Diversity of plant heat shock factors: regulation, interactions, and functions

CpHSFA2 isolated from a wild native Carica papaya genotype, with potential to confer tolerance to the combined effect of drought stress and heat shock

Many papaya producing regions are repeatedly affected by drought and high temperatures. In the present study, we investigated the individual effect of heat shock (HS), water deficit stress (WDS) and the combined effect of both types of stress (WD + HS), on the physiological performance of two contrasting papaya genotypes (Maradol and Wild). In all cases, water relations, membrane integrity, gas exchange, photochemical state of PSII and RELs of three Carica papaya transcription factors (CpHsfA1d, CpHsfA2 and CpHsfB3, in both a Wild-native genotype collected from an undisturbed site in its center of origin (Yucatán, Mexico; Wild), as well as in a commercial cultivar (Maradol). Results showed that both papaya genotypes have different physiological and molecular mechanisms to cope with individual stress and combined stresses. Wild (W) genotype exhibited greater tolerance to the three types of stresses than the commercial genotype (M), which correlates with the fact that W also showed higher relative expression levels (REL) in the three CpHsf studied: CpHsfA1d, CpHsfA2 and CpHsfB3 than M. REL of CpHsfA2 was particularly high in the HS and in the combined WD + HS treatment, as well as during the recovery phase of the WDS treatment. CpHSFA2 was then selected for further analysis of subcellular localization, finding that it accumulates in the membrane and nucleus. Taken together, it seems that CpHsfA2 plays an important role in the response to HS and WD + HS stress. Therefore, CpHsfA2 gene from the W genotype could be important to eventually improve tolerance to high temperatures and drought in commercial papaya cultivars.

A pumpkin heat shock factor CmHSF30 positively regulates thermotolerance in transgenic plants

Heat shock factors (HSFs) play a central role in regulating the responses of plants to various stresses. However, the function and regulation of HSFs in pumpkins remains largely unknown. In this study, an HSF, CmHSF30 was identified in Cucurbiamoschata, which belongs to the HSFA subfamily. The expression level of CmHSF30 was significantly upregulated in response to heat stress and exogenous phytohormone treatments, including ABA, GA, IAA, and SA. The CmHSF30 was localized in the nucleus and functions as a transcriptional activator. By overexpressing CmHSF30 in Arabidopsis and pumpkin, the function and regulation of CmHSF30 in response to heat stress were studied. The overexpression of CmHSF30 in Arabidopsis enhanced plant thermotolerance by increased germination rate and survival rate under heat stress, as evidenced by the elevated of contents chlorophyll and GSH, and SOD activity, and decreased contents of H2O2 and MDA. Furthermore, the overexpression of CmHSF30 in pumpkins also enhanced the thermotolerance of transgenic pumpkins by reducing cell death. In contrast, CRISPR/Cas9 mediated knockout of CmHSF30 decreased pumpkin thermotolerance. Besides, RT-qPCR analysis revealed that CmHSF30 plays a positive role in regulating the expression of stress-related genes, including AtHSP18.2, AtHSP20, AtHSP70, AtPP2C, and AtMYB82 from Arabidopsis and CmHSP18.2, CmHSP20, CmHSP70, CmPP2C, and CmMYB46 from pumpkin. Yeast two-hybrid showed that CmHSF30 interacts with CmMYB46. The results indicate that CmHSF30 functions as a positive regulator, enhancing plant thermotolerance by regulating target genes and reducing ROS accumulation.

Characterization of the heat shock factor RcHsfA6 in Rosa chinensis and function in the thermotolerance of Arabidopsis

BACKGROUND

Environmental stresses, especially high temperatures, severely limit the growth and development of many horticultural plants. As a woody ornamental flower with rich flower colors and flower types, rose (R. chinensis) leaves wilt and shriveled petals at high temperatures, which severely affects its growth and ornamental value. The defense mechanism of rose plants against high-temperature stress has not been fully elucidated.

RESULTS

In the present study, the transcriptomes of rose petals at normal (25 °C) and high (35 °C) temperature were compared. A total of 2519 differentially expressed genes (DEGs) were identified, including 1491 upregulated DEGs and 1028 downregulated DEGs. The plant hormone signal transduction pathway, especially the abscisic acid (ABA) signaling pathway, was the most enriched signaling pathway for DEGs in rose at high temperature. Heat shock factors (Hsfs), especially class A Hsfs, have been confirmed to be involved in thermotolerance mechanisms. Among the DEGs, eight genes were annotated as Hsfs, including 5 upregulated Hsfs at high temperature. RcHsfA6 is rapidly induced by high temperatures and is a candidate regulatory factor in the plant ABA signaling pathway. Therefore, we focused on RcHsfA6. RcHsfA6 encodes a protein containing 308 amino acids and contains typical Hsf domains, such as the DNA-binding domain (DBD), the N-terminal oligomerization domain (OD), the nuclear localization signal (NLS) and AHA motifs at the C-terminal activator domain (CTAD). The heterologous overexpression of RcHsfA6 in Arabidopsis increased the thermotolerance of Arabidopsis seeds. In addition, RcHsfA6 overexpression increased the ABA content and the expression of ABA biosynthetic gene AtABI5 and signal transduction gene AtPYL12, thereby inhibiting the germination of Arabidopsis seeds under exogenous ABA conditions.

CONCLUSIONS

Taken together, our results suggest that RcHsfA6 is involved in the high-temperature response of rose and its heterologous overexpression in Arabidopsis increased the thermotolerance of Arabidopsis at high temperatures via the ABA signaling pathway.

SmHSFA8 Enhances the Heat Tolerance of Eggplant by Regulating the SmEGY3-SmCSD1 Module and Promoting SmF3H-mediated Flavonoid Biosynthesis

High temperature (HT) is a major environmental factor that restrains eggplant growth and production. Heat shock factors (HSFs) play a vital role in the response of plants to high-temperature stress (HTS). However, the molecular mechanism by which HSFs regulate heat tolerance in eggplants remains unclear. Previously, we reported that SmEGY3 enhanced the heat tolerance of eggplant. Herein, SmHSFA8 activated SmEGY3 expression and interacted with SmEGY3 protein to enhance the activation function of SmEGY3 on SmCSD1. Virus-induced gene silencing (VIGS) and overexpression assays suggested that SmHSFA8 positively regulated heat tolerance in plants. SmHSFA8 enhanced the heat tolerance of tomato plants by promoting SlEGY3 expression, H2O2 production and H2O2-mediated retrograde signalling pathway. DNA affinity purification sequencing (DAP-seq) analysis revealed that SmHSPs (SmHSP70, SmHSP70B and SmHSP21) and SmF3H were candidate downstream target genes of SmHSFA8. SmHSFA8 regulated the expression of HSPs and F3H and flavonoid content in plants. The silencing of SmF3H by VIGS reduced the flavonoid content and heat tolerance of eggplant. In addition, exogenous flavonoid treatment alleviated the HTS damage to eggplants. These results indicated that SmHSFA8 enhanced the heat tolerance of eggplant by activating SmHSPs exprerssion, mediating the SmEGY3-SmCSD1 module, and promoting SmF3H-mediated flavonoid biosynthesis.

BAG2 mediates HsfA1a-induced thermotolerance by regulating heat shock proteins in tomato

The heat shock transcription factors (Hsfs) and Bcl-2-associated athanogene (BAG) are crucial in response to heat stress. However, the relationship and regulation mechanism between Hsfs and BAGs in plants are largely unknown. Here, we demonstrated that the HsfA1a-BAG2 module mediated thermotolerance through regulating heat shock proteins (HSPs) in tomato. Overexpression of HsfA1a in tomato increased thermotolerance and enhanced the expression of HSP70, HSP90, and BAG2, but compromised in hsfa1a mutant plants. Yeast one-hybrid, dual luciferase, electrophoretic mobility shift assay, and chromatin immunoprecipitation coupled with qPCR assays found that HsfA1a directly bound to the promoter of BAG2 to activate its expression. BAG2 interacted with HsfA1a and BAG5b both in vitro and in vivo. Importantly, BAG5b facilitated the interaction between BAG2 and HsfA1a, resulting in enhanced transcriptional activation capacity of HsfA1a to HSP70 and HSP90. Either overexpression of BAG2 or BAG5b increased thermotolerance, concomitant with sustained expression levels of HSP70 and HSP90 genes. By contrast, knockout of BAG2 or BAG5b displayed the opposite results. Furthermore, silencing of BAG2 or BAG5b in HsfA1a overexpression plants attenuated HsfA1a-induced thermotolerance and HSPs expression. Thus, HsfA1a mediated thermotolerance through transcriptionally regulating BAG2 and forming a complex with BAG2 and BAG5b to ultimately induce the expression of HSPs in tomato. Our findings provide new insights into the regulatory network of Hsfs on HSPs under heat stress in plants.

