Heat stress response in plants: a complex game with chaperones and more than twenty heat stress transcription factors

Studies on the Japanese soil-borne wheat mosaic virus movement protein highlight its ability to bind plant RNA

BACKGROUND

Plant viral movement protein (MP) function is decisive for virus cell-to-cell movement. Often, MPs also induce membrane alterations, which are believed to play a role for the establishment of viral replication compartments. Despite these central roles in virus infection, knowledge of the underlying molecular mechanisms by which MPs cause changes in plasmodesmata (PD) size exclusion limit and contribute to the formation of viral replication compartments remain far from being complete.

METHODS

To further identify host processes subverted by viral MPs, we here characterized the MP of Japanese soil-borne wheat mosaic virus (JSBWMV). We used confocal fluorescence microscopy to study the subcellular localization of MPJSBWMV and to address its functionality in promoting virus cell-to-cell movement. Using the biochemical and biophysical methods co-immunoprecipitation, fluorescence lifetime imaging, microscale thermophoresis and RNA immunoprecipitation we investigate the capacity of MPJSBWMV to multimerize and to bind viral and cellular RNAs.

RESULTS

MPJSBWMV localized to PD, promoted cell-to-cell movement by complementing a movement-deficient unrelated virus, formed multimers in-vivo and bound to viral RNA with high affinity. Using RNA immunoprecipitation, we identified host RNAs associated with the viral MP. Within the MP-RNA complexes we found RNAs encoding proteins with key functions in membrane modification, signaling, protein folding, and degradation. We propose that binding of MP to these RNAs during infection and regulation of their spatio-temporal translation may represent a mechanism for MPs to achieve PD and host control during replication and movement.

CONCLUSION

This study provides new insight into the complex interactions between viral MPs and host cellular processes.

A novel stress-inducible dCas9 system for solanaceous plants

Conditional manipulation of gene expression is essential in plant biology, yet a simple stimuli-based inducible system for regulating any plant gene is lacking. Here, we present an innovative stress-inducible CRISPR/dCas9-based gene-regulatory toolkit tailored for intentional gene regulation in solanaceous plants. We have translationally fused the transmembrane domain of a tomato membrane-bound NAC transcription factor with dCas9 to utilize the reversible-tethering-based activation mechanism. This system sequesters dCas9 to the plasma membrane under normal conditions and allows membrane detachment in response to heat induction and NLS-mediated nuclear transfer, enabling stress-inducible gene regulation. Transient assays with tomato codon-optimized dCas9-assisted inducible CRISPR activation and interference systems confirmed their superior ability on transcriptional control, rapid induction, and reversibility after stimulus withdrawal in solanaceous plants. The transformative potential of the toolkit was exemplified by enhancing tomato immunity against bacterial speck disease under elevated temperatures by precisely regulating crucial salicylic acid signalling components, SlCBP60g and SlSARD1. Additionally, it was instrumental in engineering heat-stress tolerance in tomato plants through multiplex activation of heat-responsive transcription factors, SlNAC2 and SlHSFA6b. These findings demonstrate the unprecedented temporal control offered by this novel stress-inducible toolkit over gene-expression dynamics, paving the way for favourable manipulation of complex traits in environmentally-challenged crops.

Immune Priming Promotes Thermotolerance, Whereas Thermopriming Suppresses Systemic Acquired Resistance in Arabidopsis

Heat stress and pathogens are two serious yield-limiting factors of crop plants. Plants that previously experienced high but sub-lethal temperatures become subsequently tolerant to higher temperatures through the development of acquired thermotolerance (ATT). ATT activation is associated with the elevated expression of heat shock (HS)-related genes such as HSFA2, HSFA3, and HSP101. Similarly, through the development of systemic acquired resistance (SAR), previously experienced plants achieve a higher resistance than naïve plants. SAR activation requires mobile signals and primarily depends on salicylic acid (SA) signaling. Studies to understand the interaction between ATT and SAR are limiting. To investigate the possible interconnection, we studied cross-protection between SAR and ATT on 4-week-old soil-grown Arabidopsis plants. We observed localized pathogen inoculation provides thermotolerance. Pathogens activate the expressions of HSFA2, HSFA3, HSA32, and HSP101 in pathogen-free systemic tissues. Interestingly, pathogen-induced SAR activation is impaired in hsfa2, hsfa3, and hsp101 mutants, suggesting these HS memory genes are essential for SAR induction. In contrast, thermopriming by exposing plants to sublethal temperatures, blocks SAR activation by pathogens. Thermopriming suppresses SAR mobile signal generation, accumulation of SA, and PR1 gene expression in systemic leaves. Altogether, our results demonstrate a complex interaction between SAR and ATT induction pathways in plants.

Cloning and expression analysis of RhHsf24 gene in Rose (Rosa hybrida)

Rose (Rosa hybrida) is one of the most important ornamental and perfume industry crops worldwide, both economically and culturally. Abiotic stresses, such as high temperature and salt are crucial factors influencing the quality of roses. In this study, RhHsf24 was isolated from rose (R. hybrida 'Samantha'), which encodes 295 amino acids (aa). Sequence comparison with members of Arabidopsis Hsfs family revealed that this gene is most closely related to AtHsfB1; phylogenetic tree analysis with proteins from other species showed that it clusters with R. rugosa (RrHSF24), Fragaria vesca (FvHSFB1a) and Argentina anserina (AaHSF24), which are the closest relatives and belong to the class B heat shock transcription factors. RhHsf24 was localized in the nucleus. The qRT-PCR results indicated that the gene was expressed in roots, stems, leaves, flowers and buds. Expression analysis of the gene in leaves subjected to various temperatures and durations of heat stress treatment demonstrated that RhHsf24 gene expression is induced by heat stress. Under salt stress, the expression of the RhHsf24 gene generally exhibited a high level of expression with increasing concentration. The above results preliminarily clarified the biological function of RhHsf24, and provide a genetic resource and theoretical reference for the resistance breeding of roses.

Tomato miR398 knockout disrupts ROS dynamics during stress conferring heat tolerance but hypersusceptibility to necrotroph infection

An imbalance between ROS production and scavenging during stress results in oxidative bursts, which causes cellular damage. miR398 is a regulator of ROS scavenging since it targets crucial Cu/Zn superoxide dismutases (CSDs). Established functional studies aligned miR398 with plants' heat and heavy metal stress fitness. However, a knowledge gap in the dynamics of miR398-CSD interaction for redox regulation during pathogenic development impeded their use in crop improvement programmes. We use tomato, Solanum lycopersicum, plants, and necrotrophic and biotrophic pathogens to show that a complex transcriptional and post-transcriptional regulatory circuit maintains SlmiR398 and its target SlCSD genes' level. The interaction is indispensable for ROS regulation in either the pathogenic outcome, thermal stress, or a combination of both stresses, as observed in the cultivation field. The SlmiR398 knockout plants display feeble O2∙- accumulation but enhanced levels of H2O2, several defense-related genes, metabolites, and vital HSFs and HSPs, which were heightened upon stress. Depletion of SlmiR398, although it renders thermotolerance and resilience to biotrophic pathogens likely due to the augmented hypersensitive response, facilitates necrotrophy. Thus, SlmiR398-mediated ROS regulation seemingly works at the interface of abiotic and biotic stress response for a sustainable reaction of tomato plants.

The Effect of Heat Stress on Wheat Flag Leaves Revealed by Metabolome and Transcriptome Analyses During the Reproductive Stage

In this study, we were dedicated to investigating the effect caused by heat stress on wheat flag leaves. Metabolome and transcriptome analysis were introduced to identify some key biological processes. As a result, 182 and 214 metabolites were significantly changed at the anthesis and post-anthesis stages, respectively; most of them were lipids, amino acids and derivatives, phenolic acids, and alkaloids. Aminoacyl-tRNA biosynthesis was the most significantly enriched pathway by metabolites at both two stages, each of which included 13 types of amino acid, and 12 of them were shared and up-regulated. Therefore, we further measured 22 kinds of amino acid content in ten different wheat genotypes at the post-anthesis stage. Based on the average content of each amino acid, 17 kinds of them were significantly increased after heat stress, and 4 types were significantly decreased. Both the metabolism analysis and the transcriptome analysis had a higher number of significantly changed metabolites or differential expressed genes at the post-anthesis stage, which indicated that the post-anthesis stage is more sensitive to heat stress, with 21,361 and 17,130 differential expressed genes, respectively. Two pathways, protein processing in endoplasmic reticulum and ABC transporters, were significantly enriched at two stages. The differential expressed genes in processing in endoplasmic reticulum pathway mainly encoded various types of molecular chaperones; among them, the HSP20 family was the most predominant and intensively up-regulated. The ABC transporter gene family is another pathway that is deeply involved in heat-stress response, which could be classified into five subfamilies; among them, subfamilies B and G were the most active. In summary, this study revealed the heat response pattern of amino acids, HSPs, and ABC transporter which may play a vital role during the wheat reproductive stage.

