Systematic Analysis of Hsf Family Genes in the Brassica napus Genome Reveals Novel Responses to Heat, Drought and High CO2 Stresses

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.

PbHsfC1a-coordinates ABA biosynthesis and H2O2 signalling pathways to improve drought tolerance in Pyrus betulaefolia

Abiotic stresses have had a substantial impact on fruit crop output and quality. Plants have evolved an efficient immune system to combat abiotic stress, which employs reactive oxygen species (ROS) to activate the downstream defence response signals. Although an aquaporin protein encoded by PbPIP1;4 is identified from transcriptome analysis of Pyrus betulaefolia plants under drought treatments, little attention has been paid to the role of PIP and ROS in responding to abiotic stresses in pear plants. In this study, we discovered that overexpression of PbPIP1;4 in pear callus improved tolerance to oxidative and osmotic stresses by reconstructing redox homeostasis and ABA signal pathways. PbPIP1;4 overexpression enhanced the transport of H2O2 into pear and yeast cells. Overexpression of PbPIP1;4 in Arabidopsis plants mitigates the stress effects caused by adding ABA, including stomatal closure and reduction of seed germination and seedling growth. Overexpression of PbPIP1;4 in Arabidopsis plants decreases drought-induced leaf withering. The PbPIP1;4 promoter could be bound and activated by TF PbHsfC1a. Overexpression of PbHsfC1a in Arabidopsis plants rescued the leaf from wilting under drought stress. PbHsfC1a could bind to and activate AtNCED4 and PbNCED4 promoters, but the activation could be inhibited by adding ABA. Besides, PbNCED expression was up-regulated under H2O2 treatment but down-regulated under ABA treatment. In conclusion, this study revealed that PbHsfC1a is a positive regulator of abiotic stress, by targeting PbPIP1;4 and PbNCED4 promoters and activating their expression to mediate redox homeostasis and ABA biosynthesis. It provides valuable information for breeding drought-resistant pear cultivars through gene modification.

General Analysis of Heat Shock Factors in the Cymbidium ensifolium Genome Provided Insights into Their Evolution and Special Roles with Response to Temperature

Heat shock factors (HSFs) are the key regulators of heat stress responses and play pivotal roles in tissue development and the temperature-induced regulation of secondary metabolites. In order to elucidate the roles of HSFs in Cymbidium ensifolium, we conducted a genome-wide identification of CeHSF genes and predicted their functions based on their structural features and splicing patterns. Our results revealed 22 HSF family members, with each gene containing more than one intron. According to phylogenetic analysis, 59.1% of HSFs were grouped into the A subfamily, while subfamily HSFC contained only two HSFs. And the HSF gene families were differentiated evolutionarily between plant species. Two tandem repeats were found on Chr02, and two segmental duplication pairs were observed on Chr12, Chr17, and Chr19; this provided evidence for whole-genome duplication (WGD) events in C. ensifolium. The core region of the promoter in most CeHSF genes contained cis-acting elements such as AP2/ERF and bHLH, which were associated with plant growth, development, and stress responses. Except for CeHSF11, 14, and 19, each of the remaining CeHSFs contained at least one miRNA binding site. This included binding sites for miR156, miR393, and miR319, which were responsive to temperature and other stresses. The HSF gene family exhibited significant tissue specificity in both vegetative and floral organs of C. ensifolium. CeHSF13 and CeHSF15 showed relatively significant expression in flowers compared to other genes. During flower development, CeHSF15 exhibited markedly elevated expression in the early stages of flower opening, implicating critical regulatory functions in organ development and floral scent-related regulations. During the poikilothermic treatment, CeHSF14 was upregulated over 200-fold after 6 h of heat treatment. CeHSF13 and CeHSF14 showed the highest expression at 6 h of low temperature, while the expression of CeHSF15 and CeHSF21 continuously decreased at a low temperature. The expression patterns of CeHSFs further confirmed their role in responding to temperature stress. Our study may help reveal the important roles of HSFs in plant development and metabolic regulation and show insight for the further molecular design breeding of C. ensifolium.

Genome-Wide Identification of HSF Gene Family in Kiwifruit and the Function of AeHSFA2b in Salt Tolerance

Heat shock transcription factors (HSFs) play a crucial role in regulating plant growth and response to various abiotic stresses. In this study, we conducted a comprehensive analysis of the AeHSF gene family at genome-wide level in kiwifruit (Actinidia eriantha), focusing on their functions in the response to abiotic stresses. A total of 41 AeHSF genes were identified and categorized into three primary groups, namely, HSFA, HSFB, and HSFC. Further transcriptome analysis revealed that the expression of AeHSFA2b/2c and AeHSFB1c/1d/2c/3b was strongly induced by salt, which was confirmed by qRT-PCR assays. The overexpression of AeHSFA2b in Arabidopsis significantly improved the tolerance to salt stress by increasing AtRS5, AtGolS1 and AtGolS2 expression. Furthermore, yeast one-hybrid, dual-luciferase, and electrophoretic mobility shift assays demonstrated that AeHSFA2b could bind to the AeRFS4 promoter directly. Therefore, we speculated that AeHSFA2b may activate AeRFS4 expression by directly binding its promoter to enhance the kiwifruit's tolerance to salt stress. These results will provide a new insight into the evolutionary and functional mechanisms of AeHSF genes in kiwifruit.

