Role In Heat Tolerance Research Articles

The ZmHSF08-ZmUGT92A1 module regulates heat tolerance by altering reactive oxygen species levels in maize

GTs (Glycosyltransferases) are important in plant growth and abiotic stresses. However, its role in maize heat response is far from clear. Here, we describe the constitutively expressed UDP-glycosyltransferase ZmUGT92A1, which has a highly conserved PSPG box and is localized in chloroplasts, is induced under heat stress. Functional disruption of ZmUGT92A1 leads to heat sensitivity and reactive oxygen species accumulation in maize. Metabolomics analysis revealed that ZmUGT92A1 affected multiple metabolic pathways and altered the metabolic homeostasis of flavonoids under heat stress. In vitro assay showed ZmUGT92A1 exhibits glycosyltransferase activity on flavonoids and hormones. Additionally, we identified a rapidly heat-induced transcription factor, ZmHSF08, which can directly bind and repress the promoter region of ZmUGT92A1. The ZmHSF08 overexpression line exhibits heat sensitivity and reactive oxygen species accumulation. These findings reveal that the ZmHSF08-ZmUGT92A1 module plays a role in heat tolerance in maize and provide candidate strategies for the development of heat-tolerant varieties.

Genome-wide expression analysis of novel heat-responsive microRNAs and their targets in contrasting wheat genotypes at reproductive stage under terminal heat stress.

Heat stress at terminal stage of wheat is critical and leads to huge yield losses worldwide. microRNAs (miRNAs) play significant regulatory roles in gene expression associated with abiotic and biotic stress at the post-transcriptional level. In the present study, we carried out a comparative analysis of miRNAs and their targets in flag leaves as well as developing seeds of heat tolerant (RAJ3765) and heat susceptible (HUW510) wheat genotypes under heat stress and normal conditions using small RNA and degradome sequencing. A total of 84 conserved miRNAs belonging to 35 miRNA families and 93 novel miRNAs were identified in the 8 libraries. Tae-miR9672a-3p, tae-miR9774, tae-miR9669-5p, and tae-miR5048-5p showed the highest expression under heat stress. Tae-miR9775, tae-miR9662b-3p, tae-miR1120a, tae-miR5084, tae-miR1122a, tae-miR5085, tae-miR1118, tae-miR1130a, tae-miR9678-3p, tae-miR7757-5p, tae-miR9668-5p, tae-miR5050, tae-miR9652-5p, and tae-miR9679-5p were expressed only in the tolerant genotype, indicating their role in heat tolerance. Comparison between heat-treated and control groups revealed that 146 known and 57 novel miRNAs were differentially expressed in the various tissues. Eight degradome libraries sequence identified 457 targets of the differentially expressed miRNAs. Functional analysis of the targets indicated their involvement in photosynthesis, spliceosome, biosynthesis of nucleotide sugars and protein processing in the endoplasmic reticulum, arginine and proline metabolism and endocytosis. This study increases the number of identified and novel miRNAs along with their roles involved in heat stress response in contrasting genotypes at two developing stages of wheat.

Novel discovery in roles of structural variations and RWP-RK transcription factors in heat tolerance for pearl millet

Global warming adversely affects crop production worldwide. Massive efforts have been undertaken to study mechanisms regulating heat tolerance in plants. However, the roles of structural variations (SVs) in heat stress tolerance remain unclear. In a recent article, Yan et al. (Nat Genet 1–12, 2023) constructed the first pan-genome of pearl millet (Pennisetum glaucum) and identified key SVs linked to genes involved in regulating plant tolerance to heat stress for an important crop with a superior ability to thrive in extremely hot and arid climates. Through multi-omics analyses integrating by pan-genomics, comparative genomics, transcriptomics, population genetics and and molecular biological technologies, they found RWP-RK transcription factors cooperating with endoplasmic reticulum-related genes play key roles in heat tolerance in pearl millet. The results in this paper provided novel insights to advance the understanding of the genetic and genomic basis of heat tolerance and an exceptional resource for molecular breeding to improve heat tolerance in pearl millet and other crops.

