Genetic and evolutionary dissection of melatonin response signaling facilitates the regulation of plant growth and stress responses

The expansion of gene families during evolution could generate functional diversity among their members to regulate plant growth and development. Melatonin, a phylogenetically ancient molecule, is vital for many aspects of a plant's life. Understanding the functional diversity of the molecular players involved in melatonin biosynthesis, signaling, and metabolism will facilitate the regulation of plant phenotypes. However, the molecular mechanism of melatonin response signaling elements in regulating this network still has many challenges. Here, we provide an in-depth analysis of the functional diversity and evolution of molecular components in melatonin signaling pathway. Genetic analysis of multiple mutants in plant species will shed light on the role of gene families in melatonin regulatory pathways. Phylogenetic analysis of these genes was performed, which will facilitate the identification of melatonin-related genes for future study. Based on the abovementioned signal networks, the mechanism of these genes was summarized to provide reference for studying the regulatory mechanism of melatonin in plant phenotypes. We hope that this work will facilitate melatonin research in higher plants and finely tuned spatio-temporal regulation of melatonin signaling.

Promoter activity and transcriptome analyses decipher functions of CgbHLH001 gene (Chenopodium glaucum L.) in response to abiotic stress

BACKGROUND

Our previous studies revealed that CgbHLH001 transcription factor (TF) played an important role in abiotic stress tolerance, suggesting that its promoter was a potential target in response to stress signals. In addition, the regulatory mechanism of CgbHLH001 TF is still limited.

RESULTS

In the present study, a 1512 bp of 5'-flanking sequence of CgbHLH001 gene was identified, and the sequence carried quite a few of cis-acting elements. The gene promoter displayed strong activity and was induced by multiple abiotic stress. A series of 5'-deletions of the promoter sequence resulted in a gradual decrease in its activity, especially, the 5' untranslated region (UTR) was necessary to drive promoter activity. Further, CgbHLH001 promoter drove its own gene overexpression ectopically at the transcriptional and translational levels, which in turn conferred the stress tolerance to transgenic Arabidopsis. Transcriptome analysis showed that salt stress induced a large number of genes involved in multiple biological regulatory processes. Differentially expressed genes (DEGs) that mediate phytohormone signal transduction and mitogen-activated protein kinase (MAPK) signaling pathway were widely induced and mostly upregulated under salt stress, and the transcription levels in P_bHLH::bHLH-overexpressing transgenic lines were higher than that of 35S::bHLH overexpression.

CONCLUSIONS

The CgbHLH001 promoter exhibited a positive response to abiotic stress and its 5' UTR sequence enhanced the regulation of gene expression to stress. A few important pathways and putative key genes involved in salt tolerance were identified, which can be used to elucidate the mechanism of salt tolerance and decipher the regulatory mechanism of promoters to develop an adaptation strategy for desert halophytes.

LaDAL1 Coordinates Age and Environmental Signals in the Life Cycle of Larix kaempferi

Perennial woody plants are long-lived, and their life-cycle events occur in order in each generation, but what drives the occurrence and restart of these events in their offspring is unknown. Based on its age-dependent expression pattern and function, Larix kaempferi DEFICIENS-AGAMOUS-LIKE 1 (LaDAL1), a MADS transcription factor has been suggested to be a time recorder and life-cycle event coordinator. Here, we studied the dynamic spatiotemporal expression pattern of LaDAL1 in the life cycle of L. kaempferi to analyze the molecular mechanism of life-cycle progression. In full view of the life cycle, LaDAL1 transcription was related with life-cycle progression, and its transcript level increased sharply from age 3 to 5 years, which might be the molecular characteristic of the vegetative phase change, and then stayed at a high level. During sexual reproduction, LaDAL1 transcript level decreased sequentially during meiosis and embryogenesis, suggesting that meiosis rapidly lowers the age signal, and after fertilization, the age signal was reset to "0" with the embryogenesis. When a seed germinates, the next generation restarts, and the age is re-counted. Altogether, these results not only provide important and novel insights into the life-cycle progression and transgeneration in perennial woody plants, but also advance our understanding of age recording.

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.

Novel QTL identification and candidate gene analysis for enhancing salt tolerance in soybean (Glycine max (L.) Merr.)

Soybean, a glycophyte that is sensitive to salt stress, is greatly affected by salinity at all growth stages. A mapping population derived from a cross between a salt-sensitive Korean cultivar, Cheongja 3, and a salt-tolerant landrace, IT162669, was used to identify quantitative trait loci (QTLs) conferring salt tolerance in soybean. Following treatment with 120 mM NaCl for 2 weeks, phenotypic traits representing physiological damage, leaf Na+ content, and K+/Na+ ratio were characterized. Among the QTLs mapped on a high-density genetic map harboring 2,630 single nucleotide polymorphism markers, we found two novel major loci, qST6, on chromosome 6, and qST10, on chromosome 10, which controlled traits related to ion toxicity and physiology in response to salinity, respectively. These loci were distinct from the previously known salt tolerance allele on chromosome 3. Other QTLs associated with abiotic stress overlapped with the genomic regions of qST6 and qST10, or with their paralogous regions. Based on the functional annotation and parental expression differences, we identified eight putative candidate genes, two in qST6 and six in qST10, which included a phosphoenolpyruvate carboxylase and an ethylene response factor. This study provides additional genetic resources to breed soybean cultivars with enhanced salt tolerance.

