Analysis of non-canonical auxin signaling in Arabidopis roots

Auxin is a very potent regulator of root growth, and its mode of action has thus been studied intensively. Local auxin accumulation patterns are instructive during root development in terms of de novo organ initiation and morphogenesis, but also during tropisms. Therefore, tightly regulated auxin transport mechanisms are in place to prevent unwanted auxin activities. Importantly, auxin controls its own transport through a poorly understood feedback mechanism on the abundance (trafficking) and activities of auxin transport, and defines the key to understanding flexible, adaptive root growth. Through a chemical genetics screen we found that inhibitors of auxin-induced Ca2+ modify auxin- regulated vacuolar remodeling, and impairs auxin’s ability to inhibit clathrin-mediated endocytosis. We will zoom in on the latter mechanism, and propose a subgroup III Ca2+ Dependent Kinases as Ca2+ sensitive signal transducers within this pathway. Together, these findings put new elements in a thusfar uncharacterized pathway, which seems to act independently of the canonical (TIR1-based) auxin signaling pathway.