cDNA-AFLP analysis reveals heat shock proteins play important roles in mediating cold, heat, and drought tolerance in Ammopiptanthus mongolicus

Identification of passion fruit HSF gene family and the functional analysis of PeHSF-C1a in response to heat and osmotic stress

Heat stress transcription factors (HSFs) are the major regulators of plant response to environmental stress, especially heat and drought stress. To gain a deeper understanding of the mechanisms underlying HSFs in the abiotic stress response of passion fruit, we conducted an in silico analysis of the HSF gene family. Through bioinformatics and phylogenetic analyses, we identified 18 PeHSF members and classified them into A, B, and C groups. Collinearity analysis results revealed that the expansion of the PeHSF gene family was due to the presence of segmental duplication. Furthermore, gene structure and protein domain analysis illustrated that PeHSFs in the same subgroup are relatively conserved. Conserved motif and function domain analysis suggested that PeHSF proteins possess typical conserved functional domains of the HSF family. A protein interaction network and 3D structure prediction were used to study the potential regulatory relationship of PeHSFs. Additionally, the subcellular localization results of PeHSF-A6a, PeHSF-B4b, and PeHSF-C1a were consistent with the predictions. RNA-seq and RT-qPCR analysis revealed the expression patterns of PeHSFs in different tissues of passion fruit floral organs. Promoter analysis and the expression patterns of the PeHSFs under different treatments demonstrated their involvement in various abiotic stress processes. Notably, overexpression of PeHSF-C1a consistently enhanced tolerance to drought and heat stress in Arabidopsis. Overall, our findings provide a scientific basis for further functional studies of PeHSFs that could contribute to improvement of passion fruit breeding.

Genome-wide identification and analysis of the heat shock transcription factor family in moso bamboo (Phyllostachys edulis)

Heat shock transcription factors (HSFs) are central elements in the regulatory network that controls plant heat stress response. They are involved in multiple transcriptional regulatory pathways and play important roles in heat stress signaling and responses to a variety of other stresses. We identified 41 members of the HSF gene family in moso bamboo, which were distributed non-uniformly across its 19 chromosomes. Phylogenetic analysis showed that the moso bamboo HSF genes could be divided into three major subfamilies; HSFs from the same subfamily shared relatively conserved gene structures and sequences and encoded similar amino acids. All HSF genes contained HSF signature domains. Subcellular localization prediction indicated that about 80% of the HSF proteins were located in the nucleus, consistent with the results of GO enrichment analysis. A large number of stress response-associated cis-regulatory elements were identified in the HSF upstream promoter sequences. Synteny analysis indicated that the HSFs in the moso bamboo genome had greater collinearity with those of rice and maize than with those of Arabidopsis and pepper. Numerous segmental duplicates were found in the moso bamboo HSF gene family. Transcriptome data indicated that the expression of a number of PeHsfs differed in response to exogenous gibberellin (GA) and naphthalene acetic acid (NAA). A number of HSF genes were highly expressed in the panicles and in young shoots, suggesting that they may have functions in reproductive growth and the early development of rapidly-growing shoots. This study provides fundamental information on members of the bamboo HSF gene family and lays a foundation for further study of their biological functions in the regulation of plant responses to adversity.

Proteomic Responses to Alkali Stress in Oats and the Alleviatory Effects of Exogenous Spermine Application

Alkali stress limits plant growth and yield more strongly than salt stress and can lead to the appearance of yellow leaves; however, the reasons remain unclear. In this study, we found that (1) the down-regulation of coproporphyrinogen III oxidase, protoporphyrinogen oxidase, and Pheophorbide a oxygenase in oats under alkali stress contributes to the appearance of yellow leaves (as assessed by proteome and western blot analyses). (2) Some oat proteins that are involved in the antioxidant system, root growth, and jasmonic acid (JA) and indole-3-acetic acid (IAA) synthesis are up-regulated in response to alkalinity and help increase alkali tolerance. (3) We added exogenous spermine to oat plants to improve their alkali tolerance, which resulted in higher chlorophyll contents and plant dry weights than in plants subjected to alkaline stress alone. This was due to up-regulation of chitinase and proteins related to chloroplast structure, root growth, and the antioxidant system. Spermine addition increased sucrose utilization efficiency, and promoted carbohydrate export from leaves to roots to increase energy storage in roots. Spermine addition also increased the IAA and JA contents required for root growth.

