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components of the pathways in rice responding to multiple environmental stresses
have already been elucidated. Members of the WRKY family of TFs are responsive
to both biotic and abiotic stresses and play a vital role in fine-tuning plants’ response
to simultaneous stress. In rice, WRKY13 antagonistically regulates the response to
drought and bacterial disease by selectively binding to the cis-acting elements and
specific sequences in the promoters of SNAC1 and WRKY45–1. It can also auto-
regulate its own expression by binding to its promoter (Xiao et al. 2013 ). WRKY45
imparts resistance against the fungal and bacterial pathogens in rice by differential
mechanisms (Shimono et al. 2012 ). The WRKY45-1 allele negatively regulates ABA
signalling and also increases plant susceptibility to bacterial pathogens, whilst the
WRKY45-2 allele positively regulates ABA signalling and increases resistance to
bacterial pathogens (Tao et al. 2011 ). Both alleles positively regulate resistance to
fungal blast disease (Tao et al. 2009 ). WRKY76 transcription repressor plays op-
posite role in response to rice blast disease and cold stress; over-expression of the
WRKY76 results in increased susceptibility towards blast infection but increases
tolerance to cold stress (Yokotani et al. 2013a). WRKY82 enhances defence against
biotic pathogens and tolerance against abiotic stress via the JA/ET pathways (Peng
et al. 2011 ).
Several disease-resistant cultivars have different natural expression levels of
OsMYB4 leading to varying degrees of resistance to sheath blight and leaf blight
diseases in rice (Singh et al. 2013 ). Ectopic expression of the rice OsMYB4 TF
enhances abiotic and biotic stress tolerance in many plants including Arabidopsis,
tomato and apple (Pasquali et al. 2008 ; Vannini et al. 2006 , 2007 ). The JA-induced
MYB gene, JAmyb, is induced by high salinity, osmotic stress and ROS and its over-
expression results in induction of JA-induced TFs that play an important role in
biotic stress response (Yokotani et al. 2013b).
The OsNAC6 gene acts as a transcription inducer for biotic and abiotic stress
responses in rice. Constitutive over-expression of OsNAC6 results in increased tol-
erance to dehydration and salt stress along with greater resistance to blast disease,
but with growth and yield penalty (Nakashima et al. 2007 ). OsNAC5 also enhanc-
es abiotic stress tolerance in rice and is responsive to JA, but does not cause any
negative effect on plant growth (Takasaki et al. 2010 ). A plant-specific TF family,
ethylene-responsive factor TFs, bind to the GCC sequence specifically found in the
PR genes. These TFs are mainly involved in abiotic stress responses in plants. Four
ethylene-responsive genes, BIERF1-4, are up-regulated by salt, drought, wounding
and fungal pathogens (Cao et al. 2006 ).
In addition to TFs, various protein kinases (PKs) also act as the convergence
points in biotic and abiotic stress pathways in rice. Out of the 17 known rice
MAPK genes, five are induced by both biotic and abiotic stresses (Rohila and
Yang 2007 ). OsMAPK5 is the most studied rice MAPK; it confers ABA-mediated
tolerance to abiotic stress and resistance to brown spot, whilst negatively regulat-
ing the response to rice blast fungus (Sharma et al. 2013 ). Members of the rice
CDPK family are also involved in crosstalk between biotic and abiotic stresses.
OsCDPK12 regulates genes involved in ROS scavenging in stressed plant cells