Heat Stress Transcription Factors Research Articles

Transcriptome Analysis and Metabolic Profiling Reveal the Key Regulatory Pathways in Drought Stress Responses and Recovery in Tomatoes.

Drought stress is a major abiotic factor affecting tomato production and fruit quality. However, the genes and metabolites associated with tomato responses to water deficiency and rehydration are poorly characterized. To identify the functional genes and key metabolic pathways underlying tomato responses to drought stress and recovery, drought-susceptible and drought-tolerant inbred lines underwent transcriptomic and metabolomic analyses. A total of 332 drought-responsive and 491 rehydration-responsive core genes were robustly differentially expressed in both genotypes. The drought-responsive and rehydration-responsive genes were mainly related to photosynthesis-antenna proteins, nitrogen metabolism, plant-pathogen interactions, and the MAPK signaling pathway. Various transcription factors, including homeobox-leucine zipper protein ATHB-12, NAC transcription factor 29, and heat stress transcription factor A-6b-like, may be vital for tomato responses to water status. Moreover, 24,30-dihydroxy-12(13)-enolupinol, caffeoyl hawthorn acid, adenosine 5'-monophosphate, and guanosine were the key metabolites identified in both genotypes under drought and recovery conditions. The combined transcriptomic and metabolomic analysis highlighted the importance of 38 genes involved in metabolic pathways, the biosynthesis of secondary metabolites, the biosynthesis of amino acids, and ABC transporters for tomato responses to water stress. Our results provide valuable clues regarding the molecular basis of drought tolerance and rehydration. The data presented herein may be relevant for genetically improving tomatoes to enhance drought tolerance.

Lily LlHSFC2 coordinates with HSFAs to balance heat stress response and improve thermotolerance.

Heat stress transcription factors (HSFs) are core regulators of plant heat stress response. Much research has focused on class A and B HSFs, leaving those of class C relatively understudied. Here, we reported a lily (Lilium longiflorum) heat-inducible HSFC2 homology involved in thermotolerance. LlHSFC2 was located in the nucleus and cytoplasm and exhibited a repression ability by binding heat stress element. Overexpression of LlHSFC2 in Arabidopsis, tobacco (Nicotiana benthamiana), and lily, all increased the thermotolerance. Conversely, silencing of LlHSFC2 in lily reduced its thermotolerance. LlHSFC2 could interact with itself, or interact with LlHSFA1, LlHSFA2, LlHSFA3A, and LlHSFA3B of lily, AtHSFA1e and AtHSFA2 of Arabidopsis, and NbHSFA2 of tobacco. LlHSFC2 interacted with HSFAs to accelerate their transactivation ability and act as a transcriptional coactivator. Notably, compared with the separate LlHSFA3A overexpression, co-overexpression of LlHSFC2/LlHSFA3A further enhanced thermotolerance of transgenic plants. In addition, after suffering HS, the homologous interaction of LlHSFC2 was repressed, but its heterologous interaction with the heat-inducible HSFAs was promoted, enabling it to exert its co-activation effect for thermotolerance establishment and maintenance. Taken together, we identified that LlHSFC2 plays an active role in the general balance and maintenance of heat stress response by cooperating with HSFAs, and provided an important candidate for the enhanced thermotolerance breeding of crops and horticulture plants.

Identification long non-coding RNAs, miRNAs and their targets in witches’ broom disease tolerance in cocoa (Theobroma cacao L.)

