REGULATION MECHANISM OF PLANT BZIPS TO VARIOUS STRESSES
Previous studies have found that
bZIPs play important roles in response to a variety of plant stresses,
such as salinity, drought and cold damage (Table II). Their regulation
mechanism varies depending on species of plant and types of stress.
bZIP TFs involved in salt
stress response
Under salt stress, plant cell should successively face challenges of
osmotic stress, ion toxicity and oxidative stress (Rozema et al., 2008;
Munns et al., 2005). In these responses, bZIP transcription factors play
key roles in various physiological processes in Arabidopsis
thaliana , tomato, tobacco, rice, and soybeans, etc.
In Arabidopsis thaliana , AtbZIP17 was proven as a positive
regulator in the processes salt stress responses, it activates both the
expression of salt stress response gene ATHB-7 and SES1(Liu et al., 2007, 2008); while the AtbZIP24 was revealed as a negative
regulator in plant tolerance to salinity by RNAi interference technology
(Yang et al., 2009). Tang et al. (2012b) found that heterologously
expressing Arabidopsis thaliana AtbZIP60 could increase
salt resistance and superoxide dismutase (SOD) activity of tobacco,
rice, and Pinus elliottii . In Glycine max , overexpression
of the GmbZIP1 enhances salt tolerance in transgenic plants (Gao
et al., 2011). Besides, heterologously expressing GmbZIP44 ,GmbZIP62 , and GmbZIP78 could significantly increase salt
resistance of transgenic Arabidopsis thaliana plants (Wang et
al., 2015). In maize, the ABP9 was found as a salinity
responsible bZIP gene by Zhang et al. (2011a). Then, Wang et al. (2017a)
heterologously expressed it to improve the salt tolerance of transgenic
cotton. In Oryza sativa , the OsbZIP05/OSBZ8 firstly found
with a higher transcriptional level in salt tolerant cultivar than in
salt sensitive cultivar, indicate that OsbZIP05/OSBZ8 might play
as a positive role in this stress responses (Mukherjee et al., 2006).
After that, OsbZIP12/OsABF1, OsbZIP23, OsbZIP46/OsABF2, OsBZIP71 and
OsbZIP72 were successively proven to act as positive regulators in the
process of salt tolerance (Amir Hossain et al., 2010; Chang et al.,
2017; Hossain et al., 2010; Liu et al., 2014a; Lu et al., 2009; Tang et
al. 2012a; Xiang et al., 2008; Zhang et al., 2017a). OsbZIP71 can form
both homodimers and heterodimers with Group C members of the bZIP gene
family, and overexpression of OsbZIP71 can significantly enhance
the salt tolerance of transgenic rice (Liu et al., 2014a). On the
contrary, the plants overexpressing OsbZIP10/OsABI5 showed more
obvious chlorosis than wild type under high salt concentration,
indicating that OsbZIP10/OsABI5 participates in the salt stress
tolerance response of rice as a negative regulator, and gene silencing
can reduce the sensitivity of transgenic rice to salt (Zou et al.,
2008).
Recent years, bZIPs in other
plants have also been revealed to participate salinity responsive
processes. Cheng et al. (2013) isolated a salt responsive
transcriptional factor LrbZIP in lotus root and found that transgenic
lotus with LrbZIP overexpression could grow with normal root
biomass, chlorophyll content, and electrolyte exudation rate under NaCl
treatment. Zhao et al. (2016) revealed that Brassica napus bZIP
transcription factor BnaABF2 enhanced salt tolerance of plants through
the ABA pathway.
To sum up, many bZIP genes have
been excavated in different plants and confirmed that they can
significantly enhance the salt tolerance of plants, making the bZIP gene
family a gene treasure house for improving the salt tolerance of crops.
Therefore, the use of bZIP transcription factors to improve the salt
tolerance of crops and breed new salt-tolerant varieties is of great
significance for improving agricultural productivity and improving
saline soils.