Sugarcane mosaic virus mediated changes in cytosine methylation pattern and differentially transcribed fragments in resistance-contrasting sugarcane genotypes

Sugarcane mosaic virus (SCMV) is the causal agent of sugarcane mosaic disease (SMD) in Brazil; it is mainly controlled by using resistant cultivars. Studies on the changes in sugarcane transcriptome provided the first insights about the molecular basis underlying the genetic resistance to SMD; nonetheless, epigenetic modifications such as cytosine methylation is also informative, considering its roles in gene expression regulation. In our previous study, differentially transcribed fragments (DTFs) were obtained using cDNA-amplified fragment length polymorphism by comparing mock- and SCMV-inoculated plants from two sugarcane cultivars with contrasting responses to SMD. In this study, the identification of unexplored DTFs was continued while the same leaf samples were used to evaluate SCMV-mediated changes in the cytosine methylation pattern by using methylation-sensitive amplification polymorphism. This analysis revealed minor changes in cytosine methylation in response to SCMV infection, but distinct changes between the cultivars with contrasting responses to SMD, with higher hypomethylation events 24 and 72 h post-inoculation in the resistant cultivar. The differentially methylated fragments (DMFs) aligned with transcripts, putative promoters, and genomic regions, with a preponderant distribution within CpG islands. The transcripts found were associated with plant immunity and other stress responses, epigenetic changes, and transposable elements. The DTFs aligned with transcripts assigned to stress responses, epigenetic changes, photosynthesis, lipid transport, and oxidoreductases, in which the transcriptional start site is located in proximity with CpG islands and tandem repeats. Real-time quantitative polymerase chain reaction results revealed significant upregulation in the resistant cultivar of aspartyl protease and VQ protein, respectively, selected from DMF and DTF alignments, suggesting their roles in genetic resistance to SMD and supporting the influence of cytosine methylation in gene expression. Thus, we identified new candidate genes for further validation and showed that the changes in cytosine methylation may regulate important mechanisms underlying the genetic resistance to SMD.

Enriched networks 'nucleoside/nucleotide and ribonucleoside/ribonucleotide metabolic processes' and 'response to stimulus' potentially conferred to drought adaptation of the epiphytic orchid Dendrobium wangliangii

Dendrobium wangliangii is an endangered and epiphytic orchid with tolerance to seasonally extreme arid conditions and occurs exclusively in the hot-dry valley area of southwestern China. To reveal its molecular basis responsible for ecological adaptation, large-scale transcriptome sequencing was performed using Illumina sequencing with pooled mRNA extracted from whole plants and pseudobulbs during drought and rainy seasons. Based on the target transcript selection, the differentially expressed genes were related to 8 well-known drought-tolerant categories, and to morphological traits in resistance to water stress including pseudobulbs and roots. Further gene ontology enrichment analysis revealed that 'nucleoside/nucleotide and ribonucleoside/ribonucleotide metabolic processes' and 'response to stimulus' were the two most important aspects in resistance to drought stress with respect to the whole plant. In addition, the difference in the number and category of differentially expressed genes in whole plant and stem suggested the involvement of genes specifically localized in the stem, such as GTP-binding protein, lipases, signaling related transcripts and those involved in the ATP metabolic process. The comprehensive analysis of the epiphytic orchid in response to water deprivation indicates that integral tactics lead to active adaptation as a basal defense response to drought stress by the endangered epiphyte, including the collaboration of metabolic processes, responses to a various stimulus and other candidate genes contribute to its extreme drought tolerance. Insights from this study can be further utilized to understand stress-responsive genes in other medicinally important species and to improve the drought tolerance of food crops.

Functional Characterization of Waterlogging and Heat Stresses Tolerance Gene Pyruvate decarboxylase 2 from Actinidia deliciosa

A previous report showed that both Pyruvatedecarboxylase (PDC) genes were significantly upregulated in kiwifruit after waterlogging treatment using Illumina sequencing technology, and that the kiwifruit AdPDC1 gene was required during waterlogging, but might not be required during other environmental stresses. Here, the function of another PDC gene, named AdPDC2, was analyzed. The expression of the AdPDC2 gene was determined using qRT-PCR, and the results showed that the expression levels of AdPDC2 in the reproductive organs were much higher than those in the nutritive organs. Waterlogging, NaCl, and heat could induce the expression of AdPDC2. Overexpression of kiwifruit AdPDC2 in transgenic Arabidopsis enhanced resistance to waterlogging and heat stresses in five-week-old seedlings, but could not enhance resistance to NaCl and mannitol stresses at the seed germination stage and in early seedlings. These results suggested that the kiwifruit AdPDC2 gene may play an important role in waterlogging resistance and heat stresses in kiwifruit.