Cooperative condensation of RNA-DIRECTED DNA METHYLATION 16 splicing isoforms enhances heat tolerance in Arabidopsis

Dissecting the mechanisms underlying heat tolerance is important for understanding how plants acclimate to heat stress. Here, we identify a heat-responsive gene in Arabidopsis thaliana, RNA-DIRECTED DNA METHYLATION 16 (RDM16), which encodes a pre-mRNA splicing factor. Knockout mutants of RDM16 are hypersensitive to heat stress, which is associated with impaired splicing of the mRNAs of 18 out of 20 HEAT SHOCK TRANSCRIPTION FACTOR (HSF) genes. RDM16 forms condensates upon exposure to heat. The arginine residues in intrinsically disordered region 1 (IDR1) of RDM16 are responsible for RDM16 condensation and its function in heat stress tolerance. Notably, RDM16 produces two alternatively spliced transcripts designated RDM16-LONG (RDL) and RDM16-SHORT (RDS). RDS also forms condensates and can promote RDL condensation to improve heat tolerance. Our findings provide insight into the cooperative condensation of the two RDM16 isoforms encoded by RDM16 splice variants in enhancing heat tolerance in Arabidopsis.

Transcriptome Profiling of Two Camellia japonica Cultivars with Different Heat Tolerance Reveals Heat Stress Response Mechanisms

Camellia (Camellia japonica) is a semi-shaded plant that is highly vulnerable to heat stress. To investigate the mechanisms underlying heat stress in C. japonica, two C. japonica cultivars, "Xiaotaohong" and "Zhuapolian", which exhibit significant differences in heat tolerance, were selected from four common cultivars. The selection methods included phenotypic observations and physiological index detection, including relative electric conductivity (REC), malondialdehyde (MDA) content, superoxide dismutase (SOD) enzyme activity, relative water content (RWC), and chlorophyll content. RNA-seq analysis yielded 980 million reads and identified 68,455 differentially expressed genes (DEGs) in the two C. japonica cultivars during heat stress compared to the control samples. Totals of 12,565 and 16,046 DEGs were differentially expressed at 16 h and 32 h, respectively, in "Xiaotaohong" during heat stress. In "Zhuapolian", 40,280 and 37,539 DEGs were found at 16 h and 32 h, respectively. KEGG enrichment analysis revealed that both cultivars were enriched in the "plant hormone signal transduction" and "circadian rhythm" pathways at two stages, indicating the critical role these pathways play in the heat stress response. The differences in the tolerance between the two cultivars are likely linked to pathways such as "plant hormone signal transduction", "photosynthesis", and "circadian rhythm". Some members of heat shock proteins (HSPs) are associated with the heat stress response. It is speculated that transcription factor families contributing to the tolerance differences include AP2/ERF, C3H, bHLH, bZIP, and MYB-related with a small number of heat shock factors (HSFs) also induced by the stress. In conclusion, these results reveal the changes in the physiological indices and molecular networks of two C. japonica cultivars under heat stress. This study lays the foundation for the breeding of superior heat-resistant C. japonica cultivars and for further molecular research.

Impact of heat stress on physiological characteristics and expression of heat shock proteins (HSPs) in groundnut (Arachis hypogaea L.)

The current climate change has a profound impact on agricultural production. Despite the unanimous efforts of several nations to prevent further increase in global temperatures, developing adaptive strategies by imparting heat tolerance in crop plants is essential to ensure global food security. This study demonstrates the impact of heat stress on the morphological, physiological and biochemical properties of different groundnut genotypes derived from a recombinant inbred line (RIL) population (JL 24 × 55-437). The plants were grown in controlled conditions and a high-temperature stress of 45 °C was gradually imposed by placing the plants in an environmental chamber during peak reproductive stage [25 days after sowing (DAS) to 60 DAS]. Heat tolerant genotypes had better biochemical machinery to withstand the heat stress-induced oxidative burst with higher activity of catalase and peroxidase. Also, the tolerant genotypes had lesser membrane damage as indicated by lower malondialdehyde levels. Greater expression of heat shock proteins (HSP17) transcripts alongside elevated levels of both enzymatic and non-enzymatic antioxidant activity was observed when exposed to high temperature, indicating their potential association with heat stress tolerance in groundnut.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01520-y.

SlWRKY55 coordinately acts with SlVQ11 to enhance tomato thermotolerance by activating SlHsfA2

High temperature (HT) severely restricts plant growth, development, and productivity. Plants have evolved a set of mechanisms to cope with HT, including the regulation of heat stress transcription factors (Hsfs) and heat shock proteins (Hsps). However, it is not clear how the transcriptional and translational levels of Hsfs and Hsps are controlled in tomato. Here, we reported that the HT-induced transcription factor SlWRKY55 recruited SlVQ11 to coordinately regulate defense against HT. SlWRKY55 directly bound to the promoter of SlHsfA2 and promoted its expression, which was increased by SlVQ11. Moreover, both SlWRKY55 and SlVQ11 physically interacted with SlHsfA2 to enhance the transcriptional activity of SlHsfA2. Thus, our results revealed a molecular mechanism that the SlWRKY55/SlVQ11-SlHsfA2 cascade enhanced thermotolerance and provided potential target genes for improving the adaptability of crops to HT.

Proteomic profiling of Arabidopsis nuclei reveals distinct protein accumulation kinetics upon heat stress

Heat stress (HS) impacts the nuclear proteome and, subsequently, protein activities in different nuclear compartments. In Arabidopsis thaliana, a short exposure to 37 °C leads to loss of the standard tripartite architecture of the nucleolus, the most prominent nuclear substructure, and, consequently, affects the assembly of ribosomes. Here, we report a quantitative label-free LC‒MS/MS (Liquid Chromatography coupled to tandem Mass Spectrometry) analysis to determine the nuclear proteome of Arabidopsis at 22 °C, HS (37 °C for 4 and 24 h), and a recovery phase. This analysis identified ten distinct groups of proteins based on relative abundance changes in the nucleus before, during and after HS: Early, Late, Transient, Early Persistent, Late Persistent, Recovery, Early-Like, Late-Like, Transient-Like and Continuous Groups (EG, LG, TG, EPG, LPG, RG, ELG, LLG, TLG and CG, respectively). Interestingly, the RNA polymerase I subunit NRPA3 and other main nucleolar proteins, including NUCLEOLIN 1 and FIBRILLARIN 1 and 2, were detected in RG and CG, suggesting that plants require increased nucleolar activity and likely ribosome assembly to restore protein synthesis after HS.

A high-quality genome assembly reveals adaptations underlying glossy, wax-coated leaves in the heat-tolerant wild raspberry Rubus leucanthus

With glossy, wax-coated leaves, Rubus leucanthus is one of the few heat-tolerant wild raspberry trees. To ascertain the underlying mechanism of heat tolerance, we generated a high-quality genome assembly with a genome size of 230.9 Mb and 24,918 protein-coding genes. Significantly expanded gene families were enriched in the flavonoid biosynthesis pathway and the circadian rhythm-plant pathway, enabling survival in subtropical areas by accumulating protective flavonoids and modifying photoperiodic responses. In contrast, plant-pathogen interaction and MAPK signaling involved in response to pathogens were significantly contracted. The well-known heat response elements (HSP70, HSP90, and HSFs) were reduced in R. leucanthus compared to two other heat-intolerant species, R. chingii and R. occidentalis, with transcriptome profiles further demonstrating their dispensable roles in heat stress response. At the same time, three significantly positively selected genes in the pathway of cuticular wax biosynthesis were identified, and may contribute to the glossy, wax-coated leaves of R. leucanthus. The thick, leathery, waxy leaves protect R. leucanthus against pathogens and herbivores, supported by the reduced R gene repertoire in R. leucanthus (355) compared to R. chingii (376) and R. occidentalis (449). Our study provides some insights into adaptive divergence between R. leucanthus and other raspberry species on heat tolerance.

