SUPERMAN requires its EAR motif to recruit the corepressor TOPLESS and to function as a cadastral regulator in floral patterning

The spatial regulation of gene expression is crucial for the development of complex structures such as the angiosperm flower. The combinatorial actions of floral organ identity genes, which are expressed in well-defined domains, specify the fate of lateral organs arranged in concentric whorls in the flower. SUPERMAN (SUP) contributes to this regulation by establishing a boundary between floral whorls 3 and 4 in Arabidopsis, preventing both the central spread of APETALA3 and PISTILLATA gene expression and overproliferation of male reproductive organs. SUP operates as a transcriptional repressor and harbors an ERF-associated amphiphilic repression (EAR) motif. In this work, we show that the corepressor TOPLESS (TPL) cooperates with SUP to repress APETALA3 and PISTILLATA and suppress male reproductive fate in the flower. Additionally, we demonstrate that SUP forms a physical interaction with TPL that is dependent on its EAR motif. We also specifically mutate the EAR motif of endogenous SUP in planta, showing that even a subtle change is sufficient to cause strong sup defects and interrupt TPL association. Collectively, our results indicate that SUP requires its EAR motif to recruit TPL and function as a cadastral regulator, with both proteins cooperatively establishing a gene expression boundary necessary for floral patterning.