Genome-Wide Characterization of the HSP20 Gene Family Identifies Potential Members Involved in Temperature Stress Response in Apple

The MdHSC70-MdWRKY75 module mediates basal apple thermotolerance by regulating the expression of heat shock factor genes

Heat stress severely restricts the growth and fruit development of apple (Malus domestica). Little is known about the involvement of WRKY proteins in the heat tolerance mechanism in apple. In this study, we found that the apple transcription factor (TF) MdWRKY75 responds to heat and positively regulates basal thermotolerance. Apple plants that overexpressed MdWRKY75 were more tolerant to heat stress while silencing MdWRKY75 caused the opposite phenotype. RNA-seq and reverse transcription quantitative PCR showed that heat shock factor genes (MdHsfs) could be the potential targets of MdWRKY75. Electrophoretic mobility shift, yeast one-hybrid, β-glucuronidase, and dual-luciferase assays showed that MdWRKY75 can bind to the promoters of MdHsf4, MdHsfB2a, and MdHsfA1d and activate their expression. Apple plants that overexpressed MdHsf4, MdHsfB2a, and MdHsfA1d exhibited heat tolerance and rescued the heat-sensitive phenotype of MdWRKY75-Ri3. In addition, apple heat shock cognate 70 (MdHSC70) interacts with MdWRKY75, as shown by yeast two-hybrid, split luciferase, bimolecular fluorescence complementation, and pull-down assays. MdHSC70 acts as a negative regulator of the heat stress response. Apple plants that overexpressed MdHSC70 were sensitive to heat, while virus-induced gene silencing of MdHSC70 enhanced heat tolerance. Additional research showed that MdHSC70 exhibits heat sensitivity by interacting with MdWRKY75 and inhibiting MdHsfs expression. In summary, we proposed a mechanism for the response of apple to heat that is mediated by the "MdHSC70/MdWRKY75-MdHsfs" molecular module, which enhances our understanding of apple thermotolerance regulated by WRKY TFs.

Genome-wide profile analysis of the Hsp20 family in lettuce and identification of its response to drought stress

Heat shock protein 20 (Hsp20) plays a very important role in response to abiotic stressors such as drought; however, in lettuce (Lactuca sativa L.), this gene family is poorly understood. This study used bioinformatics methods to identify 36 members of the lettuce Hsp20 family, which were named LsHsp20-1~LsHsp20-36. Subcellular localization results revealed that 26 members of the LsHsp20 protein family localized to the cytoplasm and nucleus. Additionally, 15 conserved domains were identified in the LsHsp20 protein family, with the number of amino acids ranging from 8 to 50. Gene structure analysis revealed that 15 genes (41.7%) had no introns, and 20 genes (55.5%) had one intron. The proportion of the LsHsp20 secondary structure was random coil > alpha helix > extended strand > beta turn. Chromosome positioning analysis indicated that 36 genes were unevenly distributed on nine chromosomes, and four pairs of genes were collinear. The Ka/Ks ratio of the collinear genes was less than 1, indicating that purifying selection dominated during L. sativa evolution. Thirteen pairs of genes were collinear in lettuce and Arabidopsis, and 14 pairs of genes were collinear in lettuce and tomato. A total of 36 LsHsp20 proteins were divided into 12 subgroups based on phylogenetic analysis. Three types of cis-acting elements, namely, abiotic and biotic stress-responsive, plant hormone-responsive, and plant development-related elements, were identified in the lettuce LsHsp20 family. qRT-PCR was used to analyze the expression levels of 23 LsHsp20 genes that were significantly upregulated on the 7th or 14th day of drought treatment, and the expression levels of two genes (LsHsp20-12 and LsHsp20-26) were significantly increased by 153-fold and 273-fold on the 14th and 7th days of drought treatment, respectively. The results of this study provide comprehensive information for research on the LsHsp20 gene family in lettuce and lay a solid foundation for further elucidation of Hsp20 biological functions, providing valuable information on the regulatory mechanisms of the LsHsp20 family in lettuce drought resistance.

