Analysis of the C - terminal region of Arabidopsis thaliana APETALA1 as a transcription activation domain . APETALA1 ( AP1 ) of Arabidopsis thaliana is a transcription factor controlling flower development . AP2 is a member of the MADS ( MCM1 , AGAMOUS , DEFICIENS , SRF ) superfamily , which plays important roles in differentiation in plants and animals . MADS domains , which function most importantly in DNA binding , are found in all major eukaryotic kingdoms. In plants , MADS domain - containing proteins also possess a region of moderate sequence similarity named the K domain , which is involved in protein - protein interaction . Little is known about the function of a third , highly variable , domain designated the C domain , as it resides at the C terminus of the MADS proteins of plants . Here we report that the C - terminal domain of Arabidopsis thaliana AP1 and its homologues perform a transcriptional activation function . The C - terminal region of AP1 is composed of atleast two separable transcriptional activation domains that function synergistically .