65. AP1 (APETLA 1) is one of the floral meristem identifying genes. In wild type Arabidopsis thaliana plants transformed with AP1:GUS, β glucuronidase (GUS) activity is seen in floral meristem, only after the commitment to flowering. Ectopic expression of AP1::GUS in the EMBRYONIC FLOWER (emf) mutant background results in GUS activity throughout the shoots in four day old seedlings. These observations suggest that AP1 is: –
(1) not involved in flowering
(2) involved in repression of flowering.
(3) involved in promoting flowering.
(4) stimulation of flowering in the emf background

Introduction

APETALA1 (AP1) is a fundamental floral meristem identity gene in Arabidopsis thaliana that plays a crucial role in promoting flowering and specifying floral meristem fate. Research utilizing AP1::GUS reporter constructs has revealed AP1 expression patterns tightly linked to floral transition, highlighting its role in flower induction.

AP1 Expression and Function

• In wild-type Arabidopsis, AP1 expression (observed via AP1::GUS) initiates in the floral meristem only after the plant commits to flowering, marking floral organ formation sites.​

• In the EMBRYONIC FLOWER (emf) mutants, which exhibit early and precocious flowering due to defective floral repression, ectopic AP1::GUS activity is detected throughout the shoot, even in seedlings.​

• This ectopic expression suggests that AP1 promotes flowering and that EMF genes normally repress flowering partly by suppressing AP1 expression during the vegetative phase.​

• AP1 functions in converting the inflorescence meristem to a floral meristem, activating downstream floral organ identity programs.​

Implications from emf Mutant Background

• The EMF genes repress flowering during vegetative growth to prevent premature meristem identity changes.​

• Loss of EMF function results in derepression of AP1, causing early and wider expression, which leads to early floral meristem initiation.​

• Therefore, AP1 acts as a promoter of flowering, and its spatial-temporal expression is tightly regulated to ensure normal flowering timing.​

Summary Table: AP1 Activity and Its Role in Flowering

Conclusion

APETALA1 (AP1) is critically involved in promoting flowering by establishing floral meristem identity. The observations of AP1::GUS expression in wild-type and emf mutants support AP1’s function as a floral inducer, making option (3) the correct choice.