A novel Pinellia ternata catalase gene PtCAT2 regulates drought tolerance in Arabidopsis by modulating ROS balance

Drought is one of the major abiotic stresses limiting agricultural production, particularly for shallow-rooted plants like Pinellia ternata. It damages plants via oxidative burst, but this effect could be mitigated by catalase (CAT). However, no studies have been reported on CAT homologs in P. ternata, a drought-sensitive plant species. In the present study, a novel CAT gene, PtCAT2, was functionally characterized via overexpression in Arabidopsis and analysis of cis-elements in its promoter. The isolated CAT gene was 1479 bp and encoded a protein containing 242 amino acids. The protein contains the CAT activity motif and the heme-binding site of a typical CAT, and the subcellular analysis indicated that the protein localizes at the cytoplasm and membrane. Moreover, the quantitative real-time reverse transcription PCR indicated that PtCAT2 is expressed ubiquitously in P. ternata and is strongly induced by drought stress and abscisic acid (ABA) signals. PtCAT2 overexpression enhanced the drought tolerance of Arabidopsis, as shown by the 30% increase in plant survival and a five-fold- increase in CAT activity. Moreover, PtCAT2-transgenic plants increased superoxide dismutase and peroxidase activities and reduced malondialdehyde, membrane leakage, and hydrogen peroxide (H2O2) (P<0.05). Furthermore, PtCAT2-transgenic plants showed higher tolerance to oxidative stress caused by exogenous H2O2 and retained higher chlorophyll and water contents than the WT. The mitochondria function was better maintained as presented by the higher oxygen consumption rate in transgenics under drought stress (P<0.05). The endogenous CATs and drought response-related genes were also upregulated in transgenic lines under drought stress, indicating that PtCAT2 confers drought stress tolerance by enhancing the H2O2 scavenging ability of plants to maintain their membrane integrity. These results improve our understanding of the drought response mechanisms and provide a potential breeding strategy for P. ternata genetic improvement.

Evaluation of protein's interaction and the regulatory network of some drought-responsive genes in Canola under drought and re-watering conditions

Drought stress is one of the most important environmental stresses that severely limits the growth and yield of Canola. The re-watering can compensate for the damage caused by drought stress. Investigation of protein's interaction of genes involved in important drought-responsive pathways and their regulatory network by microRNAs (miRNAs) under drought and re-watering conditions are helpful approaches to discovering drought-stress tolerance and recovery mechanisms. In this study, the protein's interaction and functional enrichment analyses of glycolysis, pentose phosphate, glyoxylate cycle, fatty acid biosynthesis, heat shock factor main genes, and the regulatory network of key genes by miRNAs were investigated by in silico analysis. Then, the relative expression of key genes and their related miRNAs were investigated in tolerant and susceptible genotypes of Canola under drought and re-watering conditions by Real-time PCR technique. The bna-miR156b/c/g, bna-miR395d/e/f, bna-miR396a, and all the studied key genes except HSFA1E and PK showed changes in expression levels in one or both genotypes after re-watering. The PPC1 and HSFB2B expression decreased, whereas the MLS and CAC3 expression increased in both genotypes under re-watering treatment after drought stress. It could cause the regulation of oxaloacetate production, the increase of the glyoxylate cycle, lipid biosynthesis, and the reduction of the negative regulation of HSFs under re-watering conditions. It seems that PPC1, G6PD2, MLS, CAC3, and HSFB2B were involved in the recovery mechanisms after drought stress of Canola. They were regulated by drought-responsive miRNAs to respond appropriately to drought stress. Therefore, regulating these genes could be important in plant recovery mechanisms.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01345-1.

Genome-Wide Characterization and Expression of the Hsf Gene Family in Salvia miltiorrhiza (Danshen) and the Potential Thermotolerance of SmHsf1 and SmHsf7 in Yeast

Salvia miltiorrhiza Bunge (Danshen) is a traditional Chinese herb with significant medicinal value. The yield and quality of Danshen are greatly affected by climatic conditions, in particular high temperatures. Heat shock factors (Hsfs) play important regulatory roles in plant response to heat and other environmental stresses. However, little is currently known about the role played by the Hsf gene family in S. miltiorrhiza. Here, we identified 35 SmHsf genes and classified them into three major groups: SmHsfA (n = 22), SmHsfB (n = 11), and SmHsfC (n = 2) using phylogenetic analysis. The gene structure and protein motifs were relatively conserved within subgroups but diverged among the different groups. The expansion of the SmHsf gene family was mainly driven by whole-genome/segmental and dispersed gene duplications. The expression profile of SmHsfs in four distinct organs revealed its members (23/35) are predominantly expressed in the root. The expression of a large number of SmHsfs was regulated by drought, ultraviolet, heat and exogenous hormones. Notably, the SmHsf1 and SmHsf7 genes in SmHsfB2 were the most responsive to heat and are conserved between dicots and monocots. Finally, heterologous expression analysis showed that SmHsf1 and SmHsf7 enhance thermotolerance in yeast. Our results provide a solid foundation for further functional investigation of SmHsfs in Danshen plants as a response to abiotic stresses.

An intrinsically disordered region-containing protein mitigates the drought-growth trade-off to boost yields

Drought stress poses a serious threat to global agricultural productivity and food security. Plant resistance to drought is typically accompanied by a growth deficit and yield penalty. Herein, we report a previously uncharacterized, dicotyledon-specific gene, Stress and Growth Interconnector (SGI), that promotes growth during drought in the oil crop rapeseed (Brassica napus) and the model plant Arabidopsis (Arabidopsis thaliana). Overexpression of SGI conferred enhanced biomass and yield under water-deficient conditions, whereas corresponding CRISPR SGI mutants exhibited the opposite effects. These attributes were achieved by mediating reactive oxygen species (ROS) homeostasis while maintaining photosynthetic efficiency to increase plant fitness under water-limiting environments. Further spatial-temporal transcriptome profiling revealed dynamic reprogramming of pathways for photosynthesis and stress responses during drought and the subsequent recovery. Mechanistically, SGI represents an intrinsically disordered region-containing protein that interacts with itself, catalase isoforms, dehydrins, and other drought-responsive positive factors, restraining ROS generation. These multifaceted interactions stabilize catalases in response to drought and facilitate their ROS-scavenging activities. Taken altogether, these findings provide insights into currently underexplored mechanisms to circumvent trade-offs between plant growth and stress tolerance that will inform strategies to breed climate-resilient, higher yielding crops for sustainable agriculture.