Genome-wide identification of salinity responsive HSP70s in common bean

The present study is aimed to identify and characterize HSP70 (PvHSP70) genes in two different common bean cultivars under salt stress. For this purpose various in silico methods such as RNAseq data and qRT-PCR analysis were used. A total of 24 candidate PvHSP70 gene were identified. Except for chromosome 4 and 7, these candidate PvHSP70 genes were distributed on the remaining chromosomes. While the lowest number of PvHSP70 genes was determined on chromosomes 1, 3, 5, 7, 9, 10 and 11 (one HSP70 gene), the highest number of PvHSP70s was on chromosomes 6 and 8 (seven HSP70 genes each). Three genes; PvHSP70-5, -9, and -10 were found to have no-introns. In addition, four tandemly and six segmentally duplicated gene couples were detected. A total of 13 PvHSP70 genes were targeted by miRNAs of 44 plant species and the most targeted genes were PvHSP70-5 and -23. The expression profile of PvHSP70 genes based on publicly available RNA-seq data was identified and salt treated leaf tissue was found to have more gene expression levels compared to the root. qRT-PCR analysis showed that the transcript concentrations of upregulated PvHSP70 genes in leaves of Zulbiye (sensitive) were mostly higher than those of Yakutiye (resistant). The present study revealed that PvHSP70 genes might play an important role in salt stress response for common bean cultivars and variability between cultivars also suggests that these genes could be used as functional markers for salt tolerance in common bean.

Cloning and expression analysis of HSP70 gene from mangrove plant Kandelia obovata under cold stress

Heat shock protein 70 (HSP70), the primary member of the HSPs that play various stress-protective roles in plants. In this study, a hsp70 gene of Kandelia obovata (KoHsp70) was cloned by rapid amplification of cDNA ends (RACE). The full-length of KoHsp70 was 2255 bp, consisting of a 5'-terminal untranslated region (UTR) of 118 bp, a 3'-terminal UTR of 178 bp, and an open reading frame (ORF) of 1959 bp. The ORF (KoHSP70) was predicted to encode a polypeptide of 652 amino acids with a theoretical molecular weight (MW) of 71.40 kDa and a pI of 5.16. The amino acid sequence analysis revealed that the KoHSP70 contained three conserved regions of HSP70 family, a bipartite nuclear localization signal sequences (NLS), an ATP/GTP-binding site motif and a cytoplasmic characteristic motif (EEVD). Homology analysis indicated that KoHSP70 shared 96.0 % identity with the known HSP70 (Gossypium hirsutum). Bioinformatics analysis indicated that the KoHSP70 was hydrophilic and had no signal peptide or transmembrane region. The mRNA expression of KoHsp70 kept relatively stable at first and then increased significantly after 48 h cold stress, and reached the highest level at 168 h after cold treatment. The results indicated that the KoHsp70 was a stress-inducible gene that might play a role in cold stress-protective response and in coping with environmental and biological stresses for K. obovata. This study provided a basis to further study the mechanism of anti-adverseness and expression characteristics under stress conditions of K. obovata.

Cloning and functional validation of molybdenum cofactor sulfurase gene from Ammopiptanthus nanus

The molybdenum cofactor sulfurase gene ( AnMCSU ) was cloned from xerophytic desert plant Ammopiptanthus nanus and validated for its function of tolerance toward abiotic stresses by heterologous expression in Arabidopsis thaliana. Molybdenum cofactor sulfurase participates in catalyzing biosynthesis of abscisic acid, which plays a crucial role in the response of plants to abiotic stresses. In this study, we cloned molybdenum cofactor sulfurase gene (AnMCSU) from a super-xerophytic desert plant, Ammopiptanthus nanus, by using rapid amplification of cDNA ends method. This gene has a total length of 2544 bp, with a 5'- and a 3'-untranslated region of 167 and 88 bp, and an open reading frame of 2289 bp, which encodes an 84.85 kDa protein of 762 amino acids. The putative amino acid sequence shares high homology and conserved amino acid residues crucial for the function of molybdenum cofactor sulfurases with other leguminous species. The encoded protein of the AnMCSU gene was located in the cytoplasm by transient expression in Nicotiana benthamiana. The result of real-time quantitative PCR showed that the expression of the AnMCSU gene was induced by heat, dehydration, high salt stresses, and ABA induction, and inhibited by cold stress. The heterologous expression of the AnMCSU gene significantly enhanced the tolerance of Arabidopsis thaliana to high salt, cold, osmotic stresses, and abscisic acid induction. All these results suggest that the AnMCSU gene might play a crucial role in the adaptation of A. nanus to abiotic stress and has potential to be applied to transgenic improvement of commercial crops.