Comprehensive analysis of Dendrobium catenatum HSP20 family genes and functional characterization of DcHSP20-12 in response to temperature stress

Heat shock proteins (HSPs) are a class of protective proteins in response to abiotic stress in plants, and HSP20 plays an essential role in response to temperature stress. However, there are few studies on HSP20 in Dendrobium catenatum. In this study, 18 DcHSP20 genes were identified from the D. catenatum genome. Phylogenetic analysis showed that DcHSP20s could be classified into six subgroups, each member of which has similar conserved motifs and gene structures. Gene expression analysis of 18 DcHSP20 genes revealed that they exhibited variable expression patterns in different plant tissues. Meanwhile, all 18 DcHSP20 genes were induced to be up-regulated under high temperature, while six genes (DcHSP20-2/9/10/12/16/17) were significantly up-regulated under low temperature. Moreover, combining gene expression under high and low temperature stress, the DcHSP20-12 gene was cloned for functional analysis. The germination ratios, fresh weights, root lengths of two DcHSP20-12-overexpressing transgenic Arabidopsis thaliana lines were significantly higher, but MDA contents were lower than that of wild-type (WT) plants under heat and cold stresses, displayed enhanced thermotolerance and cold-resistance. These results lay a foundation for the functional characterization of DcHSP20s and provide a candidate gene, DcHSP20-12, for improving the tolerance of D. catenatum to temperature stress in the future.

Heterologous overexpression of heat shock protein 20 genes of different species of yellow Camellia in Arabidopsis thaliana reveals their roles in high calcium resistance

Yellow Camellia (Camellia sect. chrysantha) is a rare ornamental plant and an important germplasm resource globally. Camellia nitidissima thrives in normal acidic soils, while Camellia limonia can adapt to the calcareous soils found in karst areas. Our previous study on the karst adaptation of yellow camellias revealed that the expression levels of heat shock protein 20(HSP20) were higher in Camellia limonia than in Camellia nitidissima. However, the functions of the HSP20 gene of Camellia limonia remain unclear to data. In this study, the HSP20 genes of Camellia limonia (ClHSP20-OE lines) and Camellia. nitidissima (CnHSP20-OE lines) were cloned and overexpressed heterologously in Arabidopsis thaliana. Additionally, we overexpressed the HSP20 gene of Arabidopsis (AtHSP20-OE lines) was also overexpressed, and the T-DNA inserted mutants (athspmutant lines) were also used to determine the functions of HSP20 genes. Under high calcium stress, the chlorophyll, nitrogen, water content and humidity of leaves were increased in ClHSP20-OE lines, while those of other lines were declined. The size of the stomatal apertures, stomatal conductance, and the photosynthetic efficiency of ClHSP20-OE lines were higher than those of the other lines. However, the accumulation of H2O2 and O2- in the leaves of ClHSP20-OE lines was the lowest among all the lines. Energy spectrum scanning revealed that the percentage of calcium on the surfaces of the leaves of ClHSP20-OE lines was relatively low, while that of athspmutant lines was the highest. The ClHSP20 gene can also affected soil humidity and the contents of soil nitrogen, phosphorus, and potassium. Transcriptome analysis revealed that the expressions of FBA5 and AT5G10770 in ClHSP20-OE lines was significantly up-regulated compared to that of CnHSP20-OE lines. Compared to that of athspmutant lines, the expressions of DREB1A and AT3G30460 was significantly upregulated in AtHSP20-OE lines, and the expression of POL was down-regulated. Our findings suggest that the HSP20 gene plays a crucial role in maintained photosynthetic rate and normal metabolism by regulating the expression of key genes under high-calcium stress. This study elucidates the mechanisms underlying the karst adaptation in Camellia. limonia and provides novel insights for future research on karst plants.

Integrative analysis of genome and transcriptome reveal the genetic basis of high temperature tolerance in pleurotus giganteus (Berk. Karun & Hyde)

BACKGROUND

Pleurotus giganteus is a commonly cultivated mushroom with notable high temperature resistance, making it significant for the growth of the edible fungi industry in the tropics. Despite its practical importance,, the genetic mechanisms underlying its ability to withstand high temperature tolerance remain elusive.

RESULTS

In this study, we performed high-quality genome sequencing of a monokaryon isolated from a thermotolerant strain of P. giganteus. The genome size was found to be 40.11 Mb, comprising 17 contigs and 13,054 protein-coding genes. Notably, some genes related to abiotic stress were identified in genome, such as genes regulating heat shock protein, protein kinase activity and signal transduction. These findings provide valuable insights into the genetic basis of P. giganteus' high temperature resistance. Furthermore, the phylogenetic tree showed that P. giganteus was more closely related to P. citrinopileatus than other Pleurotus species. The divergence time between Pleurotus and Lentinus was estimated as 153.9 Mya, and they have a divergence time with Panus at 168.3 Mya, which proved the taxonomic status of P. giganteus at the genome level. Additionally, a comparative transcriptome analysis was conducted between mycelia treated with 40 °C heat shock for 18 h (HS) and an untreated control group (CK). Among the 2,614 differentially expressed genes (DEGs), 1,303 genes were up-regulated and 1,311 were down-regulated in the HS group. The enrichment analysis showed that several genes related to abiotic stress, including heat shock protein, DnaJ protein homologue, ubiquitin protease, transcription factors, DNA mismatch repair proteins, and zinc finger proteins, were significantly up-regulated in the HS group. These genes may play important roles in the high temperature adaptation of P. giganteus. Six DEGs were selected according to fourfold expression changes and were validated by qRT-PCR, laying a good foundation for further gene function analysis.

