Ectopic over-expression of BhHsf1, a heat shock factor from the resurrection plant Boea hygrometrica, leads to increased thermotolerance and retarded growth in transgenic Arabidopsis and tobacco

Ectopic expression of an Old Yellow Enzyme (OYE3) gene from Saccharomyces cerevisiae increases the tolerance and phytoremediation of 2-nitroaniline in rice

2-nitroaniline (2-NA) is an environmental pollutant and has been extensively used as intermediates in organic synthesis. The presence of 2-NA in the environment is not only harmful for aquatic life but also mutagenic for human beings. In this study, we constructed transgenic rice expressing an Old Yellow Enzyme gene, ScOYE3, from Saccharomyces cerevisiae. The ScOYE3 transgenic plants were comprehensively investigated for their biochemical responses to 2-NA treatment and their 2-NA phytoremediation capabilities. Our results showed that the rice seedlings exposed to 2-NA stress, showed growth inhibition and biomass reduction. However, the transgenic plants exhibited strong tolerance to 2-NA stress compared to wild-type plants. Ectopic expression of ScOYE3 could effectively protect transgenic plants against 2-NA damage, which resulted in less reactive oxygen species accumulation in transgenic plants than that in wild-type plants. Our phytoremediation assay revealed that transgenic plants could eliminate more 2-NA from the medium than wild-type plants. Moreover, omics analysis was performed in order to get a deeper insight into the mechanism of ScOYE3-mediated 2-NA transformation in rice. Altogether, the function of ScOYE3 during 2-NA detoxification was characterized for the first time, which serves as strong theoretical support for the phytoremediation potential of 2-NA by Old Yellow Enzyme genes.

Autophagy: a key player in the recovery of plants from heat stress

Plants can be primed to withstand otherwise lethal heat stress (HS) through exposure to a preceding temporary and mild HS, commonly known as the 'thermopriming stimulus'. Plants have also evolved mechanisms to establish 'memories' of a previous stress encounter, or to reset their physiology to the original cellular state once the stress has ended. The priming stimulus triggers a widespread change of transcripts, proteins, and metabolites, which is crucial for maintaining the memory state but may not be required for growth and development under optimal conditions or may even be harmful. In such a scenario, recycling mechanisms such as autophagy are crucial for re-establishing cellular homeostasis and optimizing resource use for post-stress growth. While pivotal for eliminating heat-induced protein aggregates and protecting plants from the harmful impact of HS, recent evidence implies that autophagy also breaks down heat-induced protective macromolecules, including heat shock proteins, functioning as a resetting mechanism during the recovery from mild HS. This review provides an overview of the latest advances in understanding the multifaceted functions of autophagy in HS responses, with a specific emphasis on its roles in recovery from mild HS, and the modulation of HS memory.

High endoreduplication after drought-related conditions in haploid but not diploid mosses

BACKGROUND AND AIMS

Endoreduplication, the duplication of the nuclear genome without mitosis, is a common process in plants, especially in angiosperms and mosses. Accumulating evidence supports the relationship between endoreduplication and plastic responses to stress factors. Here, we investigated the level of endoreduplication in Ceratodon (Bryophyta), which includes the model organism Ceratodon purpureus.

METHODS

We used flow cytometry to estimate the DNA content of 294 samples from 67 localities and found three well-defined cytotypes, two haploids and one diploid, the haploids corresponding to C. purpureus and Ceratodon amazonum, and the diploid to Ceratodon conicus, recombination occurring between the former two.

KEY RESULTS

The endoreduplication index (EI) was significantly different for each cytotype, being higher in the two haploids. In addition, the EI of the haploids was higher during the hot and dry periods typical of the Mediterranean summer than during spring, whereas the EI of the diploid cytotype did not differ between seasons.

CONCLUSIONS

Endopolyploidy may be essential in haploid mosses to buffer periods of drought and to respond rapidly to desiccation events. Our results also suggest that the EI is closely related to the basic ploidy level, but less so to the nuclear DNA content as previously suggested.

Dynamics of chromatin accessibility and genome wide control of desiccation tolerance in the resurrection plant Haberlea rhodopensis

BACKGROUND

Drought is one of the main consequences of global climate change and this problem is expected to intensify in the future. Resurrection plants evolved the ability to withstand the negative impact of long periods of almost complete desiccation and to recover at rewatering. In this respect, many physiological, transcriptomic, proteomic and genomic investigations have been performed in recent years, however, few epigenetic control studies have been performed on these valuable desiccation-tolerant plants so far.

RESULTS

In the present study, for the first time for resurrection plants we provide evidences about the differential chromatin accessibility of Haberlea rhodopensis during desiccation stress by ATAC-seq (Assay for Transposase Accessible Chromatin with high-throughput sequencing). Based on gene similarity between species, we used the available genome of the closely related resurrection plant Dorcoceras hygrometricum to identify approximately nine hundred transposase hypersensitive sites (THSs) in H. rhodopensis. The majority of them corresponds to proximal and distal regulatory elements of different genes involved in photosynthesis, carbon metabolism, synthesis of secondary metabolites, cell signalling and transcriptional regulation, cell growth, cell wall, stomata conditioning, chaperons, oxidative stress, autophagy and others. Various types of binding motifs recognized by several families of transcription factors have been enriched from the THSs found in different stages of drought. Further, we used the previously published RNA-seq data from H. rhodopensis to evaluate the expression of transcription factors putatively interacting with the enriched motifs, and the potential correlation between the identified THS and the expression of their corresponding genes.

CONCLUSIONS

These results provide a blueprint for investigating the epigenetic regulation of desiccation tolerance in resurrection plant H. rhodopensis and comparative genomics between resurrection and non-resurrection species with available genome information.