Whole-genome identification of HSF family genes in Cerasus humilis and expression analysis under high-temperature stress

The heat shock factors (HSFs) play important roles in activating heat stress responses in plants. Cerasus humilis (Ch) is a nutrient-rich fruit tree that can resist various abiotic and biotic stressors. However, the HSFs in C. humilis have not yet been characterized and their roles remain unclear. In this study, 21 ChHSF gene members were identified after searching the entire genome of C. humilis. Gene structure and motif composition analysis revealed that 16 ChHSF genes had only one intron and the motif3 was highly conserved in family of ChHSFs. Furthermore, the cis-acting elements analysis indicated that they most ChHSFs participate in plant growth and development, abiotic stress responses, and plant hormone regulations. By analyzing the tissue specific transcriptomes, it was found that most ChHSF genes had higher expression levels in leaves than in other tissues of C.humilis. Notably, the ChHSF04 gene exhibited a striking 115.5-, 14.4-, and 16.0-fold higher expression in leaves relative to seeds, roots, and fruits, respectively. The high temperature (40 °C) treated C. humilis seedlings quantitative real-time polymerase chain reaction (qRT-PCR) was conducted on all ChHSF gene members. The results show that the expression of most ChHSF genes in the leaves was significantly upregulated and peaked at 12 h under the heat stress and the expression levels of ChHSF04, ChHSF05, ChHSF12, ChHSF13, ChHSF15 and ChHSF16 exhibited 53-, 33-, 24-, 22-, 43- and 65-fold upregulation, indicating that these genes may play important roles in early response to heat stress in C. humilis. These results provide valuable insights into the evolutionary relationship of the ChHSF gene family and its role in high temperature stress responses.

Genome-Wide Characterization, Comparative Analysis, and Expression Profiling of SWEET Genes Family in Four Cymbidium Species (Orchidaceae)

The SWEET (Sugar Will Eventually be Exported Transporters) protein family plays a key role in plant growth, adaptation, and stress responses by facilitating soluble sugar transport. However, their functions in Cymbidium remain poorly understood. This study identified 59 SWEET genes across four Cymbidium species, encoding conserved MtN3/saliva domains. Despite variations in exon-intron structures, gene motifs and domains were highly conserved. Phylogenetic analysis grouped 95 SWEET proteins from six species into four clades, with gene expansion driven by whole-genome, segmental, and tandem duplications. Cis-element analysis and expression profiling across 72 samples revealed diverse regulatory patterns. Notably, SWEET genes showed peak expression in floral development, leaf morph variations, and diurnal rhythms. qRT-PCR and transcription factor binding analysis further highlighted their regulatory roles in floral patterning, leaf variation, and metabolic rhythms. These findings provide a foundation for future studies on SWEET gene function and their potential molecular breeding value in orchids.

Back to the basics: the molecular blueprint of plant heat stress transcription factors

Heat stress transcription factors (HSFs) play a pivotal role in regulating plant responses to heat and other environmental stresses, as well as developmental processes. HSFs possess conserved domains responsible for DNA binding, oligomerization, and transcriptional regulation, which collectively enable precise and dynamic control of cellular responses to environmental stimuli. Functional diversification of HSFs has been demonstrated through genetic studies in model plants such as Arabidopsis thaliana and economically important crops like tomato, rice, and wheat. However, the underlying molecular mechanisms that govern HSF function remain only partially understood, and for a handful of HSFs. Advancements in structural biology, biochemistry, molecular biology, and genomics shed light into how HSFs mediate stress responses at the molecular level. These insights offer exciting opportunities to leverage HSF biology for gene editing and crop improvement, enabling the customization of stress tolerance traits via regulation of HSF-dependent regulatory networks to enhance thermotolerance. This review synthesizes current knowledge on HSF structure and function, providing a perspective on their roles in plant adaptation to a changing climate.

Over Time Changes in the Transcriptomic Profiles of Tomato Plants with or Without Mi-1 Gene During Their Incompatible or Compatible Interactions with the Whitefly Bemisia tabaci

Understanding the resistance mechanisms of plants against pests contributes to the sustainable deployment of plant resistance in Integrated Pest Management (IPM) programmes. The Mi-1 gene in tomato is the only one described with the capacity to provide resistance to different types of harmful organisms such as plant parasitic nematodes and pest insects, including the whitefly Bemisia tabaci MED (Mediterranean species). In this work, gene expression in the interaction of B. tabaci with susceptible tomato plants lacking the Mi-1 gene (cv. Moneymaker, compatible interaction), and with resistant plants carrying the Mi-1 gene (cv. Motelle, incompatible interaction) was studied using the oligonucleotide microarray technique. Both interactions were studied 2 and 12 days post infestation (dpi) of plants with adult insects. At 2 dpi, 159 overexpressed and 189 repressed transcripts were detected in the incompatible interaction, while these figures were 32 and 47 in the compatible one. Transcriptional reprogramming was more intense at 12 dpi but, as at 2 dpi, the number of transcripts overexpressed and repressed was higher in the incompatible (595 and 437, respectively) than in the compatible (71 and 52, respectively) interaction. According to the Mapman classification, these transcripts corresponded mainly to genes in the protein and RNA categories, some of which are involved in the defence response (signalling, respiratory burst, regulation of transcription, PRs, HSPs, cell wall or hormone signalling). These results provide a wealth of information about possible genes related to the resistance provided by the Mi-1 gene to B. tabaci, and whose role deserves further investigation.

MiR164a-targeted NAM3 inhibits thermotolerance in tomato by regulating HSFA4b-mediated redox homeostasis

Extreme weather events, including high temperatures, frequently occur and adversely affect crop growth, posing substantial challenges to global agriculture. MicroRNAs (miRNAs) play integral roles in regulating plant growth and responses to various stresses. In this study, we reveal that microRNA164a (miR164a) in tomato (Solanum lycopersicum) is a pivotal element that exhibits a rapid positive response to heat stress (HS) among multiple miRNAs, while its target NO APICAL MERISTEM 3 (NAM3) shows an opposite complementary response. MiR164a/b-5p-deficient mutant and NAM3-overexpressing plants resulted in increased sensitivity to HS, whereas mutants with reduced NAM3 levels exhibited enhanced thermotolerance. Importantly, HS-induced reactive oxygen species (ROS) accumulation and antioxidant enzyme activities were positively regulated by miR164a and negatively by NAM3, respectively. Furthermore, we demonstrated that NAM3 transcriptionally activated the expression of HSFA4b, and silencing HSFA4b improved tomato thermotolerance. HSFA4b repressed the expression of the antioxidant gene APX1 and the heat shock protein (HSP) gene HSP90, disrupting redox homeostasis and exacerbating oxidative stress. Our findings unveil a pivotal regulatory pathway governed by the miR164a-NAM3 module that confers thermotolerance in tomato via its influence on ROS-related and HSP pathways. These findings provide valuable insights into the molecular mechanisms that underpin tomato thermotolerance, which are crucial for advancing sustainable agricultural practices, particularly in the face of the challenges presented by global climate change.

Molecular aspects of heat stress sensing in land plants

Heat stress impacts all aspects of life, from evolution to global food security. Therefore, it becomes essential to understand how plants respond to heat stress, especially in the context of climate change. The heat stress response (HSR) involves three main components: sensing, signal transduction, and cellular reprogramming. Here, I focus on the heat stress sensing component. How can cells detect heat stress if it is not a signalling particle? To answer this question, I have looked at the molecular definition of heat stress. It can be defined as any particular rise in the optimum growth temperature that leads to higher-than-normal levels of reactive molecular species and macromolecular damage to biological membranes, proteins, and nucleic acid polymers (DNA and RNA). It is precisely these stress-specific alterations that are detected by heat stress sensors, upon which they would immediately trigger the appropriate level of the HSR. In addition, the work towards thermotolerance is complemented by a second type of response, here called the cellular homeostasis response (CHR). Upon mild and extreme temperature changes, the CHR is triggered by plant thermosensors, which are responsible for monitoring temperature information. Heat stress sensors and thermosensors are distinct types of molecules, each with unique modes of activation and functions. While many recent reviews provide a comprehensive overview of plant thermosensors, there remains a notable gap in the review literature regarding an in-depth analysis of plant heat stress sensors. Here, I attempt to summarise our current knowledge of the cellular sensors involved in triggering the plant HSR.