CONCLUSION

Our study successfully reported a high-quality genome of P. giganteus and identified genes associated with high-temperature tolerance through an integrative analysis of the genome and transcriptome. This study lays a crucial foundation for understanding the high-temperature tolerance mechanism of P. giganteus, providing valuable insights for genetic modification of P. giganteus strains and the development of high-temperature strains for the edible fungus industry, particularly in tropical regions.

Genome-Wide Identification, Characterization and Expression Analysis of the TaDUF724 Gene Family in Wheat (Triticum aestivum)

Unknown functional domain (DUF) proteins constitute a large number of functionally uncharacterized protein families in eukaryotes. DUF724s play crucial roles in plants. However, the insight understanding of wheat TaDUF724s is currently lacking. To explore the possible function of TaDUF724s in wheat growth and development and stress response, the family members were systematically identified and characterized. In total, 14 TaDUF724s were detected from a wheat reference genome; they are unevenly distributed across the 11 chromosomes, and, according to chromosome location, they were named TaDUF724-1 to TaDUF724-14. Evolution analysis revealed that TaDUF724s were under negative selection, and fragment replication was the main reason for family expansion. All TaDUF724s are unstable proteins; most TaDUF724s are acidic and hydrophilic. They were predicted to be located in the nucleus and chloroplast. The promoter regions of TaDUF724s were enriched with the cis-elements functionally associated with growth and development, as well as being hormone-responsive. Expression profiling showed that TaDUF724-9 was highly expressed in seedings, roots, leaves, stems, spikes and grains, and strongly expressed throughout the whole growth period. The 12 TaDUF724 were post-transcription regulated by 12 wheat MicroRNA (miRNA) through cleavage and translation. RT-qPCR showed that six TaDUF724s were regulated by biological and abiotic stresses. Conclusively, TaDUF724s were systematically analyzed using bioinformatics methods, which laid a theoretical foundation for clarifying the function of TaDUF724s in wheat.

Genome-wide identification and characterization of members of the LEA gene family in Panax notoginseng and their transcriptional responses to dehydration of recalcitrant seeds

BACKGROUND

Late embryogenesis abundant (LEA) proteins play an important role in dehydration process of seed maturation. The seeds of Panax notoginseng (Burkill) F. H. Chen are typically characterized with the recalcitrance and are highly sensitive to dehydration. However, it is not very well known about the role of LEA proteins in response to dehydration stress in P. notoginseng seeds. We will perform a genome-wide analysis of the LEA gene family and their transcriptional responses to dehydration stress in recalcitrant P. notoginseng seeds.

RESULTS

In this study, 61 LEA genes were identified from the P. notoginseng genome, and they were renamed as PnoLEA. The PnoLEA genes were classified into seven subfamilies based on the phylogenetic relationships, gene structure and conserved domains. The PnoLEA genes family showed relatively few introns and was highly conserved. Unexpectedly, the LEA_6 subfamily was not found, and the LEA_2 subfamily contained 46 (75.4%) members. Within 19 pairs of fragment duplication events, among them 17 pairs were LEA_2 subfamily. In addition, the expression of the PnoLEA genes was obviously induced under dehydration stress, but the germination rate of P. notoginseng seeds decreased as the dehydration time prolonged.

CONCLUSIONS

We found that the lack of the LEA_6 subfamily, the expansion of the LEA_2 subfamily and low transcriptional levels of most PnoLEA genes might be implicated in the recalcitrant formation of P. notoginseng seeds. LEA proteins are essential in the response to dehydration stress in recalcitrant seeds, but the protective effect of LEA protein is not efficient. These results could improve our understanding of the function of LEA proteins in the response of dehydration stress and their contributions to the formation of seed recalcitrance.