The spliceophilin CYP18-2 is mainly involved in the splicing of retained introns under heat stress in Arabidopsis.

Peptidyl-prolyl isomerase-like 1 (PPIL1) is associated with the human spliceosome complex. However, its function in pre-mRNA splicing remains unclear. In this study, we show that Arabidopsis thaliana CYCLOPHILIN 18-2 (AtCYP18-2), a PPIL1 homolog, plays an essential role in heat tolerance by regulating pre-mRNA splicing. Under heat stress conditions, AtCYP18-2 expression was upregulated in mature plants and GFP-tagged AtCYP18-2 redistributed to nuclear and cytoplasmic puncta. We determined that AtCYP18-2 interacts with several spliceosome complex BACT components in nuclear puncta and is primarily associated with the small nuclear RNAs U5 and U6 in response to heat stress. The AtCYP18-2 loss-of-function allele cyp18-2 engineered by CRISPR/Cas9-mediated gene editing exhibited a hypersensitive phenotype to heat stress relative to the wild type. Moreover, global transcriptome profiling showed that the cyp18-2 mutation affects alternative splicing of heat stress-responsive genes under heat stress conditions, particularly intron retention (IR). The abundance of most intron-containing transcripts of a subset of genes essential for thermotolerance decreased in cyp18-2 compared to the wild type. Furthermore, the intron-containing transcripts of two heat stress-related genes, HEAT SHOCK PROTEIN 101 (HSP101) and HEAT SHOCK FACTOR A2 (HSFA2), produced functional proteins. HSP101-IR-GFP localization was responsive to heat stress, and HSFA2-III-IR interacted with HSF1 and HSP90.1 in plant cells. Our findings reveal that CYP18-2 functions as a splicing factor within the BACT spliceosome complex and is crucial for ensuring the production of adequate levels of alternatively spliced transcripts to enhance thermotolerance.

High-throughput identification of novel heat tolerance genes via genome-wide pooled mutant screens in the model green alga Chlamydomonasreinhardtii.

Different high temperatures adversely affect crop and algal yields with various responses in photosynthetic cells. The list of genes required for thermotolerance remains elusive. Additionally, it is unclear how carbon source availability affects heat responses in plants and algae. We utilized the insertional, indexed, genome-saturating mutant library of the unicellular, eukaryotic green alga Chlamydomonas reinhardtii to perform genome-wide, quantitative, pooled screens under moderate (35°C) or acute (40°C) high temperatures with or without organic carbon sources. We identified heat-sensitive mutants based on quantitative growth rates and identified putative heat tolerance genes (HTGs). By triangulating HTGs with heat-induced transcripts or proteins in wildtype cultures and MapMan functional annotations, we presented a high/medium-confidence list of 933 Chlamydomonas genes with putative roles in heat tolerance. Triangulated HTGs include those with known thermotolerance roles and novel genes with little or no functional annotation. About 50% of these high-confidence HTGs in Chlamydomonas have orthologs in green lineage organisms, including crop species. Arabidopsis thaliana mutants deficient in the ortholog of a high-confidence Chlamydomonas HTG were also heat sensitive. This work expands our knowledge of heat responses in photosynthetic cells and provides engineering targets to improve thermotolerance in algae and crops.

A MITE variation-associated heat-inducible isoform of a heat-shock factor confers heat tolerance through regulation of JASMONATE ZIM-DOMAIN genes in rice.

High temperatures cause huge yield losses in rice. Heat-shock factors (Hsfs) are key transcription factors which regulate the expression of heat stress-responsive genes, but natural variation in and functional characterization of Hsfs have seldom been reported. A significant heat response locus was detected via a genome-wide association study (GWAS) using green leaf area as an indicative trait. A miniature inverted-repeat transposable element (MITE) in the promoter of a candidate gene, HTG3 (heat-tolerance gene on chromosome 3), was found to be significantly associated with heat-induced expression of HTG3 and heat tolerance (HT). The MITE-absent variant has been selected in heat-prone rice-growing regions. HTG3a is an alternatively spliced isoform encoding a functional Hsf, and experiments using overexpression and knockout rice lines showed that HTG3a positively regulates HT at both vegetative and reproductive stages. The HTG3-regulated genes were enriched for heat shock proteins and jasmonic acid signaling. Two heat-responsive JASMONATE ZIM-DOMAIN (JAZ) genes were confirmed to be directly upregulated by HTG3a, and one of them, OsJAZ9, positively regulates HT. We conclude that HTG3 plays an important role in HT through the regulation of JAZs and other heat-responsive genes. The MITE-absent allele may be valuable for HT breeding in rice.

