An Overview of Biomembrane Functions in Plant Responses to High-Temperature Stress

E3 SUMO ligase SIZ1 splicing variants localize and function according to external conditions

SIZ1 (SAP and MIZ1) is a member of the Siz/PIAS-type RING family of E3 SUMO (small ubiquitin-related modifier) ligases that play key roles in growth, development, and stress responses in plant and animal systems. Nevertheless, splicing variants of SIZ1 have not yet been characterized. Here, we identified four splicing variants of Arabidopsis (Arabidopsis thaliana) SIZ1, which encode three different protein isoforms. The SIZ1 gene encodes an 873-amino acid (aa) protein. Among the four SIZ1 splicing variants (SSVs), SSV1 and SSV4 encode identical 885 aa proteins; SSV2 encodes an 832 aa protein; and SSV3 encodes an 884 aa protein. SSV2 mainly localized to the plasma membrane, whereas SIZ1, SSV1/SSV4, and SSV3 localized to the nucleus. Interestingly, SIZ1 and all SSVs exhibited similar E3 SUMO ligase activities and preferred SUMO1 and SUMO2 for their E3 ligase activity. Transcript levels of SSV2 were substantially increased by heat treatment, while those of SSV1, SSV3, and SSV4 transcripts were unaffected by various abiotic stresses. SSV2 directly interacted with and sumoylated cyclic nucleotide-gated ion channel 6 (CNGC6), a positive thermotolerance regulator, enhancing the stability of CNGC6. Notably, transgenic siz1-2 mutants expressing SSV2 exhibited greater heat stress tolerance than wild-type plants, whereas those expressing SIZ1 were sensitive to heat stress. Furthermore, transgenic cngc6 plants overaccumulating a mutated mCNGC6 protein (K347R, a mutation at the sumoylation site) were sensitive to heat stress, similar to the cngc6 mutants, while transgenic cngc6 plants overaccumulating CNGC6 exhibited restored heat tolerance. Together, we propose that alternative splicing is an important mechanism that regulates the function of SSVs during development or under adverse conditions, including heat stress.

Differential heat-response characteristics of two plastid isoforms of triose phosphate isomerase in tomato

Heat stress causes dysfunction of the carbon-assimilation metabolism. As a member of Calvin-Benson-Bassham (CBB) cycle, the chloroplast triose phosphate isomerases (TPI) catalyse the interconversion of glyceraldehyde 3-phosphate (GAP) and dihydroxyacetone phosphate (DHAP). The tomato (Solanum lycopersicum) genome contains two individual SlTPI genes, Solyc10g054870 and Solyc01g111120, which encode the chloroplast-located proteins SlTPI1 and SlTPI2, respectively. The tpi1 and tpi2 single mutants had no visible phenotypes, but the leaves of their double mutant lines tpi1tpi2 had obviously reduced TPI activity and displayed chlorotic variegation, dysplasic chloroplasts and lower carbon-assimilation efficiency. In addition to altering carbon metabolism, proteomic data showed that the loss of both SlTPI1 and SlTPI2 severely affected photosystem proteins, reducing photosynthetic capacity. None of these phenotypes was evident in the tpi1 or tpi2 single mutants, suggesting that SlTPI1 and SlTPI2 are functionally redundant. However, the two proteins differed in their responses to heat stress; the protein encoded by the heat-induced SlTPI2 showed a higher level of thermotolerance than that encoded by the heat-suppressed SlTPI1. Notably, heat-induced transcription factors, SlWRKY21 and SlHSFA2/7, which negatively regulated SlTPI1 expression and positively regulated SlTPI2 expression, respectively. Our findings thus reveal that SlTPI1 and SlTPI2 have different thermostabilities and expression patterns in response to heat stress, which have the potential to be applied in thermotolerance strategies in crops.

Thermoprotection by a cell membrane-localized metacaspase in a green alga

Caspases are restricted to animals, while other organisms, including plants, possess metacaspases (MCAs), a more ancient and broader class of structurally related yet biochemically distinct proteases. Our current understanding of plant MCAs is derived from studies in streptophytes, and mostly in Arabidopsis (Arabidopsis thaliana) with 9 MCAs with partially redundant activities. In contrast to streptophytes, most chlorophytes contain only 1 or 2 uncharacterized MCAs, providing an excellent platform for MCA research. Here we investigated CrMCA-II, the single type-II MCA from the model chlorophyte Chlamydomonas (Chlamydomonas reinhardtii). Surprisingly, unlike other studied MCAs and similar to caspases, CrMCA-II dimerizes both in vitro and in vivo. Furthermore, activation of CrMCA-II in vivo correlated with its dimerization. Most of CrMCA-II in the cell was present as a proenzyme (zymogen) attached to the plasma membrane (PM). Deletion of CrMCA-II by genome editing compromised thermotolerance, leading to increased cell death under heat stress. Adding back either wild-type or catalytically dead CrMCA-II restored thermoprotection, suggesting that its proteolytic activity is dispensable for this effect. Finally, we connected the non-proteolytic role of CrMCA-II in thermotolerance to the ability to modulate PM fluidity. Our study reveals an ancient, MCA-dependent thermotolerance mechanism retained by Chlamydomonas and probably lost during the evolution of multicellularity.

A quick and effective method for thermostability differentiation in cucumber (Cucumis sativus L.)

High temperature affects the growth and production of cucumber. Selecting thermotolerant cucumber cultivars is conducive to coping with high temperatures and improving production. Thus, a quick and effective method for screening thermotolerant cucumber cultivars is needed. In this study, four cucumber cultivars were used to identify heat resistance indexes. The morphological, physiological and biochemical indexes were measured. When exposed to high temperatures, thermotolerant cucumber had a more stable photosystem, membrane, and oxidation-reduction systems. The impact of high temperatures on plants is multifaceted, and the accurate discrimination of heat resistance cannot be achieved solely based on a single or multiple indicators. Therefore, principal component analysis (PCA) was employed to comprehensively evaluate the heat resistance of cucumber plants. The results showed that the heat resistance obtained by PCA was significantly correlated with the heat injury index. In addition, the stepwise regression equation identified two heat-related indices, hydrogen peroxide content (H2 O2 ) and photosynthetic operating efficiency (Fq'/Fm'), and they can quickly distinguish the heat resistance of the other 8 cucumber cultivars. These results will help to accelerate the selection of thermotolerant resources and assist in cucumber breeding.

Regulation of PIN polarity in response to abiotic stress

Plants have evolved robust adaptive mechanisms to withstand the ever-changing environment. Tightly regulated distribution of the hormone auxin throughout the plant body controls an impressive variety of developmental processes that tailor plant growth and morphology to environmental conditions. The proper flow and directionality of auxin between cells is mainly governed by asymmetrically localized efflux carriers - PINs - ensuring proper coordination of developmental processes in plants. Discerning the molecular players and cellular dynamics involved in the establishment and maintenance of PINs in specific membrane domains, as well as their ability to readjust in response to abiotic stressors is essential for understanding how plants balance adaptability and stability. While much is known about how PINs get polarized, there is still limited knowledge about how abiotic stresses alter PIN polarity by acting on these systems. In this review, we focus on the current understanding of mechanisms involved in (re)establishing and maintaining PIN polarity under abiotic stresses.