The SnRK2.2-ZmHsf28-JAZ14/17 module regulates drought tolerance in maize

Abscisic acid (ABA) and jasmonic acid (JA) are important plant hormones in response to drought stress. We have identified that ZmHsf28 elevated ABA and JA accumulation to confer drought tolerance in maize; however, the underlying mechanism still remains elusive. The knockout line zmhsf28 is generated to confirm the positive role of ZmHsf28 in drought response. Multiple approaches are combined to reveal protein interaction among ZmHsf28, ZmSnRK2.2 and ZmJAZ14/17, which form a regulatory module to mediate maize drought tolerance through regulating ABA and JA key biosynthetic genes ZmNCED3 and ZmLOX8. Upon drought stress, zmhsf28 plants exhibit weaker tolerance than the WT plants with slower stomatal closure and more reactive oxygen species accumulation. ZmHsf28 interacted with ZmSnRK2.2 physically, resulting in phosphorylation at Ser220, which enhances binding to the heat shock elements of ZmNECD3 and ZmLOX8 promoters and subsequent gene expression. Meanwhile, ZmMYC2 upregulates ZmHsf28 gene expression through acting on the G-box of its promoter. Besides, ZmJAZ14/17 competitively interact with ZmHsf28 to interfere with protein interaction between ZmHsf28 and ZmSnRK2.2, blocking ZmHsf28 phosphorylation and impairing downstream gene regulation. The ZmSnRK2.2-ZmHsf28-ZmJAZ14/17 module is identified to regulate drought tolerance through coordinating ABA and JA signaling, providing the insights for breeding to improve drought resistance in maize.

Transcription factor PgCDF2 enhances heat tolerance of Physalis grisea by activating heat shock transcription factors PgHSFA1 and PgHSFB3

High temperature influence flower bud differentiation in Physalis grisea, resulting in the production of deformed fruits and affects fruit yield and quality. However, the molecular mechanisms underlying the response of P. grisea to heat stress (HS) remain unclear. In this study, HS treatment and dynamic transcriptome analysis of P. grisea identified the PgCDF2-PgHSFA1/PgHSFB3 transcriptional regulatory module as playing a key role in the response of P. grisea to HS. Gene Ontology (GO) enrichment analysis, transcriptional regulation prediction, and weighted correlation network analysis (WGCNA) of heat stress (HS)-responsive transcriptome data identified three key genes, PgCDF2, PgHSFA1 and PgHSFB3, as components of the regulatory network of heat stress in P. grisea. The expression levels of PgCDF2, PgHSFA1, and PgHSFB3 were up-regulated following exposure to HS. Silencing of PgHSFA1 and PgHSFB3 resulted in reduced heat stress tolerance and altered reactive oxygen species levels in P. grisea. Dual-luciferase assay and Electrophoretic Mobility Shift Assay (EMSA) results indicate that PgCDF2 binds to the promoters of PgHSFA1 and PgHSFB3 and activate their expression. Silencing of PgCDF2 inhibited the expression of PgHSFA1 and PgHSFB3 and also reduced the heat tolerance of P. grisea. In summary, under HS, PgCDF2 enhances the heat tolerance of P. grisea by activating the expression of PgHSFA1 and PgHSFB3. This study clarifies the role of the PgCDF2-PgHSFA1/PgHSFB3 module in the response of P. grisea to HS, providing a theoretical basis for a more in-depth analysis of the molecular mechanisms underlying this response.

A genome-wide-level insight into the HSF gene family of Rhodomyrtus tomentosa and the functional divergence of RtHSFA2a and RtHSFA2b in thermal adaptation

Heat shock transcription factor (HSF) is one of the most important regulatory elements in plant development and stress response. Rhohomyrtus tomentosa has many advantages in adapting to high temperature and high humidity climates, whereas its inherence has barely been elucidated. In this study, we aimed to characterize the HSF family and investigate the thermal adaptation mechanisms of R. tomentosa. We identified 25 HSF genes in the R. tomentosa genome. They could be classified into three classes: HSFA, HSFB, and HSFC. Gene duplication events are major motivations for the expansion of the RtHSF gene family. Most of the genes in the same subclass share similar conserved motifs and gene structures. The cis-acting elements of the promoter regions of RtHSF genes are related to development, phytohormone signaling, and stress responses, and they vary among the genes even in the same subclass, resulting in different expression patterns. Especially, there exists subfunctionalization in the RtHSFA2 subfamily in responding to various abiotic stresses, viz. RtHSFA2a is sensitive to drought, salt, and cold stresses, whilst RtHSFA2b is mainly induced by heat stress. We further proved that RtHSFA2b might be of more importance in R. tomentosa thermotolerance, for Arabidopsis plants with overexpressed RtHSFA2b outperformed those with RtHSFA2a under heat stress, and RtHSFA2b had much higher transcription activity than RtHSFA2a in regulating certain heat shock response (HSR) genes. RtHSFA2a plays a role in transactivating RtHSFA2b. All these results provide a general prospect of the RtHSF gene family and enclose a basal thermal adaptation mechanism of R. tomentosa.

Stress-responsive transcription factor families are key components of the core abiotic stress response in maize

Abiotic stresses, including drought, salt, heat, cold, flooding, and low nitrogen, have devastating impacts on agriculture and are increasing in frequency globally due to climate change. Plants can experience multiple abiotic stresses simultaneously or sequentially within a single growing season, and combinatorial stresses elicit shared or overlapping molecular and physiological responses. Here, we searched for core stress responsive genes in maize across diverse abiotic stressors through meta-analysis of public RNAseq data. Our analysis revealed significant heterogeneity in gene expression across datasets due to factors such as tissue type, genotype, and experimental conditions, which we mitigated through batch correction. Using nearly 1,900 RNAseq samples with both traditional set operations and a novel random forest machine learning approach, we identified a core set of 744 stress-responsive genes across the six stresses. These core genes are enriched in transcription factors, including stress-responsive families such as AP2/ERF-ERF, NAC, bZIP, HSF, and C2C2-CO-like. Co-expression network analysis demonstrated that these core TFs are co-expressed with stress-specific peripheral genes, supporting their role in regulating both generalized and stress-specific responses. Our results suggest that maize employs a conserved yet flexible transcriptional strategy to respond to abiotic stresses, with core TFs acting as potential regulators of both universal and stress-specific pathways. These findings provide a valuable resource for understanding stress tolerance mechanisms and for guiding future breeding and engineering efforts to enhance maize resilience under climate change.

A high temperature responsive UDP-glucosyltransferase gene OsUGT72F1 enhances heat tolerance in rice and Arabidopsis

KEY MESSAGE

OsUGT72F1 enhances heat tolerance in plants by improving ROS scavenging and modifying multiple metabolic pathways, under the regulation of transcription factors OsHSFA3 and OsHSFA4a. High temperature is one of the most critical environmental constraints affecting plant growth and development, ultimately leading to yield losses in crops such as rice (Oryza sativa L.). UDP (uridine diphosphate)-dependent glycosyltransferases (UGTs) are believed to play crucial roles in coping with environmental stresses. However, the functions for the vast majority of UGTs under high temperature stress remain largely unknown. In this study, we isolated and characterized a high temperature responsive UDP-glycosyltransferase gene OsUGT72F1 in rice. Our findings demonstrated that overexpression of OsUGT72F1 enhanced heat-stress tolerance, while the mutant plants displayed a sensitive phenotype under the same stress conditions. Ectopic expression of OsUGT72F1 in Arabidopsis thaliana also conferred improved heat tolerance to the plants. Further investigation revealed that OsUGT72F1 reduced the generation of reactive oxygen species (ROS) and boosted the activity of antioxidant enzymes, thereby alleviating oxidative damage under heat-stress conditions. Moreover, transcriptomic analysis indicated that the action of OsUGT72F1 leads to the upregulation of multiple metabolic pathways including phenylpropanoid biosynthesis, zeatin biosynthesis, and flavonoid biosynthesis. In addition, the upstream regulatory mechanism of the OsUGT72F1 gene has been identified. We found that the transcription factors OsHSFA3 and OsHSFA4a can bind to the OsUGT72F1 promoter and enhance its transcription level. Together, this study revealed that the glycosyltransferase gene OsUGT72F1 plays a vital role in the adaptive adjustment of high temperature stress in plants, revealing a new heat tolerance pathway and providing a promising gene candidate for the breeding of heat-resistant crop varieties.

BnaHSFA2, a heat shock transcription factor interacting with HSP70 and MPK11, enhances freezing tolerance in transgenic rapeseed

Heat shock transcription factors (Hsfs) play important roles in plant developmental regulations and various abiotic stress responses. However, their evolutionary mechanism of freezing tolerance remains poorly understood. In our previous transcriptomics study based on DNA methylation sequencing, the BnaHsfA2 was found to be significantly accumulated in winter rapeseed (Brassica rapa L.) under freezing stress, and the expression levels of BnaHsfA2 showed a gradual increasing trend over three years. In this study, BnaHsfA2 was isolated and characterized. Its' encoding protein has a relatively high phylogenetic relationship with the AtHsfA2; Subcellular localization results indicated that BnaHsfA2 was a nuclear protein; BnaHsfA2 exhibited higher expression levels in mature seed coats and seeds, seedling leaves, flowering filaments as well as anthers. The transcription level of BnaHsfA2 in leaves of rapeseed seedling was significantly increased at -4 °C stress for 12h and 24h. BnaHsfA2 promoter has many stress-responsive cis-regulatory elements. β-glucuronidase (GUS) staining assays indicated that the BnaHsfA2 promoter was induced under freezing stress, and it's 5'-deletion fragment from 465 to 1284 was essential for the transcriptional expression in response to freezing stress. The BnaHsfA2-transgenic rapeseed lines showed greater freezing resistance in comparison with the wild type (WT); the BnaHsfA2 overexpression lines showed increased antioxidant enzyme activities, decreased level of lipid peroxidation and reactive oxygen species (ROS) accumulation compared to the WT. Finally, yeast two-hybrid assay demonstrated that BnaHsfA2 interacted with rapeseed mitogen-activated protein kinase 11 (BnaMPK11) and heat shock factor-binding protein (BnaHsp70). The study will pave the way for further understanding the regulatory networks of BnaHsfA2 in plants under abiotic stress.