Genome-wide investigation of the AP2/ERF gene family in ginger: evolution and expression profiling during development and abiotic stresses

BACKGROUND

AP2/ERF transcription factors (TFs) constitute one of the largest TF families in plants, which play crucial roles in plant metabolism, growth, and development as well as biotic and abiotic stresses responses. Although the AP2/ERF family has been thoroughly identified in many plant species and several AP2/ERF TFs have been functionally characterized, little is known about this family in ginger (Zingiber officinale Roscoe), an important affinal drug and diet vegetable. Recent completion of the ginger genome sequencing provides an opportunity to investigate the expression profiles of AP2/ERF genes in ginger on a genome-wide basis.

RESULTS

A total of 163 AP2/ERF genes were obtained in the Z.officinale genome and renamed according to the chromosomal distribution of the ZoAP2/ERF genes. Phylogenetic analysis divided them into three subfamilies, of which 35 belonged to the AP2 subfamily, 120 to ERF, three to RAV, and five to Sololist, respectively, which is in accordance with the number of conserved domains and gene structure analysis. A total of 10 motifs were detected in ZoAP2/ERF genes, and some of the unique motifs were found to be important for the function of ZoAP2/ERF genes. The chromosomal localization, gene structure, and conserved protein motif analyses, as well as the characterization of gene duplication events provided deep insight into the evolutionary features of these ZoAP2/ERF genes. The expression profiles derived from the RNA-seq data and quantitative reserve transcription (qRT-PCR) analysis of ZoAP2/ERFs during development and responses to abiotic stresses were investigated in ginger.

CONCLUSION

A comprehensive analysis of the AP2/ERF gene expression patterns in various tissues by RNA-seq and qRT-PCR showed that they played an important role in the growth and development of ginger, and genes that might regulate rhizome and flower development were preliminary identified. In additionally, the ZoAP2/ERF family genes that responded to abiotic stresses were also identified. This study is the first time to identify the ZoAP2/ERF family, which contributes to research on evolutionary characteristics and better understanding the molecular basis for development and abiotic stress response, as well as further functional characterization of ZoAP2/ERF genes with an aim of ginger crop improvement.

Genome-Wide Identification and Expression Analysis of AP2/ERF Transcription Factor Related to Drought Stress in Cultivated Peanut (Arachis hypogaea L.)

APETALA2/ethylene response element-binding factor (AP2/ERF) transcription factors (TFs) have been found to regulate plant growth and development and response to various abiotic stresses. However, detailed information of AP2/ERF genes in peanut against drought has not yet been performed. Herein, 185 AP2/ERF TF members were identified from the cultivated peanut (A. hypogaea cv. Tifrunner) genome, clustered into five subfamilies: AP2 (APETALA2), ERF (ethylene-responsive-element-binding), DREB (dehydration-responsive-element-binding), RAV (related to ABI3/VP), and Soloist (few unclassified factors)). Subsequently, the phylogenetic relationship, intron-exon structure, and chromosomal location of AhAP2/ERF were further characterized. All of these AhAP2/ERF genes were distributed unevenly across the 20 chromosomes, and 14 tandem and 85 segmental duplicated gene pairs were identified which originated from ancient duplication events. Gene evolution analysis showed that A. hypogaea cv. Tifrunner were separated 64.07 and 66.44 Mya from Medicago truncatula L. and Glycine max L., respectively. Promoter analysis discovered many cis-acting elements related to light, hormones, tissues, and stress responsiveness process. The protein interaction network predicted the exitance of functional interaction among families or subgroups. Expression profiles showed that genes from AP2, ERF, and dehydration-responsive-element-binding subfamilies were significantly upregulated under drought stress conditions. Our study laid a foundation and provided a panel of candidate AP2/ERF TFs for further functional validation to uplift breeding programs of drought-resistant peanut cultivars.

The ABA-induced soybean ERF transcription factor gene GmERF75 plays a role in enhancing osmotic stress tolerance in Arabidopsis and soybean

BACKGROUND

Ethylene-responsive factors (ERFs) play important roles in plant growth and development and the response to adverse environmental factors, including abiotic and biotic stresses.