Response Mechanisms of Woody Plants to High-Temperature Stress

High-temperature stress is the main environmental stress that restricts the growth and development of woody plants, and the growth and development of woody plants are affected by high-temperature stress. The influence of high temperature on woody plants varies with the degree and duration of the high temperature and the species of woody plants. Woody plants have the mechanism of adapting to high temperature, and the mechanism for activating tolerance in woody plants mainly counteracts the biochemical and physiological changes induced by stress by regulating osmotic adjustment substances, antioxidant enzyme activities and transcription control factors. Under high-temperature stress, woody plants ability to perceive high-temperature stimuli and initiate the appropriate physiological, biochemical and genomic changes is the key to determining the survival of woody plants. The gene expression induced by high-temperature stress also greatly improves tolerance. Changes in the morphological structure, physiology, biochemistry and genomics of woody plants are usually used as indicators of high-temperature tolerance. In this paper, the effects of high-temperature stress on seed germination, plant morphology and anatomical structure characteristics, physiological and biochemical indicators, genomics and other aspects of woody plants are reviewed, which provides a reference for the study of the heat-tolerance mechanism of woody plants.

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.

Regulatory network of rice in response to heat stress and its potential application in breeding strategy

The rapid development of global industrialization has led to serious environmental problems, among which global warming has become one of the major concerns. The gradual rise in global temperature resulted in the loss of food production, and hence a serious threat to world food security. Rice is the main crop for approximately half of the world's population, and its geographic distribution, yield, and quality are frequently reduced due to elevated temperature stress, and breeding rice varieties with tolerance to heat stress is of immense significance. Therefore, it is critical to study the molecular mechanism of rice in response to heat stress. In the last decades, large amounts of studies have been conducted focusing on rice heat stress response. Valuable information has been obtained, which not only sheds light on the regulatory network underlying this physiological process but also provides some candidate genes for improved heat tolerance breeding in rice. In this review, we summarized the studies in this field. Hopefully, it will provide some new insights into the mechanisms of rice under high temperature stress and clues for future engineering breeding of improved heat tolerance rice.

Physiological and metabolic changes in response to Boron levels are mediated by ethylene affecting tomato fruit yield

Boron (B) is an essential nutrient for the plant, and its stress (both deficiency and toxicity) are major problems that affect crop production. Ethylene metabolism (both signaling and production) is important to plants' differently responding to nutrient availability. To better understand the connections between B and ethylene, here we investigate the function of ethylene in the responses of tomato (Solanum lycopersicum) plants to B stress (deficiency, 0 μM and toxicity, 640 μM), using ethylene related mutants, namely nonripening (nor), ripening-inhibitor (rin), never ripe (Nr), and epinastic (Epi). Our results show that B stress does not necessarily inhibit plant growth, but both B stress and ethylene signaling severely affected physiological parameters, such as photosynthesis, stomatal conductance, and chlorophyll a fluorescence. Under B toxicity, visible symptoms of toxicity appeared in the roots and margins of the older leaves through necrosis, caused by the accumulation of B which stimulated ethylene biosynthesis in the shoots. Both nor and rin (ethylene signaling) mutants presented similar responses, being these genotypes more sensitive and displaying several morphophysiological alterations, including fruit productivity reductions, in response to the B toxicity conditions. Therefore, our results suggest that physiological and metabolic changes in response to B fluctuations are likely mediated by ethylene signaling.

Malondialdehyde enhances PsbP protein release during heat stress in Arabidopsis

Under environmental conditions, plants are exposed to various abiotic and biotic stress factors, which commonly cause the oxidation of lipids and proteins. Lipid peroxidation constantly produces malondialdehyde (MDA), a secondary product of lipid peroxidation, which is covalently bound to proteins forming MDA-protein adducts. The spatial distribution of MDA-protein adducts in Arabidopsis leaves shows that MDA-protein adducts are located in the chloroplasts, uniformly spread out over the thylakoid membrane. At the lumenal side of thylakoid membrane, MDA interacts with PsbP, an extrinsic subunit of the photosystem II (PSII), which is in electrostatic interaction with the PSII core proteins. Under heat stress, when MDA is moderately enhanced, the electrostatic interaction between PsbP and PSII core proteins is weakened, and PsbP with bound MDA is released in the lumen. It is proposed here that the electrophilic MDA is bound to the nucleophilic lysine residues of PsbP, which are involved in electrostatic interactions with the negatively charged glutamate of the PSII core protein. Our data provide crucial information about the MDA binding topology in the higher plant PSII complex, which is necessary to understand better the physiological functions of MDA for plant survival under stress.

When drought meets heat - a plant omics perspective

Changes in weather patterns with emerging drought risks and rising global temperature are widespread and negatively affect crop growth and productivity. In nature, plants are simultaneously exposed to multiple biotic and abiotic stresses, but most studies focus on individual stress conditions. However, the simultaneous occurrence of different stresses impacts plant growth and development differently than a single stress. Plants sense the different stress combinations in the same or in different tissues, which could induce specific systemic signalling and acclimation responses; impacting different stress-responsive transcripts, protein abundance and modifications, and metabolites. This mini-review focuses on the combination of drought and heat, two abiotic stress conditions that often occur together. Recent omics studies indicate common or independent regulators involved in heat or drought stress responses. Here, we summarize the current research results, highlight gaps in our knowledge, and flag potential future focus areas.

Seven plant capacities to adapt to abiotic stress

Abiotic stresses such as drought and heat continue to impact crop production in a warming world. This review distinguishes seven inherent capacities that enable plants to respond to abiotic stresses and continue growing, although at a reduced rate, to achieve a productive yield. These are the capacities to selectively take up essential resources, store them and supply them to different plant parts, generate the energy required for cellular functions, conduct repairs to maintain plant tissues, communicate between plant parts, manage existing structural assets in the face of changed circumstances, and shape-shift through development to be efficient in different environments. By illustration, we show how all seven plant capacities are important for reproductive success of major crop species during drought, salinity, temperature extremes, flooding, and nutrient stress. Confusion about the term 'oxidative stress' is explained. This allows us to focus on the strategies that enhance plant adaptation by identifying key responses that can be targets for plant breeding.

Temperature perception by plants

Plants constantly face fluctuating ambient temperatures and must adapt to survive under stressful conditions. Temperature affects many aspects of plant growth and development through a complex network of transcriptional responses. Although temperature sensing is a crucial primary step in initiating transcriptional responses via Ca2+ and/or reactive oxygen species signaling, an understanding of how plants perceive temperature has remained elusive. However, recent studies have yielded breakthroughs in our understanding of temperature sensors and thermosensation mechanisms. We review recent findings on potential temperature sensors and emerging thermosensation mechanisms, including biomolecular condensate formation through phase separation in plants. We also compare the temperature perception mechanisms of plants with those of other organisms to provide insights into understanding temperature sensing by plants.

NtHSP70-8b positively regulates heat tolerance and seed size in Nicotiana tabacum

Heat stress considerably restricts the geographical distribution of crops and affects their growth, development, and productivity. HSP70 plays a critical regulatory role in plant growth response to heat stress. However, the mechanisms of this regulatory remain poorly understood. Here, an HSP70 gene, NtHSP70-8b, which is involved in the heat stress response of tobacco, was cloned and identified. The expression of NtHSP70-8b was induced by exogenous abscisic acid (ABA) treatment and abiotic stress, including heat, drought, and salt. Notably, high NtHSP70-8b expression occurred under heat stress conditions, which was consistent with the β-glucuronidase histochemical analysis. Moreover, NtHSP70-8b overexpression markedly enhanced heat stress tolerance by changing the stomatal conductance and antioxidant capacity in tobacco leaves. qRT-PCR showed that the expression levels of ABA synthesis and response genes (NtNCED3 and NtAREB), stress defence genes (NtERD10C and NtLEA5), and other HSP genes (NtHSP90 and NtHSP26a) in NtHSP70-8b-overexpressing tobacco were high under heat stress. The interaction of NtHSP70-8b with NtHSP26a was further confirmed by a luciferase complementation imaging assay. In contrast, NtHSP70-8b knockout mutants showed significantly reduced antioxidant capacity compared to the wild type (WT) under heat stress conditions, suggesting that NtHSP70-8b acts as a positive regulator of heat stress in tobacco. Moreover, NtHSP70-8b overexpression increased the 1000-seed weight. Taken together, NtHSP70-8b is involved in the heat stress response, and NtHSP70-8b overexpression contributed to enhanced tolerance to heat stress, which is thus an essential gene with potential application value for developing heat stress-tolerant crops.

