PLANT
Hormonal Cross-Talk in Plant Organogenesis
ZYGOTE
SEEDLING
EMBRYO
auxin
abscisic acid
auxin
gibberellin
auxin
cytokinin
first division
auxin
abscisic acid
cytokinin
brassinosteroids
HORMONAL CROSS-TALK
Metabolism
Biosynthesis
Degradation
Conjugation
Distribution
Perception
1. Receptors:
Histidine kinase (cytokinin) Plasmatic membrane
(ethylene) Endoplasmatic Reticulum
Kinase (brassinosteroids) Plasmatic membrane
F-box protein (auxin) Nucleus
RNA binding protein (abscisic acid) Nucleus
Lipase(gibberellin) Nucleus
2. Signal Transduction
Phosphotransfer protein
AUXIN: polar transport
Other hormones:
Passive distribution
Phosphotransfer protein
Response regulator positive or
Metalotransfer protein negative regulators
Map Kinase
Short live protein (GRASS family, Aux/IAA)
Polyadenylation signal
F-box protein
3. Transcription factors
4. Common downstream targets
HORMONAL CROSS-TALK
AUXIN
Metabolism
Biosynthesis
Degradation
Conjugation
Distribution
Perception
1. Receptors:
F-box protein (auxin) Nucleus
2. Signal Transduction
AUX/IAA
ethylene
Gibberellin ???
AUXIN: polar transport
Other hormones:
Passive distribution
3. Transcription factors
ARFs
4. Common downstream targets
Each step can be target of cross talk on the level of transcription, translation,
Postranslational modification
Cytokinin – slow negative effect
Brassinosteroids
(BIN2)
ethylene
cytokinin
ethylene
Cytokinin – slow negative effect
Gibberellin ???
ethylene
cytokinin
Brassinosteroids
(BIN2)
When three do the same...
control cytokinin ethylene auxin
it does not have to be the same...
1. Cell elongation
control cytokinin ethylene auxin
2. Root meristem growth
control cytokinin ethylene auxin
auxin
3. Lateral root initiation
auxin
-1
0
1
2
3
4
5
control cytokinin ethylene
1.Hormonal interactions - regulating cell elongation
control cytokinin ethylene auxin
DR5 auxin reporter is up-regulated
in response to ethylene
Ethylene signalling mutant are auxin sensitive
MS ethylene auxin MS ethylene auxin MS ethylene auxin
control etr1-3 ein2
Auxin signalling is required for ethylene effect
Ethylene stimulates auxin biosynthesis
(Růžička et al., 2007)
t/t-ratio
0.2
0.4
0.6
0.8
1.0
0.0
D20
D20 + ACC (10 µM)
D20 + ACC (100 µM)
12h 24h
(Swarup et al., 2007)
Stepa
TAA1-Mediated Auxin Biosynthesis Is Essential for
Hormone Crosstalk and Plant Development
TRYPTOPHAN AMINOTRANSFERASE of Arabidopsis
Stepa
Stepanova et al., 2008
Roman et al., 1994
ethylene???
Auxin flow in the root tip
AUX1
Friml et al. 2002
35S::PIN1
(Swarup et al., 2001) (Růžička et al., 2007)
Mutants in basipetal auxin transport
are ethylene resistent
MS ACC MS ACC MS ACC MS ACC
DR5::GUS
Ethylene upregulates expression
of auxin transport carriers
proPIN1-PIN1:GFP
MS ACC
Model of ethylene regulated root growth
(Růžička et al., 2007)
Conclusions:
1.Ethylene stimulates auxin biosynthesis.
-requires ethylene signalling
2. Auxin interfers with elongation of root cells.
- requires basipetal auxin distribution
- requires auxin signalling
Hormonal interactions - regulating cell elongation
control cytokinin ethylene auxin
Ethylene perception mutants are cytokinin resistant
40
60
80
100
120
140
col
etr1-3
0
20
40
MS ethylene cytokinin AVG cytokinin/AVG
MS AVG ethylene cytokinin cytokinin/AVG
Cytokinin induced accumulation of auxin
is ethylene dependent
DR5::GUS
Auxin transport mutant are cytokinin resistant
40
60
80
100
120
140
0
20
MS Acc Ba MS Acc Ba MS Acc Ba MS Acc Ba
col pin2 aux1 35Spin1
MS ethylene cytokinin MS ethylene cytokinin
Auxin transport mutant are cytokinin resistant
Pin2 x DR5::GFPCol x DR5::GFP
Conclusion:
1.Part of cytokinin effect on root growth
is mediated through ethylene and auxinis mediated through ethylene and auxin
Model of ethylene regulated root growth
cytokinin
(Chae et al., 2003)
(Růžička et al., 2007)
Hormonal interactions regulating root meristem
control cytokinin ethylene auxin
Cytokinin inhibits meristem growth
MS cytokinin cytokinin/AVG ethylene MS cytokinin cytokinin/AVG ethylene
cycB::GUS
Cytokinin inhibition of root meristem growth
is ethylene independent
root length root meristem
Auxin and cytokinin regulated root meristem growth
MS BAMS
NAA 2,4D
BA
Auxin transport mutants are defective
in root meristem growth
Blilou et al., 2005
MS ethylene CK CK/AVG
Cytokinin and ethylene regulate PIN expression differentially
MS ethylene CK CK/AVG
PIN1::GUS
PIN7::GUSPIN4::GUS
PIN3::GUS
Cytokinin modulates expression of PIN genes differentialy
MS BA
PIN2:GFP (48 h)
PIN7:GFP (24h)PIN3:GFP (24h)
PIN1:GFP (24 h)
MS BA
MS BA MS BA
0
50
100
150
200
250
300
PIN1 PIN2 PIN3 PIN7
Relativeexpression(%)
MS
1h
2h
3h
4h
5h
6h
Q-RT PCR
MS BA
0
20
40
60
80
100
120
140
0 0.1 1 10 µM BA
* * *
Cytokinin reduces auxin efflux in tobacco BY2 cells
PIN1:RFP
0,00
0,50
1,00
1,50
0 5 10 15 20 25
time (min)
M S BA
MS cytokinin MS cytokinin
Cytokinin inhibitory effect on PIN1
is ethylene independent
etr1-3 ein2
control cre1-12
MS cytokinin MS cytokinin
Cytokinin inhibitory effect on PIN1
requires CK perception
0
20
40
60
80
100
120
140
160
col
cre
ahk2-2
ahk3-3
ahk2xahk3
crexahk2
crexahk3
relativefluorescence%
ms
ba
control cre1-12
Conclusions:
1. Cytokinin regulates root meristem growth in
ethylene independent manner
2. Cytokinin antagonizes auxin regulated root
meristem growth.
3. Modulation in auxin distribution might result in3. Modulation in auxin distribution might result in
reduced root meristem size