sequential DNA affinity purification sequencing (seq-DAP-seq) data of MADS SEP3-AG tetramerization mutants.
The MADS genes encode transcription factors (TF) that act as master regulators of plant reproduction and flower development. The SEPALLATA (SEP) MADS subfamily is not only absolutely required for the development of floral organs, but also plays roles in inflorescence architecture and determinacy of the floral meristem. The SEPs act as organizers of MADS complexes and are able to form both heterodimers and heterotetramers in vitro. To date, the MADS TF complexes characterized in angiosperm floral organ development contain at least one SEP TF. Whether DNA-binding by SEP-containing dimeric MADS complexes are sufficient for launching floral organ identity programs, however, is not clear as only defects in floral meristem determinacy were observed in tetramerization impaired SEP mutants. Here we used a combination of genome-wide binding studies, high resolution structural studies of the SEP3-AGAMOUS tetramerisation domain, structure-based mutagenesis and complementation experiments in sep1 sep2 sep3 and sep1 sep2 sep3 ag-4 plants transformed with versions of SEP3 encoding tetramerization mutants. We demonstrate that while SEP3 heterodimers are able to bind DNA both in vitro and in vivo and recognize the majority of SEP3 wild type binding sites genome-wide, tetramerisation is not only required for floral meristem determinacy, but also absolutely required for floral organ identity in the second, third and fourth whorls. Overall design: In this study we applied sequential DNA affinity purification sequencing (seq-DAP-seq) to two new tetramerization mutants of SEP3AG heterotetramer: SEP3?tet3M-AG and SEP3?tet-AG?tet. We compared the DNA binding intensity of these two new mutant complexes and another previsouly analyzed mutant (SEP3?tAG) at regions bound by the SEP3AG wildtype complex (also previsoulsy analyzed in PMID 32890394) .