Abstract
High salinity seriously affects the production of chrysanthemum, so improving the salt tolerance of chrysanthemum becomes the focus and purpose of our research. The WRKY transcription factor (TF) family is highly associated with a number of processes of abiotic stress responses. We isolated DgWRKY4 from Dendranthema grandiflorum, and a protein encoded by this new gene contains two highly conserved WRKY domains and two C2H2 zinc-finger motifs. Then, we functionally characterized that DgWRKY4 was induced by salt, and DgWRKY4 overexpression in chrysanthemum resulted in increased tolerance to high salt stress compared to wild-type (WT). Under salt stress, the transgenic chrysanthemum accumulated less malondialdehyde, hydrogen peroxide (H2O2), and superoxide anion () than WT, accompanied by more proline, soluble sugar, and activities of antioxidant enzymes than WT; in addition, a stronger photosynthetic capacity and a series of up-regulated stress-related genes were also found in transgenic chrysanthemum. All results demonstrated that DgWRKY4 is a positive regulatory gene responding to salt stress, via advancing photosynthetic capacity, promoting the operation of reactive oxygen species-scavenging system, maintaining membrane stability, enhancing the osmotic adjustment, and up-regulating transcript levels of stress-related genes. So, DgWRKY4 can serve as a new candidate gene for salt-tolerant plant breeding.
Highlights
High salinity significantly limits the growth and productivity of plants worldwide
Using high-throughout sequencing technique, we obtained the transcriptome database of chrysanthemum under salinity condition
The full-length cDNA of DgWRKY4 was obtained by PCR, inserted into pCAMBIA 2300 with the control of cauliflower mosaic virus (CaMV) 35S promoter
Summary
High salinity significantly limits the growth and productivity of plants worldwide. The induced transcription factors (TFs) such as AP2/EREBP, WRKY, MYB, and bHLH play an important role in activating downstream stress-responsive genes to protect plants from salt stress persecution (Chinnusamy et al, 2006; Hennig, 2012). The WRKY TF is a big and valuable family of regulatory proteins in plants (Rushton et al, 2012). All the WRKY proteins contain one or two DNA-binding domains consisting of 60 amino acid regions with the highly conserved sequence WRKYGQK at its N-terminus and a zincfinger motif (C-X4−5-C-X22−23-H-X-H or C-X7-C-X23-H-X-C) at C-terminus (Eulgem et al, 2000; Rushton et al, 2010). WRKYGQK motif may be replaced by WRKYGKK, WRKYGEK, WRKYGSK, or WRKYDQK in some plant species (Xiu et al, 2016). The WRKY proteins can fall into three groups, group I proteins contain two WRKY domains with C-X4−5-C-X22−23-HX-H zinc-finger motifs, group II proteins just contain one WRKY domain with a C-X4−5-C-X22−23-H-X-H motif, and group III proteins contain one WRKY domain with a C-X7-C-X23-H-X-C motif
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