• 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 12. Plant 23. Plant 3

31 2

• Which seedling was germinated in the presence of the plant hormone ethylene in the dark?

1. Seedling 12. Seedling 2

1 2

What is the ethylene-response phenotype in dark-grown seedlings called?

1. Phototropism2. Radicle3. Hypocotyl tropism4. Thigmomorphogenesis5. The triple response

• Which of these seedlings is insensitive to the plant hormone ethylene?

1. Seedling 12. Seedling 23. Seedling 3

1 2 3

Noethylene

+ ethylene

How do research labs screen for mutants that are insensitive to ethylene?

Mutagenized seeds are plated on growth media that:

1. contains abscisic acid and is incubated in the dark2. contains ACC and is incubated under lights in the growth chamber3. contains ACC and is incubated in the dark4. is incubated in the dark

• Which seedling is a “constitutive ethylene-response” mutant?

1. Seedling 12. Seedling 23. Seedling 34. Seedling 4

1 2 3 4

Noethylene

+ ethylene

How do research labs screen for mutants that have a constitutive response to ethylene?

Mutagenized seeds are plated on growth media that:

1. contains abscisic acid and is incubated in the dark2. contains ACC and is incubated under lights in the growth chamber3. contains ACC and is incubated in the dark4. is incubated upside down in the dark

What kind of mutant is the abi1-1 mutant?Wild type abi1-1

Dormancy(No germination)

ABA

NO Dormancy (Germination)

NO ABA

NO Dormancy (Germination)

NO ABA

ABA

NO Dormancy (Germination)

1. ABA insensitive 3. Constitutive ABA response2. Seed germination 4. Viviparous mutant

The Arabidopsis abi1-1 mutant is ABA-insensitive

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.

Wild type abi1-1

Dormancy(No germination)

ABA

NO Dormancy (Germination)

NO ABA

NO Dormancy (Germination)

NO ABA

ABA

NO Dormancy (Germination)

abi1-1 mutants are ABA-insensitive in all their responses

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.

Root growth is not inhibited on

ABA

Guard cells are not ABA-

responsiveWildtype abi1

Germination is not inhibited on

ABA

Ethylene responses in Arabidopsis

“TripleResponse”

Inhibition of leaf cell expansion

Senescence

Ethylene-induced gene expression

• 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?

Wild type abi1-1

Dormancy(No germination)

ABA

NO Dormancy (Germination)

NO ABA

NO Dormancy (Germination)

NO ABA

ABA

NO Dormancy (Germination)

Can you make a similar table for your predicted ethylene mutants?

+ ACC

No ACC

Wild type Mutant

Ethylene insensitive mutants (“ein”)

*

+ ACC

No ACC

Wild type Mutant

Constitutive ethylene response mutants (“ctr”)

*