Heat-shock transcription factor HsfA8a regulates heat stress response in Sorbus pohuashanensis

MAIN CONCLUSION

The SpHsfA8a upregulated expression can induce the expression of multiple heat-tolerance genes, and increase the tolerance of Arabidopsis thaliana to high-temperature stress. Sorbus pohuashanensis is an ornamental tree used in courtyards. However, given its poor thermotolerance, the leaves experience sunburn owing to high temperatures in summer, severely affecting its ornamental value. Heat-shock transcription factors play a critical regulatory role in the plant response to heat stress. To explore the heat-tolerance-related genes of S. pohuashanensis to increase the tree's high-temperature tolerance, the SpHsfA8a gene was cloned from S. pohuashanensis, and its structure and expression patterns in different tissues and under abiotic stress were analyzed, as well as its function in heat tolerance, was determined via overexpression in Arabidopsis thaliana. The results showed that SpHsfA8a encodes 416 amino acids with a predicted molecular weight of 47.18 kDa and an isoelectric point of 4.63. SpHsfA8a is a hydrophilic protein without a signal peptide and multiple phosphorylation sites. It also contains a typical DNA-binding domain and is similar to MdHsfA8a in Malus domestica and PbHsfA8 in Pyrus bretschneideri. In S. pohuashanensis, SpHsfA8a is highly expressed in the roots and fruits and is strongly induced under high-temperature stress in leaves. The heterologous expression of SpHsfA8a in A. thaliana resulted in a considerably stronger growth status than that of the wild type after 6 h of treatment at 45 °C. Its proline content, catalase and peroxidase activities also significantly increased, indicating that the SpHsfA8a gene increased the tolerance of A. thaliana to high-temperature stress. SpHsfA8a could induce the expression of multiple heat-tolerance genes in A. thaliana, indicating that SpHsfA8a could strengthen the tolerance of A. thaliana to high-temperature stress through a complex regulatory network. The results of this study lay the foundation for further elucidation of the regulatory mechanism of SpHsfA8a in response of S. pohuashanensis to high-temperature stress.

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

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

GDSL Lipase Gene HTA1 Negatively Regulates Heat Tolerance in Rice Seedlings by Regulating Reactive Oxygen Species Accumulation

High temperature is a significant environmental stress that limits plant growth and agricultural productivity. GDSL lipase is a hydrolytic enzyme with a conserved GDSL sequence at the N-terminus, which has various biological functions, such as participating in plant growth, development, lipid metabolism, and stress resistance. However, little is known about the function of the GDSL lipase gene in the heat tolerance of rice. Here, we characterized a lipase family protein coding gene HTA1, which was significantly induced by high temperature in rice. Rice seedlings in which the mutant hta1 was knocked out showed enhanced heat tolerance, whereas the overexpressing HTA1 showed more sensitivity to heat stress. Under heat stress, hta1 could reduce plant membrane damage and reactive oxygen species (ROS) levels and elevate the activity of antioxidant enzymes. Moreover, real-time quantitative PCR (RT-qPCR) analysis showed that mutant hta1 significantly activated gene expression in antioxidant enzymes, heat response, and defense. In conclusion, our results suggest that HTA1 negatively regulates heat stress tolerance by modulating the ROS accumulation and the expression of heat-responsive and defense-related genes in rice seedlings. This research will provide a valuable resource for utilizing HTA1 to improve crop heat tolerance.

A rapid return to normal: temporal gene expression patterns following cold exposure in the bumble bee Bombus impatiens

Bumble bees are common in cooler climates and many species likely experience periodic exposure to very cold temperatures, but little is known about the temporal dynamics of cold response mechanisms following chill exposure, especially how persistent effects of cold exposure may facilitate tolerance of future events. To investigate molecular processes involved in the temporal response by bumble bees to acute cold exposure, we compared mRNA transcript abundance in Bombus impatiens workers exposed to 0°C for 75 min (inducing chill coma) and control bees maintained at a constant ambient temperature (28°C). We sequenced the 3' end of mRNA transcripts (TagSeq) to quantify gene expression in thoracic tissue of bees at several time points (0, 10, 30, 120 and 720 min) following cold exposure. Significant differences from control bees were only detectable within 30 min after the treatment, with most occurring at the 10 min recovery time point. Genes associated with gluconeogenesis and glycolysis were most notably upregulated, while genes related to lipid and purine metabolism were downregulated. The observed patterns of expression indicate a rapid recovery after chill coma, suggesting an acute differential transcriptional response during recovery from chill coma and return to baseline expression levels within an hour, with no long-term gene expression markers of this cold exposure. Our work highlights the functions and pathways important for acute cold recovery, provides an estimated time frame for recovery from cold exposure in bumble bees, and suggests that cold hardening may be less important for these heterothermic insects.

Genome-Wide Analysis of the HSF Gene Family Reveals Its Role in Astragalus mongholicus under Different Light Conditions

Astragalus mongholicus is a traditional Chinese medicine (TCM) with important medicinal value and is widely used worldwide. Heat shock (HSF) transcription factors are among the most important transcription factors in plants and are involved in the transcriptional regulation of various stress responses, including drought, salinity, oxidation, osmotic stress, and high light, thereby regulating growth and developmental processes. However, the HFS gene family has not yet been identified in A. mongholicus, and little is known regarding the role of HSF genes in A. mongholicus. This study is based on whole genome analysis of A. mongholicus, identifying a total of 22 AmHSF genes and analyzing their physicochemical properties. Divided into three subgroups based on phylogenetic and gene structural characteristics, including subgroup A (12), subgroup B (9), and subgroup C (1), they are randomly distributed in 8 out of 9 chromosomes of A. mongholicus. In addition, transcriptome data and quantitative real time polymerase chain reaction (qRT-PCR) analyses revealed that AmHSF was differentially transcribed in different tissues, suggesting that AmHSF gene functions may differ. Red and blue light treatment significantly affected the expression of 20 HSF genes in soilless cultivation of A. mongholicus seedlings. AmHSF3, AmHSF3, AmHSF11, AmHSF12, and AmHSF14 were upregulated after red light and blue light treatment, and these genes all had light-corresponding cis-elements, suggesting that AmHSF genes play an important role in the light response of A. mongholicus. Although the responses of soilless-cultivated A. mongholicus seedlings to red and blue light may not represent the mature stage, our results provide fundamental research for future elucidation of the regulatory mechanisms of HSF in the growth and development of A. mongholicus and its response to different light conditions.

Major transcription factor families at the nexus of regulating abiotic stress response in millets: a comprehensive review

Millets stand out as a sustainable crop with the potential to address the issues of food insecurity and malnutrition. These small-seeded, drought-resistant cereals have adapted to survive a broad spectrum of abiotic stresses. Researchers are keen on unravelling the regulatory mechanisms that empower millets to withstand environmental adversities. The aim is to leverage these identified genetic determinants from millets for enhancing the stress tolerance of major cereal crops through genetic engineering or breeding. This review sheds light on transcription factors (TFs) that govern diverse abiotic stress responses and play role in conferring tolerance to various abiotic stresses in millets. Specifically, the molecular functions and expression patterns of investigated TFs from various families, including bHLH, bZIP, DREB, HSF, MYB, NAC, NF-Y and WRKY, are comprehensively discussed. It also explores the potential of TFs in developing stress-tolerant crops, presenting a comprehensive discussion on diverse strategies for their integration.