A large part of transcripts is non-coding, which is transcribed from junk DNA; long non-coding RNAs and micro-RNAs regulate theexpression levels of mRNAs. For the first time, we identified lncRNAs and miRNAs with their regulatory role in the disease toleranceof Theobroma cacao. In this study, about 2616 lncRNAs and 153 miRNAs were identified from 10 RNA-seq data representing healthyand witches’ broom diseased tissues of cocoa. Around 604 lncRNAs are differentially expressed among healthy and diseased tissues.LncRNAs targeted 9692 mRNAs; 8827 are cis-acting, and 765 are trans-acting. Among targeted mRNAs, 281 are disease resistance-related transcripts, and 211 transcription factors (TFs) belong to more than 50 TF families, which were found to be involved in the regulation of the disease tolerance process. The identified 153 miRNAs belong to 27 miR families, and around 5337 mRNAs are targeted by the miRNAs, among them 114 codes for TFs and 170 codes for disease resistance protein. Ethylene responsive factor, bHLH, WRKY, MYB, bZIP, GTE, GATA, and heat stress transcription factors are the dominant TFs targeted by lncRNAs, and miRNAs play vital roles in disease progression and tolerance. A total of 55 lncRNAs-miRNAs interacting pair is identified, which were working on endogenous target mimics (e-TMs) mechanism and influenced the expression of 955 mRNAs. The ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) biological pathway analysis reveal that ncRNAs and their targets mRNAs code for transcription factors and genes that are involved in the disease tolerance processes, including synthesis of disease resistance proteins, amino acids, antibiotics, intracellular proteins that directly or indirectly recognize pathogen effectors are essential for plant biotic stress condition. The present study provides lncRNA and miRNA-based regulatory insight into the genes governing disease progression and tolerance in cocoa.

A LlWRKY33-LlHSFA4-LlCAT2 module confers resistance to Botrytis cinerea in lily.

Gray mold caused by Botrytis cinerea is one of the major threats in lily production. However, limited information is available about the underlying defense mechanism against B. cinerea in lily. Here, we characterized a nuclear-localized class A heat stress transcription factor (HSF)-LlHSFA4 from lily (Lilium longiflorum), which positively regulated the response to B. cinerea infection. LlHSFA4 transcript and its promoter activity were increased by B. cinerea infection in lily, indicating its involvement in the response to B. cinerea. Virus-induced gene silencing (VIGS) of LlHSFA4 impaired the resistance of lily to B. cinerea. Consistent with its role in lily, overexpression of LlHSFA4 in Arabidopsis (Arabidopsis thaliana) enhanced the resistance of transgenic Arabidopsis to B. cinerea infection. Further analysis showed that LlWRKY33 directly activated LlHSFA4 expression. We also found that both LlHSFA4 and LlWRKY33 positively regulated plant response to B. cinerea through reducing cell death and H2O2 accumulation and activating the expression of the reactive oxygen species (ROS) scavenging enzyme gene LlCAT2 (Catalase 2) by binding its prompter, which might contribute to reducing H2O2 accumulation in the infected area. Taken together, our data suggested that there may be a LlWRKY33-LlHSFA4-LlCAT2 regulatory module which confers B. cinerea resistance via reducing cell death and the ROS accumulation.

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

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

High confidence QTLs and key genes identified using Meta-QTL analysis for enhancing heat tolerance in chickpea (Cicer arietinum L.).

The rising global temperatures seriously threaten sustainable crop production, particularly the productivity and production of heat-sensitive crops like chickpeas. Multiple QTLs have been identified to enhance the heat stress tolerance in chickpeas, but their successful use in breeding programs remains limited. Towards this direction, we constructed a high-density genetic map spanning 2233.5 cM with 1069 markers. Using 138 QTLs reported earlier, we identified six Meta-QTL regions for heat tolerance whose confidence interval was reduced by 2.7-folds compared to the reported QTLs. Meta-QTLs identified on CaLG01 and CaLG06 harbor QTLs for important traits, including days to 50% flowering, days to maturity, days to flower initiation, days to pod initiation, number of filled pods, visual score, seed yield per plant, biological yield per plant, chlorophyll content, and harvest index. In addition, key genes identified in Meta-QTL regions like Pollen receptor-like kinase 3 (CaPRK3), Flowering-promoting factor 1 (CaFPF1), Flowering Locus C (CaFLC), Heat stress transcription factor A-5 (CaHsfsA5), and Pollen-specific leucine-rich repeat extensins (CaLRXs) play an important role in regulating the flowering time, pollen germination, and growth. The consensus genomic regions, and the key genes reported in this study can be used in genomics-assisted breeding for enhancing heat tolerance and developing heat-resilient chickpea cultivars.

Transcription and Metabolic Profiling Analysis of Three Discolorations in a Day of Hibiscus mutabilis.