Heat shock factor ZmHsf17 positively regulates phosphatidic acid phosphohydrolase ZmPAH1 and enhances maize thermotolerance

Heat stress adversely impacts plant growth, development, and grain yield. Heat shock factors (Hsf), especially the HsfA2 subclass, play a pivotal role in the transcriptional regulation of genes in response to heat stress. In this study, the coding sequence of maize ZmHsf17 was cloned. ZmHsf17 contained conserved domains including a DNA binding domain, oligomerization domain, and transcriptional activation domain. The protein was nuclear localized and had transcription activation activity. Yeast two-hybrid and split luciferase complementation assays confirmed the interaction of ZmHsf17 with members of the maize HsfA2 subclass. Overexpression of ZmHsf17 in maize significantly increased chlorophyll content and net photosynthetic rate, and enhanced the stability of cellular membranes. Through integrative analysis of ChIP-seq and RNA-seq datasets, ZmPAH1, encoding phosphatidic acid phosphohydrolase of lipid metabolic pathways, was identified as a target gene of ZmHsf17. The promoter fragment of ZmPAH1 was bound by ZmHsf17 in protein-DNA interaction experiments in vivo and in vitro. Lipidomic data also indicated that the overexpression of ZmHsf17 increased levels of some critical membrane lipid components of maize leaves under heat stress. This research provides new insights into the role of the ZmHsf17-ZmPAH1 module in regulating thermotolerance in maize.

Genome-Wide Analysis of the Hsf Gene Family in Rosa chinensis and RcHsf17 Function in Thermotolerance

Heat shock transcription factors (Hsfs) play an important role in response to high temperatures by binding to the promoter of the heat shock protein gene to promote its expression. As an important ornamental plant, the rose often encounters heat stress during the flowering process. However, there are few studies on the Hsf family in roses (Rosa. chinensis). In the current study, 19 Hsf genes were identified from R. chinensis and grouped into three main subfamilies (A, B, and C) according to their structural characteristics and phylogenetic analysis. The expression patterns of RcHsf genes were detected in different tissues by quantitative real-time PCR. The RcHsf genes exhibited distinct expression patterns at high temperatures, with RcHsf17 having the highest expression level. RcHsf17 was localized in the nucleus and had transcriptional activity. The overexpression of RcHsf17 increased thermotolerance in Arabidopsis, suggesting the potential role of RcHsf17 in the regulation of the high-temperature response. In addition, RcHsf17 overexpressed in Arabidopsis could enhance the response of transgenic Arabidopsis to methyl jasmonate. Collectively, this study identified and screened RcHsfs in response to high temperatures in roses, providing new insights into the functional divergence of RcHsfs and a basis for screening new varieties of rose.

Genome-Wide Characterization of the Heat Shock Transcription Factor Gene Family in Betula platyphylla Reveals Promising Candidates for Heat Tolerance

Heat stress transcription factors (HSFs) play a critical role in orchestrating cellular responses to elevated temperatures and various stress conditions. While extensively studied in model plants, the HSF gene family in Betula platyphylla remains unexplored, despite the availability of its sequenced genome. In this study, we employed bioinformatics approaches to identify 21 BpHSF genes within the Betula platyphylla genome, revealing their uneven distribution across chromosomes. These genes were categorized into three subfamilies: A, B, and C. Each was characterized by conserved protein motifs and gene structures, with notable divergence observed between subfamilies. Collinearity analysis suggested that segmental duplication events have driven the evolutionary expansion of the BpHSF gene family. Promoter region analysis identified an array of cis-acting elements linked to growth, development, hormonal regulation, and stress responses. Subcellular localization experiments confirmed the nuclear localization of BpHSFA2a, BpHSFB1a, and BpHSFC1a, consistent with in silico predictions. RNA-seq and RT-qPCR analyses revealed tissue-specific expression patterns of BpHSF genes and their dynamic responses to heat stress, with qPCR validation highlighting a significant upregulation of BpHSFA2a under high-temperature conditions. In summary, this study provided a comprehensive characterization of the HSF gene family in Betula platyphylla, laying a solid foundation for future functional studies. Particularly, BpHSFA2a emerges as a promising candidate gene for enhancing heat tolerance in Betula platyphylla, warranting further detailed investigation.

A linker histone acts as a transcription factor to orchestrate malic acid accumulation in apple in response to sorbitol

High carbohydrate availability promotes malic acid accumulation in fleshy fruits, but the underlying mechanism is not known. Here, we show that antisense repression of ALDOSE-6-PHOSPHATE REDUCTASE in apple (Malus domestica) decreases the concentrations of sorbitol and malate and the transcript levels of several genes involved in vacuolar malate transport, including the aluminum-activated malate transporter (ALMT) gene MdALMT9 (Ma1), the P-ATPase gene MdPH5, the MYB transcription factor gene MdMYB73, and the cold-induced basic helix-loop-helix transcription factor gene MdCIbHLH1, in fruit and leaves. We identified a linker histone H1 variant, MdH1.1, which complements the Arabidopsis (Arabidopsis thaliana) H1 deficient mutant and functions as a transcription factor. MdH1.1 activates MdMYB73, MdCIbHLH1, and MdPH5 expression by directly binding to their promoters. MdMYB73, in return, binds to the promoter of MdH1.1 to enhance its transcription. This MdH1.1-MdMYB73 feedback loop responds to sorbitol, regulating Ma1 expression. Antisense suppression of either MdH1.1 or MdMYB73 expression significantly decreases whereas overexpression increases Ma1 expression and malate accumulation. These findings demonstrate that MdH1.1, in addition to being an architectural protein for chromatin structure, operates as a transcription factor orchestrating malic acid accumulation in response to sorbitol, revealing how sugar signaling modulates vacuolar malate transport via a linker histone in plants.

RtHSFA9s of Rhodomyrtus tomentosa Positively Regulate Thermotolerance by Transcriptionally Activating RtHSFA2s and RtHSPs

Heat shock transcription factors (HSFs) are crucial components in heat stress response. However, the contribution of the HSFs governing the inherent thermotolerance in Rhodomyrtus tomentosa has barely been investigated. We here compared the roles of RtHSFA9a, RtHSFA9b, and RtHSFA9c in heat stress tolerance. These three genes are the results of gene duplication events, but there exist vast variations in their amino acid sequences. They are all localized to the nucleus. Arabidopsis thaliana plants with overexpressed RtHSFA9a and RtHSFA9c outperformed the wild-type plants, while the over-accumulation of RtHSFA9b had little impact on plant thermotolerance. By transiently overexpressing RtHSFA9a, RtHSFA9b, and RtHSFA9c in R. tomentosa seedlings, the mRNA abundance of heat shock response genes, including RtHSFA2a, RtHSFA2b, RtHSP17.4, RtHSP21.8, RtHSP26.5, and RtHSP70, were upregulated. Transactivation assays confirmed that there exist regulatory divergences among these three genes, viz., RtHSFA9a has the highest transcription activity in regulating RtHSFA2a, RtHSFA2b, RtHSP21.8, and RtHSP70; RtHSFA9c can transcriptionally activate RtHSFA2b, RtHSP21.8, and RtHSP70; RtHSFA9b makes limited contributions to the accumulation of RtHSFA2b, RtHSP21.8, and RtHSP70. Our results indicate that the RtHSFA9 genes make crucial contributions to the thermal adaption of R. tomentosa by positively regulating the RtHSFA2a, RtHSFA2b, and RtHSP genes, which provides novel insights into the RtHSFA9 subfamily.

