Regulation of AUXIN RESPONSE FACTOR Activity

The phytohormone auxin plays an essential role in regulating nearly every aspect of plant growth and development. The nuclear auxin signaling pathway coordinates auxin effects on cell division and cell expansion through three protein families: TRANSPORT INHIBITOR RESPONSE1/AUXIN BINDING F-BOX (TIR1/AFB) F-Box proteins, the AUXIN RESPONSE FACTOR (ARF) transcription factors, and the AUXIN/INDOLE-3-ACETIC ACID INDUCIBLE (Aux/IAA) repressor proteins. Fine-tuning of auxin response relies on protein-protein interactions within and between these protein families, however a complete picture of how these proteins interact to control their activity is still lacking. In this work, we describe the studies we undertook to demonstrate and identify a role for ARF biomolecular condensate formation in planta. We characterize features required for ARF interaction and condensate formation and provide evidence for ARF nucleo-cytoplasmic partitioning in regulating auxin response. We further examine ARF and Aux/IAA interactions and distinguish features within the interaction domain necessary for defining interaction specificity. Finally, we identify factors important for controlling ARF localization and stability. Together, this work uncovers novel insights into mechanisms governing protein-protein interactions between ARF and Aux/IAA proteins, and provides a stronger understanding of factors influencing auxin response specificity