (Lilium longiflorum) LlHB16 (HOMEOBOX PROTEIN 16) promotes thermotolerance, whereas the roles of other HD-Zip I members are still unclear. Here, we conducted a transcriptomic analysis and identified a heat-responsive HD-Zip I gene, LlHOX6 (HOMEOBOX 6). We showed that LlHOX6 represses the establishment of basal thermotolerance in lily. LlHOX6 expression was rapidly activated by high temperature, and its protein localized to the nucleus. Heterologous expression of LlHOX6 in Arabidopsis (Arabidopsis thaliana) and overexpression in lily reduced their basal thermotolerance. In contrast, silencing LlHOX6 in lily elevated basal thermotolerance. Cooverexpressing or cosilencing LlHOX6 and LlHB16 in vivo compromised their functions in modulating basal thermotolerance. LlHOX6 interacted with itself and with LlHB16, although heterologous interactions were stronger than homologous ones. Notably, LlHOX6 directly bounds DNA elements to repress the expression of the LlHB16 target genes LlHSFA2 (HEAT STRESS TRANSCRIPTION FACTOR A2) and LlMBF1c (MULTIPROTEIN BRIDGING FACTOR 1C). Moreover, LlHB16 activated itself to form a positive feedback loop, while LlHOX6 repressed LlHB16 expression. The LlHOX6-LlHB16 heterooligomers exhibited stronger DNA binding to compete for LlHB16 homooligomers, thus weakening the transactivation ability of LlHB16 for LlHSFA2 and LlMBF1c and reducing its autoactivation. Altogether, our findings demonstrate that LlHOX6 interacts with LlHB16 to limit its transactivation, thereby impairing heat stress responses in lily.

Plants and global warming: challenges and strategies for a warming world

KEY MESSAGE

In this review, we made an attempt to create a holistic picture of plant response to a rising temperature environment and its impact by covering all aspects from temperature perception to thermotolerance. This comprehensive account describing the molecular mechanisms orchestrating these responses and potential mitigation strategies will be helpful for understanding the impact of global warming on plant life. Organisms need to constantly recalibrate development and physiology in response to changes in their environment. Climate change-associated global warming is amplifying the intensity and periodicity of these changes. Being sessile, plants are particularly vulnerable to variations happening around them. These changes can cause structural, metabolomic, and physiological perturbations, leading to alterations in the growth program and in extreme cases, plant death. In general, plants have a remarkable ability to respond to these challenges, supported by an elaborate mechanism to sense and respond to external changes. Once perceived, plants integrate these signals into the growth program so that their development and physiology can be modulated befittingly. This multifaceted signaling network, which helps plants to establish acclimation and survival responses enabled their extensive geographical distribution. Temperature is one of the key environmental variables that affect all aspects of plant life. Over the years, our knowledge of how plants perceive temperature and how they respond to heat stress has improved significantly. However, a comprehensive mechanistic understanding of the process still largely elusive. This review explores how an increase in the global surface temperature detrimentally affects plant survival and productivity and discusses current understanding of plant responses to high temperature (HT) and underlying mechanisms. We also highlighted potential resilience attributes that can be utilized to mitigate the impact of global warming.

Geomagnetic Anomaly in the Growth Response of Peat Moss Sphagnum riparium to Temperature

Temperature plays an essential role in a plant's life. The current investigation reveals that photoreceptors, whose activity is affected by the geomagnetic field, are a critical element of its perception. This knowledge suggests that plants' responses to temperature could shift in different geomagnetic conditions. To test this hypothesis, we studied the change in the growth response of the peat moss Sphagnum riparium to temperature with a gradual increase in the geomagnetic Kp index. Growth data for this species were collected from Karelian mires by detailed monitoring over eight full growing seasons. The growth of 209,490 shoots was measured and 1439 growth rates were obtained for this period. The analysis showed a strong positive dependence of sphagnum growth on temperature (r = 0.58; n = 1439; P = 1.7 × 10-119), which is strongest in the Kp range from 0.87 to 1.61 (r = 0.65; n = 464; P = 4.5 × 10-58). This Kp interval is clearer after removing the seasonal contributions from the growth rate and temperature and is preserved when diurnal temperature is used. Our results are consistent with the hypothesis and show the unknown contribution of the geomagnetic field to the temperature responses of plants.

