Abstract
The APETALA2 (AP2) and ethylene-responsive element-binding factor (ERF) gene family is one of the largest plant-specific transcription factor gene families, which plays a critical role in plant development and evolution, as well as response to various stresses. The TARGET OF EAT3 (TOE3) gene is derived from Halostachys caspica and belongs to the AP2 subfamily with two AP2 DNA-binding domains. Currently, AP2 family mainly plays crucial roles in plant growth and evolution, yet there are few reports about the role of AP2 in abiotic stress tolerance. Here, we report HcTOE3, a new cold-regulated transcription factor gene, which has an important contribution to freezing tolerance. The main results showed that the expression of HcTOE3 in the H. caspica assimilating branches was strongly induced by different abiotic stresses, including high salinity, drought, and extreme temperature (heat, chilling, and freezing), as well as abscisic acid and methyl viologen treatments. Overexpressing HcTOE3 gene (OE) induced transgenic Arabidopsis plant tolerance to freezing stress. Under freezing treatment, the OE lines showed lower content of malondialdehyde and electrolyte leakage and less accumulation of reactive oxygen species compared with the wild type. However, the survival rates, antioxidant enzyme activities, and contents of osmotic adjustment substance proline were enhanced in transgenic plants. Additionally, the OE lines increased freezing tolerance by up-regulating the transcription level of cold responsive genes (CBF1, CBF2, COR15, COR47, KIN1, and RD29A) and abscisic acid signal transduction pathway genes (ABI1, ABI2, ABI5, and RAB18). Our results suggested that HcTOE3 positively regulated freezing stress and has a great potential as a candidate gene to improve plant freezing tolerance.
Highlights
Cold temperature is an important circumstance stress element, which restricts the plant growth, evolution, yield, and geographic dissemination, and it is a kind of natural disaster often encountered in agricultural production (Ding et al, 2019)
By comparing with Arabidopsis TOE proteins, two AP2 DNA-binding domain (BD) were found in the HcTOE3 protein, which are located at 130–186 and 222–279 aa, respectively
HcTOE3 protein contains a nuclear localization signal (NLS) sequence that is located at 118–125 aa (Figure 1A)
Summary
Cold temperature is an important circumstance stress element, which restricts the plant growth, evolution, yield, and geographic dissemination, and it is a kind of natural disaster often encountered in agricultural production (Ding et al, 2019). The expression of some cold temperature–related genes was regulated and induced by ABA (such as RAB18, RD29b) (Uno et al, 2000) Their promoters of these genes contained ABA response elements (ABREs), which initiated a series of plant responses to resist low temperature and enhanced plant cold tolerance (Agarwal and Jha, 2010). Plants synthesized certain cold-responsive proteins and small molecules, such as proline and soluble sugars for enhancing plant physiological response to cold stress (Kaplan and Guy, 2004; Kaplan et al, 2007) These cold-responsive proteins and small molecules were involved in regulation of cell membrane stability and osmotic potentials, as well as removing certain ROS during plant response to cold stress (Lee et al, 2002; Doherty et al, 2009)
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