signal transduction

signal transduction

1. SIGNAL TRANSDUCTION IN
PLANTS:
ABIOTIC STRESS
Arun patel
Msc A.Biotechnology

2. Stimulus
physical environment.
Receptor
On the plasmamembrane, or internal
Secondary messengers
Ca
2+
, G-proteins, Inositol Phosphate
Effector molecules
Protein kinases or phosphatases
Transcription factors
Response
germination
leaf formation
flowering
tolerance

S Signal Transduction Components

3. Review of a general model for signal transduction pathways
CELL
WALL
CYTOPLASM
Reception Transduction Response
Relay proteins and
second messengers
Activation
of cellular
responses
environmental
stimulus
Receptor
Plasma membrane
1 2 3

4. STRESS
RECEPTORS
PLC
PIP2 IP
3
+ DAG
Ca
2+
And other second
messengers
Ca
2+
Sensors
Kinases/Phosphatases
Transcription factors
PO
4 4
CIPKs/SOS2,CDPKs,MAP
Ks and various protein
phosphatases
(InsP)
Ca
2+
ext
Generic Signal Tranduction Pathway

5. Transcription factors
Major stress responsive genes
Physiological response
Early Genes Delayed Genes
(RD/KIN/COR/RAB18/RAB29B)
Encode proteins like
transcription
factors/calcium sensors.
Activate
MODULATE
STRESS TOLERANCE EFFECTORS
e.g. antioxidants osmolyte
synthesiszing enzymes.

6. (a)Before exposure to light
Tall, spindly stem/nonexpanded leaves
(morphological adaptations called etiolationetiolation
enable shoots to penetrate soil, including
short roots due to little need for water
absorption from little water loss by shoots)
Expanded leaves hindrance as shoots
push through soil/chlorophyll waste of
energy (underground)
(b) After a week’s exposure to
natural daylight
Begins to resemble typical plant w/broad
green leaves, short sturdy stems, long
roots (transformation begins w/reception
of light by specific pigment, phytochrome)
by undergoing changes (de-etiolation) de-etiolation) by
reception of signal (light) which is
transduced into responses (greening)

7. An example of signal transduction in plants: the role of phytochrome in the de-etiolation (greening)
response
CYTOPLASM
Reception
Plasma
membrane
Cell
wall
Phytochrome
activated
by light 2. One pathway uses cGMP as 2
nd

messenger that activates specific
protein kinase. Other pathway
involves increase in cytosolic level
of Ca
2+
, which activates different
protein kinase
1. 1. LightLight signal detected
by phytochrome receptor;
phytochrome undergoes
change in shape, which
then activates at least
two signal transduction
pathways
Transduction
Second messenger
produced
cGMP
Specific
protein
kinase 1
activated
NUCLEUS
1 2
Specific
protein
kinase 2
activated
3. Both pathways lead to
expression of genes for
proteins that function in
de-etiolation (greening)
response
Ca
2+
channel
opened
Ca
2+
Response3
Transcription
factor 1
Transcription
factor 2
NUCLEUS
Transcription
Translation
De-etiolation
(greening)
response
proteins
P
P

8. DroughtCold Salt
CBF1,2,3
/DREB1B
,1C.1A
SCO
F
SCB
F
MYC/MY
B
DREB2A,2
B
bZip
DRE/CRT ABRE MYCRS/MYBRS mRNA
ABA ABA ABA ABA ABA

9. G-protein-mediated pathway
G-proteins, coupled with members of the
seven transmembrane domain of the receptor
superfamily, are regulatory proteins that act as
molecular switches. They control a wide range
of biological processes

10. Regulation of G-Protein Activity
G protein-coupled receptors exhibit a common structural
motif consisting of seven membrane spanning regions.
Receptor occupation promotes interaction between the
receptor and the G protein on the interior surface of the
membrane. This induces an exchange of GDP for GTP
on the G protein a subunit and dissociation of the a
subunit from the bg heterodimer. Depending on its
isoform, the GTP-a subunit complex mediates
intracellular signaling either indirectly by acting on
effector molecules such as adenylyl cyclase (AC) or
phospholipase C (PLC), or directly by regulating ion
channel or kinase function.

12. Regulation of G-Protein Activity

15. The activity cycle of heterotrimeric
G-proteins.

16. Both G-protein and tyrosine kinase pathways can utilize
calcium as a second messenger.
Calcium concentrations in cytoplasm are normally very
low.
Where does the calcium come from?
 from the extracellular environment
 from the ER
(calcium is exported by calcium pumps within cell, to
keep internal calcium levels low)

17. How is calcium released from internal stores?
Phospholipase C is activated (different forms
are activated by receptor tyrosine kinases than
by G protein-linked receptors).
It cleaves a membrane phospholipid (PIP
2
) to
form diacylglycerol (DAG) and inositol
trisphosphate (IP
3
).

19. Both DAG and IP3 act as second messengers in many types of cell.
What about IP
3?
Ca
++
levels are now high enough to bind calmodulin.

20. Many cellular proteins have binding sites for
calcium-calmodulin complex.
Actual identities of these proteins varies within
cells.
Tend to be kinases and phosphatases.
When calcium levels drop, calmodulin releases
calcium.

21. Receptor tyrosine kinase mediated
pathway
 Receptor tyrosine kinases transmit signals
across the plasma membrane, from the cell
exterior to the cytoplasm.
 The interaction of the external domain of a
receptor tyrosine kinase with the ligand, often
a growth factor, up-regulates the enzymatic
activity of the intracellular catalytic domain,
which causes tyrosine phosphorylation of
cytoplasmic signaling molecules.

23. Conclusions
Manipulations in the signal transduction pathways could
be useful for protecting plants from various abiotic
stresses under the heat of climate change.
Over expression of G proteins in Arabidopsis and
tobacco has given these plants genetic potential to
overcome many abiotic stresses, and the same
technology is now applied on several economically
important plants such as rice, pea, tomato, and
soybean.
Studies leading to their effective manipulations can
result in plants that are genetically better equipped to
perceive and combat abiotic stresses thereby leading
to increased crop productivity.

24. The future of plant cell
signal transduction research
The main signaling pathways cross-talk with each other.
Specificity in signaling arises from the specific spatial
locations of the signaling elements.
Integration of many signals might result from multiple
phosphorylation sites.
Adapter proteins may help cross-link signaling pathways
or act as phosphorylation receptors.

25. Thanks…………………………
…….