StHsfB5 Promotes Heat Resistance by Directly Regulating the Expression of Hsp Genes in Potato

With global warming, high temperatures have become a major environmental stress that inhibits plant growth and development. Plants evolve several mechanisms to cope with heat stress accordingly. One of the important mechanisms is the Hsf (heat shock factor)-Hsp (heat shock protein) signaling pathway. Therefore, the plant transcription factor Hsf family plays important roles in response to heat stress. All Hsfs can be divided into three classes (A, B, and C). Usually, class-A Hsfs are transcriptional activators, while class-B Hsfs are transcriptional repressors. In potato, our previous work identified 27 Hsfs in the genome and analyzed HsfA3 and HsfA4C functions that promote potato heat resistance. However, the function of HsfB is still elusive. In this study, the unique B5 member StHsfB5 in potato was obtained, and its characterizations and functions were comprehensively analyzed. A quantitative real-time PCR (qRT-PCR) assay showed that StHsfB5 was highly expressed in root, and its expression was induced by heat treatment and different kinds of phytohormones. The subcellular localization of StHsfB5 was in the nucleus, which is consistent with the characterization of transcription factors. The transgenic lines overexpressing StHsfB5 showed higher heat resistance compared with that of the control nontransgenic lines and inhibitory lines. Experiments on the interaction between protein and DNA indicated that the StHsfB5 protein can directly bind to the promoters of target genes small Hsps (sHsp17.6, sHsp21, and sHsp22.7) and Hsp80, and then induce the expressions of these target genes. All these results showed that StHsfB5 may be a coactivator that promotes potato heat resistance ability by directly inducing the expression of its target genes sHsp17.6, sHsp21, sHsp22.7, and Hsp80.

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

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

The molecular basis of heat stress responses in plants

Global warming impacts crop production and threatens food security. Elevated temperatures are sensed by different cell components. Temperature increases are classified as either mild warm temperatures or excessively hot temperatures, which are perceived by distinct signaling pathways in plants. Warm temperatures induce thermomorphogenesis, while high-temperature stress triggers heat acclimation and has destructive effects on plant growth and development. In this review, we systematically summarize the heat-responsive genetic networks in Arabidopsis and crop plants based on recent studies. In addition, we highlight the strategies used to improve grain yield under heat stress from a source-sink perspective. We also discuss the remaining issues regarding the characteristics of thermosensors and the urgency required to explore the basis of acclimation under multifactorial stress combination.

It is time to move: Heat-induced translocation events

Climate change-induced temperature fluctuations impact agricultural productivity through short-term intense heat waves or long-term heat stress. Plants have evolved sophisticated strategies to deal with heat stress. Understanding perception and transduction of heat signals from outside to inside cells is essential to improve plant thermotolerance. In this review, we will focus on translocation of molecules and proteins associated with signal transduction to understand how plant cells decode signals from the environment to trigger a suitable response.

Epigenetic and transcription factors synergistically promote the high temperature response in plants

Temperature is one of the main environmental cues affecting plant growth and development, and plants have evolved multiple mechanisms to sense and acclimate to high temperature. Emerging research has shown that transcription factors, epigenetic factors, and their coordination are essential for plant temperature responses and the resulting phenological adaptation. Here, we summarize recent advances in molecular and cellular mechanisms to understand how plants acclimate to high temperature and describe how plant meristems sense and integrate environmental signals. Furthermore, we lay out future directions for new technologies to reveal heterogeneous responses in different cell types thus improving plant environmental plasticity.

Photobiotechnology for abiotic stress resilient crops: Recent advances and prospects

Massive crop failures worldwide are caused by abiotic stress. In plants, adverse environmental conditions cause extensive damage to the overall physiology and agronomic yield at various levels. Phytochromes are photosensory phosphoproteins that absorb red (R)/far red (FR) light and play critical roles in different physiological and biochemical responses to light. Considering the role of phytochrome in essential plant developmental processes, genetically manipulating its expression offers a promising approach to crop improvement. Through modulated phytochrome-mediated signalling pathways, plants can become more resistant to environmental stresses by increasing photosynthetic efficiency, antioxidant activity, and expression of genes associated with stress resistance. Plant growth and development in adverse environments can be improved by understanding the roles of phytochromes in stress tolerance characteristics. A comprehensive overview of recent findings regarding the role of phytochromes in modulating abiotic stress by discussing biochemical and molecular aspects of these mechanisms of photoreceptors is offered in this review.

