M. oryzae positively while altering abiotic stress tolerance (Tao et al. 2009), and on
the other hand, OsWRKY75 enhances M. oryzae susceptibility same time increase
adaptation of rice towards cold stress (Yokotani et al. 2013).
11.4.4 Epigenetic Regulation
Epigenetic regulation is based on the regulation of histone proteins. AtWRKY70 was
expressed epigenetically after histone protein H3K4 gets trimethylated due to
trithorax binding (ATX1). AtWRKY70 activates defense genes such as PR-1 and
THI2.1 (Alvarez-Venegas et al. 2007). AtWRKY38 and AtWRKY62 get repressed due
to the removal of acetyl groups from histone protein by histone deacetylase
19 (HDA19) and lead to enhanced susceptibility towards P. syringae (Kim et al.
2008). The promoter region of AtWRKY40 was activated due to histone methylations
and provides systemic acquired resistance (Alvarez et al. 2010). Through histone
modification at promoter regions of AtWRKY29and AtWRKY6 two histone protein
H3K4 (histone H3 lysine 4) and H3K14 increase and provide SAR against
P. syringae pv. tomato (Singh et al. 2014). Some proteins such as VQ protein also
induce histone modification and provide defense against pathogens. Two VQ
proteins sigma factor binding protein 1 (SIB1) and SIB2 interacted with AtWRKY33
and provided resistance towards Botrytis cinerea (Lai et al. 2011). Interestingly,
DNA demethylases in Arabidopsis enhance resistance against Fusarium oxysporum
by altering the modulation of genes involving pathogenicity (Le et al. 2014).
Similarly, demethylation in the promoter region of AtWRKY22 provides resistance
against P. syringae pv. tomato (Yu et al. 2013a).
11.4.5 Proteasome Regulation
In normal conditions, the production of WRKY TFs is checked by proteasomemediated degradation. OsWRKY45 has a major role in SAR against rice blast
pathogen M. oryzae which is regulated by the nuclear ubiquitin-proteasome system
(UPS). After the M. oryzae attack on rice, polyubiquitination allows the accumulation of OsWRKY45 to induce defense against M. oryzae (Matsushita et al. 2013).
Pathogen resistance is positively regulated by AtWRKY53, while leaf senescence is
negatively regulated. Ubiquitin protein ligase 5 (UPL5) interacts with the leucine
zipper domain of AtWRKY53 for degradation and accumulation of UPS. The
expression of AtWRKY53 is highly regulated by inducing pathogen response and
UPS production (Miao and Zentgraf 2010). UPS mediated degradation of transcription factor also regulates other WRKY TFs, for example, in Chinese wild grapevine
(Vitis pseudoreticulata) VpWRKY11 provides defense against pathogen
Golovinomyces cichoracearum. VpWRKY11 TF production was regulated by interaction with E3 ubiquitin ligase Erysiphe necator induced RING finger protein
1 (EIRP1) through degradation by the 26S proteasome (Yu et al. 2013a, 2013b).
340
L. S. Rajput et al.
the other hand, OsWRKY75 enhances M. oryzae susceptibility same time increase
adaptation of rice towards cold stress (Yokotani et al. 2013).
11.4.4 Epigenetic Regulation
Epigenetic regulation is based on the regulation of histone proteins. AtWRKY70 was
expressed epigenetically after histone protein H3K4 gets trimethylated due to
trithorax binding (ATX1). AtWRKY70 activates defense genes such as PR-1 and
THI2.1 (Alvarez-Venegas et al. 2007). AtWRKY38 and AtWRKY62 get repressed due
to the removal of acetyl groups from histone protein by histone deacetylase
19 (HDA19) and lead to enhanced susceptibility towards P. syringae (Kim et al.
2008). The promoter region of AtWRKY40 was activated due to histone methylations
and provides systemic acquired resistance (Alvarez et al. 2010). Through histone
modification at promoter regions of AtWRKY29and AtWRKY6 two histone protein
H3K4 (histone H3 lysine 4) and H3K14 increase and provide SAR against
P. syringae pv. tomato (Singh et al. 2014). Some proteins such as VQ protein also
induce histone modification and provide defense against pathogens. Two VQ
proteins sigma factor binding protein 1 (SIB1) and SIB2 interacted with AtWRKY33
and provided resistance towards Botrytis cinerea (Lai et al. 2011). Interestingly,
DNA demethylases in Arabidopsis enhance resistance against Fusarium oxysporum
by altering the modulation of genes involving pathogenicity (Le et al. 2014).
Similarly, demethylation in the promoter region of AtWRKY22 provides resistance
against P. syringae pv. tomato (Yu et al. 2013a).
11.4.5 Proteasome Regulation
In normal conditions, the production of WRKY TFs is checked by proteasomemediated degradation. OsWRKY45 has a major role in SAR against rice blast
pathogen M. oryzae which is regulated by the nuclear ubiquitin-proteasome system
(UPS). After the M. oryzae attack on rice, polyubiquitination allows the accumulation of OsWRKY45 to induce defense against M. oryzae (Matsushita et al. 2013).
Pathogen resistance is positively regulated by AtWRKY53, while leaf senescence is
negatively regulated. Ubiquitin protein ligase 5 (UPL5) interacts with the leucine
zipper domain of AtWRKY53 for degradation and accumulation of UPS. The
expression of AtWRKY53 is highly regulated by inducing pathogen response and
UPS production (Miao and Zentgraf 2010). UPS mediated degradation of transcription factor also regulates other WRKY TFs, for example, in Chinese wild grapevine
(Vitis pseudoreticulata) VpWRKY11 provides defense against pathogen
Golovinomyces cichoracearum. VpWRKY11 TF production was regulated by interaction with E3 ubiquitin ligase Erysiphe necator induced RING finger protein
1 (EIRP1) through degradation by the 26S proteasome (Yu et al. 2013a, 2013b).
340
L. S. Rajput et al.