Genomic identification of AP2/ERF transcription factors and functional characterization of two cold resistance-related AP2/ERF genes in celery (Apium graveolens L.)

Genome-wide identification of the AP2/ERF gene family from Limonium bicolor and functional characterization of LbAP2/ERF32 under salt stress

AP2/ERF transcription factors (TFs) play important roles in plant growth and development, plant morphogenesis and response to environmental stresses. However, their biological roles in recretohalophytes are still not fully revealed. Limonium bicolor L. is a typical recretohalophyte, which secretes excessive salt ions through the salt glands on the epidermis. Here, 64 LbAP2/ERF genes were identified in L. bicolor genome, which were unevenly distributed on the eight chromosomes. Cis-elements related to growth and development, stress response and phytohormone response are distributed in multiple LbAP2/ERF promoters. Expression analysis indicated that LbAP2/ERF genes responsed to NaCl, PEG and ABA. And the salt gland density, salt secretion of leaves and overall salt tolerance of LbAP2/ERF32 silenced lines were significantly reduced. In agreement, the genes related to salt gland development and ion transport were significantly changed in LbAP2/ERF32-silenced lines. Our findings provided fundamental information on the structure and evolutionary relationship of LbAP2/ERF gene family in salt gland development and salt secretion of L. bicolor and gave theoretical guideline for further functional study of LbAP2/ERF genes in response to abiotic stress.

Analysis of the Aging-Related AP2/ERF Transcription Factor Gene Family in Osmanthus fragrans

Ethylene-Responsive Factor (ERF) is a key element found in the middle and lower reaches of the ethylene signal transduction pathway. It is widely distributed in plants and plays important roles in plant growth and development, hormone signal transduction, and various stress processes. Although there is research on AP/ERF family members, research on AP2/ERF in Osmanthus fragrans is lacking. Thus, in this work, AP2/ERF in O. fragrans was extensively and comprehensively analyzed. A total of 298 genes encoding OfAP2/ERF proteins with complete AP2/ERF domains were identified. Based on the number of AP2/ERF domains and the similarity among amino acid sequences between AP2/ERF proteins from A. thaliana and O. fragrans, the 298 putative OfAP2/ERF proteins were divided into four different families, including AP2 (45), ERF (247), RAV (5), and SOLOIST (1). In addition, the exon-intron structure characteristics of these putative OfAP2/ERF genes and the conserved protein motifs of their encoded OfAP2/ERF proteins were analyzed, and the results were found to be consistent with those of the population classification. A tissue-specific analysis showed the spatiotemporal expression of OfAP2/ERF in the stems and leaves of O. fragrans at different developmental stages. Specifically, 21 genes were not expressed in any tissue, while high levels of expression were found for 25 OfAP2/ERF genes in several tissues, 60 genes in the roots, 34 genes in the stems, 37 genes in young leaves, 34 genes in old leaves, 32 genes in the early flowering stage, 18 genes in the full flowering stage, and 37 genes in the late flowering stage. Quantitative RT-PCR experiments showed that OfERF110a and OfERF110b had the highest expression levels at the full-bloom stage (S4), and this gradually decreased with the senescence of petals. The expression of OfERF119c decreased first and then increased, while the expression levels of OfERF4c and OfERF5a increased constantly. This indicated that these genes may play roles in flower senescence and the ethylene response. In the subsequent subcellular localization experiments, we found that ERF1-4 was localized in the nucleus, indicating that it was expressed in the nucleus. In yeast self-activation experiments, we found that OfERF112, OfERF228, and OfERF23 had self-activation activity. Overall, these results suggest that OfERFs may have the function of regulating petal senescence in O. fragrans.

Discovery of candidate genes involved in ethylene biosynthesis and signal transduction pathways related to peach bud cold resistance

Background: Low temperature pose significant challenges to peach cultivation, causing severe damage to peach buds and restricting production and distribution. Ethylene, an important phytohormone, plays a critical role in enhancing plant cold resistance. Structural genes and transcription factors involved in ethylene biosynthesis and signal transduction pathways are associated with cold resistance. However, no research has specifically addressed their roles in peach cold resistance. Methods: In this study, we aimed for cold-resistance gene discovery in cold-sensitive peach cultivar "21Shiji" (21SJ) and cold-resistance cultivar "Shijizhixing" (SJZX) using RNA-seq and gas chromatography. Results: The findings revealed that under cold stress conditions, ethylene biosynthesis in "SJZX" was significantly induced. Subsequently, a structural gene, PpACO1-1, involved in ethylene biosynthesis in peach buds was significantly upregulated and showed a higher correlation with ethylene release rate. To identify potential transcription factors associated with PpACO1-1 expression and ethylene signal transduction, weighted gene co-expression network analysis was conducted using RNA-seq data. Four transcription factors: PpERF2, PpNAC078, PpWRKY65 and PpbHLH112, were identified. Conclusion: These findings provide valuable theoretical insights for investigating the regulatory mechanisms of peach cold resistance and guiding breeding strategies.