HSFA3 functions as a positive regulator of HSFA2a to enhance thermotolerance in perennial ryegrass

Perennial ryegrass (Lolium perenne) is a widely used cool season turfgrass with outstanding turf quality and grazing tolerance. High temperature is the key factor restricting the distribution of perennial ryegrass in temperate and sub-tropic regions. In this study, we found that one HEAT SHCOK TRANSCRIPTION FACOTR (HSF) class A gene from perennial ryegrass, LpHSFA3, was highly induced by heat stress. LpHSFA3 is localized in nucleus and functions as a transcription factor. Ectopic overexpression of LpHSFA3 in Arabidopsis improved thermotolerance and rescued heat sensitive deficiency of athsfa3 mutant. Overexpression of LpHSFA3 in perennial ryegrass enhanced heat tolerance and increased survival rate in summer season as evidenced by decreased EL and MDA, increased number of green leaves and total chlorophyll content. LpHSFA3 binds to the HSE region in LpHSFA2a promoter to constitutively activate the expression of LpHSFA2a and downstream heat stress responsive genes. Ectopic overexpression of LpHSFA2a consequently rescued thermal sensitivity of athsfa3 mutant and enhanced thermotolerance of athsfa2 mutant. Perennial ryegrass protoplasts with overexpression of LpHSFA3 and LpHSFA2a exhibited induction of similar subsets of heat responsive genes. These results indicated that transcription factor LpHSFA3 functions as positive regulator of LpHSFA2a to improve thermotolerance of perennial ryegrass, providing further evidence to understand the regulatory networks of plant heat stress response.

Comparative transcriptome profiling of contrasting finger millet (Eleusine coracana (L.) Gaertn) genotypes under heat stress

BACKGROUND

Eleusine coracana (L.) Gaertn is a crucial C4 species renowned for its stress robustness and nutritional significance. Because of its adaptability traits, finger millet (ragi) is a storehouse of critical genomic resources for crop improvement. However, more knowledge about this crop's molecular responses to heat stress needs to be gained.

METHODS AND RESULTS

In the present study, a comparative RNA sequencing analysis was done in the leaf tissue of the finger millet, between the heat-sensitive (KJNS-46) and heat-tolerant (PES-110) cultivars of Ragi, in response to high temperatures. On average, each sample generated about 24 million reads. Interestingly, a comparison of transcriptomic profiling identified 684 transcripts which were significantly differentially expressed genes (DEGs) examined between the heat-stressed samples of both genotypes. The heat-induced change in the transcriptome was confirmed by qRT-PCR using a set of randomly selected genes. Pathway analysis and functional annotation analysis revealed the activation of various genes involved in response to stress specifically heat, oxidation-reduction process, water deprivation, and changes in heat shock protein (HSP) and transcription factors, calcium signaling, and kinase signaling. The basal regulatory genes, such as bZIP, were involved in response to heat stress, indicating that heat stress activates genes involved in housekeeping or related to basal regulatory processes. A substantial percentage of the DEGs belonged to proteins of unknown functions (PUFs), i.e., not yet characterized.

CONCLUSION

These findings highlight the importance of candidate genes, such as HSPs and pathways that can confer tolerance towards heat stress in ragi. These results will provide valuable information to improve the heat tolerance in heat-susceptible agronomically important varieties of ragi and other crops.

A review of changes at the phenotypic, physiological, biochemical, and molecular levels of plants due to high temperatures

MAIN CONCLUSION

This review summarizes the physiological, biochemical, and molecular regulatory network changes in plants in response to high temperature. With the continuous rise in temperature, high temperature has become an important issue limiting global plant growth and development, affecting the phenotype and physiological and biochemical processes of plants and seriously restricting crop yield and tree growth speed. As sessile organisms, plants inevitably encounter high temperatures and improve their heat tolerance by activating molecular networks related to heat stress, such as signal transduction, synthesis of metabolites, and gene expression. Heat tolerance is a polygenic trait regulated by a variety of genes, transcription factors, proteins, and metabolites. Therefore, this review summarizes the changes in physiological, biochemical and molecular regulatory networks in plants under high-temperature conditions to lay a foundation for an in-depth understanding of the mechanisms involved in plant heat tolerance responses.

Upregulation of Wheat Heat Shock Transcription Factor TaHsfC3-4 by ABA Contributes to Drought Tolerance

Drought stress can seriously affect the yield and quality of wheat (Triticum aestivum). So far, although few wheat heat shock transcription factors (Hsfs) have been found to be involved in the stress response, the biological functions of them, especially the members of the HsfC (heat shock transcription factor C) subclass, remain largely unknown. Here, we identified a class C encoding gene, TaHsfC3-4, based on our previous omics data and analyzed its biological function in transgenic plants. TaHsfC3-4 encodes a protein containing 274 amino acids and shows the basic characteristics of the HsfC class. Gene expression profiles revealed that TaHsfC3-4 was constitutively expressed in many tissues of wheat and was induced during seed maturation. TaHsfC3-4 could be upregulated by PEG and abscisic acid (ABA), suggesting that this Hsf may be involved in the regulation pathway depending on ABA in drought resistance. Further results represented that TaHsfC3-4 was localized in the nucleus but had no transcriptional activation activity. Notably, overexpression of TaHsfC3-4 in Arabidopsis thaliana pyr1pyl1pyl2pyl4 (pyr1pyl124) quadruple mutant plants complemented the ABA-hyposensitive phenotypes of the quadruple mutant including cotyledon greening, root elongation, seedling growth, and increased tolerance to drought, indicating positive roles of TaHsfC3-4 in the ABA signaling pathway and drought tolerance. Furthermore, we identified TaHsfA2-11 as a TaHsfC3-4-interacting protein by yeast two-hybrid (Y2H) screening. The experimental data show that TaHsfC3-4 can indeed interact with TaHsfA2-11 in vitro and in vivo. Moreover, transgenic Arabidopsis TaHsfA2-11 overexpression lines exhibited enhanced drought tolerance, too. In summary, our study confirmed the role of TaHsfC3-4 in response to drought stress and provided a target locus for marker-assisted selection breeding to improve drought tolerance in wheat.

Tomato plant response to heat stress: a focus on candidate genes for yield-related traits

Climate change and global warming represent the main threats for many agricultural crops. Tomato is one of the most extensively grown and consumed horticultural products and can survive in a wide range of climatic conditions. However, high temperatures negatively affect both vegetative growth and reproductive processes, resulting in losses of yield and fruit quality traits. Researchers have employed different parameters to evaluate the heat stress tolerance, including evaluation of leaf- (stomatal conductance, net photosynthetic rate, Fv/Fm), flower- (inflorescence number, flower number, stigma exertion), pollen-related traits (pollen germination and viability, pollen tube growth) and fruit yield per plant. Moreover, several authors have gone even further, trying to understand the plants molecular response mechanisms to this stress. The present review focused on the tomato molecular response to heat stress during the reproductive stage, since the increase of temperatures above the optimum usually occurs late in the growing tomato season. Reproductive-related traits directly affects the final yield and are regulated by several genes such as transcriptional factors, heat shock proteins, genes related to flower, flowering, pollen and fruit set, and epigenetic mechanisms involving DNA methylation, histone modification, chromatin remodelling and non-coding RNAs. We provided a detailed list of these genes and their function under high temperature conditions in defining the final yield with the aim to summarize the recent findings and pose the attention on candidate genes that could prompt on the selection and constitution of new thermotolerant tomato plant genotypes able to face this abiotic challenge.

A Genome-Wide Analysis and Expression Profile of Heat Shock Transcription Factor (Hsf) Gene Family in Rhododendron simsii

Heat shock transcription factors are key players in a number of transcriptional regulatory pathways that function during plant growth and development. However, their mode of action in Rhododendron simsii is still unclear. In this study, 22 RsHsf genes were identified from genomic data of R. simsii. The 22 genes were randomly distributed on 12 chromosomes, and were divided into three major groups according to their phylogenetic relationships. The structures and conserved motifs were predicted for the 22 genes. Analysis of cis-acting elements revealed stress-responsive and phytohormone-responsive elements in the gene promoter regions, but the types and number varied among the different groups of genes. Transcriptional profile analyses revealed that RsHsfs were expressed in a tissue-specific manner, with particularly high transcript levels in the roots. The transcriptional profiles under abiotic stress were detected by qRT-PCR, and the results further validated the critical function of RsHsfs. This study provides basic information about RsHsf family in R. simsii, and paves the way for further research to clarify their precise roles and to breed new stress-tolerant varieties.

