Functional roles of the birch BpRAV1 transcription factor in salt and osmotic stress response

The cold-responsive C-repeat binding factors in Betula platyphylla Suk. positively regulate cold tolerance

Cold stress is one of the most destructive abiotic stresses limiting plant growth and development. CBF (C-repeat binding factor) transcription factors and their roles in cold response have been identified in Arabidopsis as well as several other plant species. However, the biological functions and related molecular mechanisms of CBFs in birch (Betula platyphylla Suk.) remain undetermined. In this study, five cold-responsive BpCBF genes, BpCBF1, BpCBF2, BpCBF7, BpCBF10 and BpCBF12 were cloned. Via protoplast transformation, BpCBF7 was found to be localized in nucleus. The result of yeast one hybrid assay validated the binding of BpCBF7 to the CRT/DRE (C-repeat/dehydration responsive element) elements in the promoter of BpERF1.1 gene. By overexpressing and repressing BpCBFs in birch plants, it was proven that BpCBFs play positive roles in the cold tolerance. At the metabolic level, BpCBFs OE lines had lower ROS accumulation, as well as higher activities of antioxidant enzymes (SOD, POD and CAT) and higher accumulation of protective substances (soluble sugar, soluble protein and proline). Via yeast one hybrid and co-transformation of effector and reporter vectors assay, it was proven that BpCBF7 can regulate the expression of BpERF5 and BpZAT10 genes by directly binding to their promoters. An interacting protein of BpCBF7, BpWRKY17, was identified by yeast two hybrid library sequencing and the interaction was validated with in vivo methods. These results indicates that BpCBFs can increase the cold tolerance of birch plants, partly by gene regulation and protein interaction. This study provides a reference for the research on CBF transcription factors and genetic improvement of forest trees upon abiotic stresses.

Molecular identification and functional characterization of a transcription factor GeRAV1 from Gelsemium elegans

BACKGROUND

Gelsemium elegans is a traditional Chinese medicinal plant and temperature is one of the key factors affecting its growth. RAV (related to ABI3/VP1) transcription factor plays multiple roles in higher plants, including the regulation of plant growth, development, and stress response. However, RAV transcription factor in G. elegans has not been reported.

RESULTS

In this study, three novel GeRAV genes (GeRAV1-GeRAV3) were identified from the transcriptome of G. elegans under low temperature stress. Phylogenetic analysis showed that GeRAV1-GeRAV3 proteins were clustered into groups II, IV, and V, respectively. RNA-sequencing (RNA-seq) and real-time quantitative PCR (qRT-PCR) analyses indicated that the expression of GeRAV1 and GeRAV2 was increased in response to cold stress. Furthermore, the GeRAV1 gene was successfully cloned from G. elegans leaf. It encoded a hydrophilic, unstable, and non-secretory protein that contained both AP2 and B3 domains. The amino acid sequence of GeRAV1 protein shared a high similarity of 81.97% with Camptotheca acuminata CaRAV. Subcellular localization and transcriptional self-activation experiments demonstrated that GeRAV1 was a nucleoprotein without self-activating activity. The GeRAV1 gene was constitutively expressed in the leaves, stems, and roots of the G. elegans, with the highest expression levels in roots. In addition, the expression of the GeRAV1 gene was rapidly up-regulated under abscisic acid (ABA), salicylic acid (SA), and methyl jasmonate (MeJA) stresses, suggesting that it may be involved in hormonal signaling pathways. Moreover, GeRAV1 conferred improved cold and sodium chloride tolerance in Escherichia coli Rosetta cells.

CONCLUSIONS

These findings provided a foundation for further understanding on the function and regulatory mechanism of the GeRAV1 gene in response to low-temperature stress in G. elegans.

SmRAV1, an AP2 and B3 Transcription Factor, Positively Regulates Eggplant's Response to Salt Stress

Salt stress is a lethal abiotic stress threatening global food security on a consistent basis. In this study, we identified an AP2 and B3 domain-containing transcription factor (TF) named SmRAV1, and its expression levels were significantly up-regulated by NaCl, abscisic acid (ABA), and hydrogen peroxide (H2O2) treatment. High expression of SmRAV1 was observed in the roots and sepal of mature plants. The transient expression assay in Nicotiana benthamiana leaves revealed that SmRAV1 was localized in the nucleus. Silencing of SmRAV1 via virus-induced gene silencing (VIGS) decreased the tolerance of eggplant to salt stress. Significant down-regulation of salt stress marker genes, including SmGSTU10 and SmNCED1, was observed. Additionally, increased H2O2 content and decreased catalase (CAT) enzyme activity were recorded in the SmRAV1-silenced plants compared to the TRV:00 plants. Our findings elucidate the functions of SmRAV1 and provide opportunities for generating salt-tolerant lines of eggplant.