Utilization of natural alleles for heat adaptability QTLs at the flowering stage in rice

BACKGROUND

Heat stress threatens rice yield and quality at flowering stage. In this study, average relative seed setting rate under heat stress (RHSR) and genotypes of 284 varieties were used for a genome-wide association study.

RESULTS

We identified eight and six QTLs distributed on chromosomes 1, 3, 4, 5, 7 and 12 in the full population and indica, respectively. qHTT4.2 was detected in both the full population and indica as an overlapping QTL. RHSR was positively correlated with the accumulation of heat-tolerant superior alleles (SA), and indica accession contained at least two heat-tolerant SA with average RHSR greater than 43%, meeting the needs of stable production and heat-tolerant QTLs were offer yield basic for chalkiness degree, amylose content, gel consistency and gelatinization temperature. Chalkiness degree, amylose content, and gelatinization temperature under heat stress increased with accumulation of heat-tolerant SA. Gel consistency under heat stress decreased with polymerization of heat-tolerant SA. The study revealed qHTT4.2 as a stable heat-tolerant QTL that can be used for breeding that was detected in the full population and indica. And the grain quality of qHTT4.2-haplotype1 (Hap1) with chalk5, wx, and alk was better than that of qHTT4.2-Hap1 with CHALK5, WX, and ALK. Twelve putative candidate genes were identified for qHTT4.2 that enhance RHSR based on gene expression data and these genes were validated in two groups. Candidate genes LOC_Os04g52830 and LOC_Os04g52870 were induced by high temperature.

CONCLUSIONS

Our findings identify strong heat-tolerant cultivars and heat-tolerant QTLs with great potential value to improve rice tolerance to heat stress, and suggest a strategy for the breeding of yield-balance-quality heat-tolerant crop varieties.

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.

Thermal protection function of camphor on Cinnamomum camphora cell membrane by acting as a signaling molecule

Isoprenoids serve important functions in protecting plant membranes against high temperature. Cinnamomum camphora is an excellent economic tree species, and releases plenty of monoterpenes. To uncover the protective mechanism of monoterpenes on the membrane system for promoting their development and utilization as anti-high temperature agents, the membrane permeability, cell ultrastructure, membrane lipid variations and related gene expression were investigated in C. camphora fumigated with camphor, one of the main monoterpenes in the plant, after fosmidomycin (Fos) blocking the monoterpene biosynthesis under high temperature (Fos+38 °C + C). High temperature at 38 °C caused the rupture of plasma as well as chloroplast and mitochondrion membranes, deformation of chloroplasts and mitochondria, and electrolyte leakage in C. camphora. High temperature with Fos treatment (Fos+38 °C) aggravated the damage, while camphor fumigation (Fos+38 °C + C) showed alleviating effects. High temperature at 38 °C disturbed the membrane lipid equilibrium by reducing the levels of 14 phosphatidylcholine, 8 phosphatidylglycerol and 6 phosphatidylethanolamine molecules, and increasing the levels of 8 phosphatidic acid, 4 diacylglycerol, 5 phosphatidylinositol, 16 sphingomyelin and 5 ceramide phosphoethanolamine molecules. Fos+38 °C treatment primarily exhibited intensifying effects on the disturbance, while these membrane lipid levels in Fos+38 °C + C5 (5 μM camphor) treatment exhibited variation tendencies to the control at 28 °C. This should result from the expression alterations of the genes related with phospholipid biosynthesis, fatty acid metabolism, and sphingolipid metabolism. It can be speculated that camphor can maintain membrane lipid stabilization in C. camphora under high temperature by acting as a signaling molecule.

ENHANCED DISEASE SUSCEPTIBILITY 1 promotes hydrogen peroxide scavenging to enhance rice thermotolerance

Heat stress is a major factor limiting the production and geographic distribution of rice (Oryza sativa), and breeding rice varieties with tolerance to heat stress is of immense importance. Although extensive studies have revealed that reactive oxygen species (ROS) play a critical role in rice acclimation to heat stress, the molecular basis of rice controlling ROS homeostasis remains largely unclear. In this study, we discovered a novel heat stress-responsive strategy that orchestrates ROS homeostasis centering on an immune activator, rice ENHANCED DISEASE SUSCEPTIBILITY 1 (OsEDS1). OsEDS1, which confers heat stress tolerance, promotes hydrogen peroxide (H2O2) scavenging by stimulating catalase activity through the OsEDS1-catalase association. The loss-of-function mutation in OsEDS1 causes increased sensitivity to heat stress, whereas overexpression of OsEDS1 enhances thermotolerance. Furthermore, overexpression lines greatly improved rice tolerance to heat stress during the reproductive stage, which was associated with substantially increased seed setting, grain weight, and plant yield. Rice CATALASE C (OsCATC), whose activity is promoted by OsEDS1, degrades H2O2 to activate rice heat stress tolerance. Our findings greatly expand our understanding of heat stress responses in rice. We reveal a molecular framework that promotes heat tolerance through ROS homeostasis regulation, suggesting a theoretical basis and providing genetic resources for breeding heat-tolerant rice varieties.

Redox-mediated responses to high temperature in plants

As sessile organisms, plants are particularly affected by climate change and will face more frequent and extreme temperature variations in the future. Plants have developed a diverse range of mechanisms allowing them to perceive and respond to these environmental constraints, which requires sophisticated signalling mechanisms. Reactive oxygen species (ROS) are generated in plants exposed to various stress conditions including high temperatures and are presumed to be involved in stress response reactions. The diversity of ROS-generating pathways and the ability of ROS to propagate from cell to cell and to diffuse through cellular compartments and even across membranes between subcellular compartments put them at the centre of signalling pathways. In addition, their capacity to modify the cellular redox status and to modulate functions of target proteins, notably through cysteine oxidation, show their involvement in major stress response transduction pathways. ROS scavenging and thiol reductase systems also participate in the transmission of oxidation-dependent stress signals. In this review, we summarize current knowledge on the functions of ROS and oxidoreductase systems in integrating high temperature signals, towards the activation of stress responses and developmental acclimation mechanisms.

Genetic Research Progress: Heat Tolerance in Rice

Heat stress (HS) caused by high-temperature weather seriously threatens international food security. Indeed, as an important food crop in the world, the yield and quality of rice are frequently affected by HS. Therefore, clarifying the molecular mechanism of heat tolerance and cultivating heat-tolerant rice varieties is urgent. Here, we summarized the identified quantitative trait loci (Quantitative Trait Loci, QTL) and cloned rice heat tolerance genes in recent years. We described the plasma membrane (PM) response mechanisms, protein homeostasis, reactive oxygen species (ROS) accumulation, and photosynthesis under HS in rice. We also explained some regulatory mechanisms related to heat tolerance genes. Taken together, we put forward ways to improve heat tolerance in rice, thereby providing new ideas and insights for future research.