Genomic Survey of Heat Shock Proteins in Liriodendron chinense Provides Insight into Evolution, Characterization, and Functional Diversities

Heat shock proteins (HSPs) are conserved molecular chaperones whose main role is to facilitate the regulation of plant growth and stress responses. The HSP gene family has been characterized in most plants and elucidated as generally stress-induced, essential for their cytoprotective roles in cells. However, the HSP gene family has not yet been analyzed in the Liriodendron chinense genome. In current study, 60 HSP genes were identified in the L. chinense genome, including 7 LchiHSP90s, 23 LchiHSP70s, and 30 LchiHSP20s. We investigated the phylogenetic relationships, gene structure and arrangement, gene duplication events, cis-acting elements, 3D-protein structures, protein-protein interaction networks, and temperature stress responses in the identified L. chinense HSP genes. The results of the comparative phylogenetic analysis of HSP families in 32 plant species showed that LchiHSPs are closely related to the Cinnamomum kanehirae HSP gene family. Duplication events analysis showed seven segmental and six tandem duplication events that occurred in the LchiHSP gene family, which we speculated to have played an important role in the LchiHSP gene expansion and evolution. Furthermore, the Ka/Ks analysis indicated that these genes underwent a purifying selection. Analysis in the promoter region evidenced that the promoter region LchiHSPs carry many stress-responsive and hormone-related cis-elements. Investigations in the gene expression patterns of the LchiHSPs using transcriptome data and the qRT-PCR technique indicated that most LchiHSPs were responsive to cold and heat stress. In total, our results provide new insights into understanding the LchiHSP gene family function and their regulatory mechanisms in response to abiotic stresses.

Genome-Wide Identification and Expression Profiling of Heat Shock Protein 20 Gene Family in Sorbus pohuashanensis (Hance) Hedl under Abiotic Stress

Small heat shock proteins (HSP20s) are a significant factor in plant growth and development in response to abiotic stress. In this study, we investigated the role of HSP20s' response to the heat stress of Sorbus pohuashanensis introduced into low-altitude areas. The HSP20 gene family was identified based on the genome-wide data of S. pohuashanensis, and the expression patterns of tissue specificity and the response to abiotic stresses were evaluated. Finally, we identified 38 HSP20 genes that were distributed on 16 chromosomes. Phylogenetic analysis of HSP20s showed that the closest genetic relationship to S. pohuashanensis (SpHSP20s) is Malus domestica, followed by Populus trichocarpa and Arabidopsis thaliana. According to phylogenetic analysis and subcellular localization prediction, the 38 SpHSP20s belonged to 10 subfamilies. Analysis of the gene structure and conserved motifs indicated that HSP20 gene family members are relatively conserved. Synteny analysis showed that the expansion of the SpHSP20 gene family was mainly caused by segmental duplication. In addition, many cis-acting elements connected with growth and development, hormones, and stress responsiveness were found in the SpHSP20 promoter region. Analysis of expression patterns showed that these genes were closely related to high temperature, drought, salt, growth, and developmental processes. These results provide information and a theoretical basis for the exploration of HSP20 gene family resources, as well as the domestication and genetic improvement of S. pohuashanensis.

Genome-wide identification, characterization and expression of HSP 20 gene family in dove

Davidia involucrata is a significant living fossil with high abiotic stress tolerance. Although heat shock protein 20 (HSP20) has already been linked to heat stress, nothing is known about HSP20 family protein activities in D. involucrata. The functional dynamics of the D. involucrata HSP20 (DiHSP20) gene family were identified and characterized using a thorough genome-wide investigation. From the genome of D. involucrata, a total of 42 HSP20 genes were identified, which are distributed across 16 chromosomes. The DiHSP20 proteins were grouped into seven separate subfamilies by our phylogenetic analysis, which was validated by the conserved motif composition and gene structure studies. Segmental duplication events were shown to play a crucial role in the expansion of the DiHSP20 gene family. Synteny analysis revealed that 19 DiHSP20 genes of D. involucrata shared a syntenic connection with Arabidopsis genes, 39 with C. acuminata genes, and just 6 with O. sativa genes. Additionally, heat stress differently enhanced the expression levels of D. involucrata HSP20 genes. After 1 hour of heat treatment, the expression levels of most DiHSP20 genes, particularly DiHSP20-7, DiHSP20-29, DiHSP20-30, DiHSP20-32, and DiHSP20-34, were dramatically increased, suggestted that they might be employed as heat tolerance candidate genes. Overall, these findings add to our knowledge of the HSP20 family genes and provide helpful information for breeding heat stress resistance in D. involucrata.

