bZIP17 regulates heat stress tolerance at reproductive stage in Arabidopsis

The core morning clock component CCA1 enhances UPR target gene expression to facilitate ER stress recovery

The endoplasmic reticulum (ER) is a cellular organelle responsible for protein synthesis and folding. When its protein folding capacity is exceeded, unfolded or misfolded proteins accumulate, causing ER stress and triggering the unfolded protein response (UPR) to restore ER proteostasis. Although UPR gene expression in plants follows a diel cycle, the mechanisms by which the circadian clock regulates these genes remain unclear. Here, we demonstrate that sensitivity to ER stress in root growth exhibits time-of-day phases and that the circadian clock regulates UPR target gene expression during ER stress. Notably, mutations in the core morning clock component CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) impair ER stress recovery. CCA1 forms a complex with the UPR modulator basic leucine zipper 28 (bZIP28) and acts as an upstream regulator of ER stress recovery. Upon ER stress, CCA1 is stabilized and associates with bZIP28 at the ER stress response element within the BiP3 promoter, enhancing the ER stress response. Thus, CCA1 and bZIP28 coordinate a time-dependent adaptive response to ER stress to maintain ER proteostasis. Our results suggest that the circadian clock primes the timing and levels of ER chaperone expression to enhance ER stress tolerance.

Unraveling the evolution of the ATB2 subgroup basic leucine zipper transcription factors in plants and decoding the positive effects of BdibZIP44 and BdibZIP53 on heat stress in Brachypodium distachyon

In plants, basic region/leucine zipper motif (bZIP) transcription factors (TFs) stand as pivotal regulators in a broad spectrum of developmental mechanisms and adaptive strategies against environmental pressures. However, the ancestral origins and the evolutionary progression of their functional diversity across plant species have yet to be thoroughly illuminated. This study delved into the ATB2 subgroup bZIP homologs, tracing them back to the ancestral charophyte lineage predating land plant emergence, and categorized them into four distinct phylogenetic clusters (Clades A to D). Of particular note, our findings highlighted bZIP44_GBF6 and bZIP53 orthologs as angiosperm-specific innovations, distinguished by the acquisition of novel protein motifs and an intensified regime of purifying selection, reflecting their specialized evolutionary trajectories. Through synteny analysis, we uncovered that whole-genome duplication (WGD) events, post-monocot/dicot split, have played independent yet pivotal roles in shaping the bZIP44_GBF6 and bZIP53 lineages. Furthermore, an assessment of codon usage patterns disclosed a conspicuous bias in monocots favoring G3s, C3s, Gc3s, and GC content, while demonstrating a relative avoidance of T3s, A3s, and Nc usage frequencies. Functionally, we demonstrated that BdibZIP44 and BdibZIP53, localized to the nucleus, possessed the capability to dimerize, both homotypically and heterotypically. These proteins exhibited inducible expression under heat stress conditions in Brachypodium distachyon, implicating them in thermotolerance mechanisms. Overexpression studies reinforced their positive regulatory influence on heat stress resilience by augmenting the enzymatic activity of antioxidants, including catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD), which collectively enhance the clearance of deleterious reactive oxygen species (ROS). Taken together, this research significantly advanced our understanding of the origins and the adaptive evolutionary journey of ATB2 subgroup bZIP homologs in the plant kingdom. Moreover, it elucidated the vital roles of BdibZIP44 and BdibZIP53 in orchestrating a robust defense against high-temperature stress, thereby contributing to the broader discourse on plant adaptation and survival strategies under changing climatic conditions.