In this study, we used combined transcriptomics and metabolomics to analyze the H. mutabilis cultivar's genetic and physiological mechanisms during three flower color transition periods (from white to pink, then from pink to red) within the span of one day. As a result, 186 genes were found to be significantly increased with the deepening of the H. mutabilis flower color; these genes were mainly involved in the expression of peroxidase 30, zinc finger protein, phosphate transporter PHO1, etc. In contrast, 298 genes were significantly downregulated with the deepening of H. mutabilis flower color, including those involved in the expression of probable O-methyltransferase 3, copper binding protein 9, and heat stress transcription factor A-6b. Some genes showed differential expression strategies as the flower color gradually darkened. We further detected 19 metabolites that gradually increased with the deepening of the H. mutabilis flower color, including L-isoleucine, palmitic acid, L-methionine, and (+)-7-isonitrobenzene. The content of the metabolite hexadecanedioate decreased with the deepening of the H. mutabilis flower color. Combined transcriptomics and metabolomics revealed that the metabolic pathways, including those related to anthocyanin biosynthesis, cysteine and methionine metabolism, and sulfur metabolism, appear to be closely related to H. mutabilis flower color transition. This study served as the first report on the genetic and physiological mechanisms of short-term H. mutabilis flower color transition and will promote the molecular breeding of ornamental cultivars of H. mutabilis.

Transcriptome profiles of rice roots under simulated microgravity conditions and following gravistimulation.

Root system architecture affects the efficient uptake of water and nutrients in plants. The root growth angle, which is a critical component in determining root system architecture, is affected by root gravitropism; however, the mechanism of root gravitropism in rice remains largely unknown. In this study, we conducted a time-course transcriptome analysis of rice roots under conditions of simulated microgravity using a three-dimensional clinostat and following gravistimulation to detect candidate genes associated with the gravitropic response. We found that HEAT SHOCK PROTEIN (HSP) genes, which are involved in the regulation of auxin transport, were preferentially up-regulated during simulated microgravity conditions and rapidly down-regulated by gravistimulation. We also found that the transcription factor HEAT STRESS TRANSCRIPTION FACTOR A2s (HSFA2s) and HSFB2s, showed the similar expression patterns with the HSPs. A co-expression network analysis and an in silico motif search within the upstream regions of the co-expressed genes revealed possible transcriptional control of HSPs by HSFs. Because HSFA2s are transcriptional activators, whereas HSFB2s are transcriptional repressors, the results suggest that the gene regulatory networks governed by HSFs modulate the gravitropic response through transcriptional control of HSPs in rice roots.

Combined transcriptomic and metabolomic analyses of high temperature stress response of quinoa seedlings

BackgroundQuinoa (Chenopodium quinoa Willd.) originates in high altitude areas, such as the Andes, and has some inherent characteristics of cold, drought, and salinity tolerance, but is sensitive to high temperature.ResultsTo gain insight into the response mechanism of quinoa to high temperature stress, we conducted an extensive targeted metabolomic study of two cultivars, Dianli-3101 and Dianli-3051, along with a combined transcriptome analysis. A total of 794 metabolites and 54,200 genes were detected, in which the genes related to photosynthesis were found down-regulated at high temperatures, and two metabolites, lipids and flavonoids, showed the largest changes in differential accumulation. Further analysis of the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway and transcription factors revealed that quinoa inhibits photosynthesis at high temperatures, and the possible strategies being used for high temperature stress management are regulation of heat stress transcription factors (HSFs) to obtain heat tolerance, and regulation of purine metabolism to enhance stress signals for rapid response to high temperature stress. The tolerant genotype could have an enhanced response through lower purine levels. The induction of the stress response could be mediated by HSF transcription factors. The results of this study may provide theoretical references for understanding the response mechanism of quinoa to high temperature stress, and for screening potential high temperature tolerant target genes and high temperature tolerant strains.ConclusionsThese findings reveal the regulation of the transcription factor family HSF and the purinergic pathway in response to high temperature stress to improve quinoa varieties with high temperature tolerance.

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

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

Co-expression network analysis of diverse wheat landraces reveals markersof early thermotolerance and a candidate master regulator of thermotolerance genes.

