Abstract
Cold stress poses a serious threat to the survival and bloom of Verbena bonariensis. The enhancement of the cold tolerance of V. bonariensis is the central concern of our research. The WRKY transcription factor (TF) family was paid great attention to in the field of abiotic stress. The VbWRKY32 gene was obtained from V. bonariensis. The VbWRKY32 predicted protein contained two typical WRKY domains and two C2H2 zinc-finger motifs. Under cold stress, VbWRKY32 in leaves was more greatly induced than that in stems and roots. The overexpression (OE) in V. bonariensis increased cold tolerance compared with wild-type (WT). Under cold stress, the OE lines possessed showed greater recovery after cold-treatment restoration ratios, proline content, soluble sugar content, and activities of antioxidant enzymes than WT; the relative electrolyte conductivity (EL), the accumulation of malondialdehyde (MDA), hydrogen peroxide (H2O2), and superoxide anion (O2−) are lower in OE lines than that in WT. In addition, a series of cold-response genes of OE lines were compared with WT. The results revealed that VbWRKY32 worked as a positive regulator by up-regulating transcription levels of cold-responsive genes. The genes above can contribute to the elevation of antioxidant activities, maintain the membrane stability, and raise osmotic regulation ability, leading to the enhancement of the survival capacity under cold stress. According to this work, VbWRKY32 could serve as an essential gene to confer enhanced cold tolerance in plants.
Highlights
Plants are often subjected to various stresses which affects their growth and development
Comparisons of the amino acid sequences between VbWRKY32 and other WRKY proteins in plants showed that WRKYGQK and two C2H2 zinc-finger motifs were highly conserved in four plant species (Figure 2)
The phylogenetic tree was constructed with full-length amino acid sequences, the result demonstrated that VbWRKY32 belonged to group I of the WRKY family (Figure 3)
Summary
Plants are often subjected to various stresses which affects their growth and development. Several WRKY-overexpressed plants had successfully enhanced the resistance to various abiotic stresses. OsWRKY11 (WRKY group II) functioned as a positive regulator in tolerance to heat and salt stress of the transgenic rice seedlings (Wu et al, 2009). OsWRKY71 (WRKY group II) has a positive function in cold tolerance by regulating downstream target genes in rice (Kim et al, 2016). Overexpressed FcWRKY70 (WRKY group III) in tobacco and lemon conferred enhanced tolerance to drought stresses (Gong et al, 2015). Overexpression of GhWRKY25 (WRKY group I) in Nicotiana benthamiana enhanced plant tolerance to salt stress (Liu et al, 2016). Overexpressed OsWRKY30 (WRKY group I) enhanced rice resistance to disease by the salicylic acid (SA) signaling pathway (Ryu et al, 2006). Combined with the analysis of transcriptomic data, WRKY group I will be the focus of our attention
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