Genome-Wide Identification of Freezing-Responsive Genes in a Rapeseed Line NTS57 Tolerant to Low-Temperature

Winter rapeseed is a high-oil crop that exhibits significant sensitivity to low temperatures, leading to a substantial reduction in production. Hence, it is of great significance to elucidate the genomic genetic mechanism of strong freezing-resistant winter rapeseed to improve their freezing-resistant traits. In this study, global transcriptome expression profiles of the freezing-resistant cultivar NTS57 (NS) under freezing stress were obtained for the years 2015, 2016, and 2017 by RNA sequencing (RNA-seq). Most differentially expressed genes (DEGs) were involved in the plant hormone signal transduction, alpha-linolenic acid metabolism, protein processing, glutathione metabolism, and plant-pathogen interaction pathways. Antioxidant enzyme activities and lipid peroxidation levels were significantly positively and negatively correlated with overwintering rate (OWR), respectively. After freezing treatment, the formation of freezing resistance of NS was attributed to the increase in antioxidant enzyme activities and content of osmotic regulation substances, as well as the decrease in lipid peroxidation level. Furthermore, quantitative reverse transcription polymerase chain reaction (qRT-PCR) and phenotypic verification indicated that heat stress transcription factor A2 (HSFA2) and 17.6 kDa class II heat shock protein (HSP17.6) participated in the response to freezing stress. This study will further refine the regulatory network of plants against freezing stress and help to screen candidate genes for improving plant freezing resistance.

Involvement of epigenetic factors in flavonoid accumulation during plant cold adaptation

Plant responses to cold stress include either induction of flavonoid biosynthesis as part of defense responses or initially elevated levels of these substances to mitigate sudden temperature fluctuations. The role of chromatin modifying factors and, in general, epigenetic variability in these processes is not entirely clear. In this work, we review the literature to establish the relationship between flavonoids, cold and chromatin modifications. We demonstrate the relationship between cold acclimation and flavonoid accumulation, and then describe the cold adaptation signaling pathways and their relationship with chromatin modifying factors. Particular attention was paid to the cold signaling module OST1-HOS1-ICE1 and the novel function of the E3 ubiquitin protein ligase HOS1 (a protein involved in chromatin modification during cold stress) in flavonoid regulation.

Genome-Wide Identification and Expression Analysis of the HSF Gene Family in Ammopiptanthus mongolicus

Ammopiptanthus mongolicus is an ancient remnant species from the Mediterranean displaying characteristics such as high-temperature tolerance, drought resistance, cold resistance, and adaptability to impoverished soil. In the case of high-temperature tolerance, heat shock transcription factors (HSFs) are integral transcriptional regulatory proteins exerting a critical role in cellular processes. Despite extensive research on the HSF family across various species, there has been no analysis specifically focused on A. mongolicus. In this study, we identified 24 members of the AmHSF gene family based on the genome database of A. mongolicus, which were unevenly distributed over 9 chromosomes. Phylogenetic analysis showed that these 24 members can be categorized into 5 primary classes consisting of a total of 13 subgroups. Analysis of the physical and chemical properties revealed significant diversity among these proteins. With the exception of the AmHSFB3 protein, which is localized in the cytoplasm, all other AmHSF proteins were found to be situated in the nucleus. Comparison of amino acid sequences revealed that all AmHSF proteins contain a conserved DNA-binding domains structure, and the DNA-binding domains and oligomerization domains of the AmHSF gene exhibit conservation with counterparts across diverse species; we investigated the collinearity of AmHSF genes in relation to those of three other representative species. Through GO enrichment analysis, evidence emerged that AmHSF genes are involved in heat stress responses and may be involved in multiple transcriptional regulatory pathways that coordinate plant growth and stress responses. Finally, through a comprehensive analysis using transcriptome data, we examined the expression levels of 24 AmHSFs under 45 °C. The results revealed significant differences in the expression profiles of AmHSFs at different time intervals during exposure to high temperatures, highlighting their crucial role in responding to heat stress. In summary, these results provide a better understanding of the role and regulatory mechanisms of HSF in the heat stress response of A. mongolicus, meanwhile also establishing a foundation for further exploration of the biological functions of AmHSF in the adversity response of A. mongolicus.

MaHsf24, a novel negative modulator, regulates cold tolerance in banana fruits by repressing the expression of HSPs and antioxidant enzyme genes

Transcriptional regulation mechanisms underlying chilling injury (CI) development have been widely investigated in model plants and cold-sensitive fruits, such as banana (Musa acuminata). However, unlike the well-known NAC and WRKY transcription factors (TFs), the function and deciphering mechanism of heat shock factors (HSFs) involving in cold response are still fragmented. Here, we showed that hot water treatment (HWT) alleviated CI in harvested banana fruits accomplishing with reduced reactive oxygen species (ROS) accumulation and increased antioxidant enzyme activities. A cold-inducible but HWT-inhibited HSF, MaHsf24, was identified. Using DNA affinity purification sequencing (DAP-seq) combined with RNA-seq analyses, we found three heat shock protein (HSP) genes (MaHSP23.6, MaHSP70-1.1 and MaHSP70-1.2) and three antioxidant enzyme genes (MaAPX1, MaMDAR4 and MaGSTZ1) were the potential targets of MaHsf24. Subsequent electrophoretic mobility shift assay (EMSA), chromatin immunoprecipitation coupled with quantitative PCR (ChIP-qPCR) and dual-luciferase reporter (DLR) analyses demonstrated that MaHsf24 repressed the transcription of these six targets via directly binding to their promoters. Moreover, stably overexpressing MaHsf24 in tomatoes increased cold sensitivity by suppressing the expressions of HSPs and antioxidant enzyme genes, while HWT could recover cold tolerance, maintaining higher levels of HSPs and antioxidant enzyme genes, and activities of antioxidant enzymes. In contrast, transiently silencing MaHsf24 by virus-induced gene silencing (VIGS) in banana peels conferred cold resistance with the upregulation of MaHSPs and antioxidant enzyme genes. Collectively, our findings support the negative role of MaHsf24 in cold tolerance, and unravel a novel regulatory network controlling bananas CI occurrence, concerning MaHsf24-exerted inhibition of MaHSPs and antioxidant enzyme genes.

The general transcription factors (GTFs) of RNA polymerase II and their roles in plant development and stress responses

In eukaryotes, general transcription factors (GTFs) enable recruitment of RNA polymerase II (RNA Pol II) to core promoters to facilitate initiation of transcription. Extensive research in mammals and yeast has unveiled their significance in basal transcription as well as in diverse biological processes. Unlike mammals and yeast, plant GTFs exhibit remarkable degree of variability and flexibility. This is because plant GTFs and GTF subunits are often encoded by multigene families, introducing complexity to transcriptional regulation at both cellular and biological levels. This review provides insights into the general transcription mechanism, GTF composition, and their cellular functions. It further highlights the involvement of RNA Pol II-related GTFs in plant development and stress responses. Studies reveal that GTFs act as important regulators of gene expression in specific developmental processes and help equip plants with resilience against adverse environmental conditions. Their functions may be direct or mediated through their cofactor nature. The versatility of GTFs in controlling gene expression, and thereby influencing specific traits, adds to the intricate complexity inherent in the plant system.

Heat stress transcription factors as the central molecular rheostat to optimize plant survival and recovery from heat stress

Heat stress transcription factors (HSFs) are the core regulators of the heat stress (HS) response in plants. HSFs are considered as a molecular rheostat: their activities define the response intensity, incorporating information about the environmental temperature through a network of partner proteins. A prompted activation of HSFs is required for survival, for example the de novo synthesis of heat shock proteins. Furthermore, a timely attenuation of the stress response is necessary for the restoration of cellular functions and recovery from stress. In an ever-changing environment, the balance between thermotolerance and developmental processes such as reproductive fitness highlights the importance of a tightly tuned response. In many cases, the response is described as an ON/OFF mode, while in reality, it is very dynamic. This review compiles recent findings to update existing models about the HSF-regulated HS response and address two timely questions: How do plants adjust the intensity of cellular HS response corresponding to the temperature they experience? How does this adjustment contribute to the fine-tuning of the HS and developmental networks? Understanding these processes is crucial not only for enhancing our basic understanding of plant biology but also for developing strategies to improve crop resilience and productivity under stressful conditions.

An Integrated Framework for Drought Stress in Plants

With global warming, drought stress is becoming increasingly severe, causing serious impacts on crop yield and quality. In order to survive under adverse conditions such as drought stress, plants have evolved a certain mechanism to cope. The tolerance to drought stress is mainly improved through the synergistic effect of regulatory pathways, such as transcription factors, phytohormone, stomatal movement, osmotic substances, sRNA, and antioxidant systems. This study summarizes the research progress on plant drought resistance, in order to provide a reference for improving plant drought resistance and cultivating drought-resistant varieties through genetic engineering technology.

