Transcript Why so many steps?

Homework #1 is posted and due 9/17
Bonus #1 is posted and due 10/24
Discussions started this week
Why so many steps?
Multiple steps allow for signal specificity.
Different relay molecules lead to different responses
Multiple steps
allow for
signal
amplification:
Calcium is a
simple
method of
amplifying
signals
Calcium is a
common
effector.
Cytoplasmic
calcium levels
are normally
low.
During signal transduction, calcium can be
released into the cytoplasm: Perception
During signal transduction, calcium can be
released into the cytoplasm: Transduction
During signal transduction, calcium can be
released into the cytoplasm: Response
During signal transduction, calcium can be
released into the cytoplasm
General model of Ca++
signaling
General model of
Ca++ signaling
Multiple steps
allow for
signal
amplification:
Calcium is a
simple
method of
amplifying
signals
Ca++ is involved in many responses
Ca++ is involved in signal
transduction for responses of:
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•
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•
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in Plants
in Animals
Development
• Neurons
Cold
• Muscle movement
Guard cell closing
• Wounding
Osmotic shock
• Development
Light
• Fertilization
Fungal infection
• Hormones
Touch
• …
Pollen tube growth
Wounding…
How can there be specificity?
Everything has its
place…
Some Ca++ channels
have specific
effectors associated
with them:
Micro-domains
Ikeda, Science 12 Oct 2001 Vol 294:318-319
Root nodules: Nitrogen fixation
Bacteria and Plants Symbiosis
Signaling between bacteria and plants
1nM Nod
Fig 3. Shaw and
Long, Plant
Physiology, March
2003, Vol. 131, pp.
976–984
10nM Nod
A biphasic Ca++
response to Nod
factor:
1nM Nod - toward
nucleus
10nm Nod - away
from nucleus
1nM Nod
10nM Nod
1nM Nod
10nM Nod
A biphasic Ca++ response to
Nod factor:
1nM Nod - toward nucleus
10nm Nod - away from nucleus
Fig 3. Shaw and Long, Plant Physiology,
March 2003, Vol. 131, pp. 976–984
Everything has its
place…
2 hypotheses about
how Ca++ signals are
transduced:
Signatures vs.
Switches
Fig 1. Scrase-Field and Knight, Current Opinion in
Plant Biology 2003, 6:500–506
Photosynthesis:
Plants can make sugar
using energy from the
sun, water from the
ground, and CO2 from
the air.
Stomata regulate gas
exchange: CO2 in, O2 and
water out
H2 O
H2 O
Stomata
open
closed
Opening and closing of stomata
Ca++ fluxes in
guard cells in
response to
hormone or stress
that cause
stomatal closing.
Wildtype vs. det3
and gca2: mutants
that fail to close
stomata following
treatment
Fig 5. Sanders et al., The Plant Cell,
S401–S417, Supplement 2002
2 hypotheses about
how calcium
signals are
transduced:
Signatures vs.
Switches
Fig 1. Scrase-Field and Knight, Current Opinion in
Plant Biology 2003, 6:500–506
Signal Transduction
External
Stimulus
Internal
Effector…
Effector
Effector
Effector
Response
Perception
(by receptor)
Stimulus
Homework #1 is posted and due 9/17
Bonus #1 is posted and due 10/24
Discussions started this week