Applications of Molecular Markers for Developing Abiotic-Stress-Resilient Oilseed Crops

Globally, abiotic stresses, such as temperature (heat or cold), water (drought and flooding), and salinity, cause significant losses in crop production and have adverse effects on plant growth and development. A variety of DNA-based molecular markers, such as SSRs, RFLPs, AFLPs, SNPs, etc., have been used to screen germplasms for stress tolerance and the QTL mapping of stress-related genes. Such molecular-marker-assisted selection strategies can quicken the development of tolerant/resistant cultivars to withstand abiotic stresses. Oilseeds such as rapeseed, mustard, peanuts, soybeans, sunflower, safflower, sesame, flaxseed, and castor are the most important source of edible oil worldwide. Although oilseed crops are known for their capacity to withstand abiotic challenges, there is a significant difference between actual and potential yields due to the adaptation and tolerance to severe abiotic pressures. This review summarizes the applications of molecular markers to date to achieve abiotic stress tolerance in major oilseed crops. The molecular markers that have been reported for genetic diversity studies and the mapping and tagging of genes/QTLs for drought, heavy metal stress, salinity, flooding, cold and heat stress, and their application in the MAS are presented.

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

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

Genome-wide identification of heat shock transcription factor families in perennial ryegrass highlights the role of LpHSFC2b in heat stress response

Perennial ryegrass (Lolium perenne) is a cool-season turf and forage grass. Heat shock transcription factors (HSFs) play an important role in regulating plant abiotic stress. However, HSFs in perennial ryegrass have rarely been characterized. Here, 25 LpHSFs were identified from the perennial ryegrass genome. Phylogenetic analysis showed that the LpHSFs could be classified into 12 subclasses. Gene structure analysis showed that 22 LpHSFs have only one intron. Cis-acting elements analysis revealed that the promoter of 15 LpHSFs contained hormone-responsive and abiotic stress-responsive elements. Expression profile analysis indicated that 24 LpHSFs were differentially expressed under submerge, drought, heat, and cold stresses. In addition, a subclass C2 gene, LpHSFC2b, was significantly induced by abiotic stresses. The LpHSFC2b protein is localized to the nucleus, and heterologous expression of LpHSFC2b in Arabidopsis improves plant thermotolerance. This study provides insights useful for the breeding of stress tolerance in perennial ryegrass.

Genome-wide analysis and characterization of heat shock transcription factors (Hsfs) in common bean (Phaseolus vulgaris L.)

Heat shock transcription factors (Hsfs) play an essential role as transcriptional regulatory proteins against heat stress by controlling the expression of heat-responsive genes. Common bean is a highly thermosensitive crop, and, therefore, its genome sequence information is segregated, characterized here in terms of heat shock transcription factors and its evolutionary significance. In this study, a complete comprehensive set of 29 non-redundant full-length Hsf genes were identified and characterized from Phaseolus vulgaris L. (PvHsf) genome sequence. Detailed gene information such as chromosomal localization, domain position, motif organization, and exon-intron identification were analyzed. All the 29 PvHsf genes were mapped on 8 out of 11 chromosomes, indicating the gene duplication occurred in the common bean genome. Motif analysis and exon-intron structure were conserved in each group, which showed that the cytoplasmic proteins highly influence the conserved structure of PvHsfs and heat-induced response. The HSF genes were grouped into three classes, i.e., A to C and 14 groups, based on structural features and phylogenetic relationships. Only one pair of paralog sequences suggests that it may be derived from the duplication event during evolution. A comparative genomics study indicated the influence of whole-genome duplication and purifying selection on the common bean genome during development. In silico expression analysis showed the active role of class A and B family during abiotic stress conditions and higher expression in floral organs. The qRT-PCR analysis revealed PvHSFA8 as the master regulator and PvHSFB1A and PvHSFB2A induction during heat exposure in French beans.

Elucidating the functional role of heat stress transcription factor A6b (TaHsfA6b) in linking heat stress response and the unfolded protein response in wheat

TaHsfA6b-4D relocalizes intracellularly upon heat stress and play a significant role in linking the heat stress response to unfolded-protein response so as to maintain cellular homeostasis. Heat stress transcription factors (Hsfs) play a crucial role in protecting the plants against heat stress (HS). In case of wheat, TaHsfA6b-4D (earlier known as TaHsfA2d) has been identified as a seed preferential transcription factor and its role has been shown in various abiotic stresses such as heat, salt and drought stress. In the present study, a homeologue of TaHsfA6b gene (TaHsfA6b-4A) was identified and was found to be transcriptionally inactive but it localized to the nucleus. Interestingly, TaHsfA6b-4D localized to the endoplasmic reticulum-Golgi complex and peroxisomes under non-stress conditions, but was observed to accumulate in the nucleus upon HS. The expression of TaHsfA6b-4D was upregulated by dithiothreitol (DTT), which is a known ER stress inducer. Consistent with this, Arabidopsis transgenic plants overexpressing TaHsfA6b-4D performed better on DTT containing media, which further corroborated with the increased expression of ER stress marker genes in these transgenic plants in comparison to the wild type plants. Thus, these studies together suggest that TaHsfA6b-4D may relocalize intracellularly upon heat stress and may play a significant role in linking the unfolded-protein response with heat stress response so as to maintain protein homeostasis inside the cell under heat stress.