New Insights into Involvement of Low Molecular Weight Proteins in Complex Defense Mechanisms in Higher Plants

Dynamic climate changes pose a significant challenge for plants to cope with numerous abiotic and biotic stressors of increasing intensity. Plants have evolved a variety of biochemical and molecular defense mechanisms involved in overcoming stressful conditions. Under environmental stress, plants generate elevated amounts of reactive oxygen species (ROS) and, subsequently, modulate the activity of the antioxidative enzymes. In addition, an increase in the biosynthesis of important plant compounds such as anthocyanins, lignin, isoflavonoids, as well as a wide range of low molecular weight stress-related proteins (e.g., dehydrins, cyclotides, heat shock proteins and pathogenesis-related proteins), was evidenced. The induced expression of these proteins improves the survival rate of plants under unfavorable environmental stimuli and enhances their adaptation to sequentially interacting stressors. Importantly, the plant defense proteins may also have potential for use in medical applications and agriculture (e.g., biopesticides). Therefore, it is important to gain a more thorough understanding of the complex biological functions of the plant defense proteins. It will help to devise new cultivation strategies, including the development of genotypes characterized by better adaptations to adverse environmental conditions. The review presents the latest research findings on selected plant defense proteins.

Genome-wide identification, phylogeny and expression analysis of Hsf gene family in Verbena bonariensis under low-temperature stress

BACKGROUND

The heat shock transcription factor (Hsf) is a crucial regulator of plant stress resistance, playing a key role in plant stress response, growth, and development regulation.

RESULTS

In this study, we utilized bioinformatics tools to screen 25 VbHsf members, which were named VbHsf1-VbHsf25. We used bioinformatics methods to analyze the sequence structure, physicochemical properties, conserved motifs, phylogenetic evolution, chromosome localization, promoter cis-acting elements, collinearity, and gene expression of Hsf heat shock transcription factor family members under low-temperature stress. The results revealed that the majority of the Hsf genes contained motif1, motif2, and motif3, signifying that these three motifs were highly conserved in the Hsf protein sequence of Verbena bonariensis. Although there were some variations in motif deletion among the members, the domain remained highly conserved. The theoretical isoelectric point ranged from 4.17 to 9.71, with 21 members being unstable proteins and the remainder being stable proteins. Subcellular localization predictions indicated that all members were located in the nucleus. Phylogenetic analysis of the Hsf gene family in V. bonariensis and Arabidopsis thaliana revealed that the Hsf gene family of V. bonariensis could be categorized into three groups, with group A comprising 17 members and group C having at least two members. Among the 25 Hsf members, there were 1-3 exons located on seven chromosome fragments, which were unevenly distributed. Collinearity analysis demonstrated the presence of seven pairs of homologous genes in the VbHsf gene family. The Ka/Ks ratios were less than one, indicating that the VbHsf gene underwent purification selection pressure. Additionally, nine genes in V. bonariensis were found to have collinearity with A. thaliana. Promoter analysis revealed that the promoters of all VbHsf genes contained various types of cis-acting elements related to hormones and stress. Based on RNA-seq data, qRT-PCR analysis of six highly expressed genes was performed, and it was found that VbHsf5, VbHsf14, VbHsf17, VbHsf18, VbHsf20 and VbHsf21 genes were highly expressed at 12 h of low-temperature treatment, and the expression decreased after 24 h, among which VbHsf14 was up-regulated at 12 h of low-temperature by 70-fold.

CONCLUSIONS

Our study may help reveal the important roles of Hsf in plant development and show insight for the further molecular breeding of V. bonariensis.

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.

Transcription factor binding specificities of the oomycete Phytophthora infestans reflect conserved and divergent evolutionary patterns and predict function

BACKGROUND

Identifying the DNA-binding specificities of transcription factors (TF) is central to understanding gene networks that regulate growth and development. Such knowledge is lacking in oomycetes, a microbial eukaryotic lineage within the stramenopile group. Oomycetes include many important plant and animal pathogens such as the potato and tomato blight agent Phytophthora infestans, which is a tractable model for studying life-stage differentiation within the group.

RESULTS

Mining of the P. infestans genome identified 197 genes encoding proteins belonging to 22 TF families. Their chromosomal distribution was consistent with family expansions through unequal crossing-over, which were likely ancient since each family had similar sizes in most oomycetes. Most TFs exhibited dynamic changes in RNA levels through the P. infestans life cycle. The DNA-binding preferences of 123 proteins were assayed using protein-binding oligonucleotide microarrays, which succeeded with 73 proteins from 14 families. Binding sites predicted for representatives of the families were validated by electrophoretic mobility shift or chromatin immunoprecipitation assays. Consistent with the substantial evolutionary distance of oomycetes from traditional model organisms, only a subset of the DNA-binding preferences resembled those of human or plant orthologs. Phylogenetic analyses of the TF families within P. infestans often discriminated clades with canonical and novel DNA targets. Paralogs with similar binding preferences frequently had distinct patterns of expression suggestive of functional divergence. TFs were predicted to either drive life stage-specific expression or serve as general activators based on the representation of their binding sites within total or developmentally-regulated promoters. This projection was confirmed for one TF using synthetic and mutated promoters fused to reporter genes in vivo.

CONCLUSIONS

We established a large dataset of binding specificities for P. infestans TFs, representing the first in the stramenopile group. This resource provides a basis for understanding transcriptional regulation by linking TFs with their targets, which should help delineate the molecular components of processes such as sporulation and host infection. Our work also yielded insight into TF evolution during the eukaryotic radiation, revealing both functional conservation as well as diversification across kingdoms.

Differential gene expression of salt-tolerant alfalfa in response to salinity and inoculation by Ensifer meliloti

BACKGROUND

Alfalfa (Medicago sativa L.) experiences many negative effects under salinity stress, which may be mediated by recurrent selection. Salt-tolerant alfalfa may display unique adaptations in association with rhizobium under salt stress.

RESULTS

To elucidate inoculation effects on salt-tolerant alfalfa under salt stress, this study leveraged a salt-tolerant alfalfa population selected through two cycles of recurrent selection under high salt stress. After experiencing 120-day salt stress, mRNA was extracted from 8 random genotypes either grown in 0 or 8 dS/m salt stress with or without inoculation by Ensifer meliloti. Results showed 320 and 176 differentially expressed genes (DEGs) modulated in response to salinity stress or inoculation x salinity stress, respectively. Notable results in plants under 8 dS/m stress included upregulation of a key gene involved in the Target of Rapamycin (TOR) signaling pathway with a concomitant decrease in expression of the SNrK pathway. Inoculation of salt-stressed plants stimulated increased transcription of a sulfate-uptake gene as well as upregulation of the Lysine-27-trimethyltransferase (EZH2), Histone 3 (H3), and argonaute (AGO, a component of miRISC silencing complexes) genes related to epigenetic and post-transcriptional gene control.

CONCLUSIONS

Salt-tolerant alfalfa may benefit from improved activity of TOR and decreased activity of SNrK1 in salt stress, while inoculation by rhizobiumstimulates production of sulfate uptake- and other unique genes.

The heat shock factor 20-HSF4-cellulose synthase A2 module regulates heat stress tolerance in maize

Temperature shapes the geographical distribution and behavior of plants. Understanding the regulatory mechanisms underlying the plant heat stress response is important for developing climate-resilient crops, including maize (Zea mays). To identify transcription factors (TFs) that may contribute to the maize heat stress response, we generated a dataset of short- and long-term transcriptome changes following a heat treatment time course in the inbred line B73. Co-expression network analysis highlighted several TFs, including the class B2a heat shock factor (HSF) ZmHSF20. Zmhsf20 mutant seedlings exhibited enhanced tolerance to heat stress. Furthermore, DNA affinity purification sequencing and Cleavage Under Targets and Tagmentation assays demonstrated that ZmHSF20 binds to the promoters of Cellulose synthase A2 (ZmCesA2) and three class A Hsf genes, including ZmHsf4, repressing their transcription. We showed that ZmCesA2 and ZmHSF4 promote the heat stress response, with ZmHSF4 directly activating ZmCesA2 transcription. In agreement with the transcriptome analysis, ZmHSF20 inhibited cellulose accumulation and repressed the expression of cell wall-related genes. Importantly, the Zmhsf20 Zmhsf4 double mutant exhibited decreased thermotolerance, placing ZmHsf4 downstream of ZmHsf20. We proposed an expanded model of the heat stress response in maize, whereby ZmHSF20 lowers seedling heat tolerance by repressing ZmHsf4 and ZmCesA2, thus balancing seedling growth and defense.

XBAT31 regulates reproductive thermotolerance through controlling the accumulation of HSFB2a/B2b under heat stress conditions

Heat shock transcription factors (HSFs) play a crucial role in heat stress tolerance in vegetative tissues. However, their involvement in reproductive tissues and their post-translational modifications are not well understood. In this study, we identify the E3 ligase XB3 ORTHOLOG 1 IN ARABIDOPSIS THALIANA (XBAT31) as a key player in the ubiquitination and degradation of HSFB2a/B2b. Our results show that the xbat31 mutant exhibits a higher percentage of unfertile siliques and decreased expression of HSPs in flowers under heat stress conditions compared to the wild type. Conversely, the hsfb2a hsfb2b double mutant displays improved reproductive thermotolerance. We find that XBAT31 interacts with HSFB2a/B2b and mediates their ubiquitination. Furthermore, HSFB2a/B2b ubiquitination is reduced in the xbat31-1 mutant, resulting in higher accumulation of HSFB2a/B2b in flowers under heat stress conditions. Overexpression of HSFB2a or HSFB2b leads to an increase in unfertile siliques under heat stress conditions. Thus, our results dissect the important role of the XBAT31-HSFB2a/B2b module in conferring reproductive thermotolerance in plants.