RESULTS

In the present study, we identified 160 soybean ERF genes distributed across 20 chromosomes that could be clustered into eight groups based on phylogenetic relationships. A highly ABA-responsive ERF gene, GmERF75, belonging to Group VII was further characterized. Subcellular localization analysis showed that the GmERF75 protein is localized in the nucleus, and qRT-PCR results showed that GmERF75 is responsive to multiple abiotic stresses and exogenous hormones. GmERF75-overexpressing Arabidopsis lines showed higher chlorophyll content compared to WT and mutants under osmotic stress. Two independent Arabidopsis mutations of AtERF71, a gene homologous to GmERF75, displayed shorter hypocotyls, and overexpression of GmERF75 in these mutants could rescue the short hypocotyl phenotypes. Overexpressing GmERF75 in soybean hairy roots improved root growth under exogenous ABA and salt stress.

CONCLUSIONS

These results suggested that GmERF75 is an important plant transcription factor that plays a critical role in enhancing osmotic tolerance in both Arabidopsis and soybean.

Genome-wide investigation of the AP2/ERF gene family in tartary buckwheat (Fagopyum Tataricum)

BACKGROUND

AP2/ERF transcription factors perform indispensable functions in various biological processes, such as plant growth, development, biotic and abiotic stresses responses. The AP2/ERF transcription factor family has been identified in many plants, and several AP2/ERF transcription factors from Arabidopsis thaliana (A. thaliana) have been functionally characterized. However, little research has been conducted on the AP2/ERF genes of tartary buckwheat (Fagopyum tataricum), which is an important edible and medicinal crop. The recently published whole genome sequence of tartary buckwheat allowed us to study the tissue and expression profiles of AP2/ERF genes in tartary buckwheat on a genome-wide basis.

RESULTS

In this study, 134 AP2/ERF genes of tartary buckwheat (FtAP2/ERF) were identified and renamed according to the chromosomal distribution of the FtAP2/ERF genes. According to the number conserved domains and gene structure, the AP2/ERF genes were divided into three subfamilies by phylogenetic tree analysis, namely, AP2 (15 members), ERF (116 members) and RAV (3 members). A total of 10 motifs were detected in tartary buckwheat AP2/ERF genes, and some of the unique motifs were found to be important for the function of AP2/ERF genes.

CONCLUSION

A comprehensive analysis of AP2/ERF gene expression patterns in different tissues and fruit development stages by quantitative real-time PCR (qRT-PCR) showed that they played an important role in the growth and development of tartary buckwheat, and genes that might regulate flower and fruit development were preliminarily identified. This systematic analysis establishes a foundation for further studies of the functional characteristics of FtAP2/ERF genes and improvement of tartary buckwheat crops.

The Constitutive Expression of a Chrysanthemum ERF Transcription Factor Influences Flowering Time in Arabidopsis thaliana

AP2/ERF transcription factors (TFs) represent valuable targets for the genetic manipulation of crop plants, as they participate in the control of metabolism, growth and development, as well as in the plants' response to environmental stimuli. Here, an ERF TF encoded by the chrysanthemum (Chrysanthemum morifolium) genome, designated CmERF110, was cloned and functionally characterized. The predicted CmERF110 polypeptide included a conserved DNA-binding AP2/ERF domain. A transient expression experiment revealed that the protein was deposited in the nucleus, and a transactivation experiment in yeast suggested that it had no transcriptional activity. The gene was transcribed in the chrysanthemum root, stem and leaf, with its transcript level following a circadian rhythm under both long and short days. The effect of constitutively expressing the gene in Arabidopsis thaliana was to accelerate flowering. Transcriptional profiling implied that its effect on floral initiation operated through the photoperiod pathway.

Over-Expression of ERF38 Gene Enhances Salt and Osmotic Tolerance in Transgenic Poplar

Ethylene response factor (ERF) gene family plays an important role in abiotic stress responses. In this study, we isolated a salt-inducible ERF gene, ERF38 (Potri.006G138900.1), from the 84K poplar (Populus alba × Populus glandulosa) and investigated its functions in salt and osmotic tolerance. We identified that ERF38 protein was targeted to nucleus and had no self-activation. Results from yeast-one-hybrid indicated that the ERF38 protein can specifically bind to the dehydration responsive element (DRE). We then successfully transferred the ERF38 gene into the 84K poplar. Under respective salt and polyethylene glycol (PEG)-6000 stresses, four of the physiological traits, including peroxidase (POD) and superoxide dismutase (SOD) activities, soluble protein content, and proline content, increased significantly in the transgenic plants, compared to the wild type. Regarding the other two parameters, hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) content, their increments in the transgenic lines under the stresses, which were compared to the water control, were significantly low than that of the wild type. In addition, reactive oxygen species (ROS) are scavenged in the transgenic lines under the stresses, but not in the wild type (WT). Interestingly, when challenged with the stresses, expression levels of a few genes associated with POD and SOD metabolism were significantly increased in the transgenic poplars. In all, evidence from morphological, physiological, and biochemical analyses indicated that over-expression of ERF38 gene can improve salt and osmotic tolerance in the transgenic poplar.