Phylogenetic and Transcriptional Analyses of the HSP20 Gene Family in Peach Revealed That PpHSP20-32 Is Involved in Plant Height and Heat Tolerance

The heat shock protein 20 (HSP20) proteins comprise an ancient, diverse, and crucial family of proteins that exists in all organisms. As a family, the HSP20s play an obvious role in thermotolerance, but little is known about their molecular functions in addition to heat acclimation. In this study, 42 PpHSP20 genes were detected in the peach genome and were randomly distributed onto the eight chromosomes. The primary modes of gene duplication of the PpHSP20s were dispersed gene duplication (DSD) and tandem duplication (TD). PpHSP20s in the same class shared similar motifs. Based on phylogenetic analysis of HSP20s in peach, Arabidopsis thaliana, Glycine max, and Oryza sativa, the PpHSP20s were classified into 11 subclasses, except for two unclassified PpHSP20s. cis-elements related to stress and hormone responses were detected in the promoter regions of most PpHSP20s. Gene expression analysis of 42 PpHSP20 genes revealed that the expression pattern of PpHSP20-32 was highly consistent with shoot length changes in the cultivar 'Zhongyoutao 14', which is a temperature-sensitive semi-dwarf. PpHSP20-32 was selected for further functional analysis. The plant heights of three transgenic Arabidopsis lines overexpressing PpHSP20-32 were significantly higher than WT, although there was no significant difference in the number of nodes. In addition, the seeds of three over-expressing lines of PpHSP20-32 treated with high temperature showed enhanced thermotolerance. These results provide a foundation for the functional characterization of PpHSP20 genes and their potential use in the growth and development of peach.

Genome-Wide Identification and Characterization of Heat Shock Protein 20 Genes in Maize

Maize is an important cereal crop worldwide and is sensitive to abiotic stresses in fluctuant environments that seriously affect its growth, yield, and quality. The small heat shock protein (HSP20) plays a crucial role in protecting plants from abiotic stress. However, little is known about HSP20 in maize (ZmHSP20). In this study, 44 ZmHSP20s were identified, which were unequally distributed over 10 chromosomes, and 6 pairs of ZmHSP20s were tandemly presented. The gene structure of ZmHSP20s was highly conserved, with 95% (42) of the genes having no more than one intron. The analysis of the cis-element in ZmHSP20s promoter demonstrated large amounts of elements related to hormonal and abiotic stress responses, including abscisic acid (ABA), high temperature, and hypoxia. The ZmHSP20s protein had more than two conserved motifs that were predictably localized in the cytoplasm, nucleus, endoplasmic reticulum, peroxisome, mitochondria, and plasma. Phylogenetic analysis using HSP20s in Arabidopsis, rice, maize, and Solanum tuberosum indicated that ZmHSP20s were classified into 11 categories, of which each category had unique subcellular localization. Approximately 80% (35) of ZmHSP20 were upregulated under heat stress at the maize seedling stage, whereas the opposite expression profiling of 10 genes under 37 and 48 °C was detected. A total of 20 genes were randomly selected to investigate their expression under treatments of ABA, gibberellin (GA), ethylene, low temperature, drought, and waterlogging, and the results displayed that more than half of these genes were downregulated while ZmHSP20-3, ZmHSP20-7, ZmHSP20-24, and ZmHSP20-44 were upregulated under 1 h treatment of ethylene. A yeast-one-hybrid experiment was conducted to analyze the binding of four heat stress transcription factors (ZmHSFs) with eight of the ZmHSP20s promoter sequences, in which ZmHSF3, ZmHSF13, and ZmHSF17 can bind to most of these selected ZmHSP20s promoters. Our results provided a valuable resource for studying HSP20s function and offering candidates for genetic improvement under abiotic stress.

Genome-wide analysis of HSP20 gene family and expression patterns under heat stress in cucumber (Cucumis sativus L.)