Genome-Wide Analysis of Late Embryogenesis Abundant Protein Gene Family in Vigna Species and Expression of VrLEA Encoding Genes in Vigna glabrescens Reveal Its Role in Heat Tolerance.

Late embryogenesis abundant (LEA) proteins are identified in many crops for their response and role in adaptation to various abiotic stresses, such as drought, salinity, and temperature. The LEA genes have been studied systematically in several crops but not in Vigna crops. In this study, we reported the first comprehensive analysis of the LEA gene family in three legume species, namely, mung bean (Vigna radiata), adzuki bean (Vigna angularis), and cowpea (Vigna unguiculata), and the cross-species expression of VrLEA genes in a wild tetraploid species, Vigna glabrescens. A total of 201 LEA genes from three Vigna crops were identified harboring the LEA conserved motif. Among these 55, 64, and 82 LEA genes were identified in mung bean, adzuki bean, and cowpea genomes, respectively. These LEA genes were grouped into eight different classes. Our analysis revealed that the cowpea genome comprised all eight classes of LEA genes, whereas the LEA-6 class was absent in the mung bean genome. Similarly, LEA-5 and LEA-6 were absent in the adzuki bean genome. The analysis of LEA genes provides an insight into their structural and functional diversity in the Vigna genome. The genes, such as VrLEA-2, VrLEA-40, VrLEA-47, and VrLEA-55, were significantly upregulated in the heat-tolerant genotype under stress conditions indicating the basis of heat tolerance. The successful amplification and expression of VrLEA genes in V. glabrescens indicated the utility of the developed markers in mung bean improvement. The results of this study increase our understanding of LEA genes and provide robust candidate genes for future functional investigations and a basis for improving heat stress tolerance in Vigna crops.

Uncovering the Gene Regulatory Network of Maize Hybrid ZD309 under Heat Stress by Transcriptomic and Metabolomic Analysis.

Maize is an important cereal crop but is sensitive to heat stress, which significantly restricts its grain yield. To explore the molecular mechanism of maize heat tolerance, a heat-tolerant hybrid ZD309 and its parental lines (H39_1 and M189) were subjected to heat stress, followed by transcriptomic and metabolomic analyses. After six-day-heat treatment, the growth of ZD309 and its parental lines were suppressed, showing dwarf stature and rolled leaf compared with the control plants. ZD309 exhibited vigorous growth; however, M189 displayed superior heat tolerance. By transcriptomic and metabolomic analysis, hundreds to thousands of differentially expressed genes (DEGs) and metabolites (DEMs) were identified. Notably, the female parent H39 shares more DEGs and DEMs with the hybrid ZD309, indicating more genetic gain derived from the female instead of the male. A total of 299 heat shock genes detected among three genotypes were greatly aggregated in sugar transmembrane transporter activity, plasma membrane, photosynthesis, protein processing in the endoplasmic reticulum, cysteine, and methionine metabolism. A total of 150 heat-responsive metabolites detected among three genotypes were highly accumulated, including jasmonic acid, amino acids, sugar, flavonoids, coumarin, and organic acids. Integrating transcriptomic and metabolomic assays revealed that plant hormone signal transduction, cysteine, and methionine metabolism, and α-linolenic acid metabolism play crucial roles in heat tolerance in maize. Our research will be facilitated to identify essential heat tolerance genes in maize, thereby contributing to breeding heat resistance maize varieties.

Proteome changes and associated physiological roles in chickpea (Cicer arietinum) tolerance to heat stress under field conditions.