Comparatively Evolution and Expression Analysis of GRF Transcription Factor Genes in Seven Plant Species

Growth regulatory factors (GRF) are plant-specific transcription factors that play pivotal roles in growth and various abiotic stresses regulation. However, adaptive evolution of GRF gene family in land plants are still being elucidated. Here, we performed the evolutionary and expression analysis of GRF gene family from seven representative species. Extensive phylogenetic analyses and gene structure analysis revealed that the number of genes, QLQ domain and WRC domain identified in higher plants was significantly greater than those identified in lower plants. Besides, dispersed duplication and WGD/segmental duplication effectively promoted expansion of the GRF gene family. The expression patterns of GRF gene family and target genes were found in multiple floral organs and abundant in actively growing tissues. They were also found to be particularly expressed in response to various abiotic stresses, with stress-related elements in promoters, implying potential roles in floral development and abiotic stress. Our analysis in GRF gene family interaction network indicated the similar results that GRFs resist to abiotic stresses with the cooperation of other transcription factors like GIFs. This study provides insights into evolution in the GRF gene family, together with expression patterns valuable for future functional researches of plant abiotic stress biology.

Plant water use theory should incorporate hypotheses about extreme environments, population ecology, and community ecology

Plant water use theory has largely been developed within a plant-performance paradigm that conceptualizes water use in terms of value for carbon gain and that sits within a neoclassical economic framework. This theory works very well in many contexts but does not consider other values of water to plants that could impact their fitness. Here, we survey a range of alternative hypotheses for drivers of water use and stomatal regulation. These hypotheses are organized around relevance to extreme environments, population ecology, and community ecology. Most of these hypotheses are not yet empirically tested and some are controversial (e.g. requiring more agency and behavior than is commonly believed possible for plants). Some hypotheses, especially those focused around using water to avoid thermal stress, using water to promote reproduction instead of growth, and using water to hoard it, may be useful to incorporate into theory or to implement in Earth System Models.

Ectopic overexpression of TaHsfA5 promotes thermomorphogenesis in Arabidopsis thaliana and thermotolerance in Oryza sativa

Heat stress transcription factors (Hsfs) play an important role in regulating the heat stress response in plants. Among the Hsf family members, the group A members act upstream in initiating the response upon sensing heat stress and thus, impart thermotolerance to the plants. In the present study, wheat HsfA5 (TaHsfA5) was found to be one of the Hsfs, which was upregulated both in heat stress and during the recovery period after the stress. TaHsfA5 was found to interact with TaHsfA3 and TaHsfA4, both of which are known to positively regulate the heat stress-responsive genes. Apart from these, TaHsfA5 also interacted with TaHSBP2 protein, whose role has been implicated in attenuating the heat stress response. Further, its heterologous overexpression in Arabidopsis and Oryza sativa promoted thermotolerance in these plants. This indicated that TaHsfA5 positively regulated the heat stress response. Interestingly, the TaHsfA5 overexpression Arabidopsis plants when grown at warm temperatures showed  a hyper-thermomorphogenic response in comparison to the wild-type plants. This was found to be consistent with the higher expression of PIF4 and its target auxin-responsive genes in these transgenics in contrast to the wild-type plants. Thus, these results suggest the involvement of TaHsfA5 both in the heat stress response as well as in the thermomorphogenic response in plants.

Dynamic responses of PA to environmental stimuli imaged by a genetically encoded mobilizable fluorescent sensor

Membrane fluidity, permeability, and surface charges are controlled by phospholipid metabolism and transport. Despite the importance of phosphatidic acid (PA) as a bioactive molecule, the mechanical properties of PA translocation and subcellular accumulation are unknown. Here, we used a mobilizable, highly responsive genetically encoded fluorescent indicator, green fluorescent protein (GFP)-N160_RbohD, to monitor PA dynamics in living cells. The majority of GFP-N160_RbohD accumulated at the plasma membrane and sensitively responded to changes in PA levels. Cellular, pharmacological, and genetic analyses illustrated that both salinity and abscisic acid rapidly enhanced GFP-N160_RbohD fluorescence at the plasma membrane, which mainly depended on hydrolysis of phospholipase D. By contrast, heat stress induced nuclear translocation of PA indicated by GFP-N160_RbohD through a process that required diacylglycerol kinase activity, as well as secretory and endocytic trafficking. Strikingly, we showed that gravity triggers asymmetric PA distribution at the root apex, a response that is suppressed by PLDζ2 knockout. The broad utility of the PA sensor will expand our mechanistic understanding of numerous lipid-associated physiological and cell biological processes and facilitate screening for protein candidates that affect the synthesis, transport, and metabolism of PA.

