Biology Reference
In-Depth Information
Keywords
Ca
2+
infl ux Ca
2+
signature Calmodulin Ca
2+
sensors Calcium-
dependent effectors Calcium-dependent protein kinases Ca
2+
-mediated signals
4.1
Calcium Signature in Plant Immune Signal
Transduction System
Pathogen-associated molecular patterns (PAMPs) of invading pathogens is recog-
nized by pattern recognition receptors (PRRs) of host plants (Zipfel
2008
; Boutrot
et al.
2010
; Keinath et al.
2010
; Shimizu et al.
2010
; Nürnberger and Küfner
2011
;
Segonzac and Zipfel
2011
). Binding of PAMPs to PRRs and subsequent receptor
kinase activation are key steps in plant innate immunity (Kwaaitaal et al.
2011
).
One of the earliest detectable signaling events after PAMP perception is a rapid and
transient rise in cytosolic Ca
2+
levels through the function of plasma membrane-
resident Ca
2+
channels (Blume et al.
2000
; Kwaaitaal et al.
2011
; Ranf et al.
2011
).
In plant cells, the calcium ion is a ubiquitous intracellular second messenger involved
in numerous signaling pathways (McAinsh et al.
1995
; Himmelbach et al.
2003
;
Lecourieux et al.
2006
; Zhu et al.
2007
; Luan
2009
; McAinsh and Pittman
2009
;
Abdul Kadar and Lindsberg
2010
; DeFalco et al.
2010
; Dodd et al.
2010
; Hamada
et al.
2012
; Stael et al.
2012
). Second messengers are molecules that are used by
plants to encode information and deliver it downstream to proteins which decode/
interpret signals and initiate cellular responses (e.g. changes in enzyme activity, gene
expression, and cytoskeletal rearrangement) (Snedden and Fromm
2001
). Ca
2+
is a
master regulator of gene expression in plants (Galon et al.
2010a
,
b
).
Calcium ion acts as a signal carrier (Allen et al.
2000
). Calcium signaling is
modulated by specifi c calcium signatures. Spatial and temporal changes in cytosolic
calcium ([Ca
2+
]
cyt
) are referred to as “calcium signature”. These changes may proceed
as single calcium transients, oscillations, or repeated spikes/waves (Lecourieux
et al.
2006
). A combination of changes in all Ca
2+
parameters produced by a particu-
lar signal is called as a Ca
2+
signature (Luan et al.
2002
). Ca
2+
signatures are gener-
ated in the cytosol, and in noncytosolic locations including the nucleus and
chloroplast through the coordinated action of Ca
2+
infl ux and effl ux pathways
(McAinsh and Pittman
2009
). Specifi c calcium signatures are recognized by differ-
ent calcium sensors to transduce calcium-mediated signals into downstream events
(Harmon et al.
2000
; Rudd and Franklin-Tong
2001
; Sanders et al.
2002
; Reddy and
Reddy
2004
; Reddy et al.
2003
,
2011a
,
b
; Wang et al.
2012
; Hashimoto et al.
2012
).
The Ca
2+
signature controls diverse cellular processes via Ca
2+
sensors (DeFalco
et al.
2010
). Plant cells employ an array of Ca
2+
-binding proteins that serve as Ca
2+
sensors. The Ca
2+
binding proteins that function as sensors undergo conformational
changes upon Ca
2+
binding that allow them to interact with downstream effectors
(Clapham
2007
; DeFalco et al.
2010
; Hashimoto et al.
2012
). The Ca
2+
sensors
identifi ed in plants include calmodulins (CaM) (Snedden and Fromm
2001
; Reddy
and Reddy
2004
; Kang et al.
2006a
,
b
; Takabatake et al.
2007
), CaM-like and CaM-
related proteins (Jakobek et al.
1999
; Rodriguez-Concepcion et al.
1999
; Reddy
2001
; Snedden and Fromm
2001
; Luan et al.
2002
; Lecourieux et al.
2006
; DeFalco
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