A Trifolium repens flavodoxin-like quinone reductase 1 (TrFQR1) improves plant adaptability to high temperature associated with oxidative homeostasis and lipids remodeling

Maintenance of stable mitochondrial respiratory chains could enhance adaptability to high temperature, but the potential mechanism was not elucidated clearly in plants. In this study, we identified and isolated a TrFQR1 gene encoding the flavodoxin-like quinone reductase 1 (TrFQR1) located in mitochondria of leguminous white clover (Trifolium repens). Phylogenetic analysis indicated that amino acid sequences of FQR1 in various plant species showed a high degree of similarities. Ectopic expression of TrFQR1 protected yeast (Saccharomyces cerevisiae) from heat damage and toxic levels of benzoquinone, phenanthraquinone and hydroquinone. Transgenic Arabidopsis thaliana and white clover overexpressing TrFQR1 exhibited significantly lower oxidative damage and better photosynthetic capacity and growth than wild-type in response to high-temperature stress, whereas AtFQR1-RNAi A. thaliana showed more severe oxidative damage and growth retardation under heat stress. TrFQR1-transgenic white clover also maintained better respiratory electron transport chain than wild-type plants, as manifested by significantly higher mitochondrial complex II and III activities, alternative oxidase activity, NAD(P)H content, and coenzyme Q10 content in response to heat stress. In addition, overexpression of TrFQR1 enhanced the accumulation of lipids including phosphatidylglycerol, monogalactosyl diacylglycerol, sulfoquinovosyl diacylglycerol and cardiolipin as important compositions of bilayers involved in dynamic membrane assembly in mitochondria or chloroplasts positively associated with heat tolerance. TrFQR1-transgenic white clover also exhibited higher lipids saturation level and phosphatidylcholine:phosphatidylethanolamine ratio, which could be beneficial to membrane stability and integrity during a prolonged period of heat stress. The current study proves that TrFQR1 is essential for heat tolerance associated with mitochondrial respiratory chain, cellular reactive oxygen species homeostasis, and lipids remodeling in plants. TrFQR1 could be selected as a key candidate marker gene to screen heat-tolerant genotypes or develop heat-tolerant crops via molecular-based breeding.

Exogenous Kinetin Modulates ROS Homeostasis to Affect Heat Tolerance in Rice Seedlings

Heat stress caused by rapidly changing climate warming has become a serious threat to crop growth worldwide. Exogenous cytokinin (CK) kinetin (KT) has been shown to have positive effects in improving salt and drought tolerance in plants. However, the mechanism of KT in heat tolerance in rice is poorly understood. Here, we found that exogenously adequate application of KT improved the heat stress tolerance of rice seedlings, with the best effect observed when the application concentration was 10−9 M. In addition, exogenous application of 10−9 M KT promoted the expression of CK-responsive OsRR genes, reduced membrane damage and reactive oxygen species (ROS) accumulation in rice, and increased the activity of antioxidant enzymes. Meanwhile, exogenous 10−9 M KT treatment significantly enhanced the expression of antioxidant enzymes, heat activation, and defense-related genes. In conclusion, exogenous KT treatment regulates heat tolerance in rice seedlings by modulating the dynamic balance of ROS in plants under heat stress.

Pulsed electric fields-assisted extraction of valuable compounds from red grape pomace: Process optimization using response surface methodology

Background

The application of Pulsed electric fields as a mild and easily scalable electrotechnology represents an effective approach to selectively intensify the extractability of bioactive compounds from grape pomace, one of the most abundant residues generated during the winemaking process.

Objective

This study addressed the optimization of the pulsed electric fields (PEF)-assisted extraction to enhance the extraction yields of bioactive compounds from red grape pomace using response surface methodology (RSM).

Methods

The cell disintegration index (Z p ) was identified as response variable to determine the optimal PEF processing conditions in terms of field strength (E = 0.5-5 kV/cm) and energy input (WT = 1-20 kJ/kg). For the solid-liquid extraction (SLE) process the effects of temperature (20-50°C), time (30-300min), and solvent concentration (0-50% ethanol in water) on total phenolic content (TPC), flavonoid content (FC), total anthocyanin content (TAC), tannin content (TC), and antioxidant activity (FRAP) of the extracts from untreated and PEF-treated plant tissues were assessed. The phenolic composition of the obtained extracts was determined via HPLC-PDA.

Results

Results demonstrated that the application of PEF at the optimal processing conditions (E = 4.6 kV/cm, WT = 20 kJ/kg) significantly enhanced the permeabilization degree of cell membrane of grape pomace tissues, thus intensifying the subsequent extractability of TPC (15%), FC (60%), TAC (23%), TC (42%), and FRAP values (31%) concerning the control extraction. HPLC-PDA analyses showed that, regardless of the application of PEF, the most abundant phenolic compounds were epicatechin, p-coumaric acid, and peonidin 3-O-glucoside, and no degradation of the specific compounds occurred upon PEF application.

Conclusion

The optimization of the PEF-assisted extraction process allowed to significantly enhance the extraction yields of high-value-added compounds from red grape pomace, supporting further investigations of this process at a larger scale.

Impact of heat priming on heat shock responses in Origanum vulgare: Enhanced foliage photosynthetic tolerance and biphasic emissions of volatiles

Climate change enhances the frequency of heatwaves that negatively affect photosynthesis and can alter constitutive volatile emissions and elicit emissions of stress volatiles, but how pre-exposure to mildly warmer temperatures affects plant physiological responses to subsequent severe heat episodes remains unclear, especially for aromatic plants with high and complex volatile defenses. We studied the impact of heat shock (45 °C/5 min) applied alone and after exposure to moderate heat stress (35 °C/1 h, priming) on foliage photosynthesis and volatile emissions in the aromatic plant Origanum vulgare through 72 h recovery period. Heat stress decreased photosynthesis rates and stomatal conductance, whereas the reductions in photosynthesis were primarily due to non-stomatal factors. In non-primed plants, heat shock-induced reductions in photosynthetic activity were the greatest, but photosynthetic activity completely recovered by the end of the experiment. In primed plants, a certain inhibition of photosynthetic activity remained, suggesting a sustained priming effect. Heat shock enhanced the emissions of volatiles including lipoxygenase pathway volatiles, long-chained fatty acid-derived compounds, mono- and sesquiterpenes, geranylgeranyl diphosphate pathway volatiles, and benzenoids, whereas different heat treatments resulted in unique emission blends. In non-primed plants, stress-elicited emissions recovered at 72 h. In primed plants, volatile emissions were multiphasic, the first phase, between 0.5 and 10 h, reflected the primary stress response, whereas the secondary rise, between 24 and 72 h, indicated activations of different defense metabolic pathways. Our results demonstrate that exposure to mild heat leads to a sustained physiological stress memory that enhances plant resistance to subsequent severe heat stress episodes.

Elucidating the role of key physio-biochemical traits and molecular network conferring heat stress tolerance in cucumber

Cucumber is an important vegetable crop grown worldwide and highly sensitive to prevailing temperature condition. The physiological, biochemical and molecular basis of high temperature stress tolerance is poorly understood in this model vegetable crop. In the present study, a set of genotypes with contrasting response under two different temperature stress (35/30°C and 40/35°C) were evaluated for important physiological and biochemical traits. Besides, expression of the important heat shock proteins (HSPs), aquaporins (AQPs), photosynthesis related genes was conducted in two selected contrasting genotypes at different stress conditions. It was established that tolerant genotypes were able to maintain high chlorophyll retention, stable membrane stability index, higher retention of water content, stability in net photosynthesis, high stomatal conductance and transpiration in combination with less canopy temperatures under high temperature stress conditions compared to susceptible genotypes and were considered as the key physiological traits associated with heat tolerance in cucumber. Accumulation of biochemicals like proline, protein and antioxidants like SOD, catalase and peroxidase was the underlying biochemical mechanisms for high temperature tolerance. Upregulation of photosynthesis related genes, signal transduction genes and heat responsive genes (HSPs) in tolerant genotypes indicate the molecular network associated with heat tolerance in cucumber. Among the HSPs, higher accumulation of HSP70 and HSP90 were recorded in the tolerant genotype, WBC-13 under heat stress condition indicating their critical role. Besides, Rubisco S, Rubisco L and CsTIP1b were upregulated in the tolerant genotypes under heat stress condition. Therefore, the HSPs in combination with photosynthetic and aquaporin genes were the underlying important molecular network associated with heat stress tolerance in cucumber. The findings of the present study also indicated negative feedback of G-protein alpha unit and oxygen evolving complex in relation to heat stress tolerance in cucumber. These results indicate that the thermotolerant cucumber genotypes enhanced physio-biochemical and molecular adaptation under high-temperature stress condition. This study provides foundation to design climate smart genotypes in cucumber through integration of favorable physio-biochemical traits and understanding the detailed molecular network associated with heat stress tolerance in cucumber.