Interrogative proteome analyses are used to identify and quantify the expression of proteins involved in heat tolerance and to identify associated physiological processes in heat-stressed plants. The objectives of the study were to identify and quantify the expression of proteins involved in heat tolerance and to identify associated physiological processes in chickpea (Cicer arietinum L.) heat-tolerant (Acc#7) and sensitive genotype (Acc#8) from a field study. Proteomic and gene ontological analyses showed an upregulation in proteins related to protein synthesis, intracellular traffic, defence and transport in the heat-tolerant genotype compared to the susceptible one at the warmer site. Results from KEGG analyses indicate the involvement of probable sucrose-phosphate synthase (EC 2.4.1.14) and sucrose-phosphate phosphatase (EC 3.1.3.24) proteins, that were upregulated in the heat-tolerant genotype at the warmer site, in the starch and sucrose pathway. The presence of these differentially regulated proteins including HSP70, ribulose bisphosphate carboxylase/oxygenase activase, plastocyanin and protoporphyrinogen oxidase suggests their potential role in heat tolerance, at flowering growth stage, in field-grown chickpea. This observation supports unaltered physiological and biochemical performance of the heat-tolerant genotypes (Acc#7) relative to the susceptible genotype (Acc#8) in related studies (Makonya et al. 2019). Characterisation of the candidate proteins identified in the current study as well as their specific roles in the tolerance to heat stress in chickpea are integral to further crop improvement initiatives.

Downregulation of PyHRG1, encoding a novel secretory protein in the red alga Pyropia yezoensis, enhances heat tolerance

An increase in seawater temperature owing to global warming is expected to substantially limit the growth of marine algae, including Pyropia yezoensis, a commercially valuable red alga. To improve our knowledge of the genes involved in the acquisition of heat tolerance in P. yezoensis, transcriptomes sequences were obtained from both the wild-type SG104 P. yezoensis and heat-tolerant mutant Gy500. We selected 1,251 differentially expressed genes that were up- or downregulated in response to the heat stress condition and in the heat-tolerant mutant Gy500, based on fragment per million reads expression values. Among them, PyHRG1 was downregulated under heat stress in SG104 and expressed at a low level in Gy500. PyHRG1 encodes a secretory protein of 26.5 kDa. PyHRG1 shows no significant sequence homology with any known genes deposited in public databases to date. However, PyHRG1 homologs were found in other red algae, including other Pyropia species. When PyHRG1 was introduced into the single-cell green alga Chlamydomonas reinhardtii, transformed cells overexpressing PyHRG1 showed severely retarded growth. These results demonstrate that PyHRG1 encodes a novel red algae-specific protein and plays a role in heat tolerance in algae. The transcriptome sequences obtained in this study, which include PyHRG1, will facilitate future studies to understand the molecular mechanisms involved in heat tolerance in red algae.

Methylome Patterns of Cattle Adaptation to Heat Stress.

Heat stress has a detrimental impact on cattle health, welfare and productivity by affecting gene expression, metabolism and immune response, but little is known on the epigenetic mechanisms mediating the effect of temperature at the cellular and organism level. In this study, we investigated genome-wide DNA methylation in blood samples collected from 5 bulls of the heat stress resilient Nellore breed and 5 bulls of the Angus that are more heat stress susceptible, exposed to the sun and high temperature-high humidity during the summer season of the Brazilian South-East region. The methylomes were analyzed during and after the exposure by Reduced Representation Bisulfite Sequencing, which provided genome-wide single-base resolution methylation profiles. Significant methylation changes between stressful and recovery periods were observed in 819 genes. Among these, 351 were only seen in Angus, 366 were specific to Nellore, and 102 showed significant changes in methylation patterns in both breeds. KEGG and Gene Ontology (GO) enrichment analyses showed that responses were breed-specific. Interestingly, in Nellore significant genes and pathways were mainly involved in stress responses and cellular defense and were under methylated during heat stress, whereas in Angus the response was less focused. These preliminary results suggest that heat challenge induces changes in methylation patterns in specific loci, which should be further scrutinized to assess their role in heat tolerance.