Triticum aestivum L. (bread wheat) is a crop relied upon by billions of people around the world, as a major source of both income and calories. Rising global temperatures, however, pose a genuine threat to the livelihood of these people, as wheat growth and yields are extremely vulnerable to damage by heat stress. Here we present the YoGI wheat landrace panel, comprising 342 accessions that show remarkable phenotypic and genetic diversity thanks to their adaptation to different climates. We quantified the abundance of110 790 transcripts from the panel and used these data to conduct weighted co-expression network analysis and to identify hub genes in modules associated with abiotic stress tolerance. We found that the expression of three hub genes, all heat-shock proteins (HSPs), were significantly correlated with early thermotolerance in a validation panel of landraces. These hub genes belong to the same module, with one (TraesCS4D01G207500.1) being a candidate master-regulator potentially controlling the expression of the other two hub genes, as well as a suite of other HSPs and heat-stress transcription factors (HSFs). In this work, therefore, we identify three validated hub genes, the expression of which can serve as markers of thermotolerance during early development, and suggest that TraesCS4D01G207500.1 is a potential master regulator of HSP and HSF expression - presenting the YoGI landrace panel as an invaluable tool for breeders wishing to determine and introduce novel alleles into modern varieties, for the production of climate-resilient crops.

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

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

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

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

Crosstalk between endoplasmic reticulum and cytosolic unfolded protein response in tomato

Conditions that cause proteotoxicity like high temperature trigger the activation of unfolded protein response (UPR). The cytosolic (CPR) and endoplasmic reticulum (ER) UPR rely on heat stress transcription factor (HSF) and two members of the basic leucine zipper (bZIP) gene family, respectively. In tomato, HsfA1a is the master regulator of CPR. Here, we identified the core players of tomato ER-UPR including the two central transcriptional regulators, namely bZIP28 and bZIP60. Interestingly, the induction of ER-UPR genes and the activation of bZIP60 are altered in transgenic plants where HsfA1a is either overexpressed (A1aOE) or suppressed (A1CS), indicating an interplay between CPR and ER-UPR systems. Several ER-UPR genes are differentially expressed in the HsfA1a transgenic lines either exposed to heat stress or to the ER stress elicitor tunicamycin (TUN). The ectopic expression of HsfA1a is associated with higher tolerance against TUN. On the example of the ER-resident Hsp70 chaperone BIP3, we show that the presence of cis-elements required for HSF and bZIP regulation serves as a putative platform for the co-regulation of these genes by both CPR and ER-UPR mechanisms, in the case of BIP3 in a stimulatory manner under high temperatures. In addition, we show that the accumulation of HsfA1a results in higher levels of three ATG genes and a more sensitized induction of autophagy in response to ER stress which also supports the increased tolerance to ER stress of the A1aOE line. These findings provide a basis for the coordination of protein homeostasis in different cellular compartments under stress conditions.

Natural variations of HSFA2 enhance thermotolerance in grapevine.

Heat stress limits growth and development of crops including grapevine which is a popular fruit in the world. Genetic variability in crops thermotolerance is not well understood. We identified and characterized heat stress transcription factor HSFA2 in heat sensitive Vitis vinifera 'Jingxiu' (named as VvHSFA2) and heat tolerant Vitis davidii 'Tangwei' (named as VdHSFA2). The transcriptional activation activities of VdHSFA2 are higher than VvHSFA2, the variation of single amino acid (Thr315Ile) in AHA1 motif leads to the difference of transcription activities between VdHSFA2 and VvHSFA2. Based on 41 Vitis germplasms, we found that HSFA2 is differentiated at coding region among heat sensitive V. vinifera, and heat tolerant Vitis davidii and Vitis quinquangularis. Genetic evidence demonstrates VdHSFA2 and VvHSFA2 are positive regulators in grape thermotolerance, and the former can confer higher thermotolerance than the latter. Moreover, VdHSFA2 can regulate more target genes than VvHSFA2. As a target gene of both VdHSFA2 and VvHSFA2, overexpression of MBF1c enhanced the grape thermotolerance whereas dysfunction of MBF1c resulted in thermosensitive phenotype. Together, our results revealed that VdHSFA2 confers higher thermotolerance than VvHSFA2, and MBF1c acts as their target gene to induce thermotolerance. The VdHSFA2 may be adopted for molecular breeding in grape thermotolerance.

