• Which of the following is NOT one of the reasons why
Arabidopsis has been an excellent model system for
plants?
1. It is easy to grow and doesn’t take up much space.
2. It has a small genome that is completely sequenced,
and has a complete genetic map.
3. It tastes good and is valued by the farm industry.
4. It self-pollinates but can also be out-crossed by hand
for genetic crosses.
5. It has a short life cycle of ~6 weeks.
• Which plant is showing an etiolated phenotype?
1. Plant 1
2. Plant 2
3. Plant 3
1
2
3
• Which seedling was germinated in the
presence of the plant hormone ethylene in
the dark?
1
2
1. Seedling 1
2. Seedling 2
What is the ethylene-response phenotype
in dark-grown seedlings called?
1.
2.
3.
4.
5.
Phototropism
Radicle
Hypocotyl tropism
Thigmomorphogenesis
The triple response
• Which of these seedlings is insensitive to the
plant hormone ethylene?
No
ethylene
+
ethylene
1. Seedling 1
2. Seedling 2
3. Seedling 3
1
2
3
How do research labs screen for mutants that are
insensitive to ethylene?
Mutagenized seeds are plated on growth media
that:
1.
2.
3.
4.
contains abscisic acid and is incubated in the dark
contains ACC and is incubated under lights in the growth chamber
contains ACC and is incubated in the dark
is incubated in the dark
• Which seedling is a “constitutive ethyleneresponse” mutant?
1.
2.
3.
4.
No
ethylene
+
ethylene
1
3
Seedling 1
Seedling 2
Seedling 3
Seedling 4
2
4
How do research labs screen for mutants that have
a constitutive response to ethylene?
Mutagenized seeds are plated on growth media
that:
1.
2.
3.
4.
contains abscisic acid and is incubated in the dark
contains ACC and is incubated under lights in the growth chamber
contains ACC and is incubated in the dark
is incubated upside down in the dark
What kind of mutant is the abi1-1 mutant?
Wild type
ABA
Dormancy
(No germination)
NO ABA
NO Dormancy
(Germination)
1. ABA insensitive
2. Seed germination
abi1-1
ABA
NO Dormancy
(Germination)
NO ABA
NO Dormancy
(Germination)
3. Constitutive ABA response
4. Viviparous mutant
The Arabidopsis abi1-1 mutant is
ABA-insensitive
Wild type
ABA
Dormancy
(No germination)
NO ABA
NO Dormancy
(Germination)
abi1-1
ABA
NO Dormancy
(Germination)
NO ABA
NO Dormancy
(Germination)
From Koornneef, M., Reuling, G., and Karssen, C.M. (1984). The isolation and characterization of abscisic acid-insensitive mutants of Arabidopsis thaliana.
Physiologia Plantarum 61: 377-383, with permission from John Wiley and Sons.
abi1-1 mutants are ABA-insensitive
in all their responses
Germination is
not inhibited on
ABA
Wild
abi1
type
Root growth is
not inhibited on
ABA
Guard cells are
not ABAresponsive
Leung, J., Bouvier-Durand, M., Morris, P., Guerrier, D., Chefdor, F., and Giraudat, J. (1994). Arabidopsis ABA response gene ABI1: features of a calcium-modulated protein phosphatase. Science 264
1448-1452; Meyer, K., Leube, M., and Grill, E. (1994). A protein phosphatase 2C involved in ABA signal transduction in Arabidopsis thaliana. Science 264: 1452-1455.
Ethylene responses in Arabidopsis
Ethylene-induced gene expression
“Triple
Response”
Inhibition of leaf
cell expansion
Senescence
• Based on the variety of topics in this
workshop, can you think of an idea for a
mutant screen in plants?
• How would you carry out your screen?
Can you make a similar table for your
predicted ethylene mutants?
Wild type
ABA
Dormancy
(No germination)
NO ABA
NO Dormancy
(Germination)
abi1-1
ABA
NO Dormancy
(Germination)
NO ABA
NO Dormancy
(Germination)
Ethylene insensitive mutants (“ein”)
Wild type
Mutant
*
+ ACC
No ACC
Constitutive ethylene response mutants (“ctr”)
Wild type
Mutant
+ ACC
No ACC
*