bZIP TFs involved in cold stress response
Low temperature stimulation will
disturb the normal physiological and metabolic activities and further
affect the plant growth and development. The plant mainly responds to
low temperature stress through the ICE-CBF-COR pathway. When the plant
is exposed to low temperature, it induces CBFs (C-repeat-binding
Factors) expression by ICE (inducer of CBF expression), which recognizes
CRT/DRE (C-repeat/dehydration responsive element) located on the target
gene promoter and combines with COR (cold regulated genes) genes
to regulate transcriptional expression, thereby enhancing plant cold
stress resistance (Shi et al., 2018). bZIP transcription factors also
play an indispensable role in regulating plant cold stress responses.
According to incomplete
statistics, the first rice bZIP-like transcription factor identified and
reported was OsbZIP38/LIP19 of the H subfamily. Induced by low
temperature, as a Fos-like molecular switch, it is involved in the
plant’s response to cold signal pathways (Aguan et al., 1991; Aguan et
al., 1993; Shimizu et al., 2005). OsbZIP38/LIP19 and subfamily member
OsbZIP87/OsOBF1 are able to bind DNA and form homodimers, and they are
more likely to interact with OsbZIP38/LIP19 and form heterodimers to
participate in the plant’s response to cold signaling (Shimizu et al.,
2005). In addition,
OsbZIP52/RISBZ5,
OsbZIP68/ROS-bZIP1 and OsbZIP73/OsTFX1 in the rice bZIP transcription
factor family were also involved in cold resistance. OsbZIP52/RISBZ5 is
a member of the G subfamily. It is not induced by drought, salt, PEG,
and ABA, but by low temperature. It can form homodimers and specifically
bind G-box. However, the test of the cold tolerance of rice showed that
the survival rate of over-expressed OsbZIP52/RISBZ5 rice plants
was significantly lower than that of wild type. It can be seen that the
expression of OsbZIP52/RISBZ5 is inversely related to low
temperature tolerance (Liu et al., 2012). Cheng et al. (2007) found that
OsbZIP68/ROS-bZIP1 could be induced and responded quickly within 24
hours when rice was treated at 10 °C. Liu et al. (2018) identified a
total of 8 bZIP genes in rice, OsbZIP08 , OsbZIP35 ,OsbZIP38 , OsbZIP46 , OsbZIP63 , OsbZIP72 ,OsbZIP73 and OsbZIP76 , which are associated with low
temperature resistance at seedling stage. In addition, Liu et al. (2018,
2019a) also found and revealed the molecular mechanism ofOsbZIP73/OsTFX1 adapting to the cold climate in northern China by
comparing the whole genome sequences of Japonica and Indica rice.
Except for rice, carrot, soybean,
wheat, tomato and other crops have been successively excavated bZIP
transcription factors in response to low temperature stress. For
example, Ito et al. (1999) found that the expression of bZIP-like
protein Lip (Low temperature-Induced protein) in the roots of radish was
up-regulated under low temperature treatment, thereby enhancing the cold
resistance of radish. Soybeans GmbZIP44, GmbZIP62 and GmbZIP78 can
regulate and promote the synthesis of proline (plant cold tolerance
osmotic regulator) to enhance the tolerance of plants to cold stress. At
the same time, GmbZIP44, GmbZIP62, and GmbZIP78 can enhance their
ability to respond to cold damage and high salt stress by activating the
expression of their downstream genes ERF5 , KIN1 ,CORl5A , and COR78 (Liao et al., 2008). Hwang et al. (2014)
treated Brassica rapa with low temperature stress and found that
the expression of 27 BrbZIPs were significantly up-regulated, among
which Bra000256 , Bra003320 , Bra004689 ,Bra011648 , Bra020735 and Bra023540 may be the key
genes involved in the response to low temperature stress. Compared with
wild-type Arabidopsis thaliana , heterologous expression ofTabZIP6 in wheat under cold treatment significantly reduced the
expression of CBFs , key CORs and other genes in transgenic
plants, making the transgenic plants sensitive to low temperature (Cai
et al., 2018). However, the over-expressed wheat TabZIP14-B ,TaAREB3 and TabZIP60 in Arabidopsis thaliana can
significantly enhance the ability of plants to resist cold stress, and
the expression of corresponding stress-responsive genes in transgenic
plants was significantly up-regulated. In addition, transgenic plants
are more sensitive to ABA than wild type, indicating that
TabZIP14-B , TaAREB3 , and TabZIP60 all enhance the
cold resistance of plants through the ABA pathway (Wang et al., 2016a;
Zhang et al., 2015b; Zhang et al., 2017b). Xu et al. (2014) found that
over-expression of wheat bZIP transcription factor TaABL 1 (ABI-like)
elevated cold tolerance in wheat. Apple bZIP transcription factor MdHY5
can respond to low temperature stress at both the transcriptional and
protein levels. Overexpression of MdHY5 can significantly enhance
cold stress resistance in apple callus and transgenic Arabidopsis
thaliana . EMSA results indicate that MdHY5 can bind to G-Box on theMdCBF1 promoter, thereby increasing its transcription level and
regulating the expression of COR genes independent of CBF (An et
al., 2017b). Wang et al. (2017b) found that transgenic Arabidopsis
thaliana plants showed reduced survival, increased electrical
conductivity, increased malondialdehyde content, and reduced soluble
sugar content when overexpressed Camellia sinensis CsbZIP6in it. Transcriptome analysis found that the expression of
low-temperature and drought-responsive genes in over-expressed plants
was significantly lower than that of wild type, indicating thatCsbZIP6 plays a negative regulatory role in low-temperature
stress response.