ALBA3 maintains male fertility under heat stress in plants

Heat stress (HS) at the reproductive stage detrimentally affects crop yields and seed quality. However, the molecular mechanisms that protect reproductive processes in plants under HS remain largely unknown. Here, we report that Acetylation Lowers Binding Affinity 3 (ALBA3) is crucial for safeguarding male fertility against HS in Arabidopsis. ALBA3 is highly expressed in pollen, and ALBA3 is localized in the cytoplasm of both sperm and vegetative cells. Mutants lacking functional ALBA3 exhibit hypersensitivity to HS, with reduced silique length and fertility due to defects in pollen germination, pollination, pollen tube growth, and fertilization under HS. ALBA3 binds and stabilizes a subset of messenger RNAs (mRNAs) essential for pollen function, thereby protecting male fertility. Two residues in the Alba domain, K46 and L90, are critical for ALBA3's ability to bind and stabilize mRNAs and are necessary for its proper function. Interestingly, the loss of rice ALBA3 also leads to severe pollen abortion and male sterility under HS, highlighting the conserved role of ALBA3 in protecting male fertility across plant species. This study uncovers a conserved mechanism by which ALBA3 safeguards male fertility during HS by stabilizing specific mRNAs crucial for pollen function.

Morphological, Physiological, and Molecular Responses to Heat Stress in Brassicaceae

Food security is threatened by global warming, which also affects agricultural output. Various components of cells perceive elevated temperatures. Different signaling pathways in plants distinguish between the two types of temperature increases, mild warm temperatures and extremely hot temperatures. Given the rising global temperatures, heat stress has become a major abiotic challenge, affecting the growth and development of various crops and significantly reducing productivity. Brassica napus, the second-largest source of vegetable oil worldwide, faces drastic reductions in seed yield and quality under heat stress. This review summarizes recent research on the genetic and physiological impact of heat stress in the Brassicaceae family, as well as in model plants Arabidopsis and rice. Several studies show that extreme temperature fluctuations during crucial growth stages negatively affect plants, leading to impaired growth and reduced seed production. The review discusses the mechanisms of heat stress adaptation and the key regulatory genes involved. It also explores the emerging understanding of epigenetic modifications during heat stress. While such studies are limited in B. napus, contrasting trends in gene expression have been observed across different species and cultivars, suggesting these genes play a complex role in heat stress tolerance. Key knowledge gaps are identified regarding the impact of heat stress during the growth stages of B. napus. In-depth studies of these stages are still needed. The profound understanding of heat stress response mechanisms in tissue-specific models are crucial in advancing our knowledge of thermo-tolerance regulation in B. napus and supporting future breeding efforts for heat-tolerant crops.

VvFHY3 links auxin and endoplasmic reticulum stress to regulate grape anthocyanin biosynthesis at high temperatures

Anthocyanins affect quality in fruits such as grape (Vitis vinifera). High temperatures reduce anthocyanin levels by suppressing the expression of anthocyanin biosynthesis genes and decreasing the biosynthetic rate. However, the regulatory mechanisms that coordinate these 2 processes remain largely unknown. In this study, we demonstrate that high-temperature-mediated inhibition of anthocyanin biosynthesis in grape berries depends on the auxin and endoplasmic reticulum (ER) stress pathways. Inactivation of these pathways restores anthocyanin accumulation under high temperatures. We identified and characterized FAR-RED ELONGATED HYPOCOTYL3 (FHY3), a high-temperature-modulated transcription factor that activates multiple anthocyanin biosynthesis genes by binding to their promoters. The auxin response factor VvARF3 interacts with VvFHY3 and represses its transactivation activity, antagonizing VvFHY3-induced anthocyanin biosynthesis. Additionally, we found that the ER stress sensor VvbZIP17 represses anthocyanin biosynthesis. VvFHY3 suppresses VvbZIP17 activity by directly binding to the VvbZIP17 promoter to repress its transcription and by physically interacting with VvbZIP17 to block its DNA binding ability. Furthermore, AUXIN RESPONSE FACTOR 3 (ARF3) interferes with the VvFHY3-VvbZIP17 interaction, releasing VvbZIP17 to activate the unfolded protein response and further suppress anthocyanin production. Our results unravel the VvARF3-VvFHY3-VvbZIP17 regulatory module, which links the auxin and ER stress pathways to coordinately repress anthocyanin structural gene expression and biosynthesis under high-temperature stress.

