The Molecular Mechanism of Interaction Between SEPALLATA3 and APETALA1 in <scp><i>Arabidopsis thaliana</i></scp>

Flower formation has been a primary focus in botanical research, leading to the identification of multiple factors regulating flowering over the past 30 years. The MADS transcription factors SEPALLATA3 (SEP3) and APETALA1 (AP1) are essential for floral meristem development and organ identity. In Arabidopsis, SEP3 functions as a central integrator, combining MADS proteins into a tetrameric complex, with its interaction with AP1 playing a key role in sepal and petal formation. This research explores <i>AtSEP3</i> and <i>AtAP1</i>, with particular emphasis on the Leu residue in the K1 subfunctional domain of <i>AtSEP3</i>, which is necessary for their interaction. A predicted structural model of AP1 was used, followed by protein docking with SEP3, which indicated that Leu residues at positions 115 and 116 are critical binding sites. Mutations at these position were examined through yeast two-hybrid assays and other techniques, identifying Leu 116 as a significant site. Subsequent purification and EMSA analysis revealed that mutations in the leucine zipper of SEP3 decreased its DNA binding ability. Observations of transgenic plants showed that disruption of <i>AtSEP3</i> and <i>AtAP1</i> interaction resulted in extended vegetative growth, increased size and number of rosette leaves, and modifications in floral structures. This study offers new insights into the interaction mechanism between AP1 and SEP3 during flowering.