Identification of Heat Shock Transcription Factor Genes Involved in Thermotolerance of Octoploid Cultivated Strawberry

Heat Shock Transcription Factor GhHSFB2a Is Crucial for Cotton Resistance to Verticillium dahliae

Heat shock transcription factors (HSFs) play a critical regulatory role in many plant disease resistance pathways. However, the molecular mechanisms of cotton HSFs involved in resistance to the soil-borne fungus Verticillium dahliae are limited. In our previous study, we identified numerous differentially expressed genes (DEGs) in the transcriptome and metabolome of V. dahliae-inoculated Arabidopsis thaliana. In this study, we identified and functionally characterized GhHSFB2a, which is a DEG belonging to HSFs and related to cotton immunity to V. dahliae. Subsequently, the phylogenetic tree of the type two of the HSFB subfamily in different species was divided into two subgroups: A. thaliana and strawberry, which have the closest evolutionary relationship to cotton. We performed promoter cis-element analysis and showed that the defense-reaction-associated cis-acting element-FC-rich motif may be involved in the plant response to V. dahliae in cotton. The expression pattern analysis of GhHSFB2a displayed that it is transcriptional in roots, stems, and leaves and significantly higher at 12 h post-inoculation (hpi). Subcellular localization of GhHSFB2a was observed, and the results showed localization to the nucleus. Virus-induced gene silencing (VIGS) analysis exhibited that GhHSFB2a silencing increased the disease index and fungal biomass and attenuated resistance against V. dahliae. Transcriptome sequencing of wild-type and GhHSFB2a-silenced plants, followed by Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, protein-protein interaction, and validation of marker genes revealed that ABA, ethylene, linoleic acid, and phenylpropanoid pathways are involved in GhHSFB2a-mediated plant disease resistance. Ectopic overexpression of the GhHSFB2a gene in Arabidopsis showed a significant increase in the disease resistance. Cumulatively, our results suggest that GhHSFB2a is required for the cotton immune response against V. dahliae-mediated ABA, ethylene, linoleic acid, and phenylpropanoid pathways, indicating its potential role in the molecular design breeding of plants.

Transcriptomic and metabolomic profiling of strawberry during postharvest cooling and heat storage

Temperature is one of the most important factors regarding fruit postharvest, however its effects in the strawberry fruits quality in postharvest remains to be evaluated. In this study, the effects of cold and heat storage temperature on fruit quality of 'Benihoppe' strawberry were performed. The results showed that different temperatures could affect the metabolism of hormone, anthocyanin, reactive oxygen species (ROS), and transcription level of responsive factors. The synthesis of terpenoids, amino acids, and phenylpropanoids in strawberries were also changed under different temperatures, which finally changed the quality characteristics of the fruit. We found HSF20 (YZ1)-overexpressed fruits were sensitive to cold and heat conditions but CBF/NF-Y (YZ9)-overexpressed fruits promoted coloring under cold treatment. This study clarified the effect of postharvest cooling and heat treatments on quality and transcriptional mechanism of strawberries fruits. Moreover, these results provided an experimental basis for further research on improving the quality of strawberry berries during postharvest periods.

DNA methylation dynamics during stress response in woodland strawberry (Fragaria vesca)

Environmental stresses can result in a wide range of physiological and molecular responses in plants. These responses can also impact epigenetic information in genomes, especially at the level of DNA methylation (5-methylcytosine). DNA methylation is the hallmark heritable epigenetic modification and plays a key role in silencing transposable elements (TEs). Although DNA methylation is an essential epigenetic mechanism, fundamental aspects of its contribution to stress responses and adaptation remain obscure. We investigated epigenome dynamics of wild strawberry (Fragaria vesca) in response to variable ecologically relevant environmental conditions at the DNA methylation level. F. vesca methylome responded with great plasticity to ecologically relevant abiotic and hormonal stresses. Thermal stress resulted in substantial genome-wide loss of DNA methylation. Notably, all tested stress conditions resulted in marked hot spots of differential DNA methylation near centromeric or pericentromeric regions, particularly in the non-symmetrical DNA methylation context. Additionally, we identified differentially methylated regions (DMRs) within promoter regions of transcription factor (TF) superfamilies involved in plant stress-response and assessed the effects of these changes on gene expression. These findings improve our understanding on stress-response at the epigenome level by highlighting the correlation between DNA methylation, TEs and gene expression regulation in plants subjected to a broad range of environmental stresses.

Molecular insights into sensing, regulation and improving of heat tolerance in plants

Climate-change-mediated increase in temperature extremes has become a threat to plant productivity. Heat stress-induced changes in growth pattern, sensitivity to pests, plant phonologies, flowering, shrinkage of maturity period, grain filling, and increased senescence result in significant yield losses. Heat stress triggers multitude of cellular, physiological and molecular responses in plants beginning from the early sensing followed by signal transduction, osmolyte synthesis, antioxidant defense, and heat stress-associated gene expression. Several genes and metabolites involved in heat perception and in the adaptation response have been isolated and characterized in plants. Heat stress responses are also regulated by the heat stress transcription factors (HSFs), miRNAs and transcriptional factors which together form another layer of regulatory circuit. With the availability of functionally validated candidate genes, transgenic approaches have been applied for developing heat-tolerant transgenic maize, tobacco and sweet potato. In this review, we present an account of molecular mechanisms of heat tolerance and discuss the current developments in genetic manipulation for heat tolerant crops for future sustainable agriculture.