An Ethylene Over-Producing Mutant of Tomato (<i>Solanum lycopersicum</i>), Epinastic, Exhibits Tolerance to High Temperature Conditions

Above-optimal temperatures reduce yield in many crops, including tomato, largely because of the heat-sensitivity of their reproduction process. A full understanding of heat-stress (HS) response and thermotolerance of tomato reproduction is still lacking. Recently, using external application of the plant hormone ethylene, it was demonstrated that ethylene plays a role in heat-tolerance of tomato pollen (the male reproductive cells). In order to expand our understanding on involvement of ethylene in tomato pollen thermotolerance, we analyzed the response of wild type and ethylene-related tomato mutant plants to HS, at physiological and molecular levels. We report that mild chronic HS conditions highly reduce the number of viable and germinating pollen grains as well as the production of seeded fruits in wild type tomato plants, while no significant reduction was detected/observed in pollen quality, number of seeded fruits and seeds per fruit in plants of the ethylene over-producer mutant epinastic. Our findings suggest that ethylene is involved in thermotolerance of tomato reproduction, pointing to an effect on pollen viability and germination potential, highlighting candidate genes involved in pollen response to HS (like SlHSP17, SlHSP101, SlMBF1) and suggesting directions for further studies.

Comprehensive identification and analyses of the Hsf gene family in the whole-genome of three Apiaceae species

Apiaceae is a major family from Apiales and includes many important vegetable and medicinal crops. Heat shock transcription factors (Hsf) play important roles in heat tolerance during plant development. Here, we conducted systematic analyses of the Hsf gene family in three Apiaceae species, including 17 Apium graveolens (celery), 32 Coriandrum sativum (coriander), and 14 Daucus carota (carrot). A total of 73 Hsf genes were identified in three representative species, including Arabidopsis thaliana, Vitis vinifera, and Lactuca sativa. Whole-genome duplication played important roles in the Hsf gene family's expansion within Apiaceae. Interestingly, we found that coriander had more Hsf genes than celery and carrot due to greater expansion and fewer losses. Twenty-seven branches of the phylogenetic tree underwent considerable positive selection in these Apiaceae species. We also explored the expression patterns of Hsf genes in three plant organs. Collectively, this study will serve as a rich gene resource for exploring the molecular mechanisms of heat tolerance. Additionally, this is the first study to report on the Hsf gene family in Apiaceae; thus, our research will provide guidance for future comparative and functional genomic studies on the Hsf gene family and others in Apiaceae.

AtHsc70‐1 negatively regulates the basal heat tolerance in Arabidopsis thaliana through affecting the activity of HsfAs and Hsp101

Heat shock protein 70 (Hsp70) chaperones are highly conserved and essential proteins with diverse cellular functions, including plant abiotic stress tolerance. Hsp70 proteins have been linked with basal heat tolerance in plants. Hsp101 likewise is an important chaperone protein that plays a critical role in heat tolerance in plants. We observed that Arabidopsis hsc70-1 mutant seedlings show elevated basal heat tolerance compared with wild-type. Over-expression of Hsc70-1 resulted in increased heat sensitivity. Hsp101 transcript and protein levels were increased during non-heat stress (HS) and post-HS conditions in hsc70-1 mutant seedlings. In contrast, Hsp101 was repressed in Hsc70-1 over-expressing plants after post-HS conditions. Hsc70-1 showed physical interaction with HsfA1d and HsfA1e protein in the cytosol under non-HS conditions. In transient reporter gene analysis, HsfA1d, HsfA1e and HsfA2 showed transcriptional response on the Hsp101 promoter. HsfA1d and HsfA2 transcripts were at higher levels in hsc70-1 mutant compared with wild-type. We provide genetic evidence that Hsc70-1 is a negative regulator affecting HsfA1d/A1e/A2 activators, which in turn regulate Hsp101 expression and basal thermotolerance.

