60. Which one of the following plant homeotic genes does NOT encode MADS- domain transcription factor involved in floral organ specification?
(1) AP2                                                         (2) AP1
(3) AP3/P1                                                     (4) AG

 

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Introduction

Floral organ specification in plants is largely governed by homeotic genes encoding MADS-domain transcription factors, which regulate floral organ development through spatial and combinatorial gene expression patterns. Among these crucial genes, APETALA2 (AP2) stands out as the only floral homeotic gene that does not encode a MADS-domain transcription factor, but instead belongs to the AP2/ERF family of transcription factors.

APETALA2 versus Other Floral Homeotic Genes

• Most floral organ identity genes such as APETALA1 (AP1), APETALA3 (AP3), PISTILLATA (PI), and AGAMOUS (AG) encode MADS-domain transcription factors characterized by a conserved MADS-box DNA-binding domain involved in protein-protein interactions and gene regulation.

• AP2 codes for a transcription factor containing AP2 DNA-binding domains and belongs to a different family unrelated to MADS proteins.

• Despite lacking the MADS domain, AP2 plays an essential role in specifying the identity of sepals and petals and in repressing Class C gene expression in the outer floral whorls.

Functional Insights into APETALA2

• AP2 mutants lack sepals and petals, confirming its crucial function in the Class A activity of the ABC floral organ specification model.

• AP2 operates early in floral meristem specification and interacts genetically and molecularly with MADS-box proteins for cohesive floral development.

• It is regulated extensively, including by miRNA interaction (miR172), reflecting its complex control over floral organ patterning.

Summary Table: Floral Homeotic Genes and Domain Types

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Conclusion

APETALA2 is unique among floral homeotic genes in not encoding a MADS-domain transcription factor but is critically involved in floral organ identity and meristem specification. Hence, among the options, AP2 is the distinct non-MADS gene controlling Class A functions in flower development.