Large-scale analyses of heat shock transcription factors and database construction based on whole-genome genes in horticultural and representative plants

Heat shock transcription factor (Hsf) plays a critical role in regulating heat resistance. Here, 2950 Hsf family genes were identified from 111 horticultural and representative plants. More Hsf genes were detected in higher plants than lower plants. Based on all Hsf genes, we constructed a phylogenetic tree, which indicated that Hsf genes of each branch evolved independently after species differentiation. Furthermore, we uncovered the evolutionary trajectories of Hsf genes by motif analysis. There were only 6 motifs (M1 to M6) in lower plants, and then 4 novel motifs (M7-M10) appeared in higher plants. However, the motifs of some Hsf genes were lost in higher plant, indicating that Hsf genes have undergone sequence variation during the evolution. The number of Hsf gene loss was more than duplication after whole-genome duplication in higher plants. The heat response network was constructed using 24 Hsf genes, 2421 downstream, and 222 upstream genes of Arabidopsis. Further enrichment analysis revealed that Hsf genes and other transcription factors interacted with each other to response heat resistance. The global expression maps were illustrated for Hsf genes under various abiotic, biotic stresses, and several developmental stages in Arabidopsis. The syntenic and phylogenetic analyses were conducted using Hsf genes of Arabidopsis and Pan-genome of 18 Brassica rapa accessions. We also performed the expression pattern analysis of Hsf and six Hsp family genes using expression values from different tissues and heat treatments in B. rapa. The interaction network between Hsf and Hsp gene families was constructed in B. rapa, and several core genes were detected in the network. Finally, we constructed a Hsf database (http://hsfdb.bio2db.com) for researchers to retrieve Hsf gene family information. Therefore, our study will provide rich resources for the evolution and functional study of Hsf genes.

Rapid Transcriptional Reprogramming Associated With Heat Stress-Induced Unfolded Protein Response in Developing Brassica napus Anthers

Climate change associated increases in the frequency and intensity of extreme temperature events negatively impact agricultural productivity and global food security. During the reproductive phase of a plant's life cycle, such high temperatures hinder pollen development, preventing fertilization, and seed formation. At the molecular level, heat stress-induced accumulation of misfolded proteins activates a signaling pathway called unfolded protein response (UPR) in the endoplasmic reticulum (ER) and the cytoplasm to enhance the protein folding capacity of the cell. Here, we report transcriptional responses of Brassica napus anthers exposed to high temperature for 5, 15, and 30 min to decipher the rapid transcriptional reprogramming associated with the unfolded protein response. Functional classification of the upregulated transcripts highlighted rapid activation of the ER-UPR signaling pathway mediated by ER membrane-anchored transcription factor within 5 min of heat stress exposure. KEGG pathway enrichment analysis also identified "Protein processing in ER" as the most significantly enriched pathway, indicating that the unfolded protein response (UPR) is an immediate heat stress-responsive pathway during B. napus anther development. Five minutes of heat stress also led to robust induction of the cytosolic HSF-HSP heat response network. Our results present a perspective of the rapid and massive transcriptional reprogramming during heat stress in pollen development and highlight the need for investigating the nature and function of very early stress-responsive networks in plant cells. Research focusing on very early molecular responses of plant cells to external stresses has the potential to reveal new stress-responsive gene networks that can be explored further for developing climate change resilient crops.

Genetic and Physiological Responses to Heat Stress in Brassica napus

Given the current rise in global temperatures, heat stress has become a major abiotic challenge affecting the growth and development of various crops and reducing their productivity. Brassica napus, the second largest source of vegetable oil worldwide, experiences a drastic reduction in seed yield and quality in response to heat. This review outlines the latest research that explores the genetic and physiological impact of heat stress on different developmental stages of B. napus with a special attention to the reproductive stages of floral progression, organogenesis, and post flowering. Several studies have shown that extreme temperature fluctuations during these crucial periods have detrimental effects on the plant and often leading to impaired growth and reduced seed production. The underlying mechanisms of heat stress adaptations and associated key regulatory genes are discussed. Furthermore, an overview and the implications of the polyploidy nature of B. napus and the regulatory role of alternative splicing in forming a priming-induced heat-stress memory are presented. New insights into the dynamics of epigenetic modifications during heat stress are discussed. Interestingly, while such studies are scarce in B. napus, opposite trends in expression of key genetic and epigenetic components have been identified in different species and in cultivars within the same species under various abiotic stresses, suggesting a complex role of these genes and their regulation in heat stress tolerance mechanisms. Additionally, omics-based studies are discussed with emphasis on the transcriptome, proteome and metabolome of B. napus, to gain a systems level understanding of how heat stress alters its yield and quality traits. The combination of omics approaches has revealed crucial interactions and regulatory networks taking part in the complex machinery of heat stress tolerance. We identify key knowledge gaps regarding the impact of heat stress on B. napus during its yield determining reproductive stages, where in-depth analysis of this subject is still needed. A deeper knowledge of heat stress response components and mechanisms in tissue specific models would serve as a stepping-stone to gaining insights into the regulation of thermotolerance that takes place in this important crop species and support future breeding of heat tolerant crops.

Adaptation Strategies to Improve the Resistance of Oilseed Crops to Heat Stress Under a Changing Climate: An Overview

Temperature is one of the decisive environmental factors that is projected to increase by 1. 5°C over the next two decades due to climate change that may affect various agronomic characteristics, such as biomass production, phenology and physiology, and yield-contributing traits in oilseed crops. Oilseed crops such as soybean, sunflower, canola, peanut, cottonseed, coconut, palm oil, sesame, safflower, olive etc., are widely grown. Specific importance is the vulnerability of oil synthesis in these crops against the rise in climatic temperature, threatening the stability of yield and quality. The natural defense system in these crops cannot withstand the harmful impacts of heat stress, thus causing a considerable loss in seed and oil yield. Therefore, a proper understanding of underlying mechanisms of genotype-environment interactions that could affect oil synthesis pathways is a prime requirement in developing stable cultivars. Heat stress tolerance is a complex quantitative trait controlled by many genes and is challenging to study and characterize. However, heat tolerance studies to date have pointed to several sophisticated mechanisms to deal with the stress of high temperatures, including hormonal signaling pathways for sensing heat stimuli and acquiring tolerance to heat stress, maintaining membrane integrity, production of heat shock proteins (HSPs), removal of reactive oxygen species (ROS), assembly of antioxidants, accumulation of compatible solutes, modified gene expression to enable changes, intelligent agricultural technologies, and several other agronomic techniques for thriving and surviving. Manipulation of multiple genes responsible for thermo-tolerance and exploring their high expressions greatly impacts their potential application using CRISPR/Cas genome editing and OMICS technology. This review highlights the latest outcomes on the response and tolerance to heat stress at the cellular, organelle, and whole plant levels describing numerous approaches applied to enhance thermos-tolerance in oilseed crops. We are attempting to critically analyze the scattered existing approaches to temperature tolerance used in oilseeds as a whole, work toward extending studies into the field, and provide researchers and related parties with useful information to streamline their breeding programs so that they can seek new avenues and develop guidelines that will greatly enhance ongoing efforts to establish heat stress tolerance in oilseeds.

