Question

Angiosperms rely on a number of control pathways that govern when to produce reproductive structures. Briefly describe any one of these pathways, including the processes, structures and/or molecules involved.

Answer 1

Flower is the reproductive structure of the Angiosperms. Angiosperms rely on number of control pathways that govern when to produce reproductive structures. One such pathway is ABC model of flower development

The ABC model of flower development in angiosperm demonstrates the presence of three classes of genes that regulate the development of floral organs. The genes are referred to as class A genes, class B genes and class C gene. These genes and the interaction between them induce the development of floral organs.

In the flower of angiosperms there are usually four concentric whorls of organs, i.e. sepal, petal, stamen and carpel that are formed in whorl 1, whorl 2, whorl 3 and whorl 4 respectively, the whorl 1 being on the peripheral side.

• In the whorl 1 class A genes when expressed induce the development of sepals.
• The interaction between class A and class B genes induce the development of petals in the whorl 2.
• Stamens are formed in the whorl 3 as a result of interaction between class B and class C genes.
• In the whorl 4 class C gene induces the formation of carpel.

In ABC model, discovered in Arabidopsis specifies the molecular basis of organ development in flowers. It includes 5 genes APETALA1 (AP1), APETALA2 (AP2), APETALA3 (AP3), PISTILLATA (PI) and AGAMOUS (AG).

The A class genes- AP1, AP2 specifies the sepals and petals development.

The B class genes- AP3 and PI specifies the petal and stamen development.

The C class gene- AG specifies stamens and carpel development.

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