Genome editing prospects for heat stress tolerance in cereal crops

The world population is steadily growing, exerting increasing pressure to feed in the future, which would need additional production of major crops. Challenges associated with changing and unpredicted climate (such as heat waves) are causing global food security threats. Cereal crops are a staple food for a large portion of the world's population. They are mostly affected by these environmentally generated abiotic stresses. Therefore, it is imperative to develop climate-resilient cultivars to support the sustainable production of main cereal crops (Rice, wheat, and maize). Among these stresses, heat stress causes significant losses to major cereals. These issues can be solved by comprehending the molecular mechanisms of heat stress and creating heat-tolerant varieties. Different breeding and biotechnology techniques in the last decade have been employed to develop heat-stress-tolerant varieties. However, these time-consuming techniques often lack the pace required for varietal improvement in climate change scenarios. Genome editing technologies offer precise alteration in the crop genome for developing stress-resistant cultivars. CRISPR/Cas9 (Clustered regularly interspaced short palindromic repeat/Cas9), one such genome editing platform, recently got scientists' attention due to its easy procedures. It is a powerful tool for functional genomics as well as crop breeding. This review will focus on the molecular mechanism of heat stress and different targets that can be altered using CRISPR/Cas genome editing tools to generate climate-smart cereal crops. Further, heat stress signaling and essential players have been highlighted to provide a comprehensive overview of the topic.

Identification of key genes and molecular pathways regulating heat stress tolerance in pearl millet to sustain productivity in challenging ecologies

Pearl millet is a nutri-cereal that is mostly grown in harsh environments, making it an ideal crop to study heat tolerance mechanisms at the molecular level. Despite having a better-inbuilt tolerance to high temperatures than other crops, heat stress negatively affects the crop, posing a threat to productivity gain. Hence, to understand the heat-responsive genes, the leaf and root samples of two contrasting pearl millet inbreds, EGTB 1034 (heat tolerant) and EGTB 1091 (heat sensitive), were subjected to heat-treated conditions and generated genome-wide transcriptomes. We discovered 13,464 differentially expressed genes (DEGs), of which 6932 were down-regulated and 6532 up-regulated in leaf and root tissues. The pairwise analysis of the tissue-based transcriptome data of the two genotypes demonstrated distinctive genotype and tissue-specific expression of genes. The root exhibited a higher number of DEGs compared to the leaf, emphasizing different adaptive strategies of pearl millet. A large number of genes encoding ROS scavenging enzymes, WRKY, NAC, enzymes involved in nutrient uptake, protein kinases, photosynthetic enzymes, and heat shock proteins (HSPs) and several transcription factors (TFs) involved in cross-talking of temperature stress responsive mechanisms were activated in the stress conditions. Ribosomal proteins emerged as pivotal hub genes, highly interactive with key genes expressed and involved in heat stress response. The synthesis of secondary metabolites and metabolic pathways of pearl millet were significantly enriched under heat stress. Comparative synteny analysis of HSPs and TFs in the foxtail millet genome demonstrated greater collinearity with pearl millet compared to proso millet, rice, sorghum, and maize. In this study, 1906 unannotated DEGs were identified, providing insight into novel participants in the molecular response to heat stress. The identified genes hold promise for expediting varietal development for heat tolerance in pearl millet and similar crops, fostering resilience and enhancing grain yield in heat-prone environments.

Transcriptome sequencing of garlic reveals key genes related to the heat stress response

With global warming, heat stress has become an important factor that seriously affects crop yield and quality. Therefore, understanding plant responses to heat stress is important for agricultural practice, but the molecular mechanism of high-temperature tolerance in garlic remains unclear. In this study, 'Xusuan No. 6' was used as the experimental material. After heat stress for 0 (CK), 2 and 24 h, transcriptome sequencing was used to screen metabolic pathways and differentially expressed genes (DEGs) closely related to heat stress and was further verified by quantitative real-time polymerase chain reaction (qRT-PCR). A total of 86,110 unigenes obtained from the raw transcriptome sequencing data were spliced. After 2 h of heat treatment, the expression levels of 8898 genes increased, and 3829 genes were decreased in leaves. After 24 h, the expression levels of 7167 genes were upregulated, and 3176 genes were downregulated. Gene Ontology enrichment analysis showed that DEGs were mainly enriched in seven categories: cellular processes, metabolic processes, binging, catalytic activity, cellular anatomical entity and protein-containing complex response to stimulus. Kyoto Encyclopedia of Genes and Genomes pathway enrichment showed that DEGs are involved in protein processing in the endoplasmic reticulum, plant hormone signal transduction, phenylpropanoid biosynthesis, and photosynthetic antenna proteins. Six genes were selected and further verified by qRT-PCR. In this study, the full-length transcriptome of garlic was constructed, and the regulatory genes related to the heat resistance of garlic were studied. Taken together, these findings can provide a theoretical basis for the cloning of heat resistance genes in garlic and for the analysis of heat resistance mechanisms.