The genetic orchestra of salicylic acid in plant resilience to climate change induced abiotic stress: critical review

Climate change, driven by human activities and natural processes, has led to critical alterations in varying patterns during cropping seasons and is a vital threat to global food security. The climate change impose several abiotic stresses on crop production systems. These abiotic stresses include extreme temperatures, drought, and salinity, which expose agricultural fields to more vulnerable conditions and lead to substantial crop yield and quality losses. Plant hormones, especially salicylic acid (SA), has crucial roles for plant resiliency under unfavorable environments. This review explores the genetics and molecular mechanisms underlying SA's role in mitigating abiotic stress-induced damage in plants. It also explores the SA biosynthesis pathways, and highlights the regulation of their products under several abiotic stresses. Various roles and possible modes of action of SA in mitigating abiotic stresses are discussed, along with unraveling the genetic mechanisms and genes involved in responses under stress conditions. Additionally, this review investigates molecular pathways and mechanisms through which SA exerts its protective effects, such as redox signaling, cross-talks with other plant hormones, and mitogen-activated protein kinase pathways. Moreover, the review discusses potentials of using genetic engineering approaches, such as CRISPR technology, for deciphering the roles of SA in enhancing plant resilience to climate change related abiotic stresses. This comprehensive analysis bridges the gap between genetics of SA role in response to climate change related stressors. Overall goal is to highlight SA's significance in safeguarding plants and by offering insights of SA hormone for sustainable agriculture under challenging environmental conditions.

Heat-stress-responsive HvHSFA2e gene regulates the heat and drought tolerance in barley through modulation of phytohormone and secondary metabolic pathways

KEY MESSAGE

The heat stress transcription factor HSFA2e regulates both temperature and drought response via hormonal and secondary metabolism alterations. High temperature and drought are the primary yield-limiting environmental constraints for staple food crops. Heat shock transcription factors (HSF) terminally regulate the plant abiotic stress responses to maintain growth and development under extreme environmental conditions. HSF genes of subclass A2 predominantly express under heat stress (HS) and activate the transcriptional cascade of defense-related genes. In this study, a highly heat-inducible HSF, HvHSFA2e was constitutively expressed in barley (Hordeum vulgare L.) to investigate its role in abiotic stress response and plant development. Transgenic barley plants displayed enhanced heat and drought tolerance in terms of increased chlorophyll content, improved membrane stability, reduced lipid peroxidation, and less accumulation of ROS in comparison to wild-type (WT) plants. Transcriptome analysis revealed that HvHSFA2e positively regulates the expression of abiotic stress-related genes encoding HSFs, HSPs, and enzymatic antioxidants, contributing to improved stress tolerance in transgenic plants. The major genes of ABA biosynthesis pathway, flavonoid, and terpene metabolism were also upregulated in transgenics. Our findings show that HvHSFA2e-mediated upregulation of heat-responsive genes, modulation in ABA and flavonoid biosynthesis pathways enhance drought and heat stress tolerance.

Exploring the gene expression network involved in the heat stress response of a thermotolerant tomato genotype

BACKGROUND

The increase in temperatures due to the current climate change dramatically affects crop cultivation, resulting in yield losses and altered fruit quality. Tomato is one of the most extensively grown and consumed horticultural products, and although it can withstand a wide range of climatic conditions, heat stress can affect plant growth and development specially on the reproductive stage, severely influencing the final yield. In the present work, the heat stress response mechanisms of one thermotolerant genotype (E42) were investigated by exploring its regulatory gene network. This was achieved through a promoter analysis based on the identification of the heat stress elements (HSEs) mapping in the promoters, combined with a gene co-expression network analysis aimed at identifying interactions among heat-related genes.

RESULTS

Results highlighted 82 genes presenting HSEs in the promoter and belonging to one of the 52 gene networks obtained by the GCN analysis; 61 of these also interact with heat shock factors (Hsfs). Finally, a list of 13 candidate genes including two Hsfs, nine heat shock proteins (Hsps) and two GDSL esterase/lipase (GELPs) were retrieved by focusing on those E42 genes exhibiting HSEs in the promoters, interacting with Hsfs and showing variants, compared to Heinz reference genome, with HIGH and/or MODERATE impact on the translated protein. Among these, the Gene Ontology annotation analysis evidenced that only LeHsp100 (Solyc02g088610) belongs to a network specifically involved in the response to heat stress.

CONCLUSIONS

As a whole, the combination of bioinformatic analyses carried out on genomic and trascriptomic data available for tomato, together with polymorphisms detected in HS-related genes of the thermotolerant E42 allowed to determine a subset of candidate genes involved in the HS response in tomato. This study provides a novel approach in the investigation of abiotic stress response mechanisms and further studies will be conducted to validate the role of the highlighted genes.

Phenotypic Characteristics and Occurrence Basis of Leaf Necrotic Spots in Response of Weedy Rice to Imazethapyr

Weedy rice is the most challenging weed species to remove in rice production. We found a novel phenotype of seedling leaves which rapidly generates necrotic spots in response to imidazolinone herbicides in weedy rice, but its influencing factors and formation basis are still unknown. In this study, we used the leaf necrotic spot-producing type of weedy rice as the material. First, leaf necrotic spots were defined as physiological and vacuole-mediated cell necrosis by microscopic examination. The imazethapyr concentration was positively correlated with the degree of necrotic spots occurring, while the action site was in accordance with necrosis using herbicide stability tests combined with fluorescence parameters. Furthermore, transcriptome analysis revealed significant differences in the gene expression of endoplasmic reticulum stress and the lipid metabolism membrane structure damage pathway during necrosis, as confirmed by transmission electron microscopy. The light-temperature test also showed that high temperature and intense light could promote the appearance of necrotic spots. These experimental results are helpful in clarifying the process and basis of imazethapyr in inducing the rapid generation of necrotic spots in rice leaves and providing new insight into understanding the mechanism of response to imidazolinone herbicides and the control of weedy rice.

Arabidopsis HSFA9 Acts as a Regulator of Heat Response Gene Expression and the Acquisition of Thermotolerance and Seed Longevity

Heat-shock transcription factors (HSFs) are crucial for regulating plant responses to heat and various stresses, as well as for maintaining normal cellular functions and plant development. HSFA9 and HSFA2 are two of the Arabidopsis class A HSFs and their expressions are dramatically induced in response to heat shock (HS) stress among all 21 Arabidopsis HSFs. However, the detailed biological roles of their cooperation have not been fully characterized. In this study, we employed an integrated approach that combined bioinformatics, molecular genetics and computational analysis to identify and validate the molecular mechanism that controls seed longevity and thermotolerance in Arabidopsis. The acquisition of tolerance to deterioration was accompanied by a significant transcriptional switch that involved the induction of primary metabolism, reactive oxygen species and unfolded protein response, as well as the regulation of genes involved in response to dehydration, heat and hypoxia. In addition, the cis-regulatory motif analysis in normal stored and controlled deterioration treatment (CDT) seeds confirmed the CDT-repressed genes with heat-shock element (HSE) in their promoters. Using a yeast two-hybrid and molecular dynamic interaction assay, it is shown that HSFA9 acted as a potential regulator that can interact with HSFA2. Moreover, the knock-out mutants of both HSFA9 and HSFA2 displayed a significant reduction in seed longevity. These novel findings link HSF transcription factors with seed deterioration tolerance and longevity.

