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. 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. 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.

Based on the information of 25 heat shock transcription factor (Hsf) homologues in maize according to a genome-wide analysis, ZmHsf06 was cloned from maize leaves and transformed into Arabidopsis thaliana (L. Heynh.) (ecotype, Col-0). Three transgenic positive lines were selected to assess the basic and acquired thermotolerance and drought-stress tolerance under stresses and for some physiological assays. The sequence analysis indicates that ZmHsf06 contained the characteristic domains of class A type plant Hsfs. The results of qRT–PCR showed that the expression levels of ZmHsf06 were elevated by heat shock and drought stress to different extents in three transgenic lines. Phenotypic observation shows that compared with the Wt (wild-type) controls, the overexpressing ZmHsf06 of Arabidopsis plants have enhanced basal and acquired thermotolerance, stronger drought-stress tolerance and growth advantages under mild heat stress conditions. These results are further confirmed by physiological and biochemical evidence that transgenic Arabidopsis plants exhibit higher seed germination rate, longer axial-root length, higher activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), higher leaf chlorophyll content, but lower relative electrical conductivity (REC), malondialdehyde (MDA) and osmotic potential (OP) than the Wt controls after heat shock and drought treatments. ZmHsf06 may be a central representative of maize Hsfs and could be useful in molecular breeding of maize or other crops for enhanced tolerances, particularly during terminal heat and drought stresses.

Background: Heat shock transcription factors (Hsfs) are present in majority of plants and play central roles in thermotolerance, transgenerational thermomemory, and many other stress responses. Our previous paper identified at least 82 Hsf members in a genome-wide study on wheat (Triticum aestivum L.). In this study, we analyzed the Hsf expression profiles in the advanced development stages of wheat, isolated the markedly heat-responsive gene TaHsfA2–10 (GenBank accession number MK922287), and characterized this gene and its role in thermotolerance regulation in seedlings of Arabidopsis thaliana (L. Heynh.). Results: In the advanced development stages, wheat Hsf family transcription profiles exhibit different expression patterns and varying heat-responses in leaves and roots, and Hsfs are constitutively expressed to different degrees under the normal growth conditions. Overall, the majority of group A and B Hsfs are expressed in leaves while group C Hsfs are expressed at higher levels in roots. The expression of a few Hsf genes could not be detected. Heat shock (HS) caused upregulation about a quarter of genes in leaves and roots, while a number of genes were downregulated in response to HS. The highly heat-responsive gene TaHsfA2–10 was isolated through homeologous cloning. qRT-PCR revealed that TaHsfA2–10 is expressed in a wide range of tissues and organs of different development stages of wheat under the normal growth conditions. Compared to non-stress treatment, TaHsfA2–10 was highly upregulated in response to HS, H₂O_2, and salicylic acid (SA), and was downregulated by abscisic acid (ABA) treatment in two-leaf-old seedlings. Transient transfection of tobacco epidermal cells revealed subcellular localization of TaHsfA2–10 in the nucleus under the normal growth conditions. Phenotypic observation indicated that TaHsfA2–10 could improve both basal thermotolerance and acquired thermotolerance of transgenic Arabidopsis thaliana seedlings and rescue the thermotolerance defect of the T-DNA insertion mutant athsfa2 during HS. Compared to wild type (WT) seedlings, the TaHsfA2–10-overexpressing lines displayed both higher chlorophyll contents and higher survival rates. Yeast one-hybrid assay results revealed that TaHsfA2–10 had transactivation activity. The expression levels of thermotolerance-related AtHsps in the TaHsfA2–10 transgeinc Arabidopsis thaliana were higher than those in WT after HS. Conclusions: Wheat Hsf family members exhibit diversification and specificity of transcription expression patterns in advanced development stages under the normal conditions and after HS. As a markedly responsive transcriptional factor to HS, SA and H₂O₂, TaHsfA2–10 involves in thermotolerance regulation of plants through binding to the HS responsive element in promoter domain of relative Hsps and upregulating the expression of Hsp genes.

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

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