F. oxysporum f. sp. lycopersici in tomato plants (Aamir et al. 2018) Therefore,
various kinases are key regulator in controlling or modulating defense genes by
phosphorylation and activation of various WRKY TFs.
11.4.2 Autoregulation and Cross Regulation
Various external and internal stimuli induce numerous signaling pathways that form
“WRKY web.” Signaling of this WRKY web is autoregulated when WRKY TFs
interact with their own promoters while cross regulated when WRKY TFs interact
with promoters of other WRKY TFs (Eulgem and Somssich 2007). Chromatin
immunoprecipitation (ChIP) analysis on parsley showed that PcWRKY1 TF binds
to own promoter and defense gene PcPR10, whereas PcWRKY1 also binds to the
promoter of PcWRKY3 and defense gene PcPR1 (Turck et al. 2004). The members
of the same family contribute related and superfluous roles in controlling signaling
pathways by regulating each other transcription level. WRKY18, WRKY40, and
WRKY60 in A. thaliana cross regulate abscisic acid signaling by controlling each
other transcription (Yan et al. 2013). WRKY TFs regulated the defense process by
auto- and cross-regulation mechanisms with the formation of homocomplexes and
heterocomplexes (Liu et al. 2016a). WRKY web provides resistance through the
cross-regulation mechanism. Likewise, SlWRKY23 provides resistance against Oidium neolycopersici, a causal agent of tomato powdery mildew under alkaline soil
only (Kissoudis et al. 2016).
11.4.3 Positive and Negative Regulation
In some cases, same WRKY TFs provide reistance to one pathogen and susceptibility to another pathogen. For example, OsWRKY45-1 and OsWRKY45-2 found in rice
encode protein differing in a total of 10 amino acids. Upon overexpression, both the
alleles showed resistance to the rice blast fungal pathogen M. oryzae positively.
While OsWRKY45-1 regulates negative resistance towards rice bacterial blight
pathogen X. oryzae subsp. Oryzae, OsWRKY45-2 regulates positive resistance
towards the same pathogens. This is due to OsWRKY 45-1 that regulates both SA
and JA pathway genes, while OsWRKY45-1 regulates only JA pathway genes (Tao
et al. 2009). After the challenge of Botrytis cinerea, AtWRKY33 induces camalexin
biosynthetic with a positive feedback regulatory loop which provides defense
against B. cinerea (Mao et al. 2011). In contrast to that OsWRKY62 and OsWRKY76
increase susceptibility against M. oryzae and X. oryzae subsp. Oryzae, respectively,
through an alternative splicing mechanism, these WRKY TFs regulated with a
negative feedback regulation mechanism (Liu et al. 2016a, 2016b). WRKY TFs
have another interesting property that is to show the opposite effects on both types of
stress tolerance while complex communications among various signaling networks
that lead to may be positive and negative effects on the regulation of different
stresses (Bai et al. 2018). For example, OsWRKY45 provides resistance against
11 Role of WRKY Transcription Factor Superfamily in Plant Disease Management
339
various kinases are key regulator in controlling or modulating defense genes by
phosphorylation and activation of various WRKY TFs.
11.4.2 Autoregulation and Cross Regulation
Various external and internal stimuli induce numerous signaling pathways that form
“WRKY web.” Signaling of this WRKY web is autoregulated when WRKY TFs
interact with their own promoters while cross regulated when WRKY TFs interact
with promoters of other WRKY TFs (Eulgem and Somssich 2007). Chromatin
immunoprecipitation (ChIP) analysis on parsley showed that PcWRKY1 TF binds
to own promoter and defense gene PcPR10, whereas PcWRKY1 also binds to the
promoter of PcWRKY3 and defense gene PcPR1 (Turck et al. 2004). The members
of the same family contribute related and superfluous roles in controlling signaling
pathways by regulating each other transcription level. WRKY18, WRKY40, and
WRKY60 in A. thaliana cross regulate abscisic acid signaling by controlling each
other transcription (Yan et al. 2013). WRKY TFs regulated the defense process by
auto- and cross-regulation mechanisms with the formation of homocomplexes and
heterocomplexes (Liu et al. 2016a). WRKY web provides resistance through the
cross-regulation mechanism. Likewise, SlWRKY23 provides resistance against Oidium neolycopersici, a causal agent of tomato powdery mildew under alkaline soil
only (Kissoudis et al. 2016).
11.4.3 Positive and Negative Regulation
In some cases, same WRKY TFs provide reistance to one pathogen and susceptibility to another pathogen. For example, OsWRKY45-1 and OsWRKY45-2 found in rice
encode protein differing in a total of 10 amino acids. Upon overexpression, both the
alleles showed resistance to the rice blast fungal pathogen M. oryzae positively.
While OsWRKY45-1 regulates negative resistance towards rice bacterial blight
pathogen X. oryzae subsp. Oryzae, OsWRKY45-2 regulates positive resistance
towards the same pathogens. This is due to OsWRKY 45-1 that regulates both SA
and JA pathway genes, while OsWRKY45-1 regulates only JA pathway genes (Tao
et al. 2009). After the challenge of Botrytis cinerea, AtWRKY33 induces camalexin
biosynthetic with a positive feedback regulatory loop which provides defense
against B. cinerea (Mao et al. 2011). In contrast to that OsWRKY62 and OsWRKY76
increase susceptibility against M. oryzae and X. oryzae subsp. Oryzae, respectively,
through an alternative splicing mechanism, these WRKY TFs regulated with a
negative feedback regulation mechanism (Liu et al. 2016a, 2016b). WRKY TFs
have another interesting property that is to show the opposite effects on both types of
stress tolerance while complex communications among various signaling networks
that lead to may be positive and negative effects on the regulation of different
stresses (Bai et al. 2018). For example, OsWRKY45 provides resistance against
11 Role of WRKY Transcription Factor Superfamily in Plant Disease Management
339