Improving abiotic stress tolerance of forage grasses - prospects of using genome editing

Due to an increase in the consumption of food, feed, and fuel and to meet global food security needs for the rapidly growing human population, there is a necessity to obtain high-yielding crops that can adapt to future climate changes. Currently, the main feed source used for ruminant livestock production is forage grasses. In temperate climate zones, perennial grasses grown for feed are widely distributed and tend to suffer under unfavorable environmental conditions. Genome editing has been shown to be an effective tool for the development of abiotic stress-resistant plants. The highly versatile CRISPR-Cas system enables increasingly complex modifications in genomes while maintaining precision and low off-target frequency mutations. In this review, we provide an overview of forage grass species that have been subjected to genome editing. We offer a perspective view on the generation of plants resilient to abiotic stresses. Due to the broad factors contributing to these stresses the review focuses on drought, salt, heat, and cold stresses. The application of new genomic techniques (e.g., CRISPR-Cas) allows addressing several challenges caused by climate change and abiotic stresses for developing forage grass cultivars with improved adaptation to the future climatic conditions. Genome editing will contribute towards developing safe and sustainable food systems.

An extracellular vesicular mutant KRAS-associated protein complex promotes lung inflammation and tumor growth

Extracellular vesicles (EVs) contain more than 100 proteins. Whether there are EVs proteins that act as an 'organiser' of protein networks to generate a new or different biological effect from that identified in EV-producing cells has never been demonstrated. Here, as a proof-of-concept, we demonstrate that EV-G12D-mutant KRAS serves as a leader that forms a protein complex and promotes lung inflammation and tumour growth via the Fn1/IL-17A/FGF21 axis. Mechanistically, in contrast to cytosol derived G12D-mutant KRAS complex from EVs-producing cells, EV-G12D-mutant KRAS interacts with a group of extracellular vesicular factors via fibronectin-1 (Fn1), which drives the activation of the IL-17A/FGF21 inflammation pathway in EV recipient cells. We show that: (i), depletion of EV-Fn1 leads to a reduction of a number of inflammatory cytokines including IL-17A; (ii) induction of IL-17A promotes lung inflammation, which in turn leads to IL-17A mediated induction of FGF21 in the lung; and (iii) EV-G12D-mutant KRAS complex mediated lung inflammation is abrogated in IL-17 receptor KO mice. These findings establish a new concept in EV function with potential implications for novel therapeutic interventions in EV-mediated disease processes.

High Growing Temperature Changes Nutritional Value of Broccoli (Brassica oleracea L. convar. botrytis (L.) Alef. var. cymosa Duch.) Seedlings

High temperature (HT) causes physiological and biochemical changes in plants, which may influence their nutritional potential. This study aimed to evaluate the nutritional value of broccoli seedlings grown at HT on the level of phytochemicals, macro- and microelements, antioxidant capacity, and their extracts' in vitro cytotoxicity. Total phenols, soluble sugars, carotenoids, quercetin, sinapic, ferulic, p-coumaric, and gallic acid were induced by HT. Contrarily, total flavonoids, flavonols, phenolic acids, hydroxycinnamic acids, proteins, glucosinolates, chlorophyll a and b, and porphyrins were reduced. Minerals As, Co, Cr, Hg, K, Na, Ni, Pb, Se, and Sn increased at HT, while Ca, Cd, Cu, Mg, Mn, and P decreased. ABTS, FRAP, and β-carotene bleaching assay showed higher antioxidant potential of seedlings grown at HT, while DPPH showed the opposite. Hepatocellular carcinoma cells were the most sensitive toward broccoli seedling extracts. The significant difference between control and HT-grown broccoli seedling extracts was recorded in mouse embryonal fibroblasts and colorectal carcinoma cells. These results show that the temperature of seedling growth is a critical factor for their nutritional value and the biological effects of their extracts and should definitely be taken into account when growing seedlings for food purposes.

Deciphering immune responses primed by a bacterial lipopeptide in wheat towards Zymoseptoria tritici

Plant immunity induction with natural biocontrol compounds is a valuable and promising ecofriendly tool that fits with sustainable agriculture and healthy food. Despite the agroeconomic significance of wheat, the mechanisms underlying its induced defense responses remain obscure. We reveal here, using combined transcriptomic, metabolomic and cytologic approach, that the lipopeptide mycosubtilin from the beneficial bacterium Bacillus subtilis, protects wheat against Zymoseptoria tritici through a dual mode of action (direct and indirect) and that the indirect one relies mainly on the priming rather than on the elicitation of plant defense-related mechanisms. Indeed, the molecule primes the expression of 80 genes associated with sixteen functional groups during the early stages of infection, as well as the accumulation of several flavonoids during the period preceding the fungal switch to the necrotrophic phase. Moreover, genes involved in abscisic acid (ABA) biosynthesis and ABA-associated signaling pathways are regulated, suggesting a role of this phytohormone in the indirect activity of mycosubtilin. The priming-based bioactivity of mycosubtilin against a biotic stress could result from an interaction of the molecule with leaf cell plasma membranes that may mimic an abiotic stress stimulus in wheat leaves. This study provides new insights into induced immunity in wheat and opens new perspectives for the use of mycosubtilin as a biocontrol compound against Z. tritici.

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.

Physiological and transcriptomic analyses provide insight into thermotolerance in desert plant Zygophyllum xanthoxylum

BACKGROUND

Heat stress has adverse effects on the growth and reproduction of plants. Zygophyllum xanthoxylum, a typical xerophyte, is a dominant species in the desert where summer temperatures are around 40 °C. However, the mechanism underlying the thermotolerance of Z. xanthoxylum remained unclear.

RESULTS

Here, we characterized the acclimation of Z. xanthoxylum to heat using a combination of physiological measurements and transcriptional profiles under treatments at 40 °C and 45 °C, respectively. Strikingly, moderate high temperature (40 °C) led to an increase in photosynthetic capacity and superior plant performance, whereas severe high temperature (45 °C) was accompanied by reduced photosynthetic capacity and inhibited growth. Transcriptome profiling indicated that the differentially expressed genes (DEGs) were related to transcription factor activity, protein folding and photosynthesis under heat conditions. Furthermore, numerous genes encoding heat transcription shock factors (HSFs) and heat shock proteins (HSPs) were significantly up-regulated under heat treatments, which were correlated with thermotolerance of Z. xanthoxylum. Interestingly, the up-regulation of PSI and PSII genes and the down-regulation of chlorophyll catabolism genes likely contribute to improving plant performance of Z. xanthoxylum under moderate high temperature.

CONCLUSIONS

We identified key genes associated with of thermotolerance and growth in Z. xanthoxylum, which provide significant insights into the regulatory mechanisms of thermotolerance and growth regulation in Z. xanthoxylum under high temperature conditions.