Cytokinins act synergistically with heat acclimation to enhance rice thermotolerance affecting hormonal dynamics, gene expression and volatile emission

Heat stress is a frequent environmental constraint. Phytohormones can significantly affect plant thermotolerance. This study compares the effects of exogenous cytokinin meta-topolin-9-(tetrahydropyran-2-yl)purine (mT9THP) on rice (Oryza sativa) under control conditions, after acclimation by moderate temperature (A; 37 °C, 2h), heat stress (HS; 45 °C, 6h) and their combination (AHS). mT9THP is a stable cytokinin derivative that releases active meta-topolin gradually, preventing the rapid deactivation reported after exogenous cytokinin application. Under control conditions, mT9THP negatively affected jasmonic acid in leaves and abscisic and salicylic acids in crowns (meristematic tissue crucial for tillering). Exogenous cytokinin stimulated the emission of volatile organic compounds (VOC), especially 2,3-butanediol. Acclimation upregulated trans-zeatin, expression of stress- and hormone-related genes, and VOC emission. The combination of acclimation and mT9THP promoted the expression of stress markers and antioxidant enzymes and moderately increased VOC emission, including 2-ethylhexyl salicylate or furanones. AHS and HS responses shared some common features, namely, increase of ethylene precursor aminocyclopropane-1-carboxylic acid (ACC), cis-zeatin and cytokinin methylthio derivatives, as well as the expression of heat shock proteins, alternative oxidases, and superoxide dismutases. AHS specifically induced jasmonic acid and auxin indole-3-acetic acid levels, diacylglycerolipids with fewer double bonds, and VOC emissions [e.g., acetamide, lipoxygenase (LOX)-derived volatiles]. Under direct HS, exogenous cytokinin mimicked some positive acclimation effects. The combination of mT9THP and AHS had the strongest thermo-protective effect, including a strong stimulation of VOC emissions (including LOX-derived ones). These results demonstrate for the first time the crucial contribution of volatiles to the beneficial effects of cytokinin and AHS on rice thermotolerance.

Genome-wide characterization of RsHSP70 gene family reveals positive role of RsHSP70-20 gene in heat stress response in radish (Raphanus sativus L.)

Radish is an economical cool-season root vegetable crop worldwide. Heat shock protein 70 (HSP70) plays indispensable roles in plant growth, development and abiotic stress responses. Nevertheless, little information is available regarding the identification and functional characterization of HSP70 gene family in radish. Herein, a total of 34 RsHSP70 genes were identified at the radish genome level, among which nine and 25 RsHSP70s were classified into the HSP110/SSE and DnaK subfamilies, respectively. RNA-seq analysis revealed that some RsHSP70 genes had differential expression profile in radish leaf, root, stamen and pistil. A range of RsHSP70 genes exhibited differential expression under several abiotic stresses such as heat, salt and heavy metals. Intriguingly, the expression of four RsHSP70 genes (RsHSP70-7, RsHSP70-12, RsHSP70-20 and RsHSP70-22) was dramatically up-regulated under heat stress (HS). RT-qPCR and transient LUC reporter assay indicated that both the expression and promoter activity of RsHSP70-20 was strongly induced by HS. Notably, overexpression of RsHSP70-20 significantly enhanced thermotolerance by decreasing reactive oxygen species and promoting proline accumulation in radish, whereas its knock-down plants exhibited increased thermosensitivity, indicating that RsHSP70-20 positively regulate HS response in radish. These results would provide valuable information to decipher the molecular basis of RsHSP70-mediated thermotolerance in radish.

High triacylglycerol turnover is required for efficient opening of stomata during heat stress in Arabidopsis

Heat stress triggers the accumulation of triacylglycerols in Arabidopsis leaves, which increases basal thermotolerance. However, how triacylglycerol synthesis is linked to thermotolerance remains unclear and the mechanisms involved remain to be elucidated. It has been shown that triacylglycerol and starch degradation are required to provide energy for stomatal opening induced by blue light at dawn. To investigate whether triacylglycerol turnover is involved in heat-induced stomatal opening during the day, we performed feeding experiments with labeled fatty acids. Heat stress strongly induced both triacylglycerol synthesis and degradation to channel fatty acids destined for peroxisomal ß-oxidation through the triacylglycerol pool. Analysis of mutants defective in triacylglycerol synthesis or peroxisomal fatty acid uptake revealed that triacylglycerol turnover and fatty acid catabolism are required for heat-induced stomatal opening in illuminated leaves. We show that triacylglycerol turnover is continuous (1.2 mol% per min) in illuminated leaves even at 22°C. The ß-oxidation of triacylglycerol-derived fatty acids generates C₂ carbon units that are channeled into the tricarboxylic acid pathway in the light. In addition, carbohydrate catabolism is required to provide oxaloacetate as an acceptor for peroxisomal acetyl-CoA and maintain the tricarboxylic acid pathway for energy and amino acid production during the day.

