A secreted peptide acts on BIN2-mediated phosphorylation of ARFs to potentiate auxin response during lateral root development

The phytohormone auxin is a key developmental signal in plants. So far, only auxin perception has been described to trigger the release of transcription factors termed Auxin Response Factors (ARFs) from their auxin/indole-3-acetic acid (AUX/IAA) repressor proteins. Here, we show that phosphorylation of ARF7 and ARF19 by BRASSINOSTEROID-insensitive2 (BIN2) can also potentiate auxin signalling output during lateral root organogenesis. BIN2-mediated phosphorylation of ARF7 and ARF19 suppresses their interaction with AUX/IAAs, and subsequently enhances the transcriptional activity to their target genes lateral organ boundaries-domain16 (LBD16) and LBD29. In this context, BIN2 is under the control of the Tracheary element differentiation inhibitory factor (TDIF)-TDIF receptor (TDR) module. TDIF-initiated TDR signalling directly acts on BIN2-mediated ARF phosphorylation, leading to the regulation of auxin signalling during lateral root development. In summary, this study delineates a TDIF-TDR-BIN2 signalling cascade that controls regulation of ARF and AUX/IAA interaction independent of auxin perception during lateral root development.