Entamoeba histolytica: In Silico and In Vitro Oligomerization of EhHSTF5 Enhances Its Binding to the HSE of the EhPgp5 Gene Promoter

Throughout its lifecycle, Entamoeba histolytica encounters a variety of stressful conditions. This parasite possesses Heat Shock Response Elements (HSEs) which are crucial for regulating the expression of various genes, aiding in its adaptation and survival. These HSEs are regulated by Heat Shock Transcription Factors (EhHSTFs). Our research has identified seven such factors in the parasite, designated as EhHSTF1 through to EhHSTF7. Significantly, under heat shock conditions and in the presence of the antiamoebic compound emetine, EhHSTF5, EhHSTF6, and EhHSTF7 show overexpression, highlighting their essential role in gene response to these stressors. Currently, only EhHSTF7 has been confirmed to recognize the HSE as a promoter of the EhPgp5 gene (HSE_EhPgp5), leaving the binding potential of the other EhHSTFs to HSEs yet to be explored. Consequently, our study aimed to examine, both in vitro and in silico, the oligomerization, and binding capabilities of the recombinant EhHSTF5 protein (rEhHSTF5) to HSE_EhPgp5. The in vitro results indicate that the oligomerization of rEhHSTF5 is concentration-dependent, with its dimeric conformation showing a higher affinity for HSE_EhPgp5 than its monomeric state. In silico analysis suggests that the alpha 3 α-helix (α3-helix) of the DNA-binding domain (DBD5) of EhHSTF5 is crucial in binding to the major groove of HSE, primarily through hydrogen bonding and salt-bridge interactions. In summary, our results highlight the importance of oligomerization in enhancing the affinity of rEhHSTF5 for HSE_EhPgp5 and demonstrate its ability to specifically recognize structural motifs within HSE_EhPgp5. These insights significantly contribute to our understanding of one of the potential molecular mechanisms employed by this parasite to efficiently respond to various stressors, thereby enabling successful adaptation and survival within its host environment.

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.

Complex plant responses to drought and heat stress under climate change

Global climate change is predicted to result in increased yield losses of agricultural crops caused by environmental conditions. In particular, heat and drought stress are major factors that negatively affect plant development and reproduction, and previous studies have revealed how these stresses induce plant responses at physiological and molecular levels. Here, we provide a comprehensive overview of current knowledge concerning how drought, heat, and combinations of these stress conditions affect the status of plants, including crops, by affecting factors such as stomatal conductance, photosynthetic activity, cellular oxidative conditions, metabolomic profiles, and molecular signaling mechanisms. We further discuss stress-responsive regulatory factors such as transcription factors and signaling factors, which play critical roles in adaptation to both drought and heat stress conditions and potentially function as 'hubs' in drought and/or heat stress responses. Additionally, we present recent findings based on forward genetic approaches that reveal natural variations in agricultural crops that play critical roles in agricultural traits under drought and/or heat conditions. Finally, we provide an overview of the application of decades of study results to actual agricultural fields as a strategy to increase drought and/or heat stress tolerance. This review summarizes our current understanding of plant responses to drought, heat, and combinations of these stress conditions.

Genome-Wide Analysis of the Liriodendron chinense Hsf Gene Family under Abiotic Stress and Characterization of the LcHsfA2a Gene

Heat shock factors (Hsfs) play a crucial role in plant defense processes. However, the distribution and functional characteristics of Hsf genes in the relict plant Liriodendron chinense are still unclear. In this study, a total of 19 LcHsfs were identified and divided into three separate subgroups, comprising 10 LcHsfA, 7 LcHsfB, and 2 LcHsfC genes, respectively, based on their phylogenetic tree and the presence/absence of conserved protein domains. Whole-genome duplication and segmental duplication led to an expansion of the LhHsf gene family. The promoters of LcHsf genes are enriched for different types of cis-acting elements, including hormone responsive and abiotic-stress-responsive elements. The expression of LcHsfA3, LcHsfA4b, LcHsfA5, LcHsfB1b, and LcHsfB2b increased significantly as a result of both cold and drought treatments. LcHsfA2a, LcHsfA2b, and LcHsfA7 act as important genes whose expression levels correlate strongly with the expression of the LcHsp70, LcHsp110, and LcAPX genes under heat stress. In addition, we found that transiently transformed 35S:LcHsfA2a seedlings showed significantly lower levels of hydrogen peroxide (H2O2) after heat stress and showed a stronger thermotolerance. This study sheds light on the possible functions of LcHsf genes under abiotic stress and identifies potentially useful genes to target for molecular breeding, in order to develop more stress-resistant varieties.

Diurnal regulation of alternative splicing associated with thermotolerance in rice by two glycine-rich RNA-binding proteins

Rice (Oryza sativa L.) production is threatened by global warming associated with extreme high temperatures, and rice heat sensitivity is differed when stress occurs between daytime and nighttime. However, the underlying molecular mechanism are largely unknown. We show here that two glycine-rich RNA binding proteins, OsGRP3 and OsGRP162, are required for thermotolerance in rice, especially at nighttime. The rhythmic expression of OsGRP3/OsGRP162 peaks at midnight, and at these coincident times, is increased by heat stress. This is largely dependent on the evening complex component OsELF3-2. We next found that the double mutant of OsGRP3/OsGRP162 is strikingly more sensitive to heat stress in terms of survival rate and seed setting rate when comparing to the wild-type plants. Interestingly, the defect in thermotolerance is more evident when heat stress occurred in nighttime than that in daytime. Upon heat stress, the double mutant of OsGRP3/OsGRP162 displays globally reduced expression of heat-stress responsive genes, and increases of mRNA alternative splicing dominated by exon-skipping. This study thus reveals the important role of OsGRP3/OsGRP162 in thermotolerance in rice, and unravels the mechanism on how OsGRP3/OsGRP162 regulate thermotolerance in a diurnal manner.

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.

Pan-metagenome reveals the abiotic stress resistome of cigar tobacco phyllosphere microbiome

The important role of microbial associations in mediating plant protection and responses to abiotic stresses has been widely recognized. However, there have been limited studies on the functional profile of the phyllosphere microbiota from tobacco (Nicotiana tabacum), hindering our understanding of the mechanisms underlying stress resilience in this representative and easy-to-cultivate model species from the solanaceous family. To address this knowledge gap, our study employed shotgun metagenomic sequencing for the first time to analyze the genetic catalog and identify putative plant growth promoting bacteria (PGPB) candidates that confer abiotic stress resilience throughout the growth period of cigar tobacco in the phyllosphere. We identified abundant genes from specific bacterial lineages, particularly Pseudomonas, within the cigar tobacco phyllospheric microbiome. These genes were found to confer resilience against a wide range of stressors, including osmotic and drought stress, heavy metal toxicity, temperature perturbation, organic pollutants, oxidative stress, and UV light damage. In addition, we conducted a virome mining analysis on the metagenome to explore the potential roles of viruses in driving microbial adaptation to environmental stresses. Our results identified a total of 3,320 scaffolds predicted to be viral from the cigar tobacco phyllosphere metagenome, with various phages infecting Pseudomonas, Burkholderia, Enterobacteria, Ralstonia, and related viruses. Within the virome, we also annotated genes associated with abiotic stress resilience, such as alkaline phosphatase D (phoD) for nutrient solubilization and glutamate-5-semialdehyde dehydrogenase (proA) for osmolyte synthesis. These findings shed light on the unexplored roles of viruses in facilitating and transferring abiotic stress resilience in the phyllospheric microbiome through beneficial interactions with their hosts. The findings from this study have important implications for agricultural practices, as they offer potential strategies for harnessing the capabilities of the phyllosphere microbiome to enhance stress tolerance in crop plants.

GhCNGC13 and 32 Act as Critical Links between Growth and Immunity in Cotton

Cyclic nucleotide-gated ion channels (CNGCs) remain poorly studied in crop plants, most of which are polyploid. In allotetraploid Upland cotton (Gossypium hirsutum), silencing GhCNGC13 and 32 impaired plant growth and shoot apical meristem (SAM) development, while triggering plant autoimmunity. Both growth hormones (indole-3-acetic acid and gibberellin) and stress hormones (abscisic acid, salicylic acid, and jasmonate) increased, while leaf photosynthesis decreased. The silenced plants exhibited an enhanced resistance to Botrytis cinerea; however, Verticillium wilt resistance was weakened, which was associated with LIPOXYGENASE2 (LOX2) downregulation. Transcriptomic analysis of silenced plants revealed 4835 differentially expressed genes (DEGs) with functional enrichment in immunity and photosynthesis. These DEGs included a set of transcription factors with significant over-representation in the HSF, NAC, and WRKY families. Moreover, numerous members of the GhCNGC family were identified among the DEGs, which may indicate a coordinated action. Collectively, our results suggested that GhCNGC13 and 32 functionally link to photosynthesis, plant growth, and plant immunity. We proposed that GhCNGC13 and 32 play a critical role in the "growth-defense tradeoff" widely observed in crops.

Novel roles of HSFs and HSPs, other than relating to heat stress, in temperature-mediated flowering

The thermotolerant ability of heat shock factors (HSFs) and heat shock proteins (HSPs) in plants has been shown. Recently, focus has been on their function in plant growth and development under non-stress conditions. Their role in flowering has been suggested given that lower levels of HSF/HSPs resulted in altered flowering in Arabidopsis. Genetic and molecular studies of Arabidopsis HSF/HSP mutants advocated an association with temperature-mediated regulation of flowering, but the fundamental genetic mechanism behind this phenomenon remains obscure. Here we outline plausible integration between HSFs/HSPs and temperature-dependent pathways in plants regulating flowering. Moreover, we discuss how similar pathways can be present in thermoperiodic geophytic plants that require ambient high temperatures for flowering induction.