The Plant Metabolic Changes and the Physiological and Signaling Functions in the Responses to Abiotic Stress

Global climate change has altered, and will further alter, rainfall patterns and temperatures likely causing more frequent drought and heat waves, which will consequently exacerbate abiotic stresses of plants and significantly decrease the yield and quality of crops. On the one hand, the global demand for food is ever-increasing owing to the rapid increase of the human population. On the other hand, metabolic responses are one of the most important mechanisms by which plants adapt to and survive to abiotic stresses. Here we therefore summarize recent progresses including the plant primary and secondary metabolic responses to abiotic stresses and their function in plant resistance acting as antioxidants, osmoregulatory, and signaling factors, which enrich our knowledge concerning commonalities of plant metabolic responses to abiotic stresses, including their involvement in signaling processes. Finally, we discuss potential methods of metabolic fortification of crops in order to improve their abiotic stress tolerance.

M, Paudel K. Influence of high-temperature stress on rice growth and development. A review

High-temperature stress (HS) has become an alarming threat to the global food system. Rice, an important crop that supports almost half of the global population, is vulnerable to heat stress. Under the influence of HS, it shows various physiological and morphological symptoms that increase spikelet sterility, reduce grain yield, and even cause total crop failure. HS affects growth and yield in two ways: hindrance in the process of pollination and fertilization and reduction of the grain weight. The former is caused by (i) distortion of floral organs, (ii) tapetum degeneration, (iii) low pollen protein concentration, (iv) decline in pollen viability, (v) reduction in dehiscence of anther, (vi) low pollen dispersal, (vii) decrease in number of pollens on stigma, (viii) reduction in pollen grain germination, (ix) hindrance in extension of pollen tubes, and (x) shrinkage of stigma which ultimately cause spikelet infertility. The latter is caused by (i)reduced photosynthetic rate, (ii) a boost in senescence of functional leaves, (iii) reduction of biological synthesis of starch, (iv)reduced starch augmentation, (v) shrunk duration of grain filling, and (vi) declined grain weight which ultimately reduce the grain yield. However, some agronomic and breeding approaches have been adopted for developing thermo-resistant cultivars but the success is limited. In this paper, we have summarized the the morpho-physiological and molecular response of plant to HS, and a few possible management strategies.

Plant transbilayer lipid asymmetry and the role of lipid flippases

Many biological membranes present an asymmetric lipid distribution between the two leaflets that is known as the transbilayer lipid asymmetry. This asymmetry is essential for cell survival and its loss is related to apoptosis. In mammalian and yeast cells, ATP-dependent transport of lipids to the cytosolic side of the biological membranes, carried out by so-called lipid flippases, contributes to the transbilayer lipid asymmetry. Most of these lipid flippases belong to the P4-ATPase protein family, which is also present in plants. In this review, we summarize the relatively scarce literature concerning the presence of transbilayer lipid asymmetry in different plant cell membranes and revise the potential role of lipid flippases of the P4-ATPase family in generation and/or maintenance of this asymmetry.

Mechanisms of cerium-induced stress in plants: A meta-analysis

A comprehensive evaluation of the effects of cerium on plants is lacking even though cerium is extensively applied to the environment. Here, the effects of cerium on plants were meta-analyzed using a newly developed database consisting of approximately 8500 entries of published data. Cerium affects plants by acting as oxidative stressor causing hormesis, with positive effects at low concentrations and adverse effects at high doses. Production of reactive oxygen species and its linked induction of antioxidant enzymes (e.g. catalase and superoxide dismutase) and non-enzymatic antioxidants (e.g. glutathione) are major mechanisms driving plant response mechanisms. Cerium also affects redox signaling, as indicated by altered GSH/GSSG redox pair, and electrolyte leakage, Ca²⁺, K⁺, and K⁺/Na⁺, indicating an important role of K⁺ and Na⁺ homeostasis in cerium-induced stress and altered mineral (ion) balance. The responses of the plants to cerium are further extended to photosynthesis rate (A), stomatal conductance (g_s), photosynthetic efficiency of PSII, electron transport rate, and quantum yield of PSII. However, photosynthesis response is regulated not only by physiological controls (e.g. g_s), but also by biochemical controls, such as via changed Hill reaction and RuBisCO carboxylation. Cerium concentrations <0.1-25 mg L^-1 commonly enhance chlorophyll a and b, g_s, A, and plant biomass, whereas concentrations >50 mg L^-1 suppress such fitness-critical traits at trait-specific concentrations. There was no evidence that cerium enhances yields. Observations were lacking for yield response to low concentrations of cerium, whereas concentrations >50 mg Kg^-1 suppress yields, in line with the response of chlorophyll a and b. Cerium affects the uptake and tissue concentrations of several micro- and macro-nutrients, including heavy metals. This study enlightens the understanding of some mechanisms underlying plant responses to cerium and provides critical information that can pave the way to reducing the cerium load in the environment and its associated ecological and human health risks.

Harboured cation/proton antiporters modulate stress response to integrated heat and salt via up-regulating KIN1 and GOLS1 in double transgenic Arabidopsis

Recent research has pointed to improved salt tolerance by co-overexpression of Arabidopsis thaliana NHX1 (Na+ /H+ antiporter) and SOS1 (Salt Overly Sensitive1). However, functionality under salt stress accompanying heat is less understood in double transgenics. To further advance possible co-operational interactions of AtNHX1 (N) and AtSOS1 (S) under combined stress, modulation of osmolyte, redox, energy, and abscisic acid metabolism genes was analysed. The expression of the target BIP3 , KIN1 , GOLS1 , OHP2 , and CYCA3;2 in transgenic Arabidopsis seedlings were significantly regulated towards a dramatic suppression by ionic, osmotic, and heat stresses. AtNHX1 and AtSOS1 co-overexpression (NS) outpaced the single transgenics and control in terms of membrane disorganisation and the electrolyte leakage of the cell damage caused by heat and salt stress in seedlings. While NaCl slightly induced CYCA3;2 in transgenics, combined stress up-regulated KIN1 and GOLS1 , not other genes. Single N and S transgenics overexpressing AtNHX1 and AtSOS1 only appeared similar in their growth and development; however, different to WT and NS dual transgenics under heat+salt stress. Seed germination, cotyledon survival, and hypocotyl length were less influenced by combined stress in NS double transgenic lines than in single N and S and wild type. Stress combination caused significant reprogramming of gene expression profiles, mainly towards downregulation, possibly as a trade-off strategy. Analysing phenotypic, cellular, and transcriptional responses regulating growth facets of tolerant transgenic genotypes may support the ongoing efforts to achieve combined salt and heat tolerance.

Effect of Heat Stress on Some Physiological and Anatomical Characteristics of Rice (Oryza sativa L.) cv. KDML105 Callus and Seedling

Simple Summary

Climate change is currently threatening agriculture all around the world, resulting in a lack of water and restricting the growth of plants, especially rice. Rice production decreases with the increase in temperature. An improvement in fundamental knowledge is necessary to comprehend plant adaptation mechanisms as responses to heat stress. Physiological and anatomical responses of Khao Dawk Mali 105 (KDML105) rice to artificial heat stress were studied. Our findings offer useful data for projects aimed at improving heat stress tolerance in rice to enhance long-term global food security.