BnAP2-12 overexpression delays ramie flowering: evidence from AP2/ERF gene expression

Introduction

The APETALA2/ethylene response factor (AP2/ERF) superfamily plays a significant role in regulating plant gene expression in response to growth and development. To date, there have been no studies into whether the ramie AP2/ERF genes are involved in the regulation of flower development.

Methods

Here, 84 BnAP2/ERF members were identified from the ramie genome database, and various bioinformatics data on the AP2/ERF gene family, structure, replication, promoters and regulatory networks were analysed. BnAP2-12 was transferred into Arabidopsis through the flower-dipping method.

Results

Phylogenetic analysis classified the 84 BnAP2/ERF members into four subfamilies: AP2 (18), RAV (3), ERF (42), and DREB (21). The functional domain analysis of genes revealed 10 conserved motifs. Genetic mapping localised the 84 members on 14 chromosomes, among which chromosomes 1, 3, 5, and 8 had more members. Collinearity analysis revealed that 43.37% possibly resulted from replication events during the evolution of the ramie genome. Promoter sequence analysis identified classified cis-acting elements associated with plant growth and development, and responses to stress, hormones, and light. Transcriptomic comparison identified 3,635 differentially expressed genes (DEGs) between male and female flowers (1,803 and 1,832 upregulated and downregulated genes, respectively). Kyoto Encyclopaedia of Genes and Genomes pathway analysis categorised DEGs involved in metabolic pathways and biosynthesis of secondary metabolites. Gene Ontology enrichment analysis further identified enriched genes associated with pollen and female gamete formations. Of the 84 BnAP2/ERFs genes, 22 and 8 upregulated and downregulated genes, respectively, were present in female flowers. Co-expression network analysis identified AP2/ERF members associated with flower development, including BnAP2-12. Subcellular localisation analysis showed that the BnAP2-12 protein is localised in the nucleus and cell membrane. Overexpression BnAP2-12 delayed the flowering time of Arabidopsis thaliana.

Conclusion

These findings provide insights into the mechanism of ramie flower development.

The DREB transcription factor, a biomacromolecule, responds to abiotic stress by regulating the expression of stress-related genes

Abiotic stress is a crucial factor that affects plant survival and growth and even leads to plant death in severe cases. Transcription factors can enhance the ability of plants to fight against various stresses by controlling the expression of downstream genes. The dehydration response element binding protein (DREB) is the most extensive subfamily of AP2/ERF transcription factors involved in abiotic stress. However, insufficient research on the signal network of DREB transcription factors has limited plant growth and reproduction. Furthermore, field planting of DREB transcription factors and their roles under multiple stress also require extensive research. Previous reports on DREB transcription factors have focused on the regulation of DREB expression and its roles in plant abiotic stress. In recent years, there has been new progress in DREB transcription factors. Here, the structure and classification, evolution and regulation, role in abiotic stress, and application in crops of DREB transcription factors were reviewed. And this paper highlighted the evolution of DREB1/CBF, as well as the regulation of DREB transcription factors under the participation of plant hormone signals and the roles of subgroups in abiotic stress. In the future, it will lay a solid foundation for further study of DREB transcription factors and pave the way for the cultivation of resistant plants.

Multilayered regulation of secondary metabolism in medicinal plants

Medicinal plants represent a huge reservoir of secondary metabolites (SMs), substances with significant pharmaceutical and industrial potential. However, obtaining secondary metabolites remains a challenge due to their low-yield accumulation in medicinal plants; moreover, these secondary metabolites are produced through tightly coordinated pathways involving many spatiotemporally and environmentally regulated steps. The first regulatory layer involves a complex network of transcription factors; a second, more recently discovered layer of complexity in the regulation of SMs is epigenetic modification, such as DNA methylation, histone modification and small RNA-based mechanisms, which can jointly or separately influence secondary metabolites by regulating gene expression. Here, we summarize the findings in the fields of genetic and epigenetic regulation with a special emphasis on SMs in medicinal plants, providing a new perspective on the multiple layers of regulation of gene expression.

