53. Which of the floral whorls is affected in agamous (ag) mutants
    (1) Sepals and petals (2) Petals and stamens
    (3) Stamens and carpels (4) Sepals and carpels

Introduction

The AGAMOUS (AG) gene in Arabidopsis thaliana is a critical C-class homeotic gene encoding a MADS-box transcription factor that specifies the identity of reproductive floral organs: stamens (third whorl) and carpels (fourth whorl). It also regulates floral meristem determinacy, controlling the cessation of meristem activity once floral organs develop.

Role of AGAMOUS in Flower Development

• AG is expressed in the central floral meristem that gives rise to stamens and carpels but is absent in the outer whorls forming sepals and petals.​

• AG confers stamen and carpel identity and directs the floral meristem to cease proliferation, allowing determinate flower formation.​

• Loss-of-function mutations in AG cause homeotic conversions: stamens into petals and carpels into sepals, resulting in flowers with repeated sepals and petals instead of reproductive organs.​

Phenotype of agamous Mutants

• Mutant flowers exhibit the whorl composition: sepals (1st whorl), petals (2nd whorl), petals (3rd whorl, replacing stamens), and sepals (4th whorl, replacing carpels), demonstrating loss of stamens and carpels.​

• The floral meristem remains indeterminate, producing additional floral organ whorls repeatedly, resulting in abnormal flower architecture.​

Summary Table: AGAMOUS Mutation Effects on Floral Organs

Conclusion

The AGAMOUS gene mutation affects the third and fourth floral whorls by converting stamens and carpels into petals and sepals, respectively, consistent with option