MAKR6 integrates TMK and CAMEL/CANAR signalling for auxin canalization in Arabidopsis.

Adaptive plant development is orchestrated, among other means, by directional, intercellular transport of the phytohormone auxin. Self-organizing phenomena such as flexible vasculature formation depend on auxin canalization, which manifests as the gradual formation of auxin-transporting channels through feedback between auxin signalling and transport. Here we identify MAKR6 as a component of this feedback. MAKR6 transcripts accumulate in vascular cells and are tightly regulated by auxin via the Aux/IAA-ARF-WRKY23 transcriptional cascade. MAKR6 is required for auxin canalization-dependent processes, including leaf venation, vascular regeneration and de novo channel formation from local auxin sources. Mechanistically, MAKR6 interacts with the PIN1 auxin transporter and modulates its trafficking and polarization. MAKR6 also associates with and integrates TMK1/4 and CAMEL-CANAR, two key receptor-like kinase complexes involved in canalization. Together, our study establishes MAKR6 as a multifaceted regulator that couples transcriptional auxin signalling to PIN1 repolarization and coordinates multiple RLK-mediated pathways into a concerted process. This provides mechanistic insight into auxin canalization and exemplifies a framework for exploring similar regulatory nodes in other developmental contexts.