Comparative Transcriptome Analysis Revealing the Potential Mechanism of Low-Temperature Stress in Machilus microcarpa

Machilus microcarpa is a rare national tree species in China and possesses important ornamental and ecological value. M. microcarpa can be planted in low-temperature areas, depending on whether its seedlings can withstand the harm. To face this problem, the annual seedlings of M. microcarpa were subjected to five temperature treatments, and eight physiological indicators were measured. Furthermore, comparative transcriptome analysis was performed between M. microcarpa leaves treated at 25°C and -2.8°C. A total of 9,385 differentially expressed genes (DEGs) were involved in low-temperature stress in M. microcarpa. An upregulated (cobA) and five downregulated (HEM, CHLM, CRD, CLH, and PORA) genes associated with the porphyrin and chlorophyll metabolism pathway may reduce chlorophyll synthesis under low-temperature stress. Upregulation of six DEGs (two GAPDHs, PFK, PGAM, PDC, and PK) involved in the glycolysis/gluconeogenesis pathway provided energy for M. microcarpa under adverse cold conditions. Thirteen upregulated and seven downregulated genes related to antioxidant enzymes were also observed under low-temperature stress. Candidate transcription factors (TFs) played key roles in signal transduction under low-temperature stress in M. microcarpa, and quantitative real-time PCR (qRT-PCR) analysis validated the RNA-seq data. The results provide valuable information for further studies on the cold response mechanisms for low-temperature stress in M. microcarpa.

Genome-Wide Identification and Comprehensive Analysis of the AP2/ERF Gene Family in Pomegranate Fruit Development and Postharvest Preservation

Pomegranate (Punica granatum L.) is a kind of fruit with significant economic, ecological and health values. AP2/ERF transcription factors belong to a large group of factors mainly found in plants and play key roles in plant growth and development. However, AP2/ERF genes in pomegranate and their implication in development and postharvest preservation have been little described. In this study, 116 PgAP2/ERF genes in pomegranate were identified and renamed based on their chromosomal distributions. Phylogenetic relationship with genes from other species, structures, duplications, annotations, cis-elements in promoter sequences, and protein-protein interaction networks among PgAP2/ERF proteins were comprehensively explored. Expression analysis revealed several PgAP2/ERFs associated with the phenotypes of pomegranate seed hardness, including PgAP2/ERF5, PgAP2/ERF36, PgAP2/ERF58, and PgAP2/ERF86. Subsequent analysis indicated that many differentially expressed PgAP2/ERF genes are potentially important regulators of pomegranate fruit development. Furthermore, expression of more than one-half of PgAP2/ERFs was repressed in 'Tunisian soft seed' pomegranate fruit under low-temperature cold storage. The results showed that 1-MCP implicated in promoting postharvest preservation of 'Tunisian soft seed' pomegranate upregulated the PgAP2/ERF4, PgAP2/ERF15, PgAP2/ERF26, PgAP2/ERF30, PgAP2/ERF35 and PgAP2/ERF45 genes compared to those under low-temperature cold storage. This indicates that these genes are important candidate genes involved in pomegranate postharvest preservation. In summary, the findings of the present study provide an important basis for characterizing the PgAP2/ERF family genes and provide information on the candidate genes involved in pomegranate fruit development and postharvest preservation.

Characterization of the early gene expression profile in Populus ussuriensis under cold stress using PacBio SMRT sequencing integrated with RNA-seq reads

