ABC Model of Flower Development in Arabidopsis thaliana

Flower is considered as a modified shoot. Many genes are involved in the conversion of shoot meristem to floral meristem.
ABC model of floral development explains the genetics behind the formation of different whorls in a flower.
The four whorls are sepal, petal, stamens and carpel.

Flower formation is initiated by the activity of genes known as heterochrony or flowering time genes which regulate the conversion of vegetative meristem to floral meristem. Then flower meristem identity genes regulate the formation of flower. Upon initiation of flowering, a third type of genes called cadastral genes will express which govern the whorl formation of the flower. Finally the structure of this whorls and its occurrence at right place is regulated by homeotic genes.

The four whorls are sepal, petal, stamens and carpel.

ABC model was first formulated by George Haughn and Chris Somerville in 1988. Experimental material was Arabidopsis thaliana and Antirrhinum majus.

ABC model predicts that the four whorls of flower are controlled by the action of 3 genes A, B and C in Arabidopsis thaliana. The role of these genes was deduced by inducing mutation in each of these genes.

Key 1: Remember, A and C genes are equally dominant. Mutation of ‘A’ gene makes ‘C’ gene more active.

Key 2: B genes always express in association with A and C.

The above figure summarizes the ABC model and changes associated with whorl formation on mutation of A, B and C genes respectively.