Jasmonate: A Hormone of Primary Importance for Temperature Stress Response in Plants

Temperature is a critical environmental factor that plays a vital role in plant growth and development. Temperatures below or above the optimum ranges lead to cold or heat stress, respectively. Temperature stress retards plant growth and development, and it reduces crop yields. Jasmonates (JAs) are a class of oxylipin phytohormones that play various roles in growth, development, and stress response. In recent years, studies have demonstrated that cold and heat stress affect JA biosynthesis and signaling, and JA plays an important role in the response to temperature stress. Recent studies have provided a large body of information elucidating the mechanisms underlying JA-mediated temperature stress response. In the present review, we present recent advances in understanding the role of JA in the response to cold and heat stress, and how JA interacts with other phytohormones during this process.

Differential Accumulation of sHSPs Isoforms during Desiccation of the Resurrection Plant Haberlea rhodopensis Friv. under Optimal and High Temperature

Haberlea rhodopensis belongs to the small group of angiosperms that can survive desiccation to air-dry state and quickly restore their metabolism upon rehydration. In the present study, we investigated the accumulation of sHSPs and the extent of non-photochemical quenching during the downregulation of photosynthesis in H. rhodopensis leaves under desiccation at optimum (23 °C) and high temperature (38 °C). Desiccation of plants at 38 °C caused a stronger reduction in photosynthetic activity and corresponding enhancement in thermal energy dissipation. The accumulation of sHSPs was investigated by Western blot. While no expression of sHPSs was detected in the unstressed control sample, exposure of well-hydrated plants to high temperature induced an accumulation of sHSPs. Only a faint signal was observed at 50% RWC when dehydration was applied at 23 °C. Several cross-reacting polypeptide bands in the range of 16.5-19 kDa were observed in plants desiccated at high temperature. Two-dimensional electrophoresis and immunoblotting revealed the presence of several sHSPs with close molecular masses and pIs in the range of 5-8.0 that differed for each stage of treatment. At the latest stages of desiccation, fourteen different sHSPs could be distinguished, indicating that sHSPs might play a crucial role in H. rhodopensis under dehydration at high temperatures.

Characteristics and Regulating Roles of Wheat TaHsfA2-13 in Abiotic Stresses

Heat shock transcription factor (Hsf) exists widely in eukaryotes and responds to various abiotic stresses by regulating the expression of downstream transcription factors, functional enzymes, and molecular chaperones. In this study, TaHsfA2-13, a heat shock transcription factor belonging to A2 subclass, was cloned from wheat (Triticum aestivum) and its function was analyzed. TaHsfA2-13 encodes a protein containing 368 amino acids and has the basic characteristics of Hsfs. Multiple sequence alignment analysis showed that TaHsfA2-13 protein had the highest similarity with TdHsfA2c-like protein from Triticum dicoccoides, which reached 100%. The analysis of tissue expression characteristics revealed that TaHsfA2-13 was highly expressed in root, shoot, and leaf during the seedling stage of wheat. The expression of TaHsfA2-13 could be upregulated by heat stress, low temperature, H₂O₂, mannitol, salinity and multiple phytohormones. The TaHsfA2-13 protein was located in the nucleus under the normal growth conditions and showed a transcriptional activation activity in yeast. Further studies found that overexpression of TaHsfA2-13 in Arabidopsis thaliana Col-0 or athsfa2 mutant results in improved tolerance to heat stress, H₂O₂, SA and mannitol by regulating the expression of multiple heat shock protein (Hsp) genes. In summary, our study identified TaHsfA2-13 from wheat, revealed its regulatory function in varieties of abiotic stresses, and will provide a new target gene to improve stress tolerance for wheat breeding.

Overexpression of SlBBX17 affects plant growth and enhances heat tolerance in tomato

Heat stress is one of the major limiting factors that affect plant growth and production. In this study, we identified SlBBX17, which encodes a B-Box (BBX) protein and functions as a negative regulator of plant growth and a positive regulator of heat tolerance in tomato (Solanum lycopersicum). The expression of SlBBX17 is induced by hormones and heat stress. Overexpression of SlBBX17 (SlBBX17-OE) in tomato led to less chlorophyll content and lower net photosynthetic rate relative to the wild type. The growth retardation in the SlBBX17-OE plants may be attributed to the change of endogenous gibberellin (GA) metabolism and the decrease of photosynthetic capacity. SlBBX17-OE plants exhibited increased tolerance to heat stress, as reflected by the better membrane stability, higher antioxidant enzyme activities, and less reactive oxygen species (ROS) accumulation. Transcriptome analysis revealed that overexpression of SlBBX17 affected the expression of genes involved in GA biosynthetic process, photosynthesis, heat stress, ROS, and other cellular processes. The qRT-PCR analysis indicated that many SlHsf and SlHSP genes are up-regulated by SlBBX17 under heat stress. These results demonstrate that SlBBX17 plays important roles in regulating tomato growth and resistance to heat stress.

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.

Melatonin improves heat tolerance in Actinidia deliciosa via carotenoid biosynthesis and heat shock proteins expression

The whole-genome molecular mechanisms of melatonin (MT)-mediated enhancement of thermotolerance in plants has rarely been studied. In this study, the genome-wide gene expression profiles of kiwifruit seedlings primed with MT and non-MT at 45°C were analyzed by RNA-Seq. A total of 3299 differentially expressed genes (DEGs) were screened between MT and non-MT treatment, in which carotenoid biosynthesis was one of the high-enrichment pathways revealed by Kyoto Encyclopedia of Genes and Genomes analysis. Further, qRT-PCR verified that MT significantly induced the upregulated expression of the carotenoid biosynthesis gene, which was consistent with the increase of carotenoid content. In addition, 10 heat shock proteins (HSPs) were identified to have a highly upregulated expression by MT. These findings provide a set of informative and fundamental data on the role of MT in heat resistance.