Populus ussuriensis is an important and fast-growing afforestation plant species in north-eastern China. The whole-genome sequencing of P. ussuriensis has not been completed. Also, the transcriptional network of P. ussuriensis response to cold stress remains unknown. To unravel the early response of P. ussuriensis to chilling (3 °C) stress and freezing (-3 °C) stresses at the transcriptional level, we performed single-molecule real-time (SMRT) and Illumina RNA sequencing for P. ussuriensis. The SMRT long-read isoform sequencing led to the identification of 29,243,277 subreads and 575,481 circular consensus sequencing reads. Approximately 50,910 high-quality isoforms were generated, and 2272 simple sequence repeats and 8086 long non-coding RNAs were identified. The Ca2+ content and abscisic acid (ABA) content in P. ussuriensis were significantly increased under cold stresses, while the value in the freezing stress treatment group was significantly higher than the chilling stress treatment group. A total of 49 genes that are involved in the signal transduction pathways related to perception and transmission of cold stress signals, such as the Ca2+ signaling pathway, ABA signaling pathway and MAPK signaling cascade, were found to be differentially expressed. In addition, 158 transcription factors from 21 different families, such as MYB, WRKY and AP2/ERF, were differentially expressed during chilling and freezing treatments. Moreover, the measurement of physiological indicators and bioinformatics observations demonstrated the altered expression pattern of genes involved in reactive oxygen species balance and the sugar metabolism pathway during chilling and freezing stresses. This is the first report of the early responses of P. ussuriensis to cold stress, which lays the foundation for future studies on the regulatory mechanisms in cold-stress response. In addition the full-length reference transcriptome of P. ussuriensis deciphered could be used in future studies on P. ussuriensis.

Genome-Wide Identification, Characterization, and Expression Profiling of AP2/ERF Superfamily Genes under Different Development and Abiotic Stress Conditions in Pecan (Carya illinoinensis)

The ethylene-responsive element (AP2/ERF) is one of the keys and conserved transcription factors (TFs) in plants that play a vital role in regulating plant growth, development, and stress response. A total of 202 AP2/ERF genes were identified from the pecan genome and renamed according to the chromosomal distribution of the CiAP2/ERF genes. They were divided into four subfamilies according to the domain and phylogenetic analysis, including 26 AP2, 168 ERF, six RAV, and two Soloist gene family members. These genes were distributed randomly across the 16 chromosomes, and we found 19 tandem and 146 segmental duplications which arose from ancient duplication events. The gene structure and conserved motif analysis demonstrated the conserved nature of intron/exon organization and motifs among the AP2/ERF genes. Several cis-regulatory elements, which were related to light responsiveness, stress, and defense responses, were identified in the promoter regions of AP2/ERFs. The expression profiling of 202 CiAP2/ERF genes was assessed by using RNA-Seq data and qRT-PCR during development (pistillate flowering development, graft union development, and kernel development) and under abiotic stresses (waterlogging, drought). Moreover, the results suggested that the ERF-VII members may play a critical role in waterlogging stress. These findings provided new insights into AP2/ERF gene evolution and divergence in pecan and can be considered a valuable resource for further functional validation, as well as for utilization in a stress-resistance-variety development program.

AP2/ERF transcription factor GmDREB1 confers drought tolerance in transgenic soybean by interacting with GmERFs

Soybean is the main economic crop, and also the main source of oil and protein for human consumption. Drought stress has a great influence on the growth and yield of soybean crops. Therefore, improving the drought resistance of soybean, especially drought resistance in the field, is important to increase soybean yield. AP2/ERF (APETALA2/ethylene responsive factor) transcription factors are one of the largest families of transcription factors in plants. However, there has been little research on the value of applying DREB (dehydration-responsive element-binding)-like genes in improving the drought resistance of soybean. Here, we further study the value of the application of GmDREB1 in soybean. The results of drought resistance identification in the field and greenhouse showed that the overexpression of GmDREB1 could significantly enhance the drought resistance of transgenic soybean, and the yield was clearly higher than that of the wild type. GmDREB1 has transcriptional activity and is located in the nucleus. For mechanism analysis of GmDREB1 in soybean, two ERF-like transcription factors, GmERF008 and GmERF106, were shown to interact with GmDREB1 using yeast two-hybrid (Y2H) and bimolecular fluorescence complementary (BiFC) experiments. qRT-PCR (quantitative real-time PCR) results showed that the expression of many stress-related genes in GmDREB1 transgenic soybean were significantly up-regulated compared with the WT under a drought environment. In conclusion, GmDREB1 can regulate the expression of downstream stress-related genes by forming a heterodimer with ERF-like transcription factors, which can improve the drought resistance of transgenic soybean.

Genome-wide identification and expression analysis of ethylene responsive factor family transcription factors in Juglans regia

Background

Walnut is an important economic tree species with prominent economic value and ecological functions. However, in recent years, walnuts have become susceptible to drought stress, resulting in a decline in comprehensive benefits. Therefore, it is necessary to identify the regulatory molecular mechanism associated with walnut response to drought. In many plants, ethylene responsive factor (ERF) gene family plays important roles in response to biotic and abiotic stress, especial drought. Therefore, the identification and characterisation of walnut ERF genes will benefit walnut with regard to the clarification of drought response mechanism as well as the management, production, and quality of plantations.