Transcriptional Regulation of Small Heat Shock Protein 17 (sHSP-17) by Triticum aestivum HSFA2h Transcription Factor Confers Tolerance in Arabidopsis under Heat Stress

Heat shock transcription factors (HSFs) contribute significantly to thermotolerance acclimation. Here, we identified and cloned a putative HSF gene (HSFA2h) of 1218 nucleotide (acc. no. KP257297.1) from wheat cv. HD2985 using a de novo transcriptomic approach and predicted sHSP as its potential target. The expression of HSFA2h and its target gene (HSP17) was observed at the maximum level in leaf tissue under heat stress (HS), as compared to the control. The HSFA2h-pRI101 binary construct was mobilized in Arabidopsis, and further screening of T3 transgenic lines showed improved tolerance at an HS of 38 °C compared with wild type (WT). The expression of HSFA2h was observed to be 2.9- to 3.7-fold higher in different Arabidopsis transgenic lines under HS. HSFA2h and its target gene transcripts (HSP18.2 in the case of Arabidopsis) were observed to be abundant in transgenic Arabidopsis plants under HS. We observed a positive correlation between the expression of HSFA2h and HSP18.2 under HS. Evaluation of transgenic lines using different physio-biochemical traits linked with thermotolerance showed better performance of HS-treated transgenic Arabidopsis plants compared with WT. There is a need to further characterize the gene regulatory network (GRN) of HSFA2h and sHSP in order to modulate the HS tolerance of wheat and other agriculturally important crops.

SPOTTED-LEAF7 targets the gene encoding β-galactosidase9, which functions in rice growth and stress responses

β-Galactosidases (Bgals) remove terminal β-D-galactosyl residues from the nonreducing ends of β-D-galactosidases and oligosaccharides. Bgals are present in bacteria, fungi, animals, and plants and have various functions. Despite the many studies on the evolution of BGALs in plants, their functions remain obscure. Here, we identified rice (Oryza sativa) β-galactosidase9 (OsBGAL9) as a direct target of the heat stress-induced transcription factor SPOTTED-LEAF7 (OsSPL7), as demonstrated by protoplast transactivation analysis and yeast 1-hybrid and electrophoretic mobility shift assays. Knockout plants for OsBGAL9 (Osbgal9) showed short stature and growth retardation. Histochemical β-glucuronidase (GUS) analysis of transgenic lines harboring an OsBGAL9pro:GUS reporter construct revealed that OsBGAL9 is mainly expressed in internodes at the mature stage. OsBGAL9 expression was barely detectable in seedlings under normal conditions but increased in response to biotic and abiotic stresses. Ectopic expression of OsBGAL9 enhanced resistance to the rice pathogens Magnaporthe oryzae and Xanthomonas oryzae pv. oryzae, as well as tolerance to cold and heat stress, while Osbgal9 mutant plants showed the opposite phenotypes. OsBGAL9 localized to the cell wall, suggesting that OsBGAL9 and its plant putative orthologs likely evolved functions distinct from those of its closely related animal enzymes. Enzyme activity assays and analysis of the cell wall composition of OsBGAL9 overexpression and mutant plants indicated that OsBGAL9 has activity toward galactose residues of arabinogalactan proteins (AGPs). Our study clearly demonstrates a role for a member of the BGAL family in AGP processing during plant development and stress responses.

Genome-wide analysis of the heat shock transcription factor family reveals saline-alkali stress responses in Xanthoceras sorbifolium

The heat shock transcription factor (HSF) family is involved in regulating growth, development, and abiotic stress. The characteristics and biological functions of HSF family member in X. sorbifolium, an important oil and ornamental plant, have never been reported. In this study, 21 XsHSF genes were identified from the genome of X. sorbifolium and named XsHSF1-XsHSF21 based on their chromosomal positions. Those genes were divided into three groups, A, B, and C, containing 12, one, and eight genes, respectively. Among them, 20 XsHSF genes are located on 11 chromosomes. Protein structure analysis suggested that XsHSF proteins were conserved, displaying typical DNA binding domains (DBD) and oligomerization domains (OD). Moreover, HSF proteins within the same group contain specific motifs, such as motif 5 in the HSFC group. All XsHSF genes have one intron in the CDS region, except XsHSF1 which has two introns. Promoter analysis revealed that in addition to defense and stress responsiveness elements, some promoters also contained a MYB binding site and elements involved in multiple hormones responsiveness and anaerobic induction. Duplication analysis revealed that XsHSF1 and XsHSF4 genes were segmentally duplicated while XsHSF2, XsHSF9, and XsHSF13 genes might have arisen from transposition. Expression pattern analysis of leaves and roots following salt-alkali treatment using qRT-PCR indicated that five XsHSF genes were upregulated and one XsHSF gene was downregulated in leaves upon NaCl treatment suggesting these genes may play important roles in salt response. Additionally, the expression levels of most XsHSFs were decreased in leaves and roots following alkali-induced stress, indicating that those XsHSFs may function as negative regulators in alkali tolerance. MicroRNA target site prediction indicated that 16 of the XsHSF genes may be regulated by multiple microRNAs, for example XsHSF2 might be regulated by miR156, miR394, miR395, miR408, miR7129, and miR854. And miR164 may effect the mRNA levels of XsHSF3 and XsHSF17, XsHSF9 gene may be regulated by miR172. The expression trends of miR172 and miR164 in leaves and roots on salt treatments were opposite to the expression trend of XsHSF9 and XsHSF3 genes, respectively. Promoter analysis showed that XsHSFs might be involved in light and hormone responses, plant development, as well as abiotic stress responses. Our results thus provide an overview of the HSF family in X. sorbifolium and lay a foundation for future functional studies to reveal its roles in saline-alkali response.

Alternative splicing of TaHSFA6e modulates heat shock protein-mediated translational regulation in response to heat stress in wheat

Heat stress greatly threatens crop production. Plants have evolved multiple adaptive mechanisms, including alternative splicing, that allow them to withstand this stress. However, how alternative splicing contributes to heat stress responses in wheat (Triticum aestivum) is unclear. We reveal that the heat shock transcription factor gene TaHSFA6e is alternatively spliced in response to heat stress. TaHSFA6e generates two major functional transcripts: TaHSFA6e-II and TaHSFA6e-III. TaHSFA6e-III enhances the transcriptional activity of three downstream heat shock protein 70 (TaHSP70) genes to a greater extent than does TaHSFA6e-II. Further investigation reveals that the enhanced transcriptional activity of TaHSFA6e-III is due to a 14-amino acid peptide at its C-terminus, which arises from alternative splicing and is predicted to form an amphipathic helix. Results show that knockout of TaHSFA6e or TaHSP70s increases heat sensitivity in wheat. Moreover, TaHSP70s are localized in stress granule following exposure to heat stress and are involved in regulating stress granule disassembly and translation re-initiation upon stress relief. Polysome profiling analysis confirms that the translational efficiency of stress granule stored mRNAs is lower at the recovery stage in Tahsp70s mutants than in the wild types. Our finding provides insight into the molecular mechanisms by which alternative splicing improves the thermotolerance in wheat.

Exploring the Heat Shock Transcription Factor (HSF) Gene Family in Ginger: A Genome-Wide Investigation on Evolution, Expression Profiling, and Response to Developmental and Abiotic Stresses

Ginger is a valuable crop known for its nutritional, seasoning, and health benefits. However, abiotic stresses, such as high temperature and drought, can adversely affect its growth and development. Heat shock transcription factors (HSFs) have been recognized as crucial elements for enhancing heat and drought resistance in plants. Nevertheless, no previous study has investigated the HSF gene family in ginger. In this research, a total of 25 ZoHSF members were identified in the ginger genome, which were unevenly distributed across ten chromosomes. The ZoHSF members were divided into three groups (HSFA, HSFB, and HSFC) based on their gene structure, protein motifs, and phylogenetic relationships with Arabidopsis. Interestingly, we found more collinear gene pairs between ZoHSF and HSF genes from monocots, such as rice, wheat, and banana, than dicots like Arabidopsis thaliana. Additionally, we identified 12 ZoHSF genes that likely arose from duplication events. Promoter analysis revealed that the hormone response elements (MEJA-responsiveness and abscisic acid responsiveness) were dominant among the various cis-elements related to the abiotic stress response in ZoHSF promoters. Expression pattern analysis confirmed differential expression of ZoHSF members across different tissues, with most showing responsiveness to heat and drought stress. This study lays the foundation for further investigations into the functional role of ZoHSFs in regulating abiotic stress responses in ginger.