Abstract

Global warming is a serious problem, with significant negative impacts on agricultural productivity. To better understand plant anatomical adaptation mechanisms as responses to heat stress, improved basic knowledge is required. This research studied the physiological and anatomical responses of Khao Dawk Mali 105 (KDML105) to artificial heat stress. Dehusked seeds were sterilized and cultured on Murashige and Skoog (MS) medium, supplemented with 3 mg/L 2,4-Dichlorophenoxyacetic acid (2,4-D) for callus induction. The cultures were maintained at 25 °C and 35 °C for 4 weeks, while the other culture was treated with heat shock at 42 °C for 1 week before further incubation at 25 °C for 3 weeks. Results revealed that elevated temperatures (35 °C and 42 °C) adversely impacted seedling growth. Plant height, root length, leaf number per plant, fresh and dry weight, chlorophyll a, chlorophyll b and total chlorophyll content decreased after heat stress treatment, while malondialdehyde (MDA) and electrolyte leakage percentage significantly increased, compared to the control. Heat stress induced ROS accumulation, leading to lipid peroxidation and membrane instability. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) results also confirmed negative correlations between MDA, electrolyte leakage and other parameters. MDA content and electrolyte leakage are effective indicators of heat stress in rice. Surface anatomical responses of rice seedlings to heat stress were studied but significant alterations were not observed, and heat stress had no significant negative effects on KDML105 calli. Size and mass of calli increased because heat stress stimulated gene expression that induced thermotolerance. Our results provide useful information for rice breeding and heat stress tolerance programs to benefit long-term global food security.

Plasma membrane-to-organelle communication in plant stress signaling

Intracellular compartments engage in extensive communication with one another, an essential ability for cells to respond and adapt to changing environmental and developmental conditions. The plasma membrane (PM), as the interface between the cellular and the outside media, plays a central role in the perception and relay of information about external stimuli, which needs to be ultimately addressed to the relevant subcellular organelles. Interest in PM-organelle communication has increased dramatically in recent years, as examples arise that illustrate different strategies through which information from the PM can be transmitted. In this review, we will discuss mechanisms enabling PM-to-organelle communication in plants, specifically in biotic and abiotic stress signaling.

Metabolic, physiological and anatomical responses of soybean plants under water deficit and high temperature condition

Water deficit (WD) combined with high temperature (HT) is the major factor limiting agriculture worldwide, and it is predicted to become worse according to the current climate change scenario. It is thus important to understand how current cultivated crops respond to these stress conditions. Here we investigated how four soybean cultivars respond to WD and HT isolated or in combination at metabolic, physiological, and anatomical levels. The WD + HT increased the level of stress in soybean plants when compared to plants under well-watered (WW), WD, or HT conditions. WD + HT exacerbates the increases in ascorbate peroxidase activity, which was associated with the greater photosynthetic rate in two cultivars under WD + HT. The metabolic responses to WD + HT diverge substantially from plants under WW, WD, or HT conditions. Myo-inositol and maltose were identified as WD + HT biomarkers and were connected to subnetworks composed of catalase, amino acids, and both root and leaf osmotic potentials. Correlation-based network analyses highlight that the network heterogeneity increased and a higher integration among metabolic, physiological, and morphological nodes is observed under stress conditions. Beyond unveiling biochemical and metabolic WD + HT biomarkers, our results collectively highlight that the mechanisms behind the acclimation to WD + HT cannot be understood by investigating WD or HT stress separately.

Lipidomics-Assisted GWAS (lGWAS) Approach for Improving High-Temperature Stress Tolerance of Crops

High-temperature stress (HT) over crop productivity is an important environmental factor demanding more attention as recent global warming trends are alarming and pose a potential threat to crop production. According to the Sixth IPCC report, future years will have longer warm seasons and frequent heat waves. Thus, the need arises to develop HT-tolerant genotypes that can be used to breed high-yielding crops. Several physiological, biochemical, and molecular alterations are orchestrated in providing HT tolerance to a genotype. One mechanism to counter HT is overcoming high-temperature-induced membrane superfluidity and structural disorganizations. Several HT lipidomic studies on different genotypes have indicated the potential involvement of membrane lipid remodelling in providing HT tolerance. Advances in high-throughput analytical techniques such as tandem mass spectrometry have paved the way for large-scale identification and quantification of the enormously diverse lipid molecules in a single run. Physiological trait-based breeding has been employed so far to identify and select HT tolerant genotypes but has several disadvantages, such as the genotype-phenotype gap affecting the efficiency of identifying the underlying genetic association. Tolerant genotypes maintain a high photosynthetic rate, stable membranes, and membrane-associated mechanisms. In this context, studying the HT-induced membrane lipid remodelling, resultant of several up-/down-regulations of genes and post-translational modifications, will aid in identifying potential lipid biomarkers for HT tolerance/susceptibility. The identified lipid biomarkers (LIPIDOTYPE) can thus be considered an intermediate phenotype, bridging the gap between genotype–phenotype (genotype–LIPIDOTYPE–phenotype). Recent works integrating metabolomics with quantitative genetic studies such as GWAS (mGWAS) have provided close associations between genotype, metabolites, and stress-tolerant phenotypes. This review has been sculpted to provide a potential workflow that combines MS-based lipidomics and the robust GWAS (lipidomics assisted GWAS-lGWAS) to identify membrane lipid remodelling related genes and associations which can be used to develop HS tolerant genotypes with enhanced membrane thermostability (MTS) and heat stable photosynthesis (HP).

Physiological and transcriptional responses to heat stress and functional analyses of PsHSPs in tree peony (Paeonia suffruticosa)

Tree peony (Paeonia suffruticosa) is a traditional Chinese flower that is not resistant to high temperatures, and the frequent sunburn during summer limits its normal growth. The lack of understanding of the molecular mechanisms in tree peony has greatly restricted the improvement of novel heat-tolerant varieties. Therefore, we treated tree peony cultivar "Yuhong" (P. suffruticosa "Yuhong") at normal (25°C) and high temperatures (40°C) and sequenced the transcriptomes, to investigate the molecular responsive mechanisms to heat stress. By comparing the transcriptomes, a total of 7,673 differentially expressed genes (DEGs) were detected comprising 4,220 upregulated and 3,453 downregulated genes. Functional annotation showed that the DEGs were mainly related to the metabolic process, cells and binding, carbon metabolism, and endoplasmic reticulum protein processing. qRT-PCR revealed that three sHSP genes (PsHSP17.8, PsHSP21, and PsHSP27.4) were upregulated in the response of tree peony to heat stress. Tissue quantification of the transgenic lines (Arabidopsis thaliana) showed that all three genes were most highly expressed in the leaves. The survival rates of transgenic lines (PsHSP17.8, PsHSP21, and PsHSP27.4) restored to normal growth after high-temperature treatment were 43, 36, and 31%, respectively. In addition, the activity of superoxide dismutase, accumulation of free proline, and chlorophyll level was higher than those of the wild-type lines, while the malondialdehyde content and conductivity were lower, and the membrane lipid peroxidation reaction of the wild-type plant was more intense. Our research found several processes and pathways related to heat resistance in tree peony including metabolic process, single-organism process, phenylpropane biosynthesis pathway, and endoplasmic reticulum protein synthesis pathway. PsHSP17.8, PsHSP21, and PsHSP27.4 improved heat tolerance by increasing SOD activity and proline content. These findings can provide genetic resources for understanding the heat-resistance response of tree peony and benefit future germplasm innovation.

Nitric oxide, salicylic acid and oxidative stress: Is it a perfect equilateral triangle?

Nitric oxide (NO) is an endogenous free radical involved in the regulation of a wide array of physio-biochemical phenomena in plants. The biological activity of NO directly depend on its cellular concentration which usually changes under stress conditions, it participates in maintaining cellular redox equilibrium and regulating target checkpoints which control switches among development and stress. It is one of the key players in plant signalling and a plethora of evidence supports its crosstalk with other phytohormones. NO and salicylic acid (SA) cooperation is also of great physiological relevance, where NO modulates the immune response by regulating SA linked target proteins i.e., non-expressor of pathogenesis-related genes (NPR-1 and NPR-2) and Group D bZIP (basic leucine zipper domain transcription factor). Many experimental data suggest a functional cooperative role between NO and SA in mitigating the plant oxidative stress which suggests that these relationships could constitute a metabolic "equilateral triangle".