Growth-defense trade-offs and yield loss in plants with engineered cell walls

As a major component of plant secondary cell walls, lignin provides structural integrity and rigidity, and contributes to primary defense by providing a physical barrier to pathogen ingress. Genetic modification of lignin biosynthesis has been adopted to reduce the recalcitrance of lignified cell walls to improve biofuel production, tree pulping properties and forage digestibility. However, lignin-modification is often, but unpredictably, associated with dwarf phenotypes. Hypotheses suggested to explain this include: collapsed vessels leading to defects in water and solute transport; accumulation of molecule(s) that are inhibitory to plant growth or deficiency of metabolites that are critical for plant growth; activation of defense pathways linked to cell wall integrity sensing. However, there is still no commonly accepted underlying mechanism for the growth defects. Here, we discuss recent data on transcriptional reprogramming in plants with modified lignin content and their corresponding suppressor mutants, and evaluate growth-defense trade-offs as a factor underlying the growth phenotypes. New approaches will be necessary to estimate how gross changes in transcriptional reprogramming may quantitatively affect growth. Better understanding of the basis for yield drag following cell wall engineering is important for the biotechnological exploitation of plants as factories for fuels and chemicals.

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.

Integrated analysis of co-expression, conserved genes and gene families reveal core regulatory network of heat stress response in Cleistogenes songorica, a xerophyte perennial desert plant

BACKGROUND

As global warming continues, heat stress (HS) is becoming an increasingly significant factor limiting plant growth and reproduction, especially for cool-season grass species. The objective of this study was to determine the transcriptional regulatory network of Cleistogenes songorica under HS via transcriptome profiling, identify of gene families and comparative analysis across major Poaceae species.

RESULTS

Physiological analysis revealed significantly decreased leaf relative water content (RWC) but increased proline (Pro) content in C. songorica under 24 h of HS. Transcriptome profiling indicated that 16,028 and 14,645 genes were differentially expressed in the shoots and roots of C. songorica under HS, respectively. Two subgenomes of C. songorica provide equal contribution under HS on the basis of the distribution and expression of differentially expressed genes (DEGs). Furthermore, 216 DEGs were identified as key evolutionarily conserved genes involved in the response to HS in C. songorica via comparative analysis with genes of four Poaceae species; these genes were involved in the 'response to heat' and 'heat acclimation'. Notably, most of the conserved DEGs belonged to the heat-shock protein (HSP) superfamily. Similar results were also obtained from co-expression analysis. Interestingly, hub-genes of co-expression analysis were found to overlap with conserved genes, especially heat-shock protein (HSP). In C. songorica, 84 HSP and 32 heat-shock transcription factor (HSF) genes were identified in the allotetraploid C. songorica genome, and might have undergone purifying selection during evolutionary history based on syntenic and phylogenetic analysis. By analysing the expression patterns of the CsHSPs and CsHSFs, we found that the transcript abundance of 72.7% of the CsHSP genes and of 62.5% of the CsHSF genes changed under heat stress in both the shoots and roots. Finally, a core regulatory network of HS was constructed on the basis of the CsHSP, CsHSF and other responsive genes in C. songorica.

CONCLUSIONS

Regulatory network and key genes were comprehensively analysed and identified in C. songorica under HS. This study improves our knowledge of thermotolerance mechanisms in native grasses, and also provides candidate genes for potential applications in the genetic improvement of grasses.

Overexpression of wheat transcription factor (TaHsfA6b) provides thermotolerance in barley

Overexpressing a heat shock factor gene (TaHsfA6bT) from wheat provides thermotolerance in barley by constitutive expression of heat and other abiotic stress-response genes. Temperature is one of the most crucial abiotic factors defining the yield potential of temperate cereal crops, such as barley. The regulators of heat shock response (HSR), heat stress transcription factors (Hsfs), modulate the transcription level of heat-responsive genes to protect the plants from heat stress. In this study, an Hsf from wheat (TaHsfA6b) is overexpressed in barley for providing thermotolerance. Transgenic barley lines overexpressing TaHsfA6b showed improvement in thermotolerance. The constitutive overexpression of a TaHsfA6b gene upregulated the expression of major heat shock proteins and other abiotic stress-responsive genes. RNA-seq and qRT-PCR analysis confirmed the upregulation of Hsps, chaperonins, DNAJ, LEA protein genes, and genes related to anti-oxidative enzymes in transgenic lines. Excessive generation and accumulation of reactive oxygen species (ROS) occurred in wild-type (WT) plants during heat stress; however, the transgenic lines reflected improved ROS homeostasis mechanisms, showing lesser ROS accumulation under high temperature. No negative phenotypic changes were observed in overexpression lines. These results suggest that TaHsfA6b is a regulator of HSR and its overexpression altered the expression patterns of some main stress-related genes and enhanced the thermotolerance of this cereal crop.

Plant growth-regulating molecules as thermoprotectants: functional relevance and prospects for improving heat tolerance in food crops

Among various abiotic stresses, heat stress is one of the most damaging, threatening plant productivity and survival all over the world. Warmer temperatures due to climatic anomalies above optimum growing temperatures have detrimental impacts on crop yield potential as well as plant distribution patterns. Heat stress affects overall plant metabolism in terms of physiology, biochemistry, and gene expression. Membrane damage, protein degradation, enzyme inactivation, and the accumulation of reactive oxygen species are some of the harmful effects of heat stress that cause injury to various cellular compartments. Although plants are equipped with various defense strategies to counteract these adversities, their defensive means are not sufficient to defend against the ever-rising temperatures. Hence, substantial yield losses have been observed in all crop species under heat stress. Here, we describe the involvement of various plant growth-regulators (PGRs) (hormones, polyamines, osmoprotectants, antioxidants, and other signaling molecules) in thermotolerance, through diverse cellular mechanisms that protect cells under heat stress. Several studies involving the exogenous application of PGRs to heat-stressed plants have demonstrated their role in imparting tolerance, suggesting the strong potential of these molecules in improving the performance of food crops grown under high temperature.

