Testing the ABC floral-organ identity model: Double Mutants

Objectives:

To test the validity of the ABC model for floral organ identity we will:

1.  Use the model to make predictions concerning the phenotype of double or triple loss-of-function mutants and compare with the actual double mutant phenotypes.

2.  Clone and sequence the ABC genes. Look for similarities with sequenced genes already in the database.

3.  Determine the time and place of expression for each ABC gene and consider whether the expression correlates with the functional domain defined by the loss-of-function phenotype.

4.  Test regulatory interactions between ABC genes by examining how the loss-of-function of one gene affects the expression domain of another.

5.  Create gain-of-function mutants by generating transgenic plants carrying an ABC gene cDNA under the control of the CaMV35S promoter.

A Model For Control of Organ Type Mutations in Classes B and C function genes

1 2 3 4

B (AP3, PI) C (AG) A (AP2)

sepal petal stamen carpel Wild type

B C Double Mutant Expected:

A (AP2)

sepal sepal sepal sepal

Construction of ap3, ag double mutant

ap3/ap3, AG/AG x AP3/AP3,AG/ag

Wild type F1 AP3/ap3, AG/ag

F2 99 wild type; 37 Ag; 31 Ap3; 9 AgAp3 expected: 99 33 33 11

X AP3/ap3, AG/ag

ap3, ag double mutant

A Model For Control of Organ Type Mutations in Classes B and C function genes

1 2 3 4

sepal petal stamen carpel Wild type

B C Double Mutant Expected:

Observed:

A (AP2)

sepal sepal sepal sepal

sepal sepal sepal sepal

A Model For Control of Organ Type Mutations in Classes A and B function genes

1 2 3 4

B (AP3, PI) C (AG) A (AP2)

sepal petal stamen carpel Wild type

A B Double Mutant Expected: carpel carpel carpel carpel

C (AG)

ap3, ap2 double mutant

A Model For Control of Organ Type Mutations in Classes A and B function genes

1 2 3 4

sepal petal stamen carpel Wild type

A B Double Mutant Expected:

Observed:

carpel carpel carpel carpel

C (AG)

carpel carpel carpel carpel

A Model For Control of Organ Type Mutations in Classes A and C function genes

1 2 3 4

B (AP3, PI) C (AG) A (AP2)

sepal petal stamen carpel Wild type

A C Double Mutant Expected: ? ? ? ?

ap2, ag double mutant

A Model For Control of Organ Type Mutations in Classes A and C function genes

1 2 3 4

B (AP3, PI)

sepal petal stamen carpel Wild type

A C Double Mutant Expected:

Observed: Leaf/sepal/ carpel

Petal\ Stamen

Leaf/sepal/ carpel

Petal\ Stamen

? ? ? ?

A Model For Control of Organ Type Mutations in Classes A, B and C function genes

1 2 3 4

B (AP3, PI) C (AG) A (AP2)

sepal petal stamen carpel Wild type

A B C Triple Mutant Expected: ? ? ? ?

ap2 ap3, ag triple mutant

A Model For Control of Organ Type Mutations in Classes A, B and C function genes

1 2 3 4

sepal petal stamen carpel Wild type

A B C Triple Mutant Expected:

Observed:

? ? ? ? leaf leaf leaf leaf

Apetala1 Mutant

APETALA1 Gene

•  In the typical Ap1 mutant phenotype the floral perianth organs are replaced by one or two leaves and branches.

•  However, some mutant alleles of AP1 result in a phenotype like Ap2 (perianth replaced by stamens and carpels.

•  Thus AP1 is considered to regulate two processes: shoot identity and Class A floral organ type.