Genome-Wide Comparative Analysis of Heat Shock Transcription Factors Provides Novel Insights for Evolutionary History and Expression Characterization in Cotton Diploid and Tetraploid Genomes

Heat shock transcription factors (HSFs) are involved in environmental stress response and plant development, such as heat stress and flowering development. According to the structural characteristics of the HSF gene family, HSF genes were classified into three major types (HSFA, HSFB, and HSFC) in plants. Using conserved domains of HSF genes, we identified 621 HSF genes among 13 cotton genomes, consisting of eight diploid and five tetraploid genomes. Phylogenetic analysis indicated that HSF genes among 13 cotton genomes were grouped into two different clusters: one cluster contained all HSF genes of HSFA and HSFC, and the other cluster contained all HSF genes of HSFB. Comparative analysis of HSF genes in Arabidopsis thaliana, Gossypium herbaceum (A1), Gossypium arboreum (A2), Gossypium raimondii (D5), and Gossypium hirsutum (AD1) genomes demonstrated that four HSF genes were inherited from a common ancestor, A0, of all existing cotton A genomes. Members of the HSF gene family in G. herbaceum (A1) genome indicated a significant loss compared with those in G. arboretum (A2) and G. hirsutum (AD1) A genomes. However, HSF genes in G. raimondii (D5) showed relative loss compared with those in G. hirsutum (AD1) D genome. Analysis of tandem duplication (TD) events of HSF genes revealed that protein-coding genes among different cotton genomes have experienced TD events, but only the two-gene tandem array was detected in Gossypium thurberi (D1) genome. The expression analysis of HSF genes in G. hirsutum (AD1) and Gossypium barbadense (AD2) genomes indicated that the expressed HSF genes were divided into two different groups, respectively, and the expressed HSF orthologous genes between the two genomes showed totally different expression patterns despite the implementation of the same abiotic stresses. This work will provide novel insights for the study of evolutionary history and expression characterization of HSF genes in different cotton genomes and a widespread application model for the study of HSF gene families in plants.

Genome-wide identification of HSF family in peach and functional analysis of PpHSF5 involvement in root and aerial organ development

Background

Heat shock factors (HSFs) play important roles during normal plant growth and development and when plants respond to diverse stressors. Although most studies have focused on the involvement of HSFs in the response to abiotic stresses, especially in model plants, there is little research on their participation in plant growth and development or on the HSF (PpHSF) gene family in peach (Prunus persica).

Methods

DBD (PF00447), the HSF characteristic domain, was used to search the peach genome and identify PpHSFs. Phylogenetic, multiple alignment and motif analyses were conducted using MEGA 6.0, ClustalW and MEME, respectively. The function of PpHSF5 was confirmed by overexpression of PpHSF5 into Arabidopsis.

Results

Eighteen PpHSF genes were identified within the peach genome. The PpHSF genes were nonuniformly distributed on the peach chromosomes. Seventeen of the PpHSFs (94.4%) contained one or two introns, except PpHSF18, which contained three introns. The in silico-translated PpHSFs were classified into three classes (PpHSFA, PpHSFB and PpHSFC) based on multiple alignment, motif analysis and phylogenetic comparison with HSFs from Arabidopsis thaliana and Oryza sativa. Dispersed gene duplication (DSD at 67%) mainly contributed to HSF gene family expansion in peach. Promoter analysis showed that the most common cis-elements were the MYB (abiotic stress response), ABRE (ABA-responsive) and MYC (dehydration-responsive) elements. Transcript profiling of 18 PpHSFs showed that the expression trend of PpHSF5 was consistent with shoot length changes in the cultivar ‘Zhongyoutao 14’. Further analysis of the PpHSF5 was conducted in 5-year-old peach trees, Nicotiana benthamiana and Arabidopsis thaliana, respectively. Tissue-specific expression analysis showed that PpHSF5 was expressed predominantly in young vegetative organs (leaf and apex). Subcellular localization revealed that PpHSF5 was located in the nucleus in N. benthamiana cells. Two transgenic Arabidopsis lines were obtained that overexpressed PpHSF5. The root length and the number of lateral roots in the transgenic seedlings were significantly less than in WT seedlings and after cultivation for three weeks. The transgenic rosettes were smaller than those of the WT at 2–3 weeks. The two transgenic lines exhibited a dwarf phenotype three weeks after transplanting, although there was no significant difference in the number of internodes. Moreover, the PpHSF5-OE lines exhibited enhanced thermotolerance. These results indicated that PpHSF5 might be act as a suppresser of growth and development of root and aerial organs.