Cucumber is an important vegetable in China, and its yield and cultivation area are among the largest in the world. Excessive temperatures lead to high-temperature disorder in cucumber. Heat shock protein 20 (HSP20), an essential protein in the process of plant growth and development, is a universal protective protein with stress resistance. HSP20 plays crucial roles in plants under stress. In this study, we characterized the HSP20 gene family in cucumber by studying chromosome location, gene duplication, phylogenetic relationships, gene structure, conserved motifs, protein-protein interaction (PPI) network, and cis-regulatory elements. A total of 30 CsHSP20 genes were identified, distributed across 6 chromosomes, and classified into 11 distinct subgroups based on conserved motif composition, gene structure analyses, and phylogenetic relationships. According to the synteny analysis, cucumber had a closer relationship with Arabidopsis and soybean than with rice and maize. Collinearity analysis revealed that gene duplication, including tandem and segmental duplication, occurred as a result of positive selection and purifying selection. Promoter analysis showed that the putative promoters of CsHSP20 genes contained growth, stress, and hormone cis-elements, which were combined with protein-protein interaction networks to reveal their potential function mechanism. We further analyzed the gene expression of CsHSP20 genes under high stress and found that the majority of the CsHSP20 genes were upregulated, suggesting that these genes played a positive role in the heat stress-mediated pathway at the seedling stage. These results provide comprehensive information on the CsHSP20 gene family in cucumber and lay a solid foundation for elucidating the biological functions of CsHSP20. This study also provides valuable information on the regulation mechanism of the CsHSP20 gene family in the high-temperature resistance of cucumber.

Genome-wide identification and expression analysis of the Hsp20, Hsp70 and Hsp90 gene family in Dendrobium officinale

Dendrobium officinale, an important orchid plant with great horticultural and medicinal values, frequently suffers from abiotic or biotic stresses in the wild, which may influence its well-growth. Heat shock proteins (Hsps) play essential roles in the abiotic stress response of plants. However, they have not been systematically investigated in D. officinale. Here, we identified 37 Hsp20 genes (DenHsp20s), 43 Hsp70 genes (DenHsp70s) and 4 Hsp90 genes (DenHsp90s) in D. officinale genome. These genes were classified into 8, 4 and 2 subfamilies based on phylogenetic analysis and subcellular predication, respectively. Sequence analysis showed that the same subfamily members have relatively conserved gene structures and similar protein motifs. Moreover, we identified 33 pairs of paralogs containing 30 pairs of tandem duplicates and 3 pairs of segmental duplicates among these genes. There were 7 pairs in DenHsp70s under positive selection, which may have important functions in helping cells withstand extreme stress. Numerous gene promoter sequences contained stress and hormone response cis-elements, especially light and MeJA response elements. Under MeJA stress, DenHsp20s, DenHsp70s and DenHsp90s responded to varying degrees, among which DenHsp20-5,6,7,16 extremely up-regulated, which may have a strong stress resistance. Therefore, these findings could provide useful information for evolutional and functional investigations of Hsp20, Hsp70 and Hsp90 genes in D. officinale.

The heat shock protein 20 gene editing suppresses mycelial growth of Botryosphaeria dothidea and decreases its pathogenicity to postharvest apple fruits

Apple ring rot caused by Botryosphaeria dothidea is an essential and prevalent disease in the apple orchard in China. Our previous study demonstrated that dimethyl trisulfide (DT) from Chinese leek (Allium tuberosum) significantly suppressed the mycelial growth of B. dothidea and inhibited the incidence of apple ring rot postharvest. However, the mechanism underlying the inhibitory role of DT against B. dothidea is not fully understood. Comparing the control and the DT-treated B. dothidea mycelial transcriptomes revealed that heat shock protein 20 (Hsp20) strongly responded to DT treatment. This study identified four Hsp20 genes throughout the B. dothidea genome (BdHsp20_1-4). Each BdHsp20 gene had a conserved ACD with a variable N-terminal region and a short C-terminal extension. The segmental duplication event has contributed to the expansion of the BdHsp20 gene family. Compared to the wild-type strain, the CRISPR/Cas9 gene-edited BdHsp20 mutant (ΔBdHsp20) decreased the mycelial growth by 55.95% and reduced the disease symptom in postharvest apple fruit by 96.34%. However, the BdHsp20 complemented strain (ΔBdHsp20_C) significantly restored the growth and pathogenicity, which suggested that the BdHsp20 gene was closely involved in the growth and pathogenicity of B. dothidea. This study would accelerate the exploration of the molecular mechanism of the inhibitory effect of DT against B. dothidea and also provide new insights for the management of apple ring rot disease.