In-silico analysis of heat shock transcription factor (OsHSF) gene family in rice (Oryza sativa L.)

BACKGROUND

One of the most important cash crops worldwide is rice (Oryza sativa L.). Under varying climatic conditions, however, its yield is negatively affected. In order to create rice varieties that are resilient to abiotic stress, it is essential to explore the factors that control rice growth, development, and are source of resistance. HSFs (heat shock transcription factors) control a variety of plant biological processes and responses to environmental stress. The in-silico analysis offers a platform for thorough genome-wide identification of OsHSF genes in the rice genome.

RESULTS

In this study, 25 randomly dispersed HSF genes with significant DNA binding domains (DBD) were found in the rice genome. According to a gene structural analysis, all members of the OsHSF family share Gly-66, Phe-67, Lys-69, Trp-75, Glu-76, Phe-77, Ala-78, Phe-82, Ile-93, and Arg-96. Rice HSF family genes are widely distributed in the vegetative organs, first in the roots and then in the leaf and stem; in contrast, in reproductive tissues, the embryo and lemma exhibit the highest levels of gene expression. According to chromosomal localization, tandem duplication and repetition may have aided in the development of novel genes in the rice genome. OsHSFs have a significant role in the regulation of gene expression, regulation in primary metabolism and tolerance to environmental stress, according to gene networking analyses.

CONCLUSION

Six genes viz; Os01g39020, Os01g53220, Os03g25080, Os01g54550, Os02g13800 and Os10g28340 were annotated as promising genes. This study provides novel insights for functional studies on the OsHSFs in rice breeding programs. With the ultimate goal of enhancing crops, the data collected in this survey will be valuable for performing genomic research to pinpoint the specific function of the HSF gene during stress responses.

The miR165/166-PHABULOSA module promotes thermotolerance by transcriptionally and posttranslationally regulating HSFA1

Heat stress (HS) adversely affects plant growth and productivity. The Class A1 HS transcription factors (HSFA1s) act as master regulators in the plant response to HS. However, how HSFA1-mediated transcriptional reprogramming is modulated during HS remains to be elucidated. Here, we report that a module formed by the microRNAs miR165 and miR166 and their target transcript, PHABULOSA (PHB), regulates HSFA1 at the transcriptional and translational levels to control plant HS responses. HS-triggered induction of MIR165/166 in Arabidopsis thaliana led to decreased expression of target genes including PHB. MIR165/166 overexpression lines and mutations in miR165/166 target genes enhanced HS tolerance, whereas miR165/166 knockdown lines and plants expressing a miR165/166-resistant form of PHB were sensitive to HS. PHB directly repressed the transcription of HSFA1s and globally modulated the expression of HS-responsive genes. PHB and HSFA1s share a common target gene, HSFA2, which is essential for activation of plant responses to HS. PHB physically interacted with HSFA1s and exerted an antagonistic effect on HSFA1 transcriptional activity. PHB and HSFA1s co-regulated transcriptome reprogramming upon HS. Together, these findings indicate that heat-triggered regulation of the miR165/166-PHB module controls HSFA1-mediated transcriptional reprogramming and plays a critical role during HS in Arabidopsis.

Genome-wide identification, classification, and expression analysis of heat shock transcription factor family in switchgrass (Panicum virgatum L.)

Switchgrass is one of the most promising bioenergy crops and is generally cultivated in arid climates and poor soils. Heat shock transcription factors (Hsfs) are key regulators of plant responses to abiotic and biotic stressors. However, their role and mechanism of action in switchgrass have not been elucidated. Hence, this study aimed to identify the Hsf family in switchgrass and understand its functional role in heat stress signal transduction and heat tolerance by using bioinformatics and RT-PCR analysis. Forty-eight PvHsfs were identified and divided into three main classes based on their gene structure and phylogenetic relationships: HsfA, HsfB, and HsfC. The results of the bioinformatics analysis showed a DNA-binding domain (DBD) at the N-terminal in PvHsfs, and they were not evenly distributed on all chromosomes except for chromosomes 8 N and 8 K. Many cis-elements related to plant development, stress responses, and plant hormones were identified in the promoter sequence of each PvHsf. Segmental duplication is the primary force underlying Hsf family expansion in switchgrass. The results of the expression pattern of PvHsfs in response to heat stress showed that PvHsf03 and PvHsf25 might play critical roles in the early and late stages of switchgrass response to heat stress, respectively, and HsfB mainly showed a negative response to heat stress. Ectopic expression of PvHsf03 in Arabidopsis significantly increased the heat resistance of seedlings. Overall, our research lays a notable foundation for studying the regulatory network in response to deleterious environments and for further excavating tolerance genes in switchgrass.

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.

Identification of passion fruit HSF gene family and the functional analysis of PeHSF-C1a in response to heat and osmotic stress

Heat stress transcription factors (HSFs) are the major regulators of plant response to environmental stress, especially heat and drought stress. To gain a deeper understanding of the mechanisms underlying HSFs in the abiotic stress response of passion fruit, we conducted an in silico analysis of the HSF gene family. Through bioinformatics and phylogenetic analyses, we identified 18 PeHSF members and classified them into A, B, and C groups. Collinearity analysis results revealed that the expansion of the PeHSF gene family was due to the presence of segmental duplication. Furthermore, gene structure and protein domain analysis illustrated that PeHSFs in the same subgroup are relatively conserved. Conserved motif and function domain analysis suggested that PeHSF proteins possess typical conserved functional domains of the HSF family. A protein interaction network and 3D structure prediction were used to study the potential regulatory relationship of PeHSFs. Additionally, the subcellular localization results of PeHSF-A6a, PeHSF-B4b, and PeHSF-C1a were consistent with the predictions. RNA-seq and RT-qPCR analysis revealed the expression patterns of PeHSFs in different tissues of passion fruit floral organs. Promoter analysis and the expression patterns of the PeHSFs under different treatments demonstrated their involvement in various abiotic stress processes. Notably, overexpression of PeHSF-C1a consistently enhanced tolerance to drought and heat stress in Arabidopsis. Overall, our findings provide a scientific basis for further functional studies of PeHSFs that could contribute to improvement of passion fruit breeding.

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.

Plant-specific histone deacetylases associate with ARGONAUTE4 to promote heterochromatin stabilization and plant heat tolerance

High temperature causes devasting effects on many aspects of plant cells and thus enhancing plant heat tolerance is critical for crop production. Emerging studies have revealed the important roles of chromatin modifications in heat stress responses. However, how chromatin is regulated during heat stress remains unclear. We show that heat stress results in heterochromatin disruption coupled with histone hyperacetylation and DNA hypomethylation. Two plant-specific histone deacetylases HD2B and HD2C could promote DNA methylation and relieve the heat-induced heterochromatin decondensation. We noted that most DNA methylation regulated by HD2B and HD2C is lost upon heat stress. HD2B- and HD2C-regulated histone acetylation and DNA methylation are dispensable for heterochromatin maintenance under normal conditions, but critical for heterochromatin stabilization under heat stress. We further showed that HD2B and HD2C promoted DNA methylation through associating with ARGONAUTE4 in nucleoli and Cajal bodies, and facilitating its nuclear accumulation. Thus, HD2B and HD2C act both canonically and noncanonically to stabilize heterochromatin under heat stress. This study not only reveals a novel plant-specific crosstalk between histone deacetylases and key factor of DNA methylation pathway, but also uncovers their new roles in chromatic regulation of plant heat tolerance.

Regulatory Networks of lncRNAs, miRNAs, and mRNAs in Response to Heat Stress in Wheat (Triticum Aestivum L.): An Integrated Analysis

Climate change has become a major source of concern, particularly in agriculture, because it has a significant impact on the production of economically important crops such as wheat, rice, and maize. In the present study, an attempt has been made to identify differentially expressed heat stress-responsive long non-coding RNAs (lncRNAs) in the wheat genome using publicly available wheat transcriptome data (24 SRAs) representing two conditions, namely, control and heat-stressed. A total of 10,965 lncRNAs have been identified and, among them, 153, 143, and 211 differentially expressed transcripts have been found under 0 DAT, 1 DAT, and 4 DAT heat-stress conditions, respectively. Target prediction analysis revealed that 4098 lncRNAs were targeted by 119 different miRNA responses to a plethora of environmental stresses, including heat stress. A total of 171 hub genes had 204 SSRs (simple sequence repeats), and a set of target sequences had SNP potential as well. Furthermore, gene ontology analysis revealed that the majority of the discovered lncRNAs are engaged in a variety of cellular and biological processes related to heat stress responses. Furthermore, the modeled three-dimensional (3D) structures of hub genes encoding proteins, which had an appropriate range of similarity with solved structures, provided information on their structural roles. The current study reveals many elements of gene expression regulation in wheat under heat stress, paving the way for the development of improved climate-resilient wheat cultivars.