RNA-Seq Highlights Molecular Events Associated With Impaired Pollen-Pistil Interactions Following Short-Term Heat Stress in Brassica napus

The global climate change is leading to increased frequency of heatwaves with crops getting exposed to extreme temperature events. Such temperature spikes during the reproductive stage of plant development can harm crop fertility and productivity. Here we report the response of short-term heat stress events on the pollen and pistil tissues in a commercially grown cultivar of Brassica napus. Our data reveals that short-term temperature spikes not only affect pollen fitness but also impair the ability of the pistil to support pollen germination and pollen tube growth and that the heat stress sensitivity of pistil can have severe consequences for seed set and yield. Comparative transcriptome profiling of non-stressed and heat-stressed (40°C for 30 min) pollen and pistil (stigma + style) highlighted the underlying cellular mechanisms involved in heat stress response in these reproductive tissues. In pollen, cell wall organization and cellular transport-related genes possibly regulate pollen fitness under heat stress while the heat stress-induced repression of transcription factor encoding transcripts is a feature of the pistil response. Overall, high temperature altered the expression of genes involved in protein processing, regulation of transcription, pollen-pistil interactions, and misregulation of cellular organization, transport, and metabolism. Our results show that short episodes of high-temperature exposure in B. napus modulate key regulatory pathways disrupted reproductive processes, ultimately translating to yield loss. Further investigations on the genes and networks identified in the present study pave a way toward genetic improvement of the thermotolerance and reproductive performance of B. napus varieties.

Genome-Wide Analysis of the Heat Shock Transcription Factor Gene Family in Brassica juncea: Structure, Evolution, and Expression Profiles

Heat shock transcription factor (HSF) is ubiquitous in the whole biological world and plays an important role in regulating growth and development and responses to environment stress. In this study, a total of 60 HSF transcription factors in Brassica juncea genome were identified and analyzed. Phylogenetic analysis showed that HSF genes were divided into three groups namely: A, B, and C, of which group A was further divided into nine subgroups (A1-A9). The analysis of gene structure and conserved motifs showed that some homologous genes are highly conserved. There was strong conservative microcollinearity among Brassica rapa, B. juncea, and Brassica oleracea, which provides a basis for studying the replication of gene families. Moreover, the results revealed that the promoter regions of BjuHSF genes were rich in cis-elements related to growth and development, hormone signal, and stress response. The prediction of protein interaction results showed that HSFs could interact with multiple transcription factors and proteins in the genome, while functional annotation revealed that BjuHSF genes were involved in many biological processes. The expression patterns of BjuHSF genes were analyzed by qPCR, and the results showed that these genes were closely linked to stress response, hormones, and development process. These results are a foundation for further analysis of the regulation mechanism of HSF gene family.

Heat Sensing and Lipid Reprograming as a Signaling Switch for Heat Stress Responses in Wheat

Temperature is an essential physical factor that affects the plant life cycle. Almost all plant species have evolved a robust signal transduction system that enables them to sense changes in the surrounding temperature, relay this message and accordingly adjust their metabolism and cellular functions to avoid heat stress-related damage. Wheat (Triticum aestivum), being a cool-season crop, is very sensitive to heat stress. Any increase in the ambient temperature, especially at the reproductive and grain-filling stages, can cause a drastic loss in wheat yield. Heat stress causes lipid peroxidation due to oxidative stress, resulting in the damage of thylakoid membranes and the disruption of their function, which ultimately decreases photosynthesis and crop yield. The cell membrane/plasma membrane plays prominent roles as an interface system that perceives and translates the changes in environmental signals into intracellular responses. Thus, membrane lipid composition is a critical factor in heat stress tolerance or susceptibility in wheat. In this review, we elucidate the possible involvement of calcium influx as an early heat stress-responsive mechanism in wheat plants. In addition, the physiological implications underlying the changes in lipid metabolism under high-temperature stress in wheat and other plant species will be discussed. In-depth knowledge about wheat lipid reprograming can help develop heat-tolerant wheat varieties and provide approaches to solve the impact of global climate change.

Signal transduction networks during stress combination

Episodes of heat waves combined with drought can have a devastating impact on agricultural production worldwide. These conditions, as well as many other types of stress combinations, impose unique physiological and developmental demands on plants and require the activation of dedicated pathways. Here, we review recent RNA sequencing studies of stress combination in plants, and conduct a meta-analysis of the transcriptome response of plants to different types of stress combination. Our analysis reveals that each different stress combination is accompanied by its own set of stress combination-specific transcripts, and that the response of different transcription factor families is unique to each stress combination. The alarming rate of increase in global temperatures, coupled with the predicted increase in future episodes of extreme weather, highlight an urgent need to develop crop plants with enhanced tolerance to stress combination. The uniqueness and complexity of the physiological and molecular response of plants to each different stress combination, highlighted here, demonstrate the daunting challenge we face in accomplishing this goal. Dedicated efforts combining field experimentation, omics, and network analyses, coupled with advanced phenotyping and breeding methods, will be needed to address specific crops and particular stress combinations relevant to maintaining our future food chain secured.

Comprehensive analyses of the annexin (ANN) gene family in Brassica rapa, Brassica oleracea and Brassica napus reveals their roles in stress response

Annexins (ANN) are a multigene, evolutionarily conserved family of calcium-dependent and phospholipid-binding proteins that play important roles in plant development and stress resistance. However, a systematic comprehensive analysis of ANN genes of Brassicaceae species (Brassica rapa, Brassica oleracea, and Brassica napus) has not yet been reported. In this study, we identified 13, 12, and 26 ANN genes in B. rapa, B. oleracea, and B. napus, respectively. About half of these genes were clustered on various chromosomes. Molecular evolutionary analysis showed that the ANN genes were highly conserved in Brassicaceae species. Transcriptome analysis showed that different group ANN members exhibited varied expression patterns in different tissues and under different (abiotic stress and hormones) treatments. Meanwhile, same group members from Arabidopsis thaliana, B. rapa, B. oleracea, and B. napus demonstrated conserved expression patterns in different tissues. The weighted gene coexpression network analysis (WGCNA) showed that BnaANN genes were induced by methyl jasmonate (MeJA) treatment and played important roles in jasmonate (JA) signaling and multiple stress response in B. napus.

Knockout of two BnaMAX1 homologs by CRISPR/Cas9-targeted mutagenesis improves plant architecture and increases yield in rapeseed (Brassica napus L.)

