The plant hormone auxin regulates almost every aspect in the plant life cycle. Despite tremendous progress in dissecting mechanisms underlying auxin responses, some major questions remain unresolved, e.g. auxin responses in algae, as well as very fast auxin responses, are not understood. The project advances upon preliminary results from the host group. Exploiting comparative phospho-proteomics in evolutionarily distant species ranging from green algae to angiosperms, they have