XBAT31 regulates reproductive thermotolerance through controlling the accumulation of HSFB2a/B2b under heat stress conditions

Heat shock transcription factors (HSFs) play a crucial role in heat stress tolerance in vegetative tissues. However, their involvement in reproductive tissues and their post-translational modifications are not well understood. In this study, we identify the E3 ligase XB3 ORTHOLOG 1 IN ARABIDOPSIS THALIANA (XBAT31) as a key player in the ubiquitination and degradation of HSFB2a/B2b. Our results show that the xbat31 mutant exhibits a higher percentage of unfertile siliques and decreased expression of HSPs in flowers under heat stress conditions compared to the wild type. Conversely, the hsfb2a hsfb2b double mutant displays improved reproductive thermotolerance. We find that XBAT31 interacts with HSFB2a/B2b and mediates their ubiquitination. Furthermore, HSFB2a/B2b ubiquitination is reduced in the xbat31-1 mutant, resulting in higher accumulation of HSFB2a/B2b in flowers under heat stress conditions. Overexpression of HSFB2a or HSFB2b leads to an increase in unfertile siliques under heat stress conditions. Thus, our results dissect the important role of the XBAT31-HSFB2a/B2b module in conferring reproductive thermotolerance in plants.

Plants and global warming: challenges and strategies for a warming world

KEY MESSAGE

In this review, we made an attempt to create a holistic picture of plant response to a rising temperature environment and its impact by covering all aspects from temperature perception to thermotolerance. This comprehensive account describing the molecular mechanisms orchestrating these responses and potential mitigation strategies will be helpful for understanding the impact of global warming on plant life. Organisms need to constantly recalibrate development and physiology in response to changes in their environment. Climate change-associated global warming is amplifying the intensity and periodicity of these changes. Being sessile, plants are particularly vulnerable to variations happening around them. These changes can cause structural, metabolomic, and physiological perturbations, leading to alterations in the growth program and in extreme cases, plant death. In general, plants have a remarkable ability to respond to these challenges, supported by an elaborate mechanism to sense and respond to external changes. Once perceived, plants integrate these signals into the growth program so that their development and physiology can be modulated befittingly. This multifaceted signaling network, which helps plants to establish acclimation and survival responses enabled their extensive geographical distribution. Temperature is one of the key environmental variables that affect all aspects of plant life. Over the years, our knowledge of how plants perceive temperature and how they respond to heat stress has improved significantly. However, a comprehensive mechanistic understanding of the process still largely elusive. This review explores how an increase in the global surface temperature detrimentally affects plant survival and productivity and discusses current understanding of plant responses to high temperature (HT) and underlying mechanisms. We also highlighted potential resilience attributes that can be utilized to mitigate the impact of global warming.

NFXL1 functions as a transcriptional activator required for thermotolerance at reproductive stage in Arabidopsis