Plant height and branch number are essential components of rapeseed plant architecture and are directly correlated with its yield. Presently, improvement of plant architecture is a major challenge in rapeseed breeding. In this study, we first verified that the two rapeseed BnaMAX1 genes had redundant functions resembling those of Arabidopsis MAX1, which regulates plant height and axillary bud outgrowth. Therefore, we designed two sgRNAs to edit these BnaMAX1 homologs using the CRISPR/Cas9 system. The T₀ plants were edited very efficiently (56.30%-67.38%) at the BnaMAX1 target sites resulting in homozygous, heterozygous, bi-allelic and chimeric mutations. Transmission tests revealed that the mutations were passed on to the T₁ and T₂ progeny. We also obtained transgene-free lines created by the CRISPR/Cas9 editing, and no mutations were detected in potential off-target sites. Notably, simultaneous knockout of all four BnaMAX1 alleles resulted in semi-dwarf and increased branching phenotypes with more siliques, contributing to increased yield per plant relative to wild type. Therefore, these semi-dwarf and increased branching characteristics have the potential to help construct a rapeseed ideotype. Significantly, the editing resources obtained in our study provide desirable germplasm for further breeding of high yield in rapeseed.

Engineering Multiple Abiotic Stress Tolerance in Canola, Brassica napus

Impacts of climate change like global warming, drought, flooding, and other extreme events are posing severe challenges to global crop production. Contribution of Brassica napus towards the oilseed industry makes it an essential component of international trade and agroeconomics. Consequences from increasing occurrences of multiple abiotic stresses on this crop are leading to agroeconomic losses making it vital to endow B. napus crop with an ability to survive and maintain yield when faced with simultaneous exposure to multiple abiotic stresses. For an improved understanding of the stress sensing machinery, there is a need for analyzing regulatory pathways of multiple stress-responsive genes and other regulatory elements such as non-coding RNAs. However, our understanding of these pathways and their interactions in B. napus is far from complete. This review outlines the current knowledge of stress-responsive genes and their role in imparting multiple stress tolerance in B. napus. Analysis of network cross-talk through omics data mining is now making it possible to unravel the underlying complexity required for stress sensing and signaling in plants. Novel biotechnological approaches such as transgene-free genome editing and utilization of nanoparticles as gene delivery tools are also discussed. These can contribute to providing solutions for developing climate change resilient B. napus varieties with reduced regulatory limitations. The potential ability of synthetic biology to engineer and modify networks through fine-tuning of stress regulatory elements for plant responses to stress adaption is also highlighted.

Genome-Wide Identification and Characterization of Heat-Shock Transcription Factors in Rubber Tree

Heat-shock transcription factors (Hsfs) play a pivotal role in the response of plants to various stresses. The present study aimed to characterize the Hsf genes in the rubber tree, a primary global source of natural rubber. In this study, 30 Hsf genes were identified in the rubber tree using genome-wide analysis. They possessed a structurally conserved DNA-binding domain and an oligomerization domain. On the basis of the length of the insert region between HR-A and HR-B in the oligomerization domain, the 30 members were clustered into three classes, Classes A (18), B (10), and C (2). Members within the same class shared highly conserved gene structures and protein motifs. The background expression levels of 11 genes in cold-tolerant rubber-tree clone 93-14 were significantly higher than those in cold-sensitive rubber-tree clone Reken501, while four genes exhibited inverse expression patterns. Upon cold stress, 20 genes were significantly upregulated in 93-114. Of the upregulated genes, HbHsfA2b, HbHsfA3a, and HbHsfA7a were also significantly upregulated in three other cold-tolerant rubber-tree clones at one or more time intervals upon cold stress. Their nuclear localization was verified, and the protein–protein interaction network was predicted. This study provides a basis for dissecting Hsf function in the enhanced cold tolerance of the rubber tree.

Genome-Wide Identification and Characterization of FBA Gene Family in Polyploid Crop Brassica napus

Fructose-1,6-bisphosphate aldolase (FBA) is a versatile metabolic enzyme involved in multiple important processes of glycolysis, gluconeogenesis, and Calvin cycle. Despite its significance in plant biology, the identity of this gene family in oil crops is lacking. Here, we performed genome-wide identification and characterization of FBAs in an allotetraploid species, oilseed rape Brassica napus. Twenty-two BnaFBA genes were identified and divided into two groups based on integrative analyses of functional domains, phylogenetic relationships, and gene structures. Twelve and ten B. napus FBAs (BnaFBAs) were predicted to be localized in the chloroplast and cytoplasm, respectively. Notably, synteny analysis revealed that Brassica-specific triplication contributed to the expansion of the BnaFBA gene family during the evolution of B. napus. Various cis-acting regulatory elements pertinent to abiotic and biotic stresses, as well as phytohormone responses, were detected. Intriguingly, each of the BnaFBA genes exhibited distinct sequence polymorphisms. Among them, six contained signatures of selection, likely having experienced breeding selection during adaptation and domestication. Importantly, BnaFBAs showed diverse expression patterns at different developmental stages and were preferentially highly expressed in photosynthetic tissues. Our data thus provided the foundation for further elucidating the functional roles of individual BnaFBA and also potential targets for engineering to improve photosynthetic productivity in B. napus.