A lily membrane-associated NAC transcription factor LlNAC014 is involved in thermotolerance via activation of the DREB2-HSFA3 module.

The NTL (NAC with transmembrane motif 1-like) transcription factors with a conserved transmembrane motif are members of the NAC family and are important in plant development and in response to stress. However, knowledge of their regulatory pathways is scarce, especially under heat stress. Here, we cloned and identified a novel lily (Lilium longiflorum) NTL gene, LlNAC014, that increases thermotolerance. High temperature repressed LlNAC014 expression but activated its protein. LlNAC014 contained a typical transmembrane motif at its far C-terminus and was normally located on membranes, but under heat stress it entered the nucleus as a transcription factor. LlNAC014 also has a transactivation domain at its C-terminus, and its active form, LlNAC014ΔC, could function as a trans-activator in both yeast and plant cells. LlNAC014ΔC overexpression in lily and Arabidopsis increased thermotolerance, and also caused growth defects; silencing LlNAC014 in lily decreased thermotolerance. LlNAC014ΔC could constitutively activate the heat stress response by inducing the expression of heat-responsive genes, some of which were dependent on the HSF (heat stress transcription factor) pathway. Further analysis showed that LlNAC014 was a direct regulator of the DREB2-HSFA3 module, and bound to the CTT(N7)AAG element in the promoters of LlHSFA3A, LlHSFA3B, and LlDREB2B to activate their expression. Thus, LlNAC014 increased thermotolerance by sensing high temperature and translocating to the nucleus to activate the DREB2-HSFA3 module.

A conserved HSF:miR169:NF-YA loop involved in tomato and Arabidopsis heat stress tolerance.

Heat stress transcription factors (HSFs) and microRNAs (miRNAs) regulate different stress and developmental networks in plants. Regulatory feedback mechanisms are at the basis of these networks. Here, we report that plants improve their heat stress tolerance through HSF-mediated transcriptional regulation of MIR169 and post-transcriptional regulation of Nuclear Factor-YA (NF-YA) transcription factors. We show that HSFs recognize tomato (Solanum lycopersicum) and Arabidopsis MIR169 promoters using yeast one-hybrid/chromatin immunoprecipitation-quantitative PCR. Silencing tomato HSFs using virus-induced gene silencing (VIGS) reduced Sly-MIR169 levels and enhanced Sly-NF-YA9/A10 target expression. Further, Sly-NF-YA9/A10 VIGS knockdown tomato plants and Arabidopsis plants overexpressing At-MIR169d or At-nf-ya2 mutants showed a link with increased heat tolerance. In contrast, Arabidopsis plants overexpressing At-NF-YA2 and those expressing a non-cleavable At-NF-YA2 form (miR169d-resistant At-NF-YA2) as well as plants in which At-miR169d regulation is inhibited (miR169d mimic plants) were more sensitive to heat stress, highlighting NF-YA as a negative regulator of heat tolerance. Furthermore, post-transcriptional cleavage of NF-YA by elevated miR169 levels resulted in alleviation of the repression of the heat stress effector HSFA7 in tomato and Arabidopsis, revealing a retroactive control of HSFs by the miR169:NF-YA node. Hence, a regulatory feedback loop involving HSFs, miR169s and NF-YAs plays a critical role in the regulation of the heat stress response in tomato and Arabidopsis plants.

The heat stress transcription factor family in Aegilops tauschii: genome-wide identification and expression analysis under various abiotic stresses and light conditions.

Heat stress transcription factors (Hsfs) are known to play a vital role in protecting plants against various abiotic stresses. Among the wild wheat relatives, Aegilops tauschii offers an excellent source of abiotic stress tolerance genes for improvement of bread wheat. However, little is known about its stress tolerance mechanisms. In this study, 22 AetHsf genes were identified in the genome of Aegilops tauschii and their chromosomal location, exon-intron structures, sub-cellular localization, phylogenetic and syntenic relationship were analyzed. Based on the conserved motif analysis, these Hsfs were further divided into group A, B and C. The interaction network analysis and expression profile of AetHsfs in different tissues predicted their interaction with diverse types of proteins and suggested their involvement in different developmental processes of the plant. The promoter analysis of AetHsfs showed the presence of abiotic stress-responsive, phytohormone-responsive, plant development-related and light-related cis-elements. Thus, we investigated the expression of Hsfs in Aegilops tauchii seedlings under various abiotic stress conditions and irradiated with different monochromatic lights. Most of the AetHsfs were found to be upregulated by heat stress, while some showed expression in drought, salinity and high light stress as well. Notably, the expression pattern of various AetHsfs showed their responsiveness toward dark and various light conditions (blue red and far-red) as well. Thus, this study provides novel insights into the potential role of AetHsfs in stress and light signaling pathways, which can further facilitate understandingof the stress tolerance mechanisms in Aegilops tauschii.