Plants are highly susceptible to abiotic stresses, particularly heat stress during the reproductive stage. However, the specific molecular mechanisms underlying this sensitivity remain largely unknown. In the current study, we demonstrate that the Nuclear Transcription Factor, X-box Binding Protein 1-Like 1 (NFXL1), directly regulates the expression of DEHYDRATION-RESPONSIVE ELEMENT-BINDING PROTEIN 2A (DREB2A), which is crucial for reproductive thermotolerance in Arabidopsis. NFXL1 is upregulated by heat stress, and its mutation leads to a reduction in silique length (seed number) under heat stress conditions. RNA-Seq analysis reveals that NFXL1 has a global impact on the expression of heat stress responsive genes, including DREB2A, Heat Shock Factor A3 (HSFA3) and Heat Shock Protein 17.6 (HSP17.6) in flower buds. Interestingly, NFXL1 is enriched in the promoter region of DREB2A, but not of either HSFA3 or HSP17.6. Further experiments using electrophoretic mobility shift assay have confirmed that NFXL1 directly binds to the DNA fragment derived from the DREB2A promoter. Moreover, effector-reporter assays have shown that NFXL1 activates the DREB2A promoter. The DREB2A mutants are also heat stress sensitive at the reproductive stage, and DEREB2A is epistatic to NFXL1 in regulating thermotolerance in flower buds. It is known that HSFA3, a direct target of DREB2A, regulates the expression of heat shock proteins genes under heat stress conditions. Thus, our findings establish NFXL1 as a critical upstream regulator of DREB2A in the transcriptional cassette responsible for heat stress responses required for reproductive thermotolerance in Arabidopsis.

Genome-wide identification of bZIP gene family and expression analysis of BhbZIP58 under heat stress in wax gourd

BACKGROUND

The basic leucine zipper (bZIP) transcription factor family is one of the most abundant and evolutionarily conserved gene families in plants. It assumes crucial functions in the life cycle of plants, including pathogen defense, secondary metabolism, stress response, seed maturation, and flower development. Although the genome of wax gourd has been published, little is known about the functions, evolutionary background, and gene expression patterns of the bZIP gene family, which limits its utilization.

RESULTS

A total of 61 bZIP genes (BhbZIPs) were identified from wax gourd (Benincasa hispida) genome and divided into 12 subgroups. Whole-genome duplication (WGD) and dispersed duplication (DSD) were the main driving forces of bZIP gene family expansion in wax gourd, and this family may have undergone intense purifying selection pressure during the evolutionary process. We selected BhbZIP58, only one in the member of subgroup B, to study its expression patterns under different stresses, including heat, salt, drought, cold stress, and ABA treatment. Surprisingly, BhbZIP58 had a dramatic response under heat stress. BhbZIP58 showed the highest expression level in the root compared with leaves, stem, stamen, pistil, and ovary. In addition, BhbZIP58 protein was located in the nucleus and had transcriptional activation activity. Overexpression of BhbZIP58 in Arabidopsis enhanced their heat tolerance.

CONCLUSIONS

In this study, bZIP gene family is systematically bioinformatically in wax gourd for the first time. Particularly, BhbZIP58 may have an important role in heat stress. It will facilitate further research on the bZIP gene family regarding their evolutionary history and biological functions.

CRISPR-Cas-mediated unfolded protein response control for enhancing plant stress resistance

Plants consistently encounter environmental stresses that negatively affect their growth and development. To mitigate these challenges, plants have developed a range of adaptive strategies, including the unfolded protein response (UPR), which enables them to manage endoplasmic reticulum (ER) stress resulting from various adverse conditions. The CRISPR-Cas system has emerged as a powerful tool for plant biotechnology, with the potential to improve plant tolerance and resistance to biotic and abiotic stresses, as well as enhance crop productivity and quality by targeting specific genes, including those related to the UPR. This review highlights recent advancements in UPR signaling pathways and CRISPR-Cas technology, with a particular focus on the use of CRISPR-Cas in studying plant UPR. We also explore prospective applications of CRISPR-Cas in engineering UPR-related genes for crop improvement. The integration of CRISPR-Cas technology into plant biotechnology holds the promise to revolutionize agriculture by producing crops with enhanced resistance to environmental stresses, increased productivity, and improved quality traits.