Genome-Wide Identification, Classification, and Expression Analysis of the Hsf Gene Family in Carnation (Dianthus caryophyllus)

Heat shock transcription factors (Hsfs) are a class of important transcription factors (TFs) which play crucial roles in the protection of plants from damages caused by various abiotic stresses. The present study aimed to characterize the Hsf genes in carnation (Dianthus caryophyllus), which is one of the four largest cut flowers worldwide. In this study, a total of 17 non-redundant Hsf genes were identified from the D. caryophyllus genome. Specifically, the gene structure and motifs of each DcaHsf were comprehensively analyzed. Phylogenetic analysis of the DcaHsf family distinctly separated nine class A, seven class B, and one class C Hsf genes. Additionally, promoter analysis indicated that the DcaHsf promoters included various cis-acting elements that were related to stress, hormones, as well as development processes. In addition, cis-elements, such as STRE, MYB, and ABRE binding sites, were identified in the promoters of most DcaHsf genes. According to qRT-PCR data, the expression of DcaHsfs varied in eight tissues and six flowering stages and among different DcaHsfs, even in the same class. Moreover, DcaHsf-A1, A2a, A9a, B2a, B3a revealed their putative involvement in the early flowering stages. The time-course expression profile of DcaHsf during stress responses illustrated that all the DcaHsfs were heat- and drought-responsive, and almost all DcaHsfs were down-regulated by cold, salt, and abscisic acid (ABA) stress. Meanwhile, DcaHsf-A3, A7, A9a, A9b, B3a were primarily up-regulated at an early stage in response to salicylic acid (SA). This study provides an overview of the Hsf gene family in D. caryophyllus and a basis for the breeding of stress-resistant carnation.

The mitogen-activated protein kinase 4-phosphorylated heat shock factor A4A regulates responses to combined salt and heat stresses

Heat shock factors regulate responses to high temperature, salinity, water deprivation, or heavy metals. Their function in combinations of stresses is, however, not known. Arabidopsis HEAT SHOCK FACTOR A4A (HSFA4A) was previously reported to regulate responses to salt and oxidative stresses. Here we show, that the HSFA4A gene is induced by salt, elevated temperature, and a combination of these conditions. Fast translocation of HSFA4A tagged with yellow fluorescent protein from cytosol to nuclei takes place in salt-treated cells. HSFA4A can be phosphorylated not only by mitogen-activated protein (MAP) kinases MPK3 and MPK6 but also by MPK4, and Ser309 is the dominant MAP kinase phosphorylation site. In vivo data suggest that HSFA4A can be the substrate of other kinases as well. Changing Ser309 to Asp or Ala alters intramolecular multimerization. Chromatin immunoprecipitation assays confirmed binding of HSFA4A to promoters of target genes encoding the small heat shock protein HSP17.6A and transcription factors WRKY30 and ZAT12. HSFA4A overexpression enhanced tolerance to individually and simultaneously applied heat and salt stresses through reduction of oxidative damage. Our results suggest that this heat shock factor is a component of a complex stress regulatory pathway, connecting upstream signals mediated by MAP kinases MPK3/6 and MPK4 with transcription regulation of a set of stress-induced target genes.

Genome-wide identification and abiotic stress-responsive pattern of heat shock transcription factor family in Triticum aestivum L

Background

Enhancement of crop productivity under various abiotic stresses is a major objective of agronomic research. Wheat (Triticum aestivum L.) as one of the world’s staple crops is highly sensitive to heat stress, which can adversely affect both yield and quality. Plant heat shock factors (Hsfs) play a crucial role in abiotic and biotic stress response and conferring stress tolerance. Thus, multifunctional Hsfs may be potentially targets in generating novel strains that have the ability to survive environments that feature a combination of stresses.

Result

In this study, using the released genome sequence of wheat and the novel Hsf protein HMM (Hidden Markov Model) model constructed with the Hsf protein sequence of model monocot (Oryza sativa) and dicot (Arabidopsis thaliana) plants, genome-wide TaHsfs identification was performed. Eighty-two non-redundant and full-length TaHsfs were randomly located on 21 chromosomes. The structural characteristics and phylogenetic analysis with Arabidopsis thaliana, Oryza sativa and Zea mays were used to classify these genes into three major classes and further into 13 subclasses. A novel subclass, TaHsfC3 was found which had not been documented in wheat or other plants, and did not show any orthologous genes in A. thaliana, O. sativa, or Z. mays Hsf families. The observation of a high proportion of homeologous TaHsf gene groups suggests that the allopolyploid process, which occurred after the fusion of genomes, contributed to the expansion of the TaHsf family. Furthermore, TaHsfs expression profiling by RNA-seq revealed that the TaHsfs could be responsive not only to abiotic stresses but also to phytohormones. Additionally, the TaHsf family genes exhibited class-, subclass- and organ-specific expression patterns in response to various treatments.

Conclusions

A comprehensive analysis of Hsf genes was performed in wheat, which is useful for better understanding one of the most complex Hsf gene families. Variations in the expression patterns under different abiotic stress and phytohormone treatments provide clues for further analysis of the TaHsfs functions and corresponding signal transduction pathways in wheat.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5617-1) contains supplementary material, which is available to authorized users.

Extreme climatic events down-regulate the grassland biomass response to elevated carbon dioxide

Terrestrial ecosystems are considered as carbon sinks that may mitigate the impacts of increased atmospheric CO2 concentration ([CO2]). However, it is not clear what their carbon sink capacity will be under extreme climatic conditions. In this study, we used long-term (1998-2013) data from a C3 grassland Free Air CO2 Enrichment (FACE) experiment in Germany to study the combined effects of elevated [CO2] and extreme climatic events (ECEs) on aboveground biomass production. CO2 fertilization effect (CFE), which represents the promoted plant photosynthesis and water use efficiency under higher [CO2], was quantiffied by calculating the relative differences in biomass between the plots with [CO2] enrichment and the plots with ambient [CO2]. Down-regulated CFEs were found when ECEs occurred during the growing season, and the CFE decreases were statistically significant with p well below 0.05 (t-test). Of all the observed ECEs, the strongest CFE decreases were associated with intensive and prolonged heat waves. These findings suggest that more frequent ECEs in the future are likely to restrict the mitigatory effects of C3 grassland ecosystems, leading to an accelerated warming trend. To reduce the uncertainties of future projections, the atmosphere-vegetation interactions, especially the ECEs effects, are emphasized and need to be better accounted.