MdNup62 interactions with MdHSFs involved in flowering and heat-stress tolerance in apple

Because of global warming, the apple flowering period is occurring significantly earlier, increasing the probability and degree of freezing injury. Moreover, extreme hot weather has also seriously affected the development of apple industry. Nuclear pore complexes (NPCs) are main channels controlling nucleocytoplasmic transport, but their roles in regulating plant development and stress responses are still unknown. Here, we analysed the components of the apple NPC and found that MdNup62 interacts with MdNup54, forming the central NPC channel. MdNup62 was localized to the nuclear pore, and its expression was significantly up-regulated in 'Nagafu No. 2' tissue-cultured seedlings subjected to heat treatments. To determine MdNup62's function, we obtained MdNup62-overexpressed (OE) Arabidopsis and tomato lines that showed significantly reduced high-temperature resistance. Additionally, OE-MdNup62 Arabidopsis lines showed significantly earlier flowering compared with wild-type. Furthermore, we identified 62 putative MdNup62-interacting proteins and confirmed MdNup62 interactions with multiple MdHSFs. The OE-MdHSFA1d and OE-MdHSFA9b Arabidopsis lines also showed significantly earlier flowering phenotypes than wild-type, but had enhanced high-temperature resistance levels. Thus, MdNUP62 interacts with multiple MdHSFs during nucleocytoplasmic transport to regulate flowering and heat resistance in apple. The data provide a new theoretical reference for managing the impact of global warming on the apple industry.

Pumpkin (Cucurbita moschata) HSP20 Gene Family Identification and Expression Under Heat Stress

Pumpkin (Cucurbita moschata) is an important cucurbit vegetable crop that has strong resistance to abiotic stress. While heat shock protein 20 (HSP20) has been implicated in vegetable response to heat stress, little is known regarding activity of HSP20 family proteins in C. moschata. Here, we performed a comprehensive genome-wide analysis to identify and characterize the functional dynamics of the Cucurbita moschata HSP20 (CmoHSP20) gene family. A total of 33 HSP20 genes distributed across 13 chromosomes were identified from the pumpkin genome. Our phylogenetic analysis determined that the CmoHSP20 proteins fell into nine distinct subfamilies, a division supported by the conserved motif composition and gene structure analyses. Segmental duplication events were shown to play a key role in expansion of the CmoHSP20 gene family. Synteny analysis revealed that 19 and 18 CmoHSP20 genes were collinear with those in the cucumber and melon genomes, respectively. Furthermore, the expression levels of pumpkin HSP20 genes were differentially induced by heat stress. The transcript level of CmoHSP20-16, 24 and 25 were down-regulated by heat stress, while CmoHSP20-7, 13, 18, 22, 26 and 32 were up-regulated by heat stress, which could be used as heat tolerance candidate genes. Overall, these findings contribute to our understanding of vegetable HSP20 family genes and provide valuable information that can be used to breed heat stress resistance in cucurbit vegetable crops.

Genome-Wide Analysis of the HSP20 Gene Family and Expression Patterns of HSP20 Genes in Response to Abiotic Stresses in Cynodon transvaalensis

African bermudagrass (Cynodon transvaalensis Burtt-Davy) is an important warm-season turfgrass and forage grass species. Heat shock protein 20 (HSP20) is a diverse, ancient, and important protein family. To date, HSP20 genes have not been characterized genome-widely in African bermudagrass. Here, we confirmed 41 HSP20 genes in African bermudagrass genome. On the basis of the phylogenetic tree and cellular locations, the HSP20 proteins were classified into 12 subfamilies. Motif composition was consistent with the phylogeny. Moreover, we identified 15 pairs of paralogs containing nine pairs of tandem duplicates and six pairs of WGD/segmental duplicates of HSP20 genes. Unsurprisingly, the syntenic genes revealed that African bermudagrass had a closer evolutionary relationship with monocots (maize and rice) than dicots (Arabidopsis and soybean). The expression patterns of HSP20 genes were identified with the transcriptome data under abiotic stresses. According to the expression profiles, HSP20 genes could be clustered into three groups (Groups I, II, and III). Group I was the largest, and these genes were up-regulated in response to heat stress as expected. In Group II, one monocot-specific HSP20, CtHSP20-14 maintained higher expression levels under optimum temperature and low temperature, but not high temperature. Moreover, a pair of WGD/segmental duplicates CtHSP20-9 and CtHSP20-10 were among the most conserved HSP20s across different plant species, and they seemed to be positively selected in response to extreme temperatures during evolution. A total of 938 cis-elements were captured in the putative promoters of HSP20 genes. Almost half of the cis-elements were stress responsive, indicating that the expression pattern of HSP20 genes under abiotic stresses might be largely regulated by the cis-elements. Additionally, three-dimensional structure simulations and protein-protein interaction networks were incorporated to resolve the function mechanism of HSP20 proteins. In summary, the findings fulfilled the HSP20 family analysis and could provide useful information for further functional investigations of the specific HSP20s (e.g., CtHSP20-9, CtHSP20-10, and CtHSP20-14) in African bermudagrass.