Strawberry Proteome Responses to Controlled Hot and Cold Stress Partly Mimic Post-harvest Storage Temperature Effects on Fruit Quality

To determine the effect of different temperature on strawberry after harvest, physiological indicator analysis and proteomics analysis were conducted on ripened strawberry (“Sweet Charlie”) fruit stored at 4, 23, and 37°C for 10 or 20 days. Results showed that 4°C maintained a better visual quality of strawberry, and the weight loss and firmness remained stable within 3 days. Low temperature negatively affected anthocyanin but positively affected soluble sugars. Though anthocyanin content was higher with increasing temperature, anthocyanin synthesis related proteins were downregulated. Higher indole-acetic acid (IAA) content in seeds and lower abscisic acid (ABA) content were found in berry at 4°C. Antioxidant related proteins were upregulated during storage, showing a significant up-regulation of peroxidase (POD) at 4°C, and ascorbate-glutathione (AsA-GSH) cycle related proteins and heat shock proteins (HSPs) at 37°C. In addition, overexpressed sugar phosphate/phosphate translocator, 1-aminocyclopropane-1-carboxylate oxidase, and aquaporin PIP2-2 had a positive effect in response to low temperature stress for containing higher protopectin content and POD activity.

Photosynthetic heat tolerance in plants with different foliar water -uptake strategies

PREMISE

The distribution and even the survival of plant species are influenced by temperature. In an old climatically buffered infertile landscape (OCBIL) in Brazil, we previously characterized different strategies for foliar water uptake (FWU). It is possible that photosystem II tolerance to heat and excessive light intensity varies among species with different FWU capacities.

METHODS

The relationship between FWU, photoinhibition, and thermotolerance was investigated in seven species from this ecosystem.

RESULTS

The species with slow water absorption and high water absorption are those that presented less photoinhibition. Contrastingly, the species that have fast and low water absorption presented greater thermotolerance when their leaves are totally hydrated. However, when there is greater leaf dehydration, the most thermotolerant species were those with slow but high water absorption.

CONCLUSIONS

Foliar water uptake is an important trait for plants to tolerate excessive light intensity and higher temperatures. Plants in this OCBIL may be differentially affected by future global warming, and the best strategy to deal with this expected climate change is with slow and high absorption of water.

Genome-Wide Analysis of Heat Shock Transcription Factors in Ziziphus jujuba Identifies Potential Candidates for Crop Improvement Under Abiotic Stress

Plant heat shock transcription factors (Hsfs) play a significant role in adoption under abiotic stress conditions by modulating the expression of several stress-responsive genes. Analysis of the Hsf gene family will serve to understand the molecular mechanism which is involved in response to abiotic stress. The Ziziphus species grows in warm and dry regions and is inherently tolerant to abiotic stress conditions; thus, Ziziphus is a highly enriched source of genes conferring abiotic stress tolerance. Therefore, the present study provides a comprehensive genome-wide analysis of the Hsf gene family in Z. jujuba. Identified 21 non-redundant Hsf genes were grouped into three major classes (classes A, B, and C) based on the phylogenetic analysis. Promoter and gene ontology analysis suggested that ZjHsfs perform diverse functions in response to abiotic stress conditions. Two paralogous pairs resulting from tandem gene duplication events were identified. Also, physio-chemical properties of chromosomal locations, gene structure, motifs, and protein domain organization of Hsfs were analyzed. Real-time PCR expression analyses revealed that most of the Z. jujuba Hsf genes are differentially expressed in response to heat stress. The analysis suggested ZjHsf-2, ZjHsf-3, ZjHsf-5, ZjHsf-7, ZjHsf-8, ZjHsf-10, ZjHsf-12, ZjHsf-17, and ZjHsf-18 were the outstanding candidate genes for imparting heat stress tolerance and for future functional analysis. The present analysis laid the foundation for understanding the molecular mechanism of the Hsf gene family regulating Z. jujuba development and tolerance to abiotic stress conditions.

