WRKY transcription factors play important roles in plant growth development, resistance and substance metabolism regulation. However, the exact function of the response to salt stress in plants with specific WRKY transcription factors remains unclear. In this research, we isolated a new WRKY transcription factor DgWRKY5 from chrysanthemum. DgWRKY5 contains two WRKY domains of WKKYGQK and two C2H2 zinc fingers. The expression of DgWRKY5 in chrysanthemum was up-regulated under various treatments. Meanwhile, we observed higher expression levels in the leaves contrasted with other tissues. Under salt stress, the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) enzymes in transgenic chrysanthemum were significantly higher than those in WT, whereas the accumulation of H2O2, O2 − and malondialdehyde (MDA) was reduced in transgenic chrysanthemum. Several parameters including root length, root length, fresh weight, chlorophyll content and leaf gas exchange parameters in transgenic chrysanthemum were much better compared with WT under salt stress. Moreover, the expression of stress-related genes DgAPX, DgCAT, DgNCED3A, DgNCED3B, DgCuZnSOD, DgP5CS, DgCSD1 and DgCSD2 was up-regulated in DgWRKY5 transgenic chrysanthemum compared with that in WT. These results suggested that DgWRKY5 could function as a positive regulator of salt stress in chrysanthemum.

BackgroundChrysanthemum is one kind of ornamental plant well-known and widely used in the world. However, its quality and production were severely affected by low temperature conditions in winter and early spring periods. Therefore, we used the RNA-Seq platform to perform a de novo transcriptome assembly to analyze chrysanthemum (Dendranthema grandiflorum) transcription response to low temperature.ResultsUsing Illumina sequencing technology, a total of 86,444,237 high-quality clean reads and 93,837 unigenes were generated from four libraries: T01, controls; T02, 4 °C cold acclimation (CA) for 24 h; T03, − 4 °C freezing treatments for 4 h with prior CA; and T04, − 4 °C freezing treatments for 4 h without prior CA. In total, 7583 differentially expressed genes (DEGs) of 36,462 annotated unigenes were identified. We performed GO and KEGG pathway enrichment analyses, and excavated a group of important cold-responsive genes related to low temperature sensing and signal transduction, membrane lipid stability, reactive oxygen species (ROS) scavenging and osmoregulation. These genes encode many key proteins in plant biological processes, such as protein kinases, transcription factors, fatty acid desaturase, lipid-transfer proteins, antifreeze proteins, antioxidase and soluble sugars synthetases. We also verified expression levels of 10 DEGs using quantitative real-time polymerase chain reaction (qRT-PCR). In addition, we performed the determination of physiological indicators of chrysanthemum treated at low temperature, and the results were basically consistent with molecular sequencing results.ConclusionIn summary, our study presents a genome-wide transcript profile of Dendranthema grandiflorum var. jinba and provides insights into the molecular mechanisms of D. grandiflorum in response to low temperature. These data contributes to our deeper relevant researches on cold tolerance and further exploring new candidate genes for chilling-tolerance and freezing-tolerance chrysanthemum molecular breeding.Electronic supplementary materialThe online version of this article (10.1186/s12864-018-4706-x) contains supplementary material, which is available to authorized users.

Background and Objectives Basic fibroblast growth factor (bFGF) promotes cells proliferation and chemotaxis and maintains stemness while inhibits mineralized nodule formation. Bone morphogenetic protein 2 (BMP‐2) shows great potential in promoting bone formation. However, sequential application of these two growth factors on periodontal ligament stem cells (PDLSCs) has not been explored. In this study, we aimed to identify the optimal concentration and time of bFGF on PDLSCs proliferation, migration and then investigate the sequential delivery of bFGF and BMP‐2 on osteogenic differentiation of PDLSCs in vitro. Materials and Methods Periodontal ligament stem cells were isolated by limiting dilution method. Dose‐dependent additive effects of bFGF and BMP‐2 on PDLSCs were detected. Cell counting assay, cell migration assay, alkaline phosphatase (ALP) activity assay, Alizarin red staining, quantitative real‐time polymerase chain reaction (qRT‐PCR), and western blot analysis were used to determine different application modalities of bFGF and BMP‐2 on proliferation, migration, and osteogenic differentiation of PDLSCs. Results 50 ng/mL bFGF significantly promoted PDLSCs proliferation and chemotaxis while time‐dependently inhibited BMP‐2 induced ALP activity. Sequential application of 25 ng/mL bFGF for first 3 days and followed with 50 ng/mL BMP‐2 for another 9, 18, and 25 days significantly promoted PDLSCs osteogenic differentiation. Compared with bFGF and BMP‐2 simultaneous group, sequential application of bFGF and BMP‐2 group significantly enhanced ALP activity, osteogenesis‐related genes and proteins expression and mineral deposition. Conclusion Sequential application of bFGF and BMP‐2 synergistically promoted osteogenic differentiation of PDLSCs, and this sequential application modality of growth factors would provide a new strategy for periodontal regeneration.

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DgNAC1, a transcription factor of chrysanthemum, was functionally verified to confer salt stress responses by regulating stress-responsive genes. NAC transcription factors play effective roles in resistance to different abiotic stresses, and overexpressions of NAC TFs in Arabidopsis have been proved to be conducive in improving salinity tolerance. However, functions of NAC genes in chrysanthemum continue to be poorly understood. Here, we performed physiology and molecular experiments to evaluate roles of DgNAC1 in chrysanthemum salt stress responses. In this study, DgNAC1-overexpressed chrysanthemum was obviously more resistant to salt over the WT (wild type). Specifically, the transgenic chrysanthemum showed a higher survival rate and lower EC (electrolyte conductivity) than WT under salt stress. The transgenic chrysanthemum also showed fewer accumulations of MDA (malondialdehyde) and reactive oxygen species (HO and O), greater activities of SOD (superoxide dismutase), POD (peroxidase) and CAT (catalase), as well as more proline content than WT under salt stress. Furthermore, stress-responsive genes in transgenic chrysanthemum were greater up-regulated than in WT under salinity stress. Thus, all results revealed that DgNAC1 worked as a positive regulator in responses to salt stress and it may be an essential gene for molecular breeding of salt-tolerant plants.