MCTP controls nucleocytoplasmic partitioning of AUXIN RESPONSE FACTORs during lateral root development

The plant hormone auxin orchestrates almost all aspects of plant growth and development. AUXIN RESPONSE FACTORs (ARFs) control the transcription of auxin-responsive genes, forming cytoplasmic condensates to modulate auxin sensitivity and diversify auxin response regulation. However, the dynamic control of ARF distribution across different subcellular compartments remains largely obscure. Here, we show that three MULTIPLE C2 DOMAIN AND TRANSMEMBRANE REGION PROTEINs (MCTPs), MCTP3, MCTP4, and MCTP6, control ARF nucleocytoplasmic partitioning and determine lateral root development. MCTP3/4/6 are highly expressed in lateral roots and specifically interact with ARF7 and ARF19 to dissolve their cytoplasmic condensates. This promotes ARF nuclear localization in lateral root primordia and enhances auxin signaling during lateral root formation. Our findings confer MCTP as a key switch to modulate auxin responses and outline an MCTP-ARF signaling cascade that is crucial for the establishment of the plant root system. [Display omitted] •MCTP3, MCTP4, and MCTP6 are crucial for lateral root development•MCTP3, MCTP4, and MCTP6 interact with ARF7 and ARF19•MCTPs control ARF7 and ARF19 nucleocytoplasmic partitioning•MCTPs diversify auxin responses by dynamically controlling ARF protein distribution Xuan et al. report that MCTP3, MCTP4, and MCTP6 control ARF7 and ARF19 condensate dynamics and their nucleocytoplasmic partitioning. This promotes ARF localization to the nucleus and enhances auxin signaling, thereby facilitating lateral root formation and underscoring the role of MCTPs in shaping root architecture.