Auxin orchestrates gene transcription through dynamic modulation of ETT-partner complexes

The phytohormone auxin governs crucial developmental decisions throughout the entire plant life cycle. The effectors of auxin nuclear signalling are the Auxin Responsive Factors (ARFs), whose activity is modulated by the Aux/IAA repressors to ensure transcriptional regulation upon increase of auxin cellular concentration. ARF3/ETTIN (ETT), known for decades for its role during reproductive structure development, is a conserved non-canonical ARF that adopts an alternate auxin sensing method to translate cellular auxin levels into a precise transcriptional outcome. However, direct confirmation of the biological significance for such auxin dependent modulation of ETT activity has not been elucidated yet. Here, through genome-wide approaches combined with expression analyses and supported by genetic evidence, we describe how ETT through its auxin-sensing property is necessary to orchestrate auxin-driven developmental responses in the Arabidopsisshoot. Moreover, we elucidate how precise ETT-dependent transcriptional regulation involves ETT protein partners, which offer an anchor point for target sequences devoid of ETT binding sites. Our work provides a detailed understanding of a biological mechanism that facilitates, through a simple ETT-partner module, multiple levels of transcriptional and developmental diversity