positively and negatively regulates fungal and bacterial disease resistance, respectively. In parallel, phosphorylation of CDPKs, which are unique Ca
2+ sensor protein
kinases, and Calmodulin has also been observed upon MSP1 and other PAMP
perception (Gupta et al. 2019).
12.3.2 Transcription Factor (TFs)-Mediated Downstream Responses
PTI-activated defense responses include physical cell wall reinforcement, generation, and secretion of antimicrobial chemicals (such as secondary metabolite phytoalexin accumulation), and expression of TFs (Katagiri and Tsuda 2010). A number
of rice TFs have been identified that directly or indirectly play roles in the biotic and
abiotic stresses. These TFs include WRKY, MADS (MCM1, AGAMOUS,
DEFICIENS, and SRF) box, and NAC (NAM, ATAF1,2, CUC2), and of these
WRKY TFs are most characterized during rice blast infection (Ramamoorthy et al.
2008). WRKY TFs function downstream of MAPK cascades and as many as
11 WRKY TFs have been identified playing crucial roles in the rice resistance
against rice blast diseases. These TFs include OsWRKY23, OsWRKY24,
OsWRKY28,
OsWRKY45,
OsWRKY51,
OsWRKY53,
OsWRKY62,
OsWRKY70, OsWRKY71, OsWRKY72, and OsWRKY76. Using transcriptome
analysis, increased expressions of OsWRKY45, OsWRKY47, OsWRKY53,
OsWRKY55, OsWRKY62, and OsWRKY71 have been identified in response to
M. oryzae infection (Chujo et al. 2007; Ryu et al. 2006; Shimono et al. 2007; Wei
et al. 2013). Further, it was shown that overexpression of some of these genes
enhanced resistance to rice blast infection. In addition, some of the WRKY TFs
regulate rice immune response both in response to multiple pathogens. As an
example, the involvement of OsWRKY45 was shown in rice resistance against
both M. oryzae and X. oryzae pv. oryzae via SA hormone signaling and negatively
modulates resistance against the brown planthopper, Nilaparvata lugens (Lee et al.
2017; Shimono et al. 2012). Moreover, OsWRKY45 and Pb1 interaction contribute
to blast resistance through the protection of OsWRKY45 from ubiquitin proteasome
system degradation (Matsushita et al. 2013).
12.3.3 Apoplastic Reactive Oxygen Species Burst
A transient and rapid generation of apoplastic ROS is one of the earliest events in the
PTI signaling. Typically, a ROS burst is initiated within 4–6 min, reaches its peak
30–45 min, then gradually declines to the resting state 60 min after PAMP
treatments in various plant species. Apoplastic ROS burst is mediated by the activity
of a plasma membrane-localized RBOHB and several proteomics studies have
shown increased abundance and even phosphorylation of this protein in response
to M. oryzae or exogenous MSP1 treatment (Gupta et al. 2019; Kim et al. 2013).
Apoplastic ROS can act as a toxin barrier against subsequent pathogen infections
and also involved in plant cell walls strengthening by forming oxidative
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N. Khatri et al.
2+ sensor protein
kinases, and Calmodulin has also been observed upon MSP1 and other PAMP
perception (Gupta et al. 2019).
12.3.2 Transcription Factor (TFs)-Mediated Downstream Responses
PTI-activated defense responses include physical cell wall reinforcement, generation, and secretion of antimicrobial chemicals (such as secondary metabolite phytoalexin accumulation), and expression of TFs (Katagiri and Tsuda 2010). A number
of rice TFs have been identified that directly or indirectly play roles in the biotic and
abiotic stresses. These TFs include WRKY, MADS (MCM1, AGAMOUS,
DEFICIENS, and SRF) box, and NAC (NAM, ATAF1,2, CUC2), and of these
WRKY TFs are most characterized during rice blast infection (Ramamoorthy et al.
2008). WRKY TFs function downstream of MAPK cascades and as many as
11 WRKY TFs have been identified playing crucial roles in the rice resistance
against rice blast diseases. These TFs include OsWRKY23, OsWRKY24,
OsWRKY28,
OsWRKY45,
OsWRKY51,
OsWRKY53,
OsWRKY62,
OsWRKY70, OsWRKY71, OsWRKY72, and OsWRKY76. Using transcriptome
analysis, increased expressions of OsWRKY45, OsWRKY47, OsWRKY53,
OsWRKY55, OsWRKY62, and OsWRKY71 have been identified in response to
M. oryzae infection (Chujo et al. 2007; Ryu et al. 2006; Shimono et al. 2007; Wei
et al. 2013). Further, it was shown that overexpression of some of these genes
enhanced resistance to rice blast infection. In addition, some of the WRKY TFs
regulate rice immune response both in response to multiple pathogens. As an
example, the involvement of OsWRKY45 was shown in rice resistance against
both M. oryzae and X. oryzae pv. oryzae via SA hormone signaling and negatively
modulates resistance against the brown planthopper, Nilaparvata lugens (Lee et al.
2017; Shimono et al. 2012). Moreover, OsWRKY45 and Pb1 interaction contribute
to blast resistance through the protection of OsWRKY45 from ubiquitin proteasome
system degradation (Matsushita et al. 2013).
12.3.3 Apoplastic Reactive Oxygen Species Burst
A transient and rapid generation of apoplastic ROS is one of the earliest events in the
PTI signaling. Typically, a ROS burst is initiated within 4–6 min, reaches its peak
30–45 min, then gradually declines to the resting state 60 min after PAMP
treatments in various plant species. Apoplastic ROS burst is mediated by the activity
of a plasma membrane-localized RBOHB and several proteomics studies have
shown increased abundance and even phosphorylation of this protein in response
to M. oryzae or exogenous MSP1 treatment (Gupta et al. 2019; Kim et al. 2013).
Apoplastic ROS can act as a toxin barrier against subsequent pathogen infections
and also involved in plant cell walls strengthening by forming oxidative
370
N. Khatri et al.