Molecular switching in transcription through splicing and proline-isomerization regulates stress responses in plants

Abstract The Arabidopsis thaliana DREB2A transcription factor interacts with the negative regulator RCD1 and the ACID domain of subunit 25 of the transcriptional activator mediator (Med25) to integrate stress signals for gene expression, with elusive molecular interplay. Using biophysical and structural analyses together with high-throughput screening, we revealed a bivalent binding switch in DREB2A containing a novel ACID-binding motif (ABS) and the RCD1-binding motif (RIM). The RIM is lacking in a stress-induced DREB2A splice variant with retained activity. ABS and RIM bound to separate sites on Med25-ACID, and NMR uncovered a structurally heterogeneous complex deriving from a DREB2A-ABS proline residue populating cis- and trans-isomers with remote impact on the RIM. The cis-isomer stabilized an α-helix, while the trans-isomer may introduce energetic frustration facilitating rapid exchange between activators and repressors. Thus, DREB2A uses a post-transcriptionally and post-translationally modulated switch for transcriptional regulation.