Genotype-Dependent Gene Expression in Strawberry (Fragaria x ananassa) Plants Under High Temperature Stress

The differences in tolerance to high temperatures were investigated on the basis of gene expressions in two strawberry (Fragaria x ananassa Duch) cultivars which were previously determined as high temperature tolerant (Redlands Hope = R. Hope) and sensitive (Festival). Plants were exposed incrementally to 35, 40, 45, and finally 50 °C for 24 h. qRT-PCR analyses were carried out with 19 known sequences from the databases. Protein expression analyses were based on SDS-PAGE results, sequenced and then separated due to their isoelectric points. Expression levels were determined at 35, 40, and 45 °C. According to the results, tolerance of 'R. Hope' to high temperature stress can be explained with the coordination of Hsp70, Hsp90, and small heat shock proteins (sHsps) having a vital and supplementary role in stress response. Sensitive cultivar 'Festival' can respond to high temperatures only with the low molecular weight protein and transcripts that do not take a central role in high temperature stress response. Moreover, allergen gene expression triggered by high temperature were detected in both cultivars with different expression levels. The greater expression level in allergen genes observed in the sensitive cultivar 'Festival' under high temperature indicates that there is possibly a negative correlation between expression level in allergen genes and heat stress tolerance. Future studies addressing allergen gene expression under high temperature stress are required to confirm on these findings and to expand on the potential use as a molecular marker in breeding process for enhanced tolerance to high temperature.

Arabidopsis heat shock transcription factor HSFA7b positively mediates salt stress tolerance by binding to an E-box-like motif to regulate gene expression

Plant heat shock transcription factors (HSFs) are involved in heat and other abiotic stress responses. However, their functions in salt tolerance are little known. In this study, we characterized the function of a HSF from Arabidopsis, AtHSFA7b, in salt tolerance. AtHSFA7b is a nuclear protein with transactivation activity. ChIP-seq combined with an RNA-seq assay indicated that AtHSFA7b preferentially binds to a novel cis-acting element, termed the E-box-like motif, to regulate gene expression; it also binds to the heat shock element motif. Under salt conditions, AtHSFA7b regulates its target genes to mediate serial physiological changes, including maintaining cellular ion homeostasis, reducing water loss rate, decreasing reactive oxygen species accumulation, and adjusting osmotic potential, which ultimately leads to improved salt tolerance. Additionally, most cellulose synthase-like (CSL) and cellulose synthase (CESA) family genes were inhibited by AtHSFA7b; some of them were randomly selected for salt tolerance characterization, and they were mainly found to negatively modulate salt tolerance. By contrast, some transcription factors (TFs) were induced by AtHSFA7b; among them, we randomly identified six TFs that positively regulate salt tolerance. Thus, AtHSFA7b serves as a transactivator that positively mediates salinity tolerance mainly through binding to the E-box-like motif to regulate gene expression.

Identification, Expression Analysis of the Hsf Family, and Characterization of Class A4 in Sedum Alfredii Hance under Cadmium Stress

Sedum alfredii Hance, a cadmium (Cd)/zinc (Zn)/lead (Pb) co-hyperaccumulating species, is a promising phytoremediation candidate because it accumulates substantial amounts of heavy metal ions without showing any obvious signs of poisoning. The heat shock transcription factor (Hsf) family plays crucial roles in plant growth, development, and stress responses. Although the roles of some Hsfs in abiotic stress have been well studied in model plants, the Hsf family has not been systematically investigated in heavy metal hyperaccumulators. Here, we comprehensively analyzed the Hsf gene family in S. alfredii based on a transcriptome under Cd stress. There were 22 Hsf members that were identified and phylogenetically clustered into three classes, namely, SaHsfA, SaHsfB, and SaHsfC. All of the three classes shared similar motifs. The expression profiles of the 22 Hsf members showed significant differences: 18 SaHsfs were responsive to Cd stress, as were multiple SaHsp genes, including SaHsp18.1, SaHsp22, SaHsp26.5, SaHsp70, SaHsp90, and SaHsp101. Two class A4 members, SaHsfA4a and SaHsfA4c, exhibited transcriptional activation activities. Overexpression of SaHsfA4a and SaHsfA4c in transgenic yeast indicated an improved tolerance to Cd stress and Cd accumulation. Our results suggest SaHsfs play important regulatory roles in heavy metal stress responses, and provide a reference for further studies on the mechanism of heavy metal stress regulation by SaHsfs.

Photoreceptor PhyB Involved in Arabidopsis Temperature Perception and Heat-Tolerance Formation

The influence of temperature on plants is essential. However, our knowledge on the intricate regulation process underlying heat stress (HS) response in plants is limited. Recently, information about thermal sensors in vivo has begun to emerge. In this study, another primary environmental stimulus, light, was verified once again to work with temperature synergistically on plants, through the modulation of numerous biological processes. With the application of transcriptomic analysis, a substantial number of heat-responsive genes were detected involved in both light- and phytohormone-mediated pathways in Arabidopsis. During this process, phytoreceptor phyB acts as a molecular switch to turn on or turn off several other genes HS response, under different light conditions. Furthermore, a morphological study showed the afunction of phyB enhanced plants thermal tolerance, confirming the important role of this phytochrome in temperature perception and response in plants. This study adds data to the picture of light and temperature signaling cross-talk in plants, which is important for the exploration of complicated HS responses or light-mediated mechanisms. Furthermore, based on its influence on Arabidopsis thermal response in both morphological and physiological levels, phyB is a photoreceptor, as revealed before, as well as an essential thermal sensor in plants.