DISTRIBUTION AND CLASSIFICATION OF BZIP TRANSCRIPTION FACTORS
Currently, there are at least 64
families of transcription factors have been found in plants
(Pérez-Rodriguez et al., 2010). According to their differences in
DNA-binding domains, transcription factors can be defined as different
families, such as bZIP, NAC, MYB, EREBP/AP2, Zinc-finger, etc. Among
which, bZIPs (basic region/leucine zipper motifs) are widely found in
humans, animals and plants, insects and microorganisms. To date, a large
number of bZIP transcription factors have been identified in almost all
eukaryotes. There are 77, 89, 247, 92, 89, 69, 125, 64, 55, 114 bZIP
transcription factors been found in Arabidopsis thaliana ,Oryza sativa , Glycine max , Sorghum bicolor ,Hordeum vulgare L , Solanum lycopersicum , Zea mays ,Cucumis sativus , Vitis vinifera and Malus
domestica , respectively (Baloglu et al., 2014; Corrêa et al., 2008; Li
et al., 2015, 2016; Liu et al., 2014b; Nijhawan et al., 2008; Pourabed
et al., 2015; Wang et al. 2011; Wei et al., 2012; Zhang et al. 2018).
Only 25, 21 and 21 bZIP transcription factors were found in yeast,
nematode, and fruit fly (Riechmann et al., 2000). Compared to other
eukaryotes, plants have more bZIP homologous proteins and more conserved
amino acid sequences in these homologies (Ali et al., 2016). Studies
have shown that the structures of bZIP protein are closely related to
its biological function. Jakoby et al. (2002) used MEME (multiple em for
motif elicitation) to analyze a large number of bZIP transcription
factors in Arabidopsis thaliana . Based on the characteristics of
both the bZIP and other conserved motifs, the 75 bZIPs
in Arabidopsis thalianawere classified into 10 subfamilies of A, B, C, D, E, F, G, H, I and S.
With similar method, the bZIP transcription factor family genes in other
plants have also been categorized. The 131 bZIP transcription factors
isolated from the soybean genome were also divided into abovementioned
10 subfamilies A-S (Liao et al., 2008). Though the 89 members of the
bZIP transcription factor family in rice were also divided into 10
subfamilies, the subfamily S was replaced with J (Nijhawan et al.,
2008). It seems that most of these subfamilies of bZIPs are conserved
among different plants. Corrêa et al. (2008) identified the possible
non-redundant complete sets of bZIPs in rice, comprising 92 proteins,
and in black cottonwood, comprising 89 proteins. Based on both bZIP
domain and other conserved motifs similarities, these collections of
bZIPs together with the 77 bZIPs from Arabidopsis were categorized into
13 subfamilies, including A, B, C, D, E, F, G, H, I, J, K, L, and S,
three subgroups J, K and L were added.
With the advancement of bioinformatics, more and more conversed motifs,
except bZIP, were identified for categorizing bZIP subfamilies. Hence,
the classification of bZIP transcription factors has become more and
more sophisticated and scientific. Recent years, there are increasing
reports on regulation mechanism of various bZIPs on different stress
responses (Hwang et al., 2014; Ji et al., 2013; van Leene et al., 2016;
Liu et al., 2012; Tsugama et al., 2016; Wang et al., 2019; Zhang et al.,
2017a, b). Specific roles of bZIPs in different subgroups might also be
categorized into corresponding biological pathways, considering plenty
of functional annotated bZIPs been classified into the known subfamilies
with those sophisticated and scientific bioinformatics.