Phospholipids and flowering regulation

A better understanding of how plants adjust their flowering under unfavourable environmental conditions is key to developing climate-resilient crops. Recently, Susila et al. demonstrated that phospholipids controlling the transport of florigen (FLOWERING LOCUS T; FT) act as an additional layer to prevent flowering under unfavourable conditions.

Patatin-like phospholipase A-induced alterations in lipid metabolism and jasmonic acid production affect the heat tolerance of Gracilariopsis lemaneiformis

High temperatures seriously limit the growth and productivity of Gracilariopsis lemaneiformis. By hydrolyzing glycerolipids into lysophospholipids (LPs) and free fatty acids (FFAs), patatin-like phospholipase A (pPLA) plays an important role in stress responses. GlpPLA expression was up-regulated under heat stress, however, the regulation of pPLA in heat tolerance of G. lemaneiformis is unknown. In this study, G. lemaneiformis under heat stress was treated with bromoenololide (BEL), a chemical inhibitor of pPLA, to evaluate the cellular function of pPLA in this species. When pPLA was inhibited through BEL treatment, the sensitivity of G. lemaneiformis to heat stress increased and the biomass and maximum and effective quantum yield of photosystem II decreased. Moreover, BEL treatment resulted in a significant decrease in many lipid molecular species, all of which are mainly composed of 16C, 18C, and 20C fatty acids. Consistently, FFA levels and LPs contents in G. lemaneiformis under BEL treatment showed a significant decrease. The first step in the synthesis of jasmonic acid (JA) is the lipoxygenase (LOX)-mediated oxygenation of linolenic acid (C18:3). BEL treatment decreased JA and C18:3 accumulation and markedly downregulated the expression of GILOX under heat stress. Together, these results indicate that pPLA is closely related to the growth of G. lemaneiformis under heat stress, and pPLA is involved in the lipid metabolism and JA biosynthesis of G. lemaneiformis in response to heat stress. This research broadens the understanding of the heat stress adaptation mechanism of G. lemaneiformis.

Light Intensity- and Spectrum-Dependent Redox Regulation of Plant Metabolism

Both light intensity and spectrum (280–800 nm) affect photosynthesis and, consequently, the formation of reactive oxygen species (ROS) during photosynthetic electron transport. ROS, together with antioxidants, determine the redox environment in tissues and cells, which in turn has a major role in the adjustment of metabolism to changes in environmental conditions. This process is very important since there are great spatial (latitude, altitude) and temporal (daily, seasonal) changes in light conditions which are accompanied by fluctuations in temperature, water supply, and biotic stresses. The blue and red spectral regimens are decisive in the regulation of metabolism because of the absorption maximums of chlorophylls and the sensitivity of photoreceptors. Based on recent publications, photoreceptor-controlled transcription factors such as ELONGATED HYPOCOTYL5 (HY5) and changes in the cellular redox environment may have a major role in the coordinated fine-tuning of metabolic processes during changes in light conditions. This review gives an overview of the current knowledge of the light-associated redox control of basic metabolic pathways (carbon, nitrogen, amino acid, sulphur, lipid, and nucleic acid metabolism), secondary metabolism (terpenoids, flavonoids, and alkaloids), and related molecular mechanisms. Light condition-related reprogramming of metabolism is the basis for proper growth and development of plants; therefore, its better understanding can contribute to more efficient crop production in the future.

Reproductive-Stage Heat Stress in Cereals: Impact, Plant Responses and Strategies for Tolerance Improvement

Reproductive-stage heat stress (RSHS) poses a major constraint to cereal crop production by damaging main plant reproductive structures and hampering reproductive processes, including pollen and stigma viability, pollination, fertilization, grain setting and grain filling. Despite this well-recognized fact, research on crop heat stress (HS) is relatively recent compared to other abiotic stresses, such as drought and salinity, and in particular, RSHS studies in cereals are considerably few in comparison with seedling-stage and vegetative-stage-centered studies. Meanwhile, climate change-exacerbated HS, independently or synergistically with drought, will have huge implications on crop performance and future global food security. Fortunately, due to their sedentary nature, crop plants have evolved complex and diverse transient and long-term mechanisms to perceive, transduce, respond and adapt to HS at the molecular, cell, physiological and whole plant levels. Therefore, uncovering the molecular and physiological mechanisms governing plant response and tolerance to RSHS facilitates the designing of effective strategies to improve HS tolerance in cereal crops. In this review, we update our understanding of several aspects of RSHS in cereals, particularly impacts on physiological processes and yield; HS signal perception and transduction; and transcriptional regulation by heat shock factors and heat stress-responsive genes. We also discuss the epigenetic, post-translational modification and HS memory mechanisms modulating plant HS tolerance. Moreover, we offer a critical set of strategies (encompassing genomics and plant breeding, transgenesis, omics and agronomy) that could accelerate the development of RSHS-resilient cereal crop cultivars. We underline that a judicious combination of all of these strategies offers the best foot forward in RSHS tolerance improvement in cereals. Further, we highlight critical shortcomings to RSHS tolerance investigations in cereals and propositions for their circumvention, as well as some knowledge gaps, which should guide future research priorities. Overall, our review furthers our understanding of HS tolerance in plants and supports the rational designing of RSHS-tolerant cereal crop cultivars for the warming climate.

32Pi Labeled Transgenic Wheat Shows the Accumulation of Phosphatidylinositol 4,5-bisphosphate and Phosphatidic Acid Under Heat and Osmotic Stress

The ensuing heat stress drastically affects wheat plant growth and development, consequently compromising its grain yield. There are many thermoregulatory processes/mechanisms mediated by ion channels, lipids, and lipid-modifying enzymes that occur in the plasma membrane and the chloroplast. With the onset of abiotic or biotic stresses, phosphoinositide-specific phospholipase C (PI-PLC), as a signaling enzyme, hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP₂) to generate inositol 1,4,5-trisphosphate (IP₃) and diacylglycerol (DAG) which is further phosphorylated into phosphatidic acid (PA) as a secondary messenger and is involved in multiple processes. In the current study, a phospholipase C (PLC) signaling pathway was investigated in spring wheat (Triticum aestivum L.) and evaluated its four AtPLC5 overexpressed (OE)/transgenic lines under heat and osmotic stresses through ³²P_i radioactive labeling. Naturally, the wheat harbors only a small amount of PIP₂. However, with the sudden increase in temperature (40°C), PIP₂ levels start to rise within 7.5 min in a time-dependent manner in wild-type (Wt) wheat. While the Phosphatidic acid (PA) level also elevated up to 1.6-fold upon exposing wild-type wheat to heat stress (40°C). However, at the anthesis stage, a significant increase of ∼4.5-folds in PIP₂ level was observed within 30 min at 40°C in AtPLC5 over-expressed wheat lines. Significant differences in PIP₂ level were observed in Wt and AtPLC5-OE lines when treated with 1200 mM sorbitol solution. It is assumed that the phenomenon might be a result of the activation of PLC/DGK pathways. Together, these results indicate that heat stress and osmotic stress activate several lipid responses in wild-type and transgenic wheat and can explain heat and osmotic stress tolerance in the wheat plant.

How do plants feel the heat and survive?

Climate change is increasingly affecting the quality of life of organisms on Earth. More frequent, extreme, and lengthy heat waves are contributing to the sixth mass extinction of complex life forms in the Earth's history. From an anthropocentric point of view, global warming is a major threat to human health because it also compromises crop yields and food security. Thus, achieving agricultural productivity under climate change calls for closer examination of the molecular mechanisms of heat-stress resistance in model and crop plants. This requires a better understanding of the mechanisms by which plant cells can sense rising temperatures and establish effective molecular defenses, such as molecular chaperones and thermoprotective metabolites, as reviewed here, to survive extreme diurnal variations in temperature and seasonal heat waves.