Weighted Gene Co-expression Network Analysis (WGCNA) Reveals the Hub Role of Protein Ubiquitination in the Acquisition of Desiccation Tolerance in Boea hygrometrica

Boea hygrometrica can survive extreme drought conditions and has been used as a model to study desiccation tolerance. A genome-wide transcriptome analysis of B. hygrometrica showed that the plant can survive rapid air-drying after experiencing a slow soil-drying acclimation phase. In addition, a weighted gene co-expression network analysis was used to study the transcriptomic datasets. A network comprising 22 modules was constructed, and seven modules were found to be significantly related to desiccation response using an enrichment analysis. Protein ubiquitination was observed to be a common process linked to hub genes in all the seven modules. Ubiquitin-modified proteins with diversified functions were identified using immunoprecipitation coupled with mass spectrometry. The lowest level of ubiquitination was noted at the full soil drying priming stage, which coincided the accumulation of dehydration-responsive gene BhLEA2. The highly conserved RY motif (CATGCA) was identified from the promoters of ubiquitin-related genes that were downregulated in the desiccated samples. An in silico gene expression analysis showed that the negative regulation of ubiquitin-related genes is potentially mediated via a B3 domain-containing transcription repressor VAL1. This study suggests that priming may involve the transcriptional regulation of several major processes, and the transcriptional regulation of genes in protein ubiquitination may play a hub role to deliver acclimation signals to posttranslational level in the acquisition of desiccation tolerance in B. hygrometrica.

A cytosolic class II small heat shock protein, PfHSP17.2, confers resistance to heat, cold, and salt stresses in transgenic Arabidopsis

We cloned and characterized the full-length coding sequence of a small heat shock (sHSP) gene, PfHSP17.2, from Primula forrestii leaves following heat stress treatment. Homology and phylogenetic analysis suggested that PfHSP17.2 is a cytosolic class II sHSP, which was further supported by the cytosolic localization of transient expression of PfHSP17.2 fused with green fluorescent protein reporter. Expression analysis showed that PfHSP17.2 was highly inducible by heat stress in almost all the vegetative and generative tissues and was expressed under salt, cold, and oxidative stress conditions as well. Moreover, the expression of PfHSP17.2 in P. forrestii was detected in certain developmental growth stages. Transgenic Arabidopsis thaliana constitutively expressing PfHSP17.2 displayed increased thermotolerance and higher resistance to salt and cold compared with wild type plants. It is suggested that PfHSP17.2 plays a key role in heat and other abiotic stresses.

Dehydration survival of crop plants and its measurement

Dehydration survival under drought stress is defined in this review as the transition from plant activity into a quiescent state of life preservation, which will be terminated by either recovery or death, depending on the stress regime and the plant's resilience. Dehydration survival is a popular phenotype by which functional genomics attempts to test gene function in drought resistance and survival. The available reports on phenotyping and genotyping of dehydration survival in genomic studies indicate that the measurement of this trait is often biased to the extent that misguided interpretations are likely to occur. This review briefly discusses the physiological basis of dehydration survival in resurrection plants and crop plants, and concludes that in phenotyping dehydration survival there is a need to distinguish between dehydration avoidance and dehydration tolerance (also termed desiccation tolerance) in affecting survival and recovery. Without this distinction, functional genomics studies of the trait might be biased. Survival due to dehydration avoidance is expressed by the capacity to maintain a relatively high plant water status as the plant is desiccated. Survival due to dehydration tolerance is expressed by delayed mortality (mortality at a relatively low plant water status) as affected by the resilience of plant metabolism. The common test of dehydration survival, using the relative recovery after a given number of stress days, is therefore insufficient because it is mainly driven by dehydration avoidance and so ignores a possible role for dehydration tolerance. Conceivable methods for more accurate phenotyping of the two components of dehydration survival are proposed and discussed.

BhbZIP60 from Resurrection Plant Boea hygrometrica Is an mRNA Splicing-Activated Endoplasmic Reticulum Stress Regulator Involved in Drought Tolerance

Adverse environmental conditions cause endoplasmic reticulum (ER) stress in plants. To mitigate ER stress damage, ER associated transcription factors and inositol-requiring enzyme-1 (IRE1)-mediated bZIP60 mRNA splicing are activated in plants. A drought-induced gene, encoding the ortholog of AtbZIP60, was identified in the resurrection plant Boea hygrometrica, termed BhbZIP60. In response to ER stress and dehydration, BhbZIP60 mRNA can be spliced to create a frame shift in the C terminus by the excision of 23b segment in a manner of its ortholog in other plants, thus translocating to the nucleus instead of the cytoplasm. The splicing-activated BhbZIP60 (BhbZIP60S) could function in the same way as its Arabidopsis ortholog by restoring the molecular phenotype of the mutant atbzip60. When overexpressed in Arabidopsis, BhbZIP60S provided transgenic plants with enhanced tolerance to drought, tunicamycin and mannitol stresses with upregulation of the expressions of ER quality control (QC) genes (BiP2, BiP3, CNX1, and sPDI) and abscisic acid (ABA) responsive genes (RD29A, RAB18, and RD17). Furthermore, in the yeast one-hybrid system, BhbZIP60S was capable of interacting with ER stress responsive elements (ERSE and ERSE-II) that exist in the promoters of known ER-QC genes, but not binding to ABA responsive cis-elements (ABREs). Our results demonstrated that drought-induced BhbZIP60 may have a function in drought tolerance via the splicing-activated BhbZIP60S to mediate ER-QC by direct binding to the promoters of ER-QC genes. This study evidently demonstrates the involvement of ER-QC in the drought tolerance of Arabidopsis and the desiccation tolerance of the resurrection plant B. hygrometrica.

The Plant Heat Stress Transcription Factors (HSFs): Structure, Regulation, and Function in Response to Abiotic Stresses

Abiotic stresses such as high temperature, salinity, and drought adversely affect the survival, growth, and reproduction of plants. Plants respond to such unfavorable changes through developmental, physiological, and biochemical ways, and these responses require expression of stress-responsive genes, which are regulated by a network of transcription factors (TFs), including heat stress transcription factors (HSFs). HSFs play a crucial role in plants response to several abiotic stresses by regulating the expression of stress-responsive genes, such as heat shock proteins (Hsps). In this review, we describe the conserved structure of plant HSFs, the identification of HSF gene families from various plant species, their expression profiling under abiotic stress conditions, regulation at different levels and function in abiotic stresses. Despite plant HSFs share highly conserved structure, their remarkable diversification across plants reflects their numerous functions as well as their integration into the complex stress signaling and response networks, which can be employed in crop improvement strategies via biotechnological intervention.

