MDF regulates a network of auxin-dependent and -independent pathways of adventitious root regeneration in Arabidopsis.

Plants exhibit strong plasticity in growth and development, seen clearly in lateral and adventitious root development from differentiated tissues in response to environmental stresses. Previous studies have demonstrated the role of both auxin-dependent and auxin-independent signalling pathways in regulating the de novo formation of adventitious roots (ARs) from differentiated tissues, such as leaf petiole in Arabidopsis. One important question is how the auxin-dependent and -independent pathways are coordinated. To investigate this question, we used a combined approach of inducible gene expression, mutant, and signalling reporter gene analysis during AR regeneration in the Arabidopsis petiole to understand regulatory relationships. Auxin signalling components AXR1 and AXR3, and the PIN trafficking protein VAMP714, are each required for AR initiation, as is the ethylene signalling repressor POLARIS, but not EIN2. We identify the RNA splicing regulator MDF and the transcription factor RAP2.7 as new positive regulators of both the auxin-independent and auxin-dependent pathways, and show that MDF regulates RAP2.7, WOX5 and NAC1; while RAP2.7 regulates WOX5 but not NAC1 or YUC1. NAC1 is required for de novo root formation in a pathway independent of YUC1, WOX5 or RAP2.7. We propose a model in which MDF represents a point of molecular crosstalk between auxin-dependent and -independent regeneration processes.