Methods

‘ERF’ was compared against the walnut transcriptome, and the JrERFs with a complete open reading frame (ORF) were identified by ORF Finder. The molecular weights, amino acid residues, and theoretical isoelectric point (pI) were predicted by ExPASy. The distribution of JrERFs in chromosome locations was determined based on walnut genome data from NCBI. The intron-exon structures and conserved domains were analysed using Gene Structure Display Server 2.0 and CD-Search, accordingly. Multi-sequence alignment and a phylogenetic tree were constructed by ClustalX2.1 and MEGA7, respectively. The conserved motifs were acquired using MEME. Total RNA was isolated using the cetyltrimethylammonium ammonium bromide (CTAB) method (Yang et al., 2018). Gene expression was determined by using real-time quantitative polymerase chain reaction (qRT-PCR) analysis and calculated according to the 2^−ΔΔCT method (Livak & Schmittgen, 2001).

Results

A total of 44 JrERFs were identified from the walnut transcriptome, whose ORFs were 450–1,239 bp in length. The molecular weights of the JrERF proteins (consisting 149–412 amino acids) were 16.81–43.71 kDa, with pI ranging from 4.8 (JrERF11) to 9.89 (JrERF03). The JrERFs can be divided into six groups (B1–B6), and among the groups, B6 contained the most number of members. Each JrERF contained 1–6 motifs and each motif comprised 9–50 amino acids. Among the motifs, motif1, motif2, and motif3 were the most abundant. More than 40% of JrERFs were up-regulated continuously when subjected to ethephon (ETH), PEG₆₀₀₀, and PEG₆₀₀₀+ETH treatments. Of all the JrERFs, JrERF11 showed the highest expression. Therefore, we conclude that walnut ERF genes are highly conserved and involved in the regulation of drought response in the presence of ETH. JrERFs are possibly important candidate genes for molecular breeding; hence, the findings of this study provides the theoretical basis for further investigation of ERF genes in walnut and other species.

Impact of Genomic and Transcriptomic Resources on Apiaceae Crop Breeding Strategies

The Apiaceae taxon is one of the most important families of flowering plants and includes thousands of species used for food, flavoring, fragrance, medical and industrial purposes. This study had the specific intent of reviewing the main genomics and transcriptomic data available for this family and their use for the constitution of new varieties. This was achieved starting from the description of the main reproductive systems and barriers, with particular reference to cytoplasmic (CMS) and nuclear (NMS) male sterility. We found that CMS and NMS systems have been discovered and successfully exploited for the development of varieties only in Foeniculum vulgare, Daucus carota, Apium graveolens and Pastinaca sativa; whereas, strategies to limit self-pollination have been poorly considered. Since the constitution of new varieties benefits from the synergistic use of marker-assisted breeding in combination with conventional breeding schemes, we also analyzed and discussed the available SNP and SSR marker datasets (20 species) and genomes (8 species). Furthermore, the RNA-seq studies aimed at elucidating key pathways in stress tolerance or biosynthesis of the metabolites of interest were limited and proportional to the economic weight of each species. Finally, by aligning 53 plastid genomes from as many species as possible, we demonstrated the precision offered by the super barcoding approach to reconstruct the phylogenetic relationships of Apiaceae species. Overall, despite the impressive size of this family, we documented an evident lack of molecular data, especially because genomic and transcriptomic resources are circumscribed to a small number of species. We believe that our contribution can help future studies aimed at developing molecular tools for boosting breeding programs in crop plants of the Apiaceae family.

Genome-wide investigation of the AP2/ERF superfamily and their expression under salt stress in Chinese willow (Salix matsudana)