Global Transcriptome Analysis Reveals Acclimation-Primed Processes Involved in the Acquisition of Desiccation Tolerance in Boea hygrometrica

Boea hygrometrica resurrection plants require a period of acclimation by slow soil-drying in order to survive a subsequent period of rapid desiccation. The molecular basis of this observation was investigated by comparing gene expression profiles under different degrees of water deprivation. Transcripts were clustered according to the expression profiles in plants that were air-dried (rapid desiccation), soil-dried (gradual desiccation), rehydrated (acclimated) and air-dried after acclimation. Although phenotypically indistinguishable, it was shown by principal component analysis that the gene expression profiles in rehydrated, acclimated plants resemble those of desiccated plants more closely than those of hydrated acclimated plants. Enrichment analysis based on gene ontology was performed to deconvolute the processes that accompanied desiccation tolerance. Transcripts associated with autophagy and α-tocopherol accumulation were found to be activated in both air-dried, acclimated plants and soil-dried non-acclimated plants. Furthermore, transcripts associated with biosynthesis of ascorbic acid, cell wall catabolism, chaperone-assisted protein folding, respiration and macromolecule catabolism were activated and maintained during soil-drying and rehydration. Based on these findings, we hypothesize that activation of these processes leads to the establishment of an optimal physiological and cellular state that enables tolerance during rapid air-drying. Our study provides a novel insight into the transcriptional regulation of critical priming responses to enable survival following rapid dehydration in B. hygrometrica.

TaHsfA6f is a transcriptional activator that regulates a suite of heat stress protection genes in wheat (Triticum aestivum L.) including previously unknown Hsf targets

Heat stress is a significant environmental factor adversely affecting crop yield. Crop adaptation to high-temperature environments requires transcriptional reprogramming of a suite of genes involved in heat stress protection. This study investigated the role of TaHsfA6f, a member of the A6 subclass of heat shock transcription factors, in the regulation of heat stress protection genes in Triticum aestivum (bread wheat), a poorly understood phenomenon in this crop species. Expression analysis showed that TaHsfA6f was expressed constitutively in green organs but was markedly up-regulated during heat stress. Overexpression of TaHsfA6f in transgenic wheat using a drought-inducible promoter resulted in up-regulation of heat shock proteins (HSPs) and a number of other heat stress protection genes that included some previously unknown Hsf target genes such as Golgi anti-apoptotic protein (GAAP) and the large isoform of Rubisco activase. Transgenic wheat plants overexpressing TaHsfA6f showed improved thermotolerance. Transactivation assays showed that TaHsfA6f activated the expression of reporter genes driven by the promoters of several HSP genes (TaHSP16.8, TaHSP17, TaHSP17.3, and TaHSP90.1-A1) as well as TaGAAP and TaRof1 (a co-chaperone) under non-stress conditions. DNA binding analysis revealed the presence of high-affinity TaHsfA6f-binding heat shock element-like motifs in the promoters of these six genes. Promoter truncation and mutagenesis analyses identified TaHsfA6f-binding elements that were responsible for transactivation of TaHSP90.1-A1 and TaGAAP by TaHsfA6f. These data suggest that TaHsfA6f is a transcriptional activator that directly regulates TaHSP, TaGAAP, and TaRof1 genes in wheat and its gene regulatory network has a positive impact on thermotolerance.

Jasmonates: Emerging Players in Controlling Temperature Stress Tolerance

The sedentary life of plants has forced them to live in an environment that is characterized by the presence of numerous challenges in terms of biotic and abiotic stresses. Phytohormones play essential roles in mediating plant physiology and alleviating various environmental perturbations. Jasmonates are a group of oxylipin compounds occurring ubiquitously in the plant kingdom that play pivotal roles in response to developmental and environmental cues. Jasmonates (JAs) have been shown to participate in unison with key factors of other signal transduction pathway, including those involved in response to abiotic stress. Recent findings have furnished large body of information suggesting the role of jasmonates in cold and heat stress. JAs have been shown to regulate C-repeat binding factor (CBF) pathway during cold stress. The interaction between the integrants of JA signaling and components of CBF pathway demonstrates a complex relationship between the two. JAs have also been shown to counteract chilling stress by inducing ROS avoidance enzymes. In addition, several lines of evidence suggest the positive regulation of thermotolerance by JA. The present review provides insights into biosynthesis, signal transduction pathway of jasmonic acid and their role in response to temperature stress.

LlHSFA1, a novel heat stress transcription factor in lily (Lilium longiflorum), can interact with LlHSFA2 and enhance the thermotolerance of transgenic Arabidopsis thaliana

A heat stress transcription factor LlHSFA1 in lily and its relationship with LlHSFA2 was investigated, and its function in enhancing thermotolerance was confirmed by analyzing transgenic Arabidopsis thaliana overexpressed LlHSFA1. A large family of heat stress transcription factors that are involved in the heat stress response in plants can induce the expression of multiple genes related to thermotolerance including heat-shock proteins. In this study, a novel class A1 HSF named LlHSFA1 was isolated from leaves of lily (Lilium longiflorum cv. 'White Heaven') using the rapid amplification of cDNA ends technique. Analysis of the deduced amino acid sequence and construction of a phylogenetic tree showed that LlHSFA1 contained five critical domains and motifs and belonged to the A1 family of HSFs. Following the heat treatment of lily leaves, transcription of LlHSFA1 was induced to a varying extent, related to the time of measurement. The induced expression peak of LlHSFA1 occurred prior to that of LlHSFA2, during the early phase of heat stress. Following transient expression of LlHSFA1 in Nicotiana benthamiana, LlHSFA1 was found to be localized in both the nucleus and the cytoplasm. Analysis using bimolecular fluorescence complementation and a yeast two-hybrid assay demonstrated that LlHSFA1 could interact with LlHSFA2. Use of a yeast one-hybrid assay confirmed that LlHSFA1 had transcriptional activation activity. In transgenic Arabidopsis lines overexpressing LlHSFA1 under unstressed conditions, the expression of some putative target genes was up-regulated, in comparison with expression in wild-type plants, and furthermore, the thermotolerance of the transgenic lines was enhanced. Overall, LlHSFA1 was demonstrated to play an important role in the heat stress response of lily and to be a novel candidate gene for application in lily breeding, using genetic modification approaches.