Dynamic transcriptome analysis unravels key regulatory genes of maize root growth and development in response to potassium deficiency

MAIN CONCLUSION

Integrated root phenotypes and transcriptome analysis have revealed key candidate genes responsible for maize root growth and development in potassium deficiency. Potassium (K) is a vital macronutrient for plant growth, but our understanding of its regulatory mechanisms in maize root system architecture (RSA) and K+ uptake remains limited. To address this, we conducted hydroponic and field trials at different growth stages. K+ deficiency significantly inhibited maize root growth, with metrics like total root length, primary root length, width and maximum root number reduced by 50% to 80% during early seedling stages. In the field, RSA traits exhibited maximum values at the silking stage but continued to decline thereafter. Furthermore, K deprivation had a pronounced negative impact on root morphology and RSA growth and grain yield. RNA-Seq analysis identified 5972 differentially expressed genes (DEGs), including 17 associated with K+ signaling, transcription factors, and transporters. Weighted gene co-expression network analysis revealed 23 co-expressed modules, with enrichment of transcription factors at different developmental stages under K deficiency. Several DEGs and transcription factors were predicted as potential candidate genes responsible for maize root growth and development. Interestingly, some of these genes exhibited homology to well-known regulators of root architecture or development in Arabidopsis, such as Zm00001d014467 (AtRCI3), Zm00001d011237 (AtWRKY9), and Zm00001d030862 (AtAP2/ERF). Identifying these key genes helps to provide a deeper understanding of the molecular mechanisms governing maize root growth and development under nutrient deficient conditions offering potential benefits for enhancing maize production and improving stress resistance through targeted manipulation of RSA traits in modern breeding efforts.

Epigenetic and transcription factors synergistically promote the high temperature response in plants

Temperature is one of the main environmental cues affecting plant growth and development, and plants have evolved multiple mechanisms to sense and acclimate to high temperature. Emerging research has shown that transcription factors, epigenetic factors, and their coordination are essential for plant temperature responses and the resulting phenological adaptation. Here, we summarize recent advances in molecular and cellular mechanisms to understand how plants acclimate to high temperature and describe how plant meristems sense and integrate environmental signals. Furthermore, we lay out future directions for new technologies to reveal heterogeneous responses in different cell types thus improving plant environmental plasticity.

Transcriptional Regulators of Plant Adaptation to Heat Stress

Heat stress (HS) is becoming an increasingly large problem for food security as global warming progresses. As sessile species, plants have evolved different mechanisms to cope with the disruption of cellular homeostasis, which can impede plant growth and development. Here, we summarize the mechanisms underlying transcriptional regulation mediated by transcription factors, epigenetic regulators, and regulatory RNAs in response to HS. Additionally, cellular activities for adaptation to HS are discussed, including maintenance of protein homeostasis through protein quality control machinery, and autophagy, as well as the regulation of ROS homeostasis via a ROS-scavenging system. Plant cells harmoniously regulate their activities to adapt to unfavorable environments. Lastly, we will discuss perspectives on future studies for improving urban agriculture by increasing crop resilience to HS.

De novo full-length transcriptome analysis of two ecotypes of Phragmites australis (swamp reed and dune reed) provides new insights into the transcriptomic complexity of dune reed and its long-term adaptation to desert environments

BACKGROUND

The extremely harsh environment of the desert is changing dramatically every moment, and the rapid adaptive stress response in the short term requires enormous energy expenditure to mobilize widespread regulatory networks, which is all the more detrimental to the survival of the desert plants themselves. The dune reed, which has adapted to desert environments with complex and variable ecological factors, is an ideal type of plant for studying the molecular mechanisms by which Gramineae plants respond to combinatorial stress of the desert in their natural state. But so far, the data on the genetic resources of reeds is still scarce, therefore most of their research has focused on ecological and physiological studies.

RESULTS

In this study, we obtained the first De novo non-redundant Full-Length Non-Chimeric (FLNC) transcriptome databases for swamp reeds (SR), dune reeds (DR) and the All of Phragmites australis (merged of iso-seq data from SR and DR), using PacBio Iso-Seq technology and combining tools such as Iso-Seq3 and Cogent. We then identified and described long non-coding RNAs (LncRNA), transcription factor (TF) and alternative splicing (AS) events in reeds based on a transcriptome database. Meanwhile, we have identified and developed for the first time a large number of candidates expressed sequence tag-SSR (EST-SSRs) markers in reeds based on UniTransModels. In addition, through differential gene expression analysis of wild-type and homogenous cultures, we found a large number of transcription factors that may be associated with desert stress tolerance in the dune reed, and revealed that members of the Lhc family have an important role in the long-term adaptation of dune reeds to desert environments.

