55. Plants with apetala2 mutation show a phenotype that lacks
    (1) sepals only.
    (2) both sepals and petals.
    (3) petals only.
    (4) stamens only.

Introduction

APETALA2 (AP2) is a key floral homeotic gene in Arabidopsis that plays a major role in the development and specification of sepals and petals. Unlike many other floral organ identity genes, AP2 is involved in class A functions and also helps regulate floral organogenesis and floral meristem identity. Mutations in AP2 severely affect sepals and petals, causing homeotic transformations.

Function of APETALA2 in Floral Development

• AP2 encodes a transcription factor containing the AP2 DNA-binding domain, and it regulates the expression of many genes involved in early flower development.​

• AP2 is responsible for specifying sepals and petals (the outer two whorls of the flower) and suppressing the expression of class C genes (e.g., AGAMOUS) in these whorls.​

• AP2 mutations lead to loss or alteration of sepals and petals, often causing sepals to transform into carpels and petals to transform into stamens, indicating the loss of class A gene function.​

Phenotype of apetala2 Mutants

• Lack of sepals and petals, replaced by carpeloid and stamen-like structures, respectively.​

• Flowers exhibit homeotic conversions consistent with loss of class A function.

• AP2 also has roles beyond floral organ identity, including seed development and flowering time regulation.​

Summary Table: Impact of AP2 Mutation on Floral Organs

Conclusion

Mutation in the APETALA2 gene causes loss or transformation of both sepals and petals in Arabidopsis flowers, making option (2) the correct choice.