Genome-wide identification and characterization of tomato 14-3-3 (SlTFT) genes and functional analysis of SlTFT6 under heat stress

The plant 14-3-3 proteins are essential for many biological processes and responses to abiotic stress. We performed genome-wide identification and analysis of the 14-3-3 family genes in tomato. To explore the properties of the thirteen Sl14-3-3 found in the tomato genome, their chromosomal location, phylogenetic, and syntenic relationships were analyzed. The Sl14-3-3 promoters were found to have a number of growth-, hormone-, and stress-responsive cis-regulatory elements. Moreover, the qRT-PCR assay revealed that Sl14-3-3 genes are responsive to heat and osmotic stress. Subcellular localization experiments evidenced that the SlTFT3/6/10 proteins occur in the nucleus and cytoplasm Additional analysis on Sl14-3-3 putative interactor proteins revealed a number of prospective clients that potentially participate in stress reactions and developmental processes. Furthermore, overexpression of an Sl14-3-3 family gene, SlTFT6, improved tomato plants thermotolerance. Taken together, the study provides basic information on tomato 14-3-3 family genes in plant growth and abiotic stress response (high temperature stress), which can be helpful to further study the underlying molecular mechanisms.

Physiological and gene expression changes of Cryptomeria fortunei Hooibrenk families under heat stress

Heat stress is one of the major abiotic stresses affecting plant growth and productivity. Cryptomeria fortunei (Chinese cedar) is an excellent timber and landscaping tree species in southern China thanks to its beautiful appearance, straight texture and ability to purify the air and improve the environment. In this study, we first screened 8 excellent C. fortunei families (#12, #21, #37, #38, #45, #46, #48, #54) in a second generation seed orchard. We then analyzed the electrolyte leakage (EL) and lethal temperature at 50% (LT₅₀) values under heat stress, to identify the families with the best heat resistance (#48) and the lowest heat resistance (#45) and determine the physiological and morphological response of different threshold-resistance of C. fortune to heat stress. The relative conductivity of the C. fortunei families showed an increasing trend with increasing temperature, following an "S" curve, and the half-lethal temperature ranges between 39°C and 43.2°C. The activities of SOD and POD fluctuated in the early stage of stress but decreased after 37°C. We observed the changes in the cell ultrastructure at 43°C, and the mesophyll cell structure of #48 was less damaged than that of #45. Eight heat resistance gene, including CfAPX1, CfAPX2, CfHSP11, CfHSP21, CfHSP70, CfHSFA1a, CfHSFB2a and CfHSFB4, were all up-regulated in #45 and #48, and there were significant differences between #45 and #48 under different heat stress treatments. We found a significant difference in heat tolerance between #45 and #48, such that #48 shows higher heat tolerance capability and could be exploited in breeding programs. We conclude that the strongly heat-resistant family had a more stable physiological state and a wider range of heat stress adaptations.

Phylogenetic and expression analyses of HSF gene families in wheat (Triticum aestivum L.) and characterization of TaHSFB4-2B under abiotic stress

The heat shock transcription factors (HSFs) family is widely present in eukaryotes including plants. Recent studies have indicated that HSF is a multifunctional group of genes involved in plant growth and development, as well as response to abiotic stresses. Here we combined the bioinformatic, molecular biology way to dissect the function of Hsf, specifically HsfB4 in wheat under abiotic stresses. In this study, we identified 78 TaHSF genes in wheat (Triticum aestivum) and analyzed their phylogenetic relationship and expression regulation motifs. Next, the expression profiles of TaHSFs and AtHSFs were analyzed in different tissues as well as in response to abiotic stress. Furthermore, to explore the role of HSFB4 in abiotic stress response, we cloned TaHSFB4-2B from the wheat variety, Chinese Spring. Subcellular localization analysis showed that TaHSFB4-2B was localized in the nucleus. In addition, We observed TaHSFB4-2B was highly expressed in the root and stem, its transcription was induced under long-term heat shock, cold, and salinity stress. Additionally, overexpression of TaHSFB4-2B suppressed seed germination and growth in Arabidopsis with salinity and mannitol treatment. It also modulated the expression of stress-responsive genes, including AtHSP17.8, AtHSP17.6A, AtHSP17.6C, CAT2, and SOS1, under both normal and stress conditions. From these finding, we propose that TaHSFB4-2B act as a negative regulator of abiotic stress response in the plant.

Transcriptome profiling disclosed the effect of single and combined drought and heat stress on reprogramming of genes expression in barley flag leaf

Despite numerous studies aimed at unraveling the genetic background of barley's response to abiotic stress, the modulation of the transcriptome induced by combinatorial drought and increased temperature remains largely unrecognized. Very limited studies were done, especially on the flag leaf, which plays an important role in grain filling in cereals. In the present study, transcriptome profiles, along with chlorophyll fluorescence parameters and yield components, were compared between barley genotypes with different flag leaf sizes under single and combined drought and heat stress. High-throughput mRNA sequencing revealed 2,457 differentially expressed genes, which were functionally interpreted using Gene Ontology term enrichment analysis. The transcriptomic signature under double stress was more similar to effects caused by drought than by elevated temperature; it was also manifested at phenotypic and chlorophyll fluorescence levels. Both common and stress-specific changes in transcript abundance were identified. Genes regulated commonly across stress treatments, determining universal stress responses, were associated, among others, with responses to drought, heat, and oxidative stress. In addition, changes specific to the size of the flag leaf blade were found. Our study allowed us to identify sets of genes assigned to various processes underlying the response to drought and heat, including photosynthesis, the abscisic acid pathway, and lipid transport. Genes encoding LEA proteins, including dehydrins and heat shock proteins, were especially induced by stress treatments. Some association between genetic composition and flag leaf size was confirmed. However, there was no general coincidence between SNP polymorphism of genotypes and differential expression of genes induced by stress factors. This research provided novel insight into the molecular mechanisms of barley flag leaf that determine drought and heat response, as well as their co-occurrence.

Burning questions for a warming and changing world: 15 unknowns in plant abiotic stress

We present unresolved questions in plant abiotic stress biology as posed by 15 research groups with expertise spanning eco-physiology to cell and molecular biology. Common themes of these questions include the need to better understand how plants detect water availability, temperature, salinity, and rising carbon dioxide (CO2) levels; how environmental signals interface with endogenous signaling and development (e.g. circadian clock and flowering time); and how this integrated signaling controls downstream responses (e.g. stomatal regulation, proline metabolism, and growth versus defense balance). The plasma membrane comes up frequently as a site of key signaling and transport events (e.g. mechanosensing and lipid-derived signaling, aquaporins). Adaptation to water extremes and rising CO2 affects hydraulic architecture and transpiration, as well as root and shoot growth and morphology, in ways not fully understood. Environmental adaptation involves tradeoffs that limit ecological distribution and crop resilience in the face of changing and increasingly unpredictable environments. Exploration of plant diversity within and among species can help us know which of these tradeoffs represent fundamental limits and which ones can be circumvented by bringing new trait combinations together. Better defining what constitutes beneficial stress resistance in different contexts and making connections between genes and phenotypes, and between laboratory and field observations, are overarching challenges.