CONCLUSIONS

Our results provide a positive and usable genetic resource for Phragmites australis with a widespread adaptability and resistance, and provide a genetic database for subsequent reeds genome annotation and functional genomic studies.

The hot science in rice research: How rice plants cope with heat stress

Global climate change has great impacts on plant growth and development, reducing crop productivity worldwide. Rice (Oryza sativa L.), one of the world's most important food crops, is susceptible to high-temperature stress from seedling stage to reproductive stage. In this review, we summarize recent advances in understanding the molecular mechanisms underlying heat stress responses in rice, including heat sensing and signalling, transcriptional regulation, transcript processing, protein translation, and post-translational regulation. We also highlight the irreversible effects of high temperature on reproduction and grain quality in rice. Finally, we discuss challenges and opportunities for future research on heat stress responses in rice.

A competition-attenuation mechanism modulates thermoresponsive growth at warm temperatures in plants

Global warming has profound impact on growth and development, and plants constantly adjust their internal circadian clock to cope with external environment. However, how clock-associated genes fine-tune thermoresponsive growth in plants is little understood. We found that loss-of-function mutation of REVEILLE5 (RVE5) reduces the expression of circadian gene EARLY FLOWERING 4 (ELF4) in Arabidopsis, and confers accelerated hypocotyl growth under warm-temperature conditions. Both RVE5 and CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) accumulate at warm temperatures and bind to the same EE cis-element presented on ELF4 promoter, but the transcriptional repression activity of RVE5 is weaker than that of CCA1. The binding of CCA1 to ELF4 promoter is enhanced in the rve5-2 mutant at warm temperatures, and overexpression of ELF4 in the rve5-2 mutant background suppresses the rve5-2 mutant phenotype at warm temperatures. Therefore, the transcriptional repressor RVE5 finetunes ELF4 expression via competing at a cis-element with the stronger transcriptional repressor CCA1 at warm temperatures. Such a competition-attenuation mechanism provides a balancing system for modulating the level of ELF4 and thermoresponsive hypocotyl growth under warm-temperature conditions.

m6A RNA methylation impairs gene expression variability and reproductive thermotolerance in Arabidopsis

Heat-imposed crop failure is often attributed to reduced thermotolerance of floral tissues; however, the underlying mechanism remains unknown. Here, we demonstrate that m⁶A RNA methylation increases in Arabidopsis flowers and negatively regulates gene expression variability. Stochastic gene expression provides flexibility to cope with environmental stresses. We find that reduced transcriptional fluctuation is associated with compromised activation of heat-responsive genes. Moreover, disruption of an RNA demethylase AtALKBH10B leads to lower gene expression variability, suppression of heat-activated genes, and strong reduction of plant fertility. Our work proposes a novel role for RNA methylation in the bet-hedging strategy of heat stress response.

ER Stress and the Unfolded Protein Response: Homeostatic Regulation Coordinate Plant Survival and Growth

The endoplasmic reticulum (ER), a eukaryotic organelle, is the major site of protein biosynthesis. The disturbance of ER function by biotic or abiotic stress triggers the accumulation of misfolded or unfolded proteins in the ER. The unfolded protein response (UPR) is the best-studied ER stress response. This transcriptional regulatory system senses ER stress, activates downstream genes that function to mitigate stress, and restores homeostasis. In addition to its conventional role in stress responses, recent reports indicate that the UPR is involved in plant growth and development. In this review, we summarize the current knowledge of ER stress sensing and the activation and downstream regulation of the UPR. We also describe how the UPR modulates both plant growth and stress tolerance by maintaining ER homeostasis. Lastly, we propose that the UPR is a major component of the machinery that balances the trade-off between plant growth and survival in a dynamic environment.

