MAKR6 targets TMK and CAMEL-CANAR receptor complexes for auxin canalization in Arabidopsis

Adaptive plant development is orchestrated, among others, by directional, intercellular transport of the phytohormone auxin. Self-organizing development, such as flexible vasculature formation, depends on the auxin canalization manifested by the gradual formation of auxin transport channels via the feedback between auxin signalling and transport. Herein, we identify MAKR6 as a key, novel component of this feedback. MAKR6 expression highly accumulates in vascular cells and is tightly regulated by auxin via the Aux/IAA-ARF-WRKY23 transcriptional network. MAKR6 is indispensable for auxin canalization-dependent processes including leaf venation, vasculature regeneration, and de novo auxin channel formation from the local auxin sources. Mechanistically, MAKR6 directly interacts with the PIN1 auxin transporter to modulate its trafficking and polarization. MAKR6 also associates with and links two key receptor-like kinase (RLK) complexes involved in canalization, TMK1/4 and the CAMEL-CANAR. Together, our study establishes MAKR6 as a multifaceted regulator that couples transcriptional auxin signalling to PIN1 repolarization and coordinates multiple RLK-mediated signalling pathways in canalization. This provides mechanistic insights into auxin canalization and exemplifies a framework for exploring similar regulatory nodes in other developmental contexts.