AP2/ERF transcription factors (TFs) play indispensable roles in plant growth, development, and especially in various abiotic stresses responses. The AP2/ERF TF family has been discovered and classified in more than 50 species. However, little is known about the AP2/ERF gene family of Chinese willow (Salix matsudana), which is a tetraploid ornamental tree species that is widely planted and is also considered as a species that can improve the soil salinity of coastal beaches. In this study, 364 AP2/ERF genes of Salix matsudana (SmAP2/ERF) were identified depending on the recently produced whole genome sequencing data of Salix matsudana. These genes were renamed according to the chromosomal location of the SmAP2/ERF genes. The SmAP2/ERF genes included three major subfamilies: AP2 (55 members), ERF (301 members), and RAV (six members) and two Soloist genes. Genes’ structure and conserved motifs were analyzed in SmAP2/ERF family members, and introns were not found in most genes of the ERF subfamily, some unique motifs were found to be important for the function of SmAP2/ERF genes. Syntenic relationships between the SmAP2/ERF genes and AP2/ERF genes from Populus trichocarpa and Salix purpurea showed that Salix matsudana is genetically more closely related to Populus trichocarpa than to Salix purpurea. Evolution analysis on paralog gene pairs suggested that progenitor of S. matsudana originated from hybridization between two different diploid salix germplasms and underwent genome duplication not more than 10 Mya. RNA sequencing results demonstrated the differential expression patterns of some SmAP2/ERF genes under salt stress and this information can help reveal the mechanism of salt tolerance regulation in Salix matsudana.

Identification, classification, and characterization of AP2/ERF superfamily genes in Masson pine (Pinus massoniana Lamb.)

Transcription factors (TFs) play crucial regulatory roles in controlling the expression of the target genes in plants. APETALA2/Ethylene-responsive factors (AP2/ERF) are part of a large superfamily of plant-specific TFs whose members are involved in the control of plant metabolism, development and responses to various biotic and abiotic stresses. However, the AP2/ERF superfamily has not been identified systematically in Masson pine (Pinus massoniana), which is one of the most important conifer in southern China. Therefore, we performed systematic identification of the AP2/ERF superfamily using transcriptome sequencing data from Masson pine. In the current study, we obtained 88 members of the AP2/ERF superfamily. All PmAP2/ERF members could be classified into 3 main families, AP2 (7 members), RAV (7 members), ERF (73 members) families, and a soloist protein. Subcellular localization assays suggested that two members of PmAP2/ERF were nuclear proteins. Based on pine wood nematode (PWN) inoculated transcriptome and qPCR analysis, we found that many members of PmAP2/ERF could respond to PWN inoculation and PWN related treatment conditions in vitro. In general, members of the AP2/ERF superfamily play an important role in the response of Masson pine responds to PWN. Furthermore, the roles of the AP2/ERF superfamily in other physiological activities of Masson pine remain to be further studied.

Whole-genome characterization of Rosa chinensis AP2/ERF transcription factors and analysis of negative regulator RcDREB2B in Arabidopsis

BACKGROUND

Rose (Rosa chinensis) is a traditional famous flower with valuable ornamental characteristics. However, drought stress restricts its growth and development, leading to an abnormal phenotype. One of the main transcription factor (TF) protein groups in the plant kingdom are the APETALA2/ethylene-responsive factor (AP2/ERF) proteins and are potentially involved in the growth and stress responses of various plants.

RESULTS

Our investigation mainly focused on exploring the genome of rose and thereby we discovered 135 apparent AP2/ERF TFs. Phylogenic analyses revealed that RcAP2/ERF genes are categorized into DREB, Soloist, AP2, and ERF subfamilies, and are further classified these into 17 groups, with the same as Malus domestica and Arabidopsis thaliana. The analysis of the gene structure revealed that the introns ranged from 0 to 9 in number. Pattern examination demonstrated that the RcAP2/ERF predominantly consists of typical AP2 domains, of which the 2nd motif is the most ubiquitous. Distributions of cis-acting elements indicated that members of the AP2/ERF family are frequently involved in growth and development, phytohormone and stress response in rose species. Also, the distribution mapping of the rose chromosomes indicated that AP2/ERF class genes are dispersed among all seven chromosomes. Additionally, we isolated a novel DREB A2 subgroup gene and named it RcDREB2B. Subsequently, the RcDREB2B transcript accumulation was repressed under the mild and severe drought stress in the root samples of rose. RcDREB2B was targeted to the nucleus and exhibited transactivation in yeast cells. The overexpression of RcDREB2B was found to promote sensitivity to a higher salt concentration, ABA, and PEG at the germination and post-germination stages. Twelve putative osmotic and ABA-related genes were impaired in RcDREB2B-overexpressing plants.

CONCLUSIONS

The results provide comprehensive information regarding the gene structure, phylogenic, and distribution of the rose AP2/ERF family and bring insight into the complex transcriptional gene regulation of RcAP2/ERF. Findings in this study would also contribute to further understanding of the RcDREB2B gene in rose.