Unfolded protein response in balancing plant growth and stress tolerance

The ER (endoplasmic reticulum) is the largest membrane-bound multifunctional organelle in eukaryotic cells, serving particularly important in protein synthesis, modification, folding and transport. UPR (unfolded protein response) is one of the systematized strategies that eukaryotic cells employ for responding to ER stress, a condition represents the processing capability of ER is overwhelmed and stressed. UPR is usually triggered when the protein folding capacity of ER is overloaded, and indeed, mounting studies were focused on the stress responding side of UPR. In plants, beyond stress response, accumulating evidence suggests that UPR is essential for growth and development, and more importantly, the necessity of UPR in this regard requires its endogenous basal activation even without stress. Then plants must have to fine tune the activation level of UPR pathway for balancing growth and stress response. In this review, we summarized the recent progresses in plant UPR, centering on its role in controlling plant reproduction and root growth, and lay out some outstanding questions to be addressed in the future.

Reproductive-Stage Heat Stress in Cereals: Impact, Plant Responses and Strategies for Tolerance Improvement

Reproductive-stage heat stress (RSHS) poses a major constraint to cereal crop production by damaging main plant reproductive structures and hampering reproductive processes, including pollen and stigma viability, pollination, fertilization, grain setting and grain filling. Despite this well-recognized fact, research on crop heat stress (HS) is relatively recent compared to other abiotic stresses, such as drought and salinity, and in particular, RSHS studies in cereals are considerably few in comparison with seedling-stage and vegetative-stage-centered studies. Meanwhile, climate change-exacerbated HS, independently or synergistically with drought, will have huge implications on crop performance and future global food security. Fortunately, due to their sedentary nature, crop plants have evolved complex and diverse transient and long-term mechanisms to perceive, transduce, respond and adapt to HS at the molecular, cell, physiological and whole plant levels. Therefore, uncovering the molecular and physiological mechanisms governing plant response and tolerance to RSHS facilitates the designing of effective strategies to improve HS tolerance in cereal crops. In this review, we update our understanding of several aspects of RSHS in cereals, particularly impacts on physiological processes and yield; HS signal perception and transduction; and transcriptional regulation by heat shock factors and heat stress-responsive genes. We also discuss the epigenetic, post-translational modification and HS memory mechanisms modulating plant HS tolerance. Moreover, we offer a critical set of strategies (encompassing genomics and plant breeding, transgenesis, omics and agronomy) that could accelerate the development of RSHS-resilient cereal crop cultivars. We underline that a judicious combination of all of these strategies offers the best foot forward in RSHS tolerance improvement in cereals. Further, we highlight critical shortcomings to RSHS tolerance investigations in cereals and propositions for their circumvention, as well as some knowledge gaps, which should guide future research priorities. Overall, our review furthers our understanding of HS tolerance in plants and supports the rational designing of RSHS-tolerant cereal crop cultivars for the warming climate.

Proteolytic Activation of Plant Membrane-Bound Transcription Factors

Due to the presence of a transmembrane domain, the subcellular mobility plan of membrane-bound or membrane-tethered transcription factors (MB-TFs) differs from that of their cytosolic counterparts. The MB-TFs are mostly locked in (sub)cellular membranes, until they are released by a proteolytic cleavage event or when the transmembrane domain (TMD) is omitted from the transcript due to alternative splicing. Here, we review the current knowledge on the proteolytic activation mechanisms of MB-TFs in plants, with a particular focus on regulated intramembrane proteolysis (RIP), and discuss the analogy with the proteolytic cleavage of MB-TFs in animal systems. We present a comprehensive inventory of all known and predicted MB-TFs in the model plant Arabidopsis thaliana and examine their experimentally determined or anticipated subcellular localizations and membrane topologies. We predict proteolytically activated MB-TFs by the mapping of protease recognition sequences and structural features that facilitate RIP in and around the TMD, based on data from metazoan intramembrane proteases. Finally, the MB-TF functions in plant responses to environmental stresses and in plant development are considered and novel functions for still uncharacterized MB-TFs are forecasted by means of a regulatory network-based approach.