Haploid Genome Analysis Reveals a Tandem Cluster of Four HSP20 Genes Involved in the High-Temperature Adaptation of Coriolopsis trogii

Coriolopsis trogii is a typical thermotolerant basidiomycete fungus, but its thermotolerance mechanisms are currently unknown. In this study, two monokaryons of C. trogii strain Ct001 were assembled: Ct001_29 had a genome assembly size of 38.85 Mb and encoded 13,113 genes, while Ct001_31 was 40.19 Mb in length and encoded 13,309 genes. Comparative intra- and interstrain genomic analysis revealed the rich genetic diversity of C. trogii, which included more than 315,194 single-nucleotide polymorphisms (SNPs), 30,387 insertion/deletions (indels), and 1,460 structural variations. Gene family analysis showed that the expanded families of C. trogii were functionally enriched in lignocellulose degradation activities. Furthermore, a total of 14 allelic pairs of heat shock protein 20 (HSP20) genes were identified in the C. trogii genome. The expression profile obtained from RNA sequencing (RNA-Seq) showed that four tandem-duplicated allelic pairs, HSP20.5 to HSP20.8, had more than 5-fold higher expression at 35°C than at 25°C. In particular, HSP20.5 and HSP20.8 were the most highly expressed HSP20 genes. Allelic expression bias was found for HSP20.5 and HSP20.8; the expression of Ct29HSP20.8 was at least 1.34-fold higher than that of Ct31HSP20.8, and that of Ct31HSP20.5 was at least 1.5-fold higher than that of Ct29HSP20.5. The unique structural and expression profiles of the HSP20 genes revealed by these haplotype-resolved genomes provide insight into the molecular mechanisms of high-temperature adaptation in C. trogii. IMPORTANCE Heat stress is one of the most frequently encountered environmental stresses for most mushroom-forming fungi. Currently available fungal genomes are mostly haploid because high heterozygosity hinders diploid genome assembly. Here, two haplotype genomes of C. trogii, a thermotolerant basidiomycete, were assembled separately. A conserved tandem cluster of four HSP20 genes showing allele-specific expression was found to be closely related to high-temperature adaptation in C. trogii. The obtained haploid genomes and their comparison offer a more thorough understanding of the genetic background of C. trogii. In addition, the responses of HSP20 genes at 35°C, which may contribute to the growth and survival of C. trogii at high temperatures, could inform the selection and breeding of elite strains in the future.

Differential Modulation of Heat-Inducible Genes Across Diverse Genotypes and Molecular Cloning of a sHSP From Pearl Millet [Pennisetum glaucum (L.) R. Br.]

The survival, biomass, and grain yield of most of the crops are negatively influenced by several environmental stresses. The present study was carried out by using transcript expression profiling for functionally clarifying the role of genes belonging to a small heat shock protein (sHSP) family in pearl millet under high-temperature stress. Transcript expression profiling of two high-temperature-responsive marker genes, Pgcp70 and PgHSF, along with physio-biochemical traits was considered to screen out the best contrasting genotypes among the eight different pearl millet inbred lines in the seedling stage. Transcript expression pattern suggested the existence of differential response among different genotypes upon heat stress in the form of accumulation of heat shock-responsive gene transcripts. Genotypes, such as WGI 126, TT-1, TT-6, and MS 841B, responded positively toward high-temperature stress for the transcript accumulation of both Pgcp70 and PgHSF and also indicated a better growth under heat stress. PPMI-69 showed the least responsiveness to transcript induction; moreover, it supports the membrane stability index (MSI) data for scoring thermotolerance, thereby suggesting the efficacy of transcript expression profiling as a molecular-based screening technique for the identification of thermotolerant genes and genotypes at particular crop growth stages. The contrasting genotypes, such as PPMI-69 (thermosusceptible) and WGI-126 and TT-1 (thermotolerant), are further utilized for the characterization of thermotolerance behavior of sHSP by cloning a PgHSP16.97 from the thermotolerant cv. WGI-126. In addition, the investigation was extended for the identification and characterization of 28 different HSP20 genes through a genome-wide search in the pearl millet genome and an understanding of their expression pattern using the RNA-sequencing (RNA-Seq) data set. The outcome of the present study indicated that transcript profiling can be a very useful technique for high-throughput screening of heat-tolerant genotypes in the seedling stage. Also, the identified PgHSP20s genes can provide further insights into the molecular regulation of pearl millet stress tolerance, thereby bridging them together to fight against the unpredicted nature of abiotic stress.