A celery transcriptional repressor AgERF8 negatively modulates abscisic acid and salt tolerance

Ethylene response factors (ERFs) widely exist in plants and have been reported to be an important regulator of plant abiotic stress. Celery, a common economic vegetable of Apiaceae, contains lots of ERF transcription factors (TFs) with various functions. AP2/ERF TFs play positive or negative roles in plant growth and stress response. Here, AgERF8, a gene encoding EAR-type AP2/ERF TF, was identified. The AgERF8 mRNA accumulated in response to both abscisic acid (ABA) signaling and salt treatment. AgERF8 was proving to be a nucleus-located protein and could bind to GCC-box. The overexpression of AgERF8 in Arabidopsis repressed the transcription of downstream genes, AtBGL and AtBCH. Arabidopsis overexpressing AgERF8 gene showed inhibited root growth under ABA and NaCl treatments. AgERF8 transgenic lines showed low tolerance to ABA and salt stress than wild-type plants. Low increment in SOD and POD activities, increased accumulation of MDA, and significantly decreased plant fresh weights and chlorophyll levels were detected in AgERF8 hosting lines after treated with ABA and NaCl. Furthermore, the overexpression of AgERF8 also inhibited the levels of ascorbic acid and antioxidant-related genes (AtCAT1, AtSOD1, AtPOD, AtSOS1, AtAPX1, and AtP5CS1) expression in transgenic Arabidopsis. This finding indicated that AgERF8 negatively affected the resistance of transgenic Arabidopsis to ABA and salt stress through regulating downstream genes expression and relevant physiological changes. It will provide a potential sight to further understand the functions of ERF TFs in celery.

Molecular characterization and systematic analysis of NtAP2/ERF in tobacco and functional determination of NtRAV-4 under drought stress

The APETALA2/ethylene response factor (AP2/ERF) transcription factor (TF) superfamily play crucial roles in plant growth and development as well as biotic and abiotic stresses response. Here, we systematically characterized 375 AP2/ERF TFs in the Nicotiana tabacum genome. Phylogenetic tree topology and conserved domain number allowed TF classifications into three families of 29 AP2, 341 ERF, and 5 RAV genes, which were unevenly distributed throughout 24 tobacco chromosomes. Gene family expansions were retained from whole genome or segmental duplications followed by tandem duplication. Gene structure and motif analysis revealed intra-group conservation. MicroRNA target site prediction identified nine miR172 family members targeting six NtAP2-family genes; 41 NtAP2/ERFs participated in protein co-regulatory networks. NtAP2/ERF gene global expression profiles ascertained by RNA-seq displayed diverse expression patterns across tissues and under different abiotic and biotic stresses (including drought, cold, and Phytopthora parasitica inoculation). As determined by qRT-PCR, the expression of NtAP2/ERF were induced by five hormone and four abiotic stress. RNA interference of NtRAV-4 in tobacco accelerates seed germination, enhance root development and leaf photosynthetic ability. Suppression of NtRAV-4 increases drought tolerance by improving antioxidant defense ability and reduced relative electrolyte leakage under drought stress. These results enhance understanding of NtAP2/ERF gene function and will facilitate genetic improvement of tobacco stress tolerance.

Advances in AP2/ERF super-family transcription factors in plant

In the whole life process, many factors including external and internal factors affect plant growth and development. The morphogenesis, growth, and development of plants are controlled by genetic elements and are influenced by environmental stress. Transcription factors contain one or more specific DNA-binding domains, which are essential in the whole life cycle of higher plants. The AP2/ERF (APETALA2/ethylene-responsive element binding factors) transcription factors are a large group of factors that are mainly found in plants. The transcription factors of this family serve as important regulators in many biological and physiological processes, such as plant morphogenesis, responsive mechanisms to various stresses, hormone signal transduction, and metabolite regulation. In this review, we summarized the advances in identification, classification, function, regulatory mechanisms, and the evolution of AP2/ERF transcription factors in plants. AP2/ERF family factors are mainly classified into four major subfamilies: DREB (Dehydration Responsive Element-Binding), ERF (Ethylene-Responsive-Element-Binding protein), AP2 (APETALA2) and RAV (Related to ABI3/VP), and Soloists (few unclassified factors). The review summarized the reports about multiple regulatory functions of AP2/ERF transcription factors in plants. In addition to growth regulation and stress responses, the regulatory functions of AP2/ERF in plant metabolite biosynthesis have been described. We also discussed the roles of AP2/ERF transcription factors in different phytohormone-mediated signaling pathways in plants. Genomic-wide analysis indicated that AP2/ERF transcription factors were highly conserved during plant evolution. Some public databases containing the information of AP2/ERF have been introduced. The studies of AP2/ERF factors will provide important bases for plant regulatory mechanisms and molecular breeding.