A novel membrane-bound E3 ubiquitin ligase enhances the thermal resistance in plants

High temperature stress disturbs cellular homoeostasis and results in a severe retardation in crop growth and development. Thus, it is important to reveal the mechanism of plants coping with heat stress. In this study, a novel gene that we identified from Brassica napus, referred to as BnTR1, was found to play a key role in heat stress response in planta. BnTR1 is a membrane-bound RINGv (C₄HC₃) protein that displays E3 ligase activity in vitro. We demonstrated that modest expression of BnTR1 is sufficient to minimize adverse environmental influence and confers thermal resistance on development without any detrimental effects in B. napus and Oryza sativa. Our investigation into the action mechanism indicates that BnTR1 is likely to be involved in mediating Ca²⁺ dynamics by regulating the activity of calcium channels, which further alters the transcripts of heat shock factors and heat shock proteins contributing to plant thermotolerance. Hence, our study identified BnTR1 as a novel key factor underlying a conserved mechanism conferring thermal resistance in plants.

Understanding desiccation tolerance using the resurrection plant Boea hygrometrica as a model system

Vegetative tissues of Boea hygrometrica, a member of the Gesneriaceae family, can tolerate severe water loss to desiccated state and fully recover upon rehydration. Unlike many other so called "resurrection plants," the detached leaves of B. hygrometrica also possess the same level of capacity for desiccation tolerance (DT) as that of whole plant. B. hygrometrica is distributed widely from the tropics to northern temperate regions in East Asia and grows vigorously in areas around limestone rocks, where dehydration occurs frequently, rapidly, and profoundly. The properties of detached B. hygrometrica leaves and relative ease of culture have made it a useful system to study the adaptive mechanisms of DT. Extensive studies have been conducted to identify the physiological, cellular, and molecular mechanisms underlying DT in the last decade, including specific responses to water stress, such as cell wall folding and pigment-protein complex stabilizing in desiccated leaves. In this review, the insight into the structural, physiological, and biochemical, and molecular alterations that accompany the acquisition of DT in B. hygrometrica is described. Finally a future perspective is proposed, with an emphasis on the emerging regulatory roles of retroelements and histone modifications in the acquisition of DT, and the need of establishment of genome sequence database and high throughput techniques to identify novel regulators for fully understanding of the matrix of DT.

Evidence of current impact of climate change on life: a walk from genes to the biosphere

We review the evidence of how organisms and populations are currently responding to climate change through phenotypic plasticity, genotypic evolution, changes in distribution and, in some cases, local extinction. Organisms alter their gene expression and metabolism to increase the concentrations of several antistress compounds and to change their physiology, phenology, growth and reproduction in response to climate change. Rapid adaptation and microevolution occur at the population level. Together with these phenotypic and genotypic adaptations, the movement of organisms and the turnover of populations can lead to migration toward habitats with better conditions unless hindered by barriers. Both migration and local extinction of populations have occurred. However, many unknowns for all these processes remain. The roles of phenotypic plasticity and genotypic evolution and their possible trade-offs and links with population structure warrant further research. The application of omic techniques to ecological studies will greatly favor this research. It remains poorly understood how climate change will result in asymmetrical responses of species and how it will interact with other increasing global impacts, such as N eutrophication, changes in environmental N : P ratios and species invasion, among many others. The biogeochemical and biophysical feedbacks on climate of all these changes in vegetation are also poorly understood. We here review the evidence of responses to climate change and discuss the perspectives for increasing our knowledge of the interactions between climate change and life.

Generating high temperature tolerant transgenic plants: Achievements and challenges

Production of plants tolerant to high temperature stress is of immense significance in the light of global warming and climate change. Plant cells respond to high temperature stress by re-programming their genetic machinery for survival and reproduction. High temperature tolerance in transgenic plants has largely been achieved either by over-expressing heat shock protein genes or by altering levels of heat shock factors that regulate expression of heat shock and non-heat shock genes. Apart from heat shock factors, over-expression of other trans-acting factors like DREB2A, bZIP28 and WRKY proteins has proven useful in imparting high temperature tolerance. Besides these, elevating the genetic levels of proteins involved in osmotic adjustment, reactive oxygen species removal, saturation of membrane-associated lipids, photosynthetic reactions, production of polyamines and protein biosynthesis process have yielded positive results in equipping transgenic plants with high temperature tolerance. Cyclic nucleotide gated calcium channel proteins that regulate calcium influxes across the cell membrane have recently been shown to be the key players in induction of high temperature tolerance. The involvement of calmodulins and kinases in activation of heat shock factors has been implicated as an important event in governing high temperature tolerance. Unfilled gaps limiting the production of high temperature tolerant transgenic plants for field level cultivation are discussed.

CaWRKY40, a WRKY protein of pepper, plays an important role in the regulation of tolerance to heat stress and resistance to Ralstonia solanacearum infection

WRKY proteins form a large family of plant transcription factors implicated in the modulation of numerous biological processes, such as growth, development and responses to various environmental stresses. However, the roles of the majority WRKY family members, especially in non-model plants, remain poorly understood. We identified CaWRKY40 from pepper. Transient expression in onion epidermal cells showed that CaWRKY40 can be targeted to nuclei and activates expression of a W-box-containing reporter gene. CaWRKY40 transcripts are induced in pepper by Ralstonia solanacearum and heat shock. To assess roles of CaWRKY40 in plant stress responses we performed gain- and loss-of-function experiments. Overexpression of CaWRKY40 enhanced resistance to R. solanacearum and tolerance to heat shock in tobacco. In contrast, silencing of CaWRKY40 enhanced susceptibility to R. solanacearum and impaired thermotolerance in pepper. Consistent with its role in multiple stress responses, we found CaWRKY40 transcripts to be induced by signalling mechanisms mediated by the stress hormones salicylic acid (SA), jasmonic acid (JA) and ethylene (ET). Overexpression of CaWRKY40 in tobacco modified the expression of hypersensitive response (HR)-associated and pathogenesis-related genes. Collectively, our results suggest that CaWRKY40 orthologs are regulated by SA, JA and ET signalling and coordinate responses to R. solanacearum attacks and heat stress in pepper and tobacco.

