binding specific region, which undergoes conformational changes and passes it to
downstream effector signal molecules (Clapham et al. 2007; Gifford et al. 2007). In
plants variety of sensory proteins are discovered such as calmodulin (CaM),
calmodulin-like (CML), calcineurin B-like (CBL), and Ca
2+ -dependent protein
kinases (CDPK). The sensor proteins possess Ca
2+ binding region and EF-hand
domain, which undergoes conformational changes and further passes the message to
downstream players. These sensor proteins have varying number of EF-hands
depending on the length of amino acid residues. Some other type of Ca
2+ binding
proteins are calnexin, calreticulin, annexins, and C2 domain containing proteins
(Reddy and Reddy 2004; Sarwat and Tuteja 2007; Davies 2014). These other
proteins lack EF-hand, hence they have different mechanism to bind with Ca
2+ .
Ca
2+ -sensor proteins are categorized into two classes based on their mechanism:
sensor responder and sensor relayer (Sanders et al. 2002). Ca
2+ sensor relayer
proteins lack enzymatic activity and only conformational changes govern their
interaction with Ca
2+ and downstream factors. CaM, CML, and CBL have this
type of activating–deactivating mechanism (Luan et al. 2002). CDPKs have dual
characteristics of sensing as well as relaying. Ca
2+ binding domain induces conformational change in the protein and Ser-Thr domain has kinase activity (Sanders et al.
1999; Luan et al. 2002; Hrabak et al. 2003). So CDPKs solely activate and transduce
the signal through phosphorylation cascade. The Ca
2+ -binding sensors play a significant role of relaying signals upon herbivory attack. Ca
2+ binds with their sensors in
cytosol in a way coming from plasma membrane in the spike of Ca
2+ ions. Sensors
measure the intensity and specific signature to decipher the Ca
2+ code. As per the
signature specificity it regulates downstream to rectify the signal cascade. In Plants
CaM, CBL, and CDPK are the main class of Ca
2+ sensors during herbivory attack
(Erb and Reymond 2019).
16.4.1 Calmodulin
Calmodulin (CaM) is a highly conserved protein sensor in plant species (Perochon
et al. 2011). Plants encode multiple genes for these proteins, hence many similar
isoforms of CaMs are present in the cytosol (Snedden and Fromm 1998). Seven
different genes of 4 CaM studied in Arabidopsis (CaM &CaM 4; CaM 2, CaM 3 &
CaM 5; CaM 6 and CaM 7) (Batistič and Kudla 2012). The isoforms of CaMs
respond according to different developmental processes and stress signals. Studies
suggested its other locations than cytosol such as in nucleus (Levy et al. 2004),
chloroplast (Chigri et al. 2012; Yang and Poovaiah 2000), peroxisome (Yang and
Poovaiah 2002), and organellar membranes (Schiøtt et al. 2004; Urquhart et al.
2007). CaM is small sized, positively charged protein of ~150 amino acid residues.
They have two EF-hands motifs with globular domains connected by pliable central
helix (Gifford et al. 2007). When Ca
2+ binds to the CaM, its tertiary structure
changes and its hydrophobic clefts expose, which sequentially interacts with its
next downstream target. Upon herbivory, CaM binds with Ca
2+ and regulates
downstream targets to rectify signal cascade.
498
A. Kumar et al.
downstream effector signal molecules (Clapham et al. 2007; Gifford et al. 2007). In
plants variety of sensory proteins are discovered such as calmodulin (CaM),
calmodulin-like (CML), calcineurin B-like (CBL), and Ca
2+ -dependent protein
kinases (CDPK). The sensor proteins possess Ca
2+ binding region and EF-hand
domain, which undergoes conformational changes and further passes the message to
downstream players. These sensor proteins have varying number of EF-hands
depending on the length of amino acid residues. Some other type of Ca
2+ binding
proteins are calnexin, calreticulin, annexins, and C2 domain containing proteins
(Reddy and Reddy 2004; Sarwat and Tuteja 2007; Davies 2014). These other
proteins lack EF-hand, hence they have different mechanism to bind with Ca
2+ .
Ca
2+ -sensor proteins are categorized into two classes based on their mechanism:
sensor responder and sensor relayer (Sanders et al. 2002). Ca
2+ sensor relayer
proteins lack enzymatic activity and only conformational changes govern their
interaction with Ca
2+ and downstream factors. CaM, CML, and CBL have this
type of activating–deactivating mechanism (Luan et al. 2002). CDPKs have dual
characteristics of sensing as well as relaying. Ca
2+ binding domain induces conformational change in the protein and Ser-Thr domain has kinase activity (Sanders et al.
1999; Luan et al. 2002; Hrabak et al. 2003). So CDPKs solely activate and transduce
the signal through phosphorylation cascade. The Ca
2+ -binding sensors play a significant role of relaying signals upon herbivory attack. Ca
2+ binds with their sensors in
cytosol in a way coming from plasma membrane in the spike of Ca
2+ ions. Sensors
measure the intensity and specific signature to decipher the Ca
2+ code. As per the
signature specificity it regulates downstream to rectify the signal cascade. In Plants
CaM, CBL, and CDPK are the main class of Ca
2+ sensors during herbivory attack
(Erb and Reymond 2019).
16.4.1 Calmodulin
Calmodulin (CaM) is a highly conserved protein sensor in plant species (Perochon
et al. 2011). Plants encode multiple genes for these proteins, hence many similar
isoforms of CaMs are present in the cytosol (Snedden and Fromm 1998). Seven
different genes of 4 CaM studied in Arabidopsis (CaM &CaM 4; CaM 2, CaM 3 &
CaM 5; CaM 6 and CaM 7) (Batistič and Kudla 2012). The isoforms of CaMs
respond according to different developmental processes and stress signals. Studies
suggested its other locations than cytosol such as in nucleus (Levy et al. 2004),
chloroplast (Chigri et al. 2012; Yang and Poovaiah 2000), peroxisome (Yang and
Poovaiah 2002), and organellar membranes (Schiøtt et al. 2004; Urquhart et al.
2007). CaM is small sized, positively charged protein of ~150 amino acid residues.
They have two EF-hands motifs with globular domains connected by pliable central
helix (Gifford et al. 2007). When Ca
2+ binds to the CaM, its tertiary structure
changes and its hydrophobic clefts expose, which sequentially interacts with its
next downstream target. Upon herbivory, CaM binds with Ca
2+ and regulates
downstream targets to rectify signal cascade.
498
A. Kumar et al.