Antiliver Fibrosis Screening of Active Ingredients from Apium graveolens L. Seeds via GC-TOF-MS and UHPLC-MS/MS

Although several studies have been performed on Apium graveolens L.(celery) seeds, their antiliver fibrosis effects remain to be unexplored. Firstly, we detected the effects of celery seeds extracted with different concentrations of aqueous ethanol on the proliferation of HSC-LX2 cells. Then, we detected the effects of fractions of the optimal effect extract on the proliferation and apoptosis of HSC-LX2 cells. Finally, the compounds of petroleum ether (PP), ethyl acetate (PE), n-butyl alcohol (PB), and water fractions (PW) of the optimal effect extract were determined by GC-TOF-MS and UHPLC-MS/MS, to confirm the potentially antifibrotic compounds combined with pharmacodynamic experiment of monomer compounds in vitro. The results revealed that 60% ethanol extract of celery seeds (60-extract) exhibited remarkable inhibition effect on the proliferation of HSC-LX2 cells compared with 95% ethanol and aqueous extract. Besides, it validated that the inhibition rates of PP, PE, PB, and PW on the proliferation of HSC-LX2 cells were 75.14%, 73.52%, 54.09%, and 43.36%, and their percentage of apoptotic cells were 37.5%, 4.3%, 0.7%, and 0.1% at high doses, respectively. Additionally, it was manifested that apigenin, aesculetin, and butylphthalide have major contribution to the overall compounds of celery seeds, and the inhibition effects on the cell proliferation clearly elevated with increase in their contents. In essence, apigenin, aesculetin, and butylphthalide may hopefully become the natural products of antiliver fibrosis, which laid a foundation for the subsequent development of celery seeds as antiliver fibrosis drugs.

Transcriptome-Wide Identification, Evolutionary Analysis, and GA Stress Response of the GRAS Gene Family in Panax ginseng C. A. Meyer

GRAS transcription factors are a kind of plant-specific transcription factor that have been found in a variety of plants. According to previous studies, GRAS proteins are widely involved in the physiological processes of plant signal transduction, stress, growth and development. The Jilin ginseng (Panax ginseng C.A. Meyer) is a heterogeneous tetraploid perennial herb of the Araliaceae family, ginseng genus. Important information regarding the GRAS transcription factors has not been reported in ginseng. In this study, 59 Panax ginseng GRAS (PgGRAS) genes were obtained from the Jilin ginseng transcriptome data and divided into 13 sub-families according to the classification of Arabidopsis thaliana. Through systematic evolution, structural variation, function and gene expression analysis, we further reveal GRAS’s potential function in plant growth processes and its stress response. The expression of PgGRAS genes responding to gibberellin acids (GAs) suggests that these genes could be activated after application concentration of GA. The qPCR analysis result shows that four PgGRAS genes belonging to the DELLA sub-family potentially have important roles in the GA stress response of ginseng hairy roots. This study provides not only a preliminary exploration of the potential functions of the GRAS genes in ginseng, but also valuable data for further exploration of the candidate PgGRAS genes of GA signaling in Jilin ginseng, especially their roles in ginseng hairy root development and GA stress response.

Celery and Celeriac: A Critical View on Present and Future Breeding

Cultivated for the crispy petioles and round, fleshy, and flavored hypocotyl celery and celeriac have over two centuries of breeding history in Europe. In this review paper we summarized the most recent advances touching when necessary the historical context of celery and celeriac breeding. In the post genomic era of research, the genome sequence of celery is only partially available. We comprised however in this paper the most important aspects of celery genetics that are available today and have applicability in celery modern cultivars development. We discussed the problems and traits that drive the main celery and celeriac breeding goals, like hybrid seed production, disease resistance, and interesting enlarged hypocotyl and petiole characteristics. Besides the classical breeding traits we covered the potential of integration of existing cultivars as sources for consumer oriented traits like nutraceuticals and health promoting substances. Sustainability is a subject that is continuously growing in popularity and we looked at the genetic base of celery and celeriac that makes them sources for abiotic stress resistance and candidates for phytoremediation. We explored the fundamental concepts gained in various fields of celery and related species research, as resources for future improvement of celery and celeriac germplasm. We forecast what the next years will bring to Apium breeding.