HOS15 represses flowering by promoting GIGANTEA degradation in response to low temperature in Arabidopsis

Flowering is the primary stage of the plant developmental transition and is tightly regulated by environmental factors such as light and temperature. However, the mechanisms by which temperature signals are integrated into the photoperiodic flowering pathway are still poorly understood. Here, we demonstrate that HOS15, which is known as a GI transcriptional repressor in the photoperiodic flowering pathway, controls flowering time in response to low ambient temperature. At 16°C, the hos15 mutant exhibits an early flowering phenotype, and HOS15 acts upstream of photoperiodic flowering genes (GI, CO, and FT). GI protein abundance is increased in the hos15 mutant and is insensitive to the proteasome inhibitor MG132. Furthermore, the hos15 mutant has a defect in low ambient temperature-mediated GI degradation, and HOS15 interacts with COP1, an E3 ubiquitin ligase for GI degradation. Phenotypic analyses of the hos15 cop1 double mutant revealed that repression of flowering by HOS15 is dependent on COP1 at 16°C. However, the HOS15-COP1 interaction was attenuated at 16°C, and GI protein abundance was additively increased in the hos15 cop1 double mutant, indicating that HOS15 acts independently of COP1 in GI turnover at low ambient temperature. This study proposes that HOS15 controls GI abundance through multiple modes as an E3 ubiquitin ligase and transcriptional repressor to coordinate appropriate flowering time in response to ambient environmental conditions such as temperature and day length.

Physiological responses induced by phospholipase C isoform 5 upon heat stress in Arabidopsis thaliana

Plant's perception of heat stress involves several pathways and signaling molecules, such as phosphoinositide, which is derived from structural membrane lipids phosphatidylinositol. Phospholipase C (PLC) is a well-known signaling enzyme containing many isoforms in different organisms. In the present study, Phospholipase C Isoform 5 (PLC5) was investigated for its role in thermotolerance in Arabidopsis thaliana. Two over-expressing lines and one knock-down mutant of PLC5 were first treated at a moderate temperature (37 °C) and left for recovery. Then again exposed to a high temperature (45 °C) to check the seedling viability and chlorophyll contents. Root behavior and changes in ³²P_i labeled phospholipids were investigated after their exposure to high temperatures. Over-expression of PLC5 (PLC5 OE) exhibited quick and better phenotypic recovery with bigger and greener leaves followed by chlorophyll contents as compared to wild-type (Col-0) and PLC5 knock-down mutant in which seedling recovery was compromised. PLC5 knock-down mutant illustrated well-developed root architecture under controlled conditions but stunted secondary roots under heat stress as compared to over-expressing PLC5 lines. Around 2.3-fold increase in phosphatidylinositol 4,5-bisphosphate level was observed in PLC5 OE lines upon heat stress compared to wild-type and PLC5 knock-down mutant lines. A significant increase in phosphatidylglycerol was also observed in PLC5 OE lines as compared to Col-0 and PLC5 knock-down mutant lines. The results of the present study demonstrated that PLC5 over-expression contributes to heat stress tolerance while maintaining its photosynthetic activity and is also observed to be associated with primary and secondary root growth in Arabidopsis thaliana.

Arabidopsis LSH10 transcription factor and OTLD1 histone deubiquitinase interact and transcriptionally regulate the same target genes

Histone ubiquitylation/deubiquitylation plays a major role in the epigenetic regulation of gene expression. In plants, OTLD1, a member of the ovarian tumor (OTU) deubiquitinase family, deubiquitylates histone 2B and represses the expression of genes involved in growth, cell expansion, and hormone signaling. OTLD1 lacks the intrinsic ability to bind DNA. How OTLD1, as well as most other known plant histone deubiquitinases, recognizes its target genes remains unknown. Here, we show that Arabidopsis transcription factor LSH10, a member of the ALOG protein family, interacts with OTLD1 in living plant cells. Loss-of-function LSH10 mutations relieve the OTLD1-promoted transcriptional repression of the target genes, resulting in their elevated expression, whereas recovery of the LSH10 function results in down-regulated transcription of the same genes. We show that LSH10 associates with the target gene chromatin as well as with DNA sequences in the promoter regions of the target genes. Furthermore, without LSH10, the degree of H2B monoubiquitylation in the target promoter chromatin increases. Hence, our data suggest that OTLD1-LSH10 acts as a co-repressor complex potentially representing a general mechanism for the specific function of plant histone deubiquitinases at their target chromatin.