Genome-wide analysis of HSF family and overexpression of PsnHSF21 confers salt tolerance in Populus simonii × P. nigra

Heat shock transcription factor (HSF) is an important TF that performs a dominant role in plant growth, development, and stress response network. In this study, we identified a total of 30 HSF members from poplar, which are unevenly distributed on 17 chromosomes. The poplar HSF family can be divided into three subfamilies, and the members of the same subfamily share relatively conserved domains and motifs. HSF family members are acidic and hydrophilic proteins that are located in the nucleus and mainly carry out gene expansion through segmental replication. In addition, they have rich collinearity across plant species. Based on RNA-Seq analysis, we explored the expression pattern of PtHSFs under salt stress. Subsequently, we cloned the significantly upregulated PtHSF21 gene and transformed it into Populus simonii × P. nigra. Under salt stress, the transgenic poplar overexpressing PtHSF21 had a better growth state and higher reactive oxygen scavenging ability. A yeast one-hybrid experiment indicated PtHSF21 could improve salt tolerance by specifically binding to the anti-stress cis-acting element HSE. This study comprehensively profiled the fundamental information of poplar HSF family members and their responses to salt stress and specifically verified the biological function of PtHSF21, which provides clues for understanding the molecular mechanism of poplar HSF members in response to salt stress.

Gain-of-function of the cytokinin response activator ARR1 increases heat shock tolerance in Arabidopsis thaliana

In addition to its well-established role in plant development, the hormone cytokinin regulates plant responses to biotic and abiotic stresses. It was previously shown that cytokinin signaling acts negatively upon drought and osmotic stress tolerance and that gain-of-function of the cytokinin response regulator ARR1 causes osmotic stress hypersensitivity. Here we show that increased ARR1 action increases tolerance to heat shock and that this is correlated with increased accumulation of the heat shock proteins Hsp17.6 and Hsp70. These results show that the heat shock tolerance of plants can be elevated by increasing the expression of a cytokinin response activator.

The Re-Localization of Proteins to or Away from Membranes as an Effective Strategy for Regulating Stress Tolerance in Plants

The membranes of plant cells are dynamic structures composed of phospholipids and proteins. Proteins harboring phospholipid-binding domains or lipid ligands can localize to membranes. Stress perception can alter the subcellular localization of these proteins dynamically, causing them to either associate with or detach from membranes. The mechanisms behind the re-localization involve changes in the lipidation state of the proteins and interactions with membrane-associated biomolecules. The functional significance of such re-localization includes the regulation of molecular transport, cell integrity, protein folding, signaling, and gene expression. In this review, proteins that re-localize to or away from membranes upon abiotic and biotic stresses will be discussed in terms of the mechanisms involved and the functional significance of their re-localization. Knowledge of the re-localization mechanisms will facilitate research on increasing plant stress adaptability, while the study on re-localization of proteins upon stresses will further our understanding of stress adaptation strategies in plants.

Identification, classification, and expression profile analysis of heat shock transcription factor gene family in Salvia miltiorrhiza

In response to abiotic stresses, transcription factors are essential. Heat shock transcription factors (HSFs), which control gene expression, serve as essential regulators of plant growth, development, and stress response. As a model medicinal plant, Salvia miltiorrhiza is a crucial component in the treatment of cardiovascular illnesses. But throughout its growth cycle, S.miltiorrhiza is exposed to a series of abiotic challenges, including heat and drought. In this study, 35 HSF genes were identified based on genome sequencing of Salvia miltiorrhiza utilizing bioinformatics techniques. Additionally, 35 genes were classified into three groups by phylogeny and gene structural analysis, comprising 22 HSFA, 11 HSFB, and two HSFC. The distribution and sequence analysis of motif showed that SmHSFs were relatively conservative. In SmHSF genes, analysis of the promoter region revealed the presence of many cis-acting elements linked to stress, hormones, and growth and development, suggesting that these factors have regulatory roles. The majority of SmHSFs were expressed in response to heat and drought stress, according to combined transcriptome and real-time quantitative PCR (qRT-PCR) analyses. In conclusion, this study looked at the SmHSF gene family using genome-wide identification, evolutionary analysis, sequence characterization, and expression analysis. This research serves as a foundation for further investigations into the role of HSF genes and their molecular mechanisms in plant stress responses.

A long noncoding RNA HILinc1 enhances pear thermotolerance by stabilizing PbHILT1 transcripts through complementary base pairing

As global warming intensifies, heat stress has become a major environmental constraint threatening crop production and quality worldwide. Here, we characterize Heat-induced long intergenic noncoding RNA 1 (HILinc1), a cytoplasm-enriched lincRNA that plays a key role in thermotolerance regulation of pear (Pyrus spp.). HILinc1 Target 1 (PbHILT1) which is the target transcript of HILinc1, was stabilized via complementary base pairing to upregulate its expression. PbHILT1 could bind to Heat shock transcription factor A1b (PbHSFA1b) to enhance its transcriptional activity, leading to the upregulation of a major downstream transcriptional regulator, Multiprotein bridging factor 1c (PbMBF1c), during heat response. Transient overexpressing of either HILinc1 or PbHILT1 increases thermotolerance in pear, while transient silencing of HILinc1 or PbHILT1 makes pear plants more heat sensitive. These findings provide evidences for a new regulatory mechanism by which HILinc1 facilitates PbHSFA1b activity and enhances pear thermotolerance through stabilizing PbHILT1 transcripts.

Heat stress in pear cultivar results in upregulation of long non-coding RNA HILinc1, which binds to and stabilizes PbHILT1 mRNA, which codes for a protein that interacts with heat shock factor A1b, improving thermotolerance.

Molecular insights into mechanisms underlying thermo-tolerance in tomato

Plant productivity is being seriously compromised by climate-change-induced temperature extremities. Agriculture and food safety are threatened due to global warming, and in many cases the negative impacts have already begun. Heat stress leads to significant losses in yield due to changes in growth pattern, plant phonologies, sensitivity to pests, flowering, grain filling, maturity period shrinkage, and senescence. Tomato is the second most important vegetable crop. It is very sensitive to heat stress and thus, yield losses in tomato due to heat stress could affect food and nutritional security. Tomato plants respond to heat stress with a variety of cellular, physiological, and molecular responses, beginning with the early heat sensing, followed by signal transduction, antioxidant defense, osmolyte synthesis and regulated gene expression. Recent findings suggest that specific plant organs are extremely sensitive to heat compared to the entire plant, redirecting the research more towards generative tissues. This is because, during sexual reproduction, developing pollens are the most sensitive to heat. Often, just a few degrees of temperature elevation during pollen development can have a negative effect on crop production. Furthermore, recent research has discovered certain genetic and epigenetic mechanisms playing key role in thermo-tolerance and have defined new directions for tomato heat stress response (HSR). Present challenges are to increase the understanding of molecular mechanisms underlying HS, and to identify superior genotypes with more tolerance to extreme temperatures. Several metabolites, genes, heat shock factors (HSFs) and microRNAs work together to regulate the plant HSR. The present review provides an insight into molecular mechanisms of heat tolerance and current knowledge of genetic and epigenetic control of heat-tolerance in tomato for sustainable agriculture in the future. The information will significantly contribute to improve breeding programs for development of heat tolerant cultivars.

Heat shock factor HSFA2 fine-tunes resetting of thermomemory via plastidic metalloprotease FtsH6

Plants 'memorize' stressful events and protect themselves from future, often more severe, stresses. To maximize growth after stress, plants 'reset' or 'forget' memories of stressful situations, which requires an intricate balance between stress memory formation and the degree of forgetfulness. HEAT SHOCK PROTEIN 21 (HSP21) encodes a small heat shock protein in plastids of Arabidopsis thaliana. HSP21 functions as a key component of thermomemory, which requires a sustained elevated level of HSP21 during recovery from heat stress. A heat-induced metalloprotease, filamentation temperature-sensitive H6 (FtsH6), degrades HSP21 to its pre-stress abundance, thereby resetting memory during the recovery phase. The transcription factor heat shock factor A2 (HSFA2) activates downstream genes essential for mounting thermomemory, acting as a positive regulator in the process. Here, using a yeast one-hybrid screen, we identify HSFA2 as an upstream transactivator of the resetting element FtsH6. Constitutive and inducible overexpression of HSFA2 increases expression of FtsH6, whereas it is drastically reduced in the hsfa2 knockout mutant. Chromatin immunoprecipitation reveals in planta binding of HSFA2 to the FtsH6 promoter. Importantly, overexpression of HSFA2 improves thermomemory more profoundly in ftsh6 than wild-type plants. Thus, by activating both memory-supporting and memory-resetting genes, HSFA2 acts as a cellular homeostasis factor during thermomemory.