Heat Stress Effects and Tolerance in Wheat: A Review

Wheat is a major cereal crop and considered as source of basic calories and protein for more than 80% of the world population. Regarding the global climate change at the past few decades, the impact of rising temperature on wheat production is gaining concern worldwide. Heat and drought are the major abiotic stress limiting the wheat production. Heat stress interrupts the important physiological and biochemical process of the plant. High temperature stress reduces grain number, photosynthetic activity and chlorophyll content and starch synthesis in the endosperm. Reactive oxygen species accumulated under heat stress cause severe oxidative damage to the crop. Plant rapidly produces heat shock proteins to minimize the effect of heat stress. Several traits such as stay green, chlorophyll fluorescence and canopy temperature play significant role in heat tolerance. In order to develop new crop varieties that can cope with future climate, knowledge of heat stress effect and tolerance at physiological, biochemical and morphological level is highly important.

The transcriptional and post-transcriptional regulation in perennial creeping bentgrass in response to γ-aminobutyric acid (GABA) and heat stress

Persistent high temperature inhibits plant growth and development. The γ-aminobutyric acid (GABA) plays a key role in heat tolerance in plants. The increase in endogenous GABA level induced by exogenous GABA effectively alleviated heat damage in creeping bentgrass. Global investigation into mRNAs and miRNAs found that the regulation of HSFs pathways and enhanced carbon metabolism, biosynthesis of amino acids, and plant hormone signal transduction were important adaptive response to heat stress. GABA-induced heat tolerance was closely related to phenylpropanoid biosynthesis, further improved HSFs pathways, and the upregulation of CAD3, ACS, AER, and CA1 associated with lignin and lipids biosynthesis, photosynthesis and water use, and antioxidant defense. Dramatic changes of miR398s, cca-miR156b, aly-miR159c-3p, and ata-miR408-3p had a close correlation with heat-survival. The especial vvi-miR845c, ama-miR156, and other novel miRNAs such as novel-24223, novel-2964, and novel-10098 could be involved in GABA-regulated heat tolerance. The integrated analysis of mRNAs and miRNAs facilitates uncovering of adaptative response in perennial plants under high temperature environmental condition and also reveals that GABA acting as a critical plant growth regulator induces heat tolerance in creeping bentgrass involved in physiological, transcriptional, and post-transcriptional regulation. Particularly, current results provide some key candidate genes and miRNAs for further investigating their potential roles in heat tolerance in non-model plants.

PtsHSP19.6, a small heat-shock protein from the marine red alga Pyropia tenera (Rhodophyta), aggregates into granules and enhances heat tolerance

The marine red alga Pyropia tenera (Rhodophyta) is one of the most valuable and widely cultivated Pyropia species. Temperature is a major factor that affects the growth and life cycle of Pyropia. Small heat-shock proteins (sHSPs) play a crucial role in heat stress response. Among sHSPs isolated from P. tenera, PtsHSP19.6 showed the strongest response to heat stress but not to other abiotic stresses such as desiccation and freezing. Although an α-crystallin domain was found in PtsHSP19.6, its amino acid sequence showed low homology with known sHSPs, except those from red algae. This led us to investigate whether PtsHSP19.6 from red algae has chaperone activity and is involved in high-temperature tolerance. PtsHSP19.6 significantly reduced the thermal aggregation of alcohol dehydrogenase used as a substrate. When PtsHSP19.6 was introduced into Escherichia coli, the transformed cells grew better than the control cells under high-temperature conditions. Fluorescence of the PtsHSP19.6-GFP fusion protein was detected from granules in the cytoplasm. The in vitro analysis data showed that PtsHSP19.6 forms oligomers with a molecular weight greater than 240 kDa in solution. This study showed that PtsHSP19.6 from P. tenera forms oligomers in solution and plays a role in heat tolerance, with a chaperone function similar to that observed in green plants.

PRLH and SOD1 gene variations associated with heat tolerance in Chinese cattle.

