Ca 2+ signaling in plant Light Cold stress Heat shock Mechanical stresses (Touch, wind & Wounding)...
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Transcript of Ca 2+ signaling in plant Light Cold stress Heat shock Mechanical stresses (Touch, wind & Wounding)...
![Page 1: Ca 2+ signaling in plant Light Cold stress Heat shock Mechanical stresses (Touch, wind & Wounding) Pathogen invading Phytohormones (Auxin, ABA, GA) Gravity.](https://reader030.fdocuments.in/reader030/viewer/2022032606/56649eab5503460f94bb1ac9/html5/thumbnails/1.jpg)
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Ca2+ signaling in plant
LightCold stressHeat shockMechanical stresses(Touch, wind &Wounding)Pathogen invadingPhytohormones(Auxin, ABA, GA)Gravity
[Ca2+]cyt
AM, FM, DU
DiverseCellularResponses
PrimaryCa2+-SignalDecoder
CalmodulinsCDPKsOther CBPs
Amplitude (AM)
Duration (DU)
Frequency (FM)
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Model of Ca2+/calmodulin-mediated network in plants
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• Calcineurin is a Ca2+, CaM-dependent protein phosphatase that is highly conserved in eukaryotes from yeast to mammals. Calcineurin is composed of two subunits. - catalytic subunit, calcineurin A (CaM-binding domain)- regulatory subunit, calcineurin B
• CaM and CBL(calcineurin B–like) protein are small proteins that contain multipleCa2+ binding domains but lack other effector domains, such as the kinase domain in CDPKs.CBLs interact with target proteins and regulate their activity. CBLs are encoded by a multigene family of at least 10 members in Arabidopsis.Unlike CaMs, which interact with a large variety of target proteins, CBLs appear to interact with a single family of protein kinases.
• CBL-interacting protein kinase (CIPK) all contain a unique C-terminal region that is both required and sufficient for interaction with the AtCBL-type but not calmodulin-type Ca2+ binding proteins from plants. Interactions between the kinases and AtCBLs require micromolar concentrations of Ca2+,suggesting that increases in cellular Ca2+ concentrations may trigger the formation of AtCBL–kinase complexes in vivo.
Calcineurin, CBL proteins, CIPK
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A schematic presentation of calcineurin to CBL–CIPK
• Calcineurin B(CNB)• Calmodulin (CaM)• Calcineurin A (CNA)• Calcineurin B-like protein (CBL)
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AtCBL4
AtCBL5
AtCBL9
AtCBL1
AtCBL2
AtCBL3
AtCBL6
AtCBL7
AtCBL8
Phylogenetic tree of AtCBL proteins in Arabidopsis thaliana
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Overall structure of the AtCBL2–AtCIPK14 complex
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CBL1, CBL2, CBL3, and CBL9 interacted with CIPK6, CIPK16, and CIPK23
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Regulatory features of CBL–CIPK interactions
• CBLs interact with CIPKs through the C-terminal non kinase domain, which contains a conserved region among different CIPK members.-hydrophobic interaction with CBL proteins
• Regulatory feature concerns the role of Ca2+ in the CBL–CIPK interaction. Initial analysis of interaction between CBL1 and CIPK1 showed a requirement for micromolar levels of Ca2+.
• Regulatory C-terminal domain of CIPKs include the motif for interacting with a group of type-2C protein phosphatases (PP2Cs).
• Activating CIPK kinase activity, certain structural features of CBLs also suggest that these Ca2+-sensors can change cellular localization of the CBL–CIPK complexes.
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Regulation of ion homeostasis by the SOS pathway during salt stress
SOS : Salt overly sensitive
SOS2 : CIPK24
SOS3 : CBL4
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Hypothetical model of alternative targeting of CIPK24/SOS2 to plasmamembrane (PM) or tonoplast by CBL4/SOS3 or CBL10.
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Stress and ABA Induction of CBL1 Protein Expression Patterns of the CBL9 Gene
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Hypothetical Model of CIPK3 Function
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Abiotic stress signaling through the CBL-CIPK network
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A working model of the Ca2+-dependent pathway for potassium (K)channel activation in low-K response
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Signaling pathways that regulate the expression and activities of ion transporters to maintain a low cytoplasmic concentration of Na+ under salt stress
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1. Calcineurin B-like proteins (CBLs) represent a unique family of plant calcium sensors that relay signals by interacting with a family of protein kinases (CIPKs).
2. SOS3, a Ca2+ sensor, transduces the signal downstream after activating and interacting with SOS2 protein kinase.
3. This SOS3-SOS2 complex activates the Na+/H+ antiporter activity of SOS1 thereby reestablish cellular ion homeostasis.
SOS : Salt Overly Sensitive gene
SOS 1 : Na+/H+ andtiporter of plasma membrane
SOS 2 : CBL-interacting protein kinases (CIPKs_24)
SOS 3 : Calcineurin B-like protein, (CBL4 _ calcium sensor like calmodulin)
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Expression pattern of the CBL10 gene.
F : flower
S: stems
L : rosette leaves
R : roots
SH : shoots
SL : siliques
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The cbl10 mutant is hypersensitive to NaCl
175mM NaCl
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Mature cbl10 mutant plants are hypersensitive to NaCl
300mM NaCl
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NaCl hypersensitivity of the cbl10 mutant is caused by defects in ion homeostasis.
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NaCl hypersensitivity of the cbl10 mutant is caused by defects in ion homeostasis
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CBL10 interacts with CIPK24
CBL10+
CIPK24GST CIPK CBL10
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CBL10 is localized to punctate structures and vacuolar membranes
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CBL10 co-localizes with endosomal and tonoplast marker proteins
ARA6CBL10
CBL10 ARA7
CBL10
CBL1
FM4-64
FM4-64
CBL10
CBL1
TPC1
TPC1
ARA6, ARA7 : endosomesFM4-64 : plasma membraneTPC1 : vacuolar membrane
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CBL10 interacts with CIPK24 at the tonoplast
CBL10::CIPK24
DAPI/FM4-64
TPC1
CBL1::CIPK24
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Hypothetical model of CBL10 function
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Summary
1. The CBL protein CBL10 functions as a crucial regulator of salt tolerance in Arabidopsis.
2. Cbl10 mutant plants exhibited significant growth defects and showed hypersensitive cell
death in leaf tissues under high-salt conditions.
3. The Na+ content of the cbl10 mutant was significantly lower than in the wild type under
either normal or high-salt conditions, suggesting that CBL10 mediates a novel Ca2+- signaling pathway for salt tolerance.
4. The CBL10 protein physically interacts with the salt-tolerance factor CIPK24 (SOS2), and
CBL10-CIPK24 (SOS2) complex is associated with the vacuolar compartments that are
responsible for salt storage and detoxification in plant cells.
5. These findings suggest that CBL10 and CIPK24 (SOS2) constitute a novel salt-tolerance
pathway that regulates the sequestration/compartmentalization of Na+ in plant cells.
6. These results identified CIPK24 as a multi-functional protein kinase that regulates different
aspects of salt tolerance by interacting with distinct CBL calcium sensors.