The RAV transcription factor TEMPRANILLO1 involved in ethylene-mediated delay of chrysanthemum flowering

TEMPRANILLO1 (TEM1) is a transcription factor belonging to related to ABI3 and VP1 family, which is also known as ethylene response DNA-binding factor 1 and functions as a repressor of flowering in Arabidopsis. Here, a putative homolog of AtTEM1 was isolated and characterized from chrysanthemum, designated as CmTEM1. Exogenous application of ethephon leads to an upregulation in the expression of CmTEM1. Knockdown of CmTEM1 promotes floral initiation, while overexpression of CmTEM1 retards floral transition. Further phenotypic observations suggested that CmTEM1 involves in the ethylene-mediated inhibition of flowering. Transcriptomic analysis established that expression of the flowering integrator CmAFL1, a member of the APETALA1/FRUITFULL subfamily, was downregulated significantly in CmTEM1-overexpressing transgenic plants compared with wild-type plants but was verified to be upregulated in amiR-CmTEM1 lines by quantitative RT-PCR. In addition, CmTEM1 is capable of binding to the promoter of the CmAFL1 gene to inhibit its transcription. Moreover, the genetic evidence supported the notion that CmTEM1 partially inhibits floral transition by targeting CmAFL1. In conclusion, these findings demonstrate that CmTEM1 acts as a regulator of ethylene-mediated delayed flowering in chrysanthemum, partly through its interaction with CmAFL1.

Genome-Wide Identification and Characterization of WRKY Transcription Factors in Betula platyphylla Suk. and Their Responses to Abiotic Stresses

The WRKY transcription factor (TF) family is one the largest plant-specific transcription factor families. It has been proven to play significant roles in multiple plant biological processes, especially stress response. Although many WRKY TFs have been identified in various plant species, WRKYs in white birch (Betula platyphylla Suk.) remain to be studied. Here, we identified a total of 68 BpWRKYs, which could be classified into four main groups. The basic physiochemical properties of these TFs were analyzed using bioinformatics tools, including molecular weight, isoelectric point, chromosome location, and predicted subcellular localization. Most BpWRKYs were predicted to be located in the nucleus. Synteny analysis found 17 syntenic gene pairs among BpWRKYs and 52 syntenic gene pairs between BpWRKYs and AtWRKYs. The cis-acting elements in the promoters of BpWRKYs could be enriched in multiple plant biological processes, including stress response, hormone response, growth and development, and binding sites. Tissue-specific expression analysis using qRT-PCR showed that most BpWRKYs exhibited highest expression levels in the root. After ABA, salt (NaCl), or cold treatment, different BpWRKYs showed different expression patterns at different treatment times. Furthermore, the results of the Y2H assay proved the interaction between BpWRKY17 and a cold-responsive TF, BpCBF7. By transient expression assay, BpWRKY17 and BpWRKY67 were localized in the nucleus, consistent with the previous prediction. Our study hopes to shed light for research on WRKY TFs and plant stress response.

Genome-Wide Identification and Expression Profiles of C-Repeat Binding Factor Transcription Factors in Betula platyphylla under Abiotic Stress

CBF (C-repeat binding factor) transcription factor subfamily belongs to AP2/ERF (Apetala 2/ethylene-responsive factor) transcription factor family, known for playing a vital role in plant abiotic stress response. Although some CBF transcription factors have been identified in several species, such as Arabidopsis, tobacco, tomato and poplar, research of CBF focus mainly on model plant Arabidopsis and have not been reported in Betula platyphylla yet. In this study, a total of 20 BpCBF subfamily members were identified. The conserved domains, physicochemical properties, exon-intron gene structure and the structure of conserved protein motifs of BpCBFs were analyzed via bioinformatic tools. The collinearity analysis of CBF genes was performed between Betula platyphylla and Arabidopsis thaliana, Betula platyphylla, and Populus trichocarpa. The cis-acting elements in the promoter region of BpCBFs were identified, which were mainly environmental stress-related and hormone-related element components. In this case, the expression patterns of the 20 BpCBFs upon ABA or salt treatment were investigated. Most of these transcription factors were responsive to ABA or salt stress in different plant tissues. The up-regulation trend upon cold treatment of the six cold-responsive genes validated by qRT-PCR was consistent with the result of RNA-seq. BpCBF7 showed transcription activating activity. This study sheds light on the responses of BpCBFs to abiotic stress and provides a reference for further study of CBF transcription factors in woody plants.

Genome-Wide Analysis of the RAV Gene Family in Wheat and Functional Identification of TaRAV1 in Salt Stress

RAV transcription factors (TFs) are unique to higher plants and contain both B3 and APETALA2 (AP2) DNA binding domains. Although sets of RAV genes have been identified from several species, little is known about this family in wheat. In this study, 26 RAV genes were identified in the wheat genome. These wheat RAV TFs were phylogenetically clustered into three classes based on their amino acid sequences. A TaRAV gene located on chromosome 1D was cloned and named TaRAV1. TaRAV1 was expressed in roots, stems, leaves, and inflorescences, and its expression was up-regulated by heat while down-regulated by salt, ABA, and GA. Subcellular localization analysis revealed that the TaRAV1 protein was localized in the nucleus. The TaRAV1 protein showed DNA binding activity in the EMSA assay and transcriptional activation activity in yeast cells. Overexpressing TaRAV1 enhanced the salt tolerance of Arabidopsis and upregulated the expression of SOS genes and other stress response genes. Collectively, our data suggest that TaRAV1 functions as a transcription factor and is involved in the salt stress response by regulating gene expression in the SOS pathway.