With the proposed global climate change, heat tolerance is becoming increasingly important to the sustainability of livestock production systems. Results from previous studies showed that variants in the prolactin releasing hormone (PRLH) (AC_000160.1:g.11764610G>A) and superoxide dismutase 1 (SOD1) (AC_000158.1:g.3116044T>A) genes play an important role in heat tolerance in African indicine cattle. However, it is unknown whether or not the mutations are associated with heat tolerance in Chinese cattle. In this study, PCR and DNA sequencing were used to genotype two missense mutations in 725 individuals of 30 cattle breeds. Analysis results demonstrated that two classes of base substitution were detected at two loci: AC_000160.1:g.11764610G>A and AC_000158.1:g.3116044T>A or T>C respectively, with amino acid substitutions arginine to histidine and phenylalanine to isoleucine or leucine. The frequencies of the G and T alleles of the two loci gradually diminished from northern groups to southern groups of native Chinese cattle, whereas the frequencies of A and A or C alleles showed a contrary pattern, displaying a significant geographical difference across native Chinese cattle breeds. Additionally, analysis of these two loci in Chinese indigenous cattle revealed that two SNPs were significantly associated with mean annual temperature (T), relative humidity (RH) and temperature humidity index (THI) (P<0.01), suggesting that cattle with A or C alleles were distributed in regions with higher T, RH and THI. Our results suggest that the two mutations of PRLH and SOD1 genes in Chinese cattle were associated with the heat tolerance.

Effects of heat stress on changes in physiology and anatomy in two cultivars of Rhododendron

Rhododendron×hybridum, an ornamental plant, is usually heat sensitive. High temperatures cause an array of morphological, anatomical, physiological, biochemical changes in plants, which affect plant growth and development. Evaluating difference between two cultivars in R. may facilitate future understand the heat tolerance mechanisms. We conducted a comparative study on growing plants of R. ‘Lan Yin’ and R. ‘Liu Qiu Hong’ at 38/30°C (day/night) and 25/17°C (day/night) to elucidate the heat tolerance mechanism of Rhododendron in terms of morphology, physiology, anatomy and biology. After the plants were subjected to 38/30°C (day/night) incubation for 6d, the chlorophyll and carotenoid contents decreased, malondialdehyde (MDA) and hydrogen peroxide (H2O2) accompanying lesser increase in R. ‘Lan Yin’ revealed that the heat resistant cultivar was easier to adjust physiologically in heat disappearing. Morphologically, the xylem vessels, leaf ultrastructure and chloroplast of R. ‘Lan Yin’ is superior to R. ‘Liu Qiu Hong’, and R. ‘Lan Yin’ had a decreased stomatal opening and stomatal aperture under heat stress, confirming stomatal factors play a crucial role in heat tolerance in R. cultivars. The electrolyte leakage increased, superoxide dismutase (SOD) and peroxidase (POD) activities, osmotic adjustment solute contents (proline, total soluble protein, and sugar) decreased to scavenge reactive oxygenspecies (ROS) and maintain cell membrane stability in two cultivars, but R. ‘Lan Yin’ had a higher level relatively, which may suggests that CMT may use a reliable index for selecting heat-tolerant cultivars of R. In addition, there was evidence of plasmolysis and chloroplast damage in R. ‘Liu Qiu Hong’.

The Arabidopsis endoplasmic reticulum associated degradation pathways are involved in the regulation of heat stress response

The Cytosolic Protein Response (CPR) in the cytosol and the Unfolded Protein Response (UPR) and ER-associated degradation (ERAD) in the endoplasmic reticulum are major pathways of the cellular proteostasis network. However, despite years of effort, how these protein quality control systems coordinated invivo remains largely unknown, particularly in plants. In this study, the roles of two evolutionarily conserved ERAD pathways (DOA10 and HRD1) in heat stress response were investigated through reverse genetic approaches in Arabidopsis. Phenotypic analysis of the mutants showed that the two ERAD pathways additively play negative roles in heat tolerance, which was demonstrated by higher survival rate and lower electrolyte leakage in the loss of function mutants compared to the wild type plants. Importantly, gene expression analysis revealed that the mutant plants showed elevated transcriptional regulation of several downstream genes, including those encoding CPR and UPR marker genes, under both basal and heat stress conditions. Finally, multiple components of ERAD genes exhibited rapid response to increasing temperature. Taken together, our data not only unravels key insights into the crosstalk between different protein quality control processes, but also provides candidate genes to genetically improve plant heat tolerance in the future.