Designed transcriptional regulators for trait development

Development is largely controlled by proteins that regulate gene expression at the level of transcription. These regulatory proteins, the genes that control them, and the genes that they control, are organized in a hierarchical structure of complex interactions. Altering the expression of genes encoding regulatory proteins controlling critical nodes in this hierarchy has potential for dramatic phenotypic modification. Constitutive over-expression of genes encoding regulatory proteins in transgenic plants has resulted in agronomically interesting phenotypes along with developmental abnormalities. For trait development, the magnitude and timing of expression of genes encoding key regulatory proteins will need to be precisely controlled and targeted to specific cells and tissues at certain developmental timepoints. Such control is made possible by designed transcriptional regulators which are fusions of engineered DNA binding proteins and activator or repressor domains. Expression of genes encoding such designed transcriptional regulators enable the selective modulation of endogenous gene expression. Genes encoding proteins controlling regulatory networks are prime targets for up- or down-regulation via such designed transcriptional regulators.

Ectopic overexpression of SlHsfA3, a heat stress transcription factor from tomato, confers increased thermotolerance and salt hypersensitivity in germination in transgenic Arabidopsis

Plant heat stress transcription factors (Hsfs) are the critical components involved in mediating responses to various environmental stressors. However, the detailed roles of many plant Hsfs are far from fully understood. In this study, an Hsf (SlHsfA3) was isolated from the cultivated tomato (Solanum lycopersicum, Sl) and functionally characterized at the genetic and developmental levels. The nucleus-localized SlHsfA3 was basally and ubiquitously expressed in different plant organs. The expression of SlHsfA3 was induced dramatically by heat stress, moderately by high salinity, and slightly by drought, but was not induced by abscisic acid (ABA). The ectopic overexpression of SlHsfA3 conferred increased thermotolerance and late flowering phenotype to transgenic Arabidopsis plants. Moreover, SlHsfA3 played a negative role in controlling seed germination under salt stress. RNA-sequencing data demonstrated that a number of heat shock proteins (Hsps) and stress-associated genes were induced in Arabidopsis plants overexpressing SlHsfA3. A gel shift experiment and transient expression assays in Nicotiana benthamiana leaves demonstrated that SlHsfA3 directly activates the expression of SlHsp26.1-P and SlHsp21.5-ER. Taken together, our results suggest that SlHsfA3 behaves as a typical Hsf to contribute to plant thermotolerance. The late flowering and seed germination phenotypes and the RNA-seq data derived from SlHsfA3 overexpression lines lend more credence to the hypothesis that plant Hsfs participate in diverse physiological and biochemical processes related to adverse conditions.

Some like it hot, some like it warm: phenotyping to explore thermotolerance diversity

Plants have evolved overlapping but distinct cellular responses to different aspects of high temperature stress. These responses include basal thermotolerance, short- and long-term acquired thermotolerance, and thermotolerance to moderately high temperatures. This 'thermotolerance diversity' means that multiple phenotypic assays are essential for fully describing the functions of genes involved in heat stress responses. A large number of genes with potential roles in heat stress responses have been identified using genetic screens and genome wide expression studies. We examine the range of phenotypic assays that have been used to characterize thermotolerance phenotypes in both Arabidopsis and crop plants. Three major variables differentiate thermotolerance assays: (1) the heat stress regime used, (2) the developmental stage of the plants being studied, and (3) the actual phenotype which is scored. Consideration of these variables will be essential for deepening our understanding of the molecular genetics of plant thermotolerance.

Molecular mechanisms of desiccation tolerance in resurrection plants

Resurrection plants are a small but diverse group of land plants characterized by their tolerance to extreme drought or desiccation. They have the unique ability to survive months to years without water, lose most of the free water in their vegetative tissues, fall into anabiosis, and, upon rewatering, quickly regain normal activity. Thus, they are fundamentally different from other drought-surviving plants such as succulents or ephemerals, which cope with drought by maintaining higher steady state water potential or via a short life cycle, respectively. This review describes the unique physiological and molecular adaptations of resurrection plants enabling them to withstand long periods of desiccation. The recent transcriptome analysis of Craterostigma plantagineum and Haberlea rhodopensis under drought, desiccation, and subsequent rehydration revealed common genetic pathways with other desiccation-tolerant species as well as unique genes that might contribute to the outstanding desiccation tolerance of the two resurrection species. While some of the molecular responses appear to be common for both drought stress and desiccation, resurrection plants also possess genes that are highly induced or repressed during desiccation with no apparent sequence homologies to genes of other species. Thus, resurrection plants are potential sources for gene discovery. Further proteome and metabolome analyses of the resurrection plants contributed to a better understanding of molecular mechanisms that are involved in surviving severe water loss. Understanding the cellular mechanisms of desiccation tolerance in this unique group of plants may enable future molecular improvement of drought tolerance in crop plants.

HbCIPK2, a novel CBL-interacting protein kinase from halophyte Hordeum brevisubulatum, confers salt and osmotic stress tolerance

Protein kinases play an important role in regulating the response to abiotic stress in plant. CIPKs are plant-specific signal transducers, and some members have been identified. However, the precise functions of novel CIPKs still remain unknown. Here we report that HbCIPK2 is a positive regulator of salt and osmotic stress tolerance. HbCIPK2 was screened out of the differentially expressed fragments from halophyte Hordeum brevisubulatum by cDNA-AFLP technique, and was a single-copy gene without intron. Expression of HbCIPK2 was increased by salt, drought and ABA treatment. HbCIPK2 is mainly localized to the plasma membrane and nucleus. Ectopic expression of 35S:HbCIPK2 not only rescued the salt hypersensitivity in Arabidopsis mutant sos2-1, but also enhanced salt tolerance in Arabidopsis wild type, and exhibited tolerance to osmotic stress during germination. The HbCIPK2 contributed to the ability to prevent K(+) loss in root and to accumulate less Na(+) in shoot resulting in K(+) /Na(+) homeostasis and protection of root cell from death, which is consistent with the gene expression profile of HbCIPK2-overexpressing lines. These findings imply possible novel HbCIPK2-mediated salt signalling pathways or networks in H. brevisubulatum.

