B ACCA B carpel petal stamen sepal

normal flower

A mutant sepals are replaced by carpels

B mutant petals are replaced by sepals

C mutant stamens are replaced by petals

C mutant carpels are replaced by a new flower

sepal petal stamen carpel B B ACCA What gene prevents the B gene from being active in the center of flowers?

In SUPERMAN mutants (SUP), the B activity expands into the center of the flower and converts the two carpels into two stamens. ACCA BB stamen sepal petal stamen

Superman mutant

The SUPERMAN gene normally functions to prevent B gene activity in the center of flowers ACCA BB stamen sepal petal stamen

sepal petal stamen carpel B B ACCA What happens if the B and C genes are both inactivated in the BC double mutant?

normal BC mutant sepal petal stamen carpel B B ACCA AAAA sepal *

“BC” double mutant all organs are sepals

B ACCA B carpel petal stamen sepal

petal stamen carpel B B ACCA What happens if the A, B and C genes are all inactivated in the ABC triple mutant?

ABC mutant leaf * normal sepal petal stamen carpel B B ACCA

“ABC” triple mutant all organs are leaves

“Flower organs are modified leaves.” Goethe, 1790

All flower organs are converted into leaves in the abc triple mutant. The ABC genes are necessary to convert leaves into each of the flower organs.

The A and B genes are necessary for petal development. What would happen if the A and B genes were mis-expressed in leaves? Are the A and B genes sufficient to convert normal leaves into petals?

leafpetal? A+B

“D” mutant all organs are sepals

AB CD

D Activity is required for petal, stamen and carpel development The D gene is expressed in cells that will form petals, stamens and carpels. The D gene is required for the activity of the B and C genes.

sepal stamen petal carpel petal stamen sepal B ACCA B DD

normal D mutant sepal petal stamen carpel B B ACCA AAAA sepal * DD

The A, B and D genes are necessary for petal development. What would happen if the A, B and D genes were mis-expressed in leaves? Are the A, B and D genes sufficient to convert normal leaves into petals?

Regulatory region Petals, stamens and carpels D GENE Coding Region leaves Add Leaf regulatory region: Remove regulatory region:

leafpetal A+B+D ?

leafpetal A+B+D

A = sepals A + B + D = petals C + D = carpels B + C + D = stamens

The ABCD genes act alone, or in combination, to specify the four types of flower organs The ABCD genes are sufficient to convert leaves into flower organs The ABCD model is applicable to all flowering plants

Regulatory region stamens and carpels C GENE Coding Region sepals Add sepal regulatory region: Remove regulatory region:

mis-expression of B activity petal stamen ACCA B B

mis-expression of B activity

mis-expression of B and C activity stamen B B CC

mis-expression of B and C activity

mis-expression of C activity

C mutant B AAAA B sepal petal *

Reduction in C activity

mis-expression of A and B activity in C mutant petal * B B A A

mis-expression of A and B activity in a C mutant