Comparison of Gene Expression Changes in Three Wheat Varieties with Different Susceptibilities to Heat Stress Using RNA-Seq Analysis.

Wheat is highly susceptible to heat stress, which significantly reduces grain yield. In this study, we used RNA-seq technology to analyze the transcript expression at three different time-points after heat treatment in three cultivars differing in their susceptibility to heat stress: Jopum, Keumkang, and Olgeuru. A total of 11,751, 8850, and 14,711; 10,959, 7946, and 14,205; and 22,895, 13,060, and 19,408 differentially-expressed genes (log2 fold-change > 1 and FDR (padj) < 0.05) were identified in Jopum, Keumkang, and Olgeuru in the control vs. 6-h, in the control vs. 12-h, and in the 6-h vs. 12-h heat treatment, respectively. Functional enrichment analysis showed that the biological processes for DEGs, such as the cellular response to heat and oxidative stress—and including the removal of superoxide radicals and the positive regulation of superoxide dismutase activity—were significantly enriched among the three comparisons in all three cultivars. Furthermore, we investigated the differential expression patterns of reactive oxygen species (ROS)-scavenging enzymes, heat shock proteins, and heat-stress transcription factors using qRT-PCR to confirm the differences in gene expression among the three varieties under heat stress. This study contributes to a better understanding of the wheat heat-stress response at the early growth stage and the varietal differences in heat tolerance.

Genome-Wide Identification and Characterization of Heat Shock Protein 20 Genes in Maize.

Maize is an important cereal crop worldwide and is sensitive to abiotic stresses in fluctuant environments that seriously affect its growth, yield, and quality. The small heat shock protein (HSP20) plays a crucial role in protecting plants from abiotic stress. However, little is known about HSP20 in maize (ZmHSP20). In this study, 44 ZmHSP20s were identified, which were unequally distributed over 10 chromosomes, and 6 pairs of ZmHSP20s were tandemly presented. The gene structure of ZmHSP20s was highly conserved, with 95% (42) of the genes having no more than one intron. The analysis of the cis-element in ZmHSP20s promoter demonstrated large amounts of elements related to hormonal and abiotic stress responses, including abscisic acid (ABA), high temperature, and hypoxia. The ZmHSP20s protein had more than two conserved motifs that were predictably localized in the cytoplasm, nucleus, endoplasmic reticulum, peroxisome, mitochondria, and plasma. Phylogenetic analysis using HSP20s in Arabidopsis, rice, maize, and Solanum tuberosum indicated that ZmHSP20s were classified into 11 categories, of which each category had unique subcellular localization. Approximately 80% (35) of ZmHSP20 were upregulated under heat stress at the maize seedling stage, whereas the opposite expression profiling of 10 genes under 37 and 48 °C was detected. A total of 20 genes were randomly selected to investigate their expression under treatments of ABA, gibberellin (GA), ethylene, low temperature, drought, and waterlogging, and the results displayed that more than half of these genes were downregulated while ZmHSP20-3, ZmHSP20-7, ZmHSP20-24, and ZmHSP20-44 were upregulated under 1 h treatment of ethylene. A yeast-one-hybrid experiment was conducted to analyze the binding of four heat stress transcription factors (ZmHSFs) with eight of the ZmHSP20s promoter sequences, in which ZmHSF3, ZmHSF13, and ZmHSF17 can bind to most of these selected ZmHSP20s promoters. Our results provided a valuable resource for studying HSP20s function and offering candidates for genetic improvement under abiotic stress.