Molecular mechanisms of desiccation tolerance in resurrection plants

Resurrection plants are a small but diverse group of land plants characterized by their tolerance to extreme drought or desiccation. They have the unique ability to survive months to years without water, lose most of the free water in their vegetative tissues, fall into anabiosis, and, upon rewatering, quickly regain normal activity. Thus, they are fundamentally different from other drought-surviving plants such as succulents or ephemerals, which cope with drought by maintaining higher steady state water potential or via a short life cycle, respectively. This review describes the unique physiological and molecular adaptations of resurrection plants enabling them to withstand long periods of desiccation. The recent transcriptome analysis of Craterostigma plantagineum and Haberlea rhodopensis under drought, desiccation, and subsequent rehydration revealed common genetic pathways with other desiccation-tolerant species as well as unique genes that might contribute to the outstanding desiccation tolerance of the two resurrection species. While some of the molecular responses appear to be common for both drought stress and desiccation, resurrection plants also possess genes that are highly induced or repressed during desiccation with no apparent sequence homologies to genes of other species. Thus, resurrection plants are potential sources for gene discovery. Further proteome and metabolome analyses of the resurrection plants contributed to a better understanding of molecular mechanisms that are involved in surviving severe water loss. Understanding the cellular mechanisms of desiccation tolerance in this unique group of plants may enable future molecular improvement of drought tolerance in crop plants.

Transcription factor OsHsfC1b regulates salt tolerance and development in Oryza sativa ssp. japonica

BACKGROUND AND AIMS

Salt stress leads to attenuated growth and productivity in rice. Transcription factors like heat shock factors (HSFs) represent central regulators of stress adaptation. Heat shock factors of the classes A and B are well established as regulators of thermal and non-thermal stress responses in plants; however, the role of class C HSFs is unknown. Here we characterized the function of the OsHsfC1b (Os01g53220) transcription factor from rice.

METHODOLOGY

We analysed the expression of OsHsfC1b in the rice japonica cultivars Dongjin and Nipponbare exposed to salt stress as well as after mannitol, abscisic acid (ABA) and H(2)O(2) treatment. For functional characterization of OsHsfC1b, we analysed the physiological response of a T-DNA insertion line (hsfc1b) and two artificial micro-RNA (amiRNA) knock-down lines to salt, mannitol and ABA treatment. In addition, we quantified the expression of small Heat Shock Protein (sHSP) genes and those related to signalling and ion homeostasis by quantitative real-time polymerase chain reaction in roots exposed to salt. The subcellular localization of OsHsfC1b protein fused to green fluorescent protein (GFP) was determined in Arabidopsis mesophyll cell protoplasts.

PRINCIPAL RESULTS

Expression of OsHsfC1b was induced by salt, mannitol and ABA, but not by H(2)O(2). Impaired function of OsHsfC1b in the hsfc1b mutant and the amiRNA lines led to decreased salt and osmotic stress tolerance, increased sensitivity to ABA, and temporal misregulation of salt-responsive genes involved in signalling and ion homeostasis. Furthermore, sHSP genes showed enhanced expression in knock-down plants under salt stress. We observed retarded growth of hsfc1b and knock-down lines in comparison with control plants under non-stress conditions. Transient expression of OsHsfC1b fused to GFP in protoplasts revealed nuclear localization of the transcription factor.

CONCLUSIONS

OsHsfC1b plays a role in ABA-mediated salt stress tolerance in rice. Furthermore, OsHsfC1b is involved in the response to osmotic stress and is required for plant growth under non-stress conditions.

Plant molecular stress responses face climate change

Environmental stress factors such as drought, elevated temperature, salinity and rising CO₂ affect plant growth and pose a growing threat to sustainable agriculture. This has become a hot issue due to concerns about the effects of climate change on plant resources, biodiversity and global food security. Plant adaptation to stress involves key changes in the '-omic' architecture. Here, we present an overview of the physiological and molecular programs in stress adaptation focusing on how genes, proteins and metabolites change after individual and multiple environmental stresses. We address the role which '-omics' research, coupled to systems biology approaches, can play in future research on plants seemingly unable to adapt as well as those which can tolerate climatic change.

Cloning and characterization of HsfA2 from Lily (Lilium longiflorum)

Heat shock transcription factors (Hsfs) are the terminal components of the signal transduction chain mediating the activation of genes responsive to both heat stress and a large number of chemical stressors. This paper aims to clone Hsf from lily and characterize its function by analyses of mRNA expression, transactivation activity and thermotolerance of transgenic Arabidopsis. In this study, the gene encoding HsfA2 with 1,053 bp open reading frame (ORF) was cloned by rapid amplification of cDNA ends (RACE) technique from Lilium longiflorum 'White heaven'. Multiple alignment and phylogenetic analyses showed that the deduced protein was a novel member of the Hsf class A2. Expression analyses by RT-PCR indicated that LlHsfA2 expression was induced by heat shock and H(2)O(2) treatment, but not by NaCl. It was also found that the expression of LlHsfA2 correlated with thermotolerance in Lilium longiflorum 'White heaven' and Oriental hybrid 'Acapulco' under heat stress. Furthermore, yeast one-hybrid assay showed that LlHsfA2 had transactivation activity. In addition, overexpression of LlHsfA2 activated the downstream genes including Hsp101, Hsp70, Hsp25.3 and Apx2 and enhanced the thermotolerance of transgenic Arabidopsis plants. Taken together, our data suggest that LlHsfA2 is a novel and functional HsfA2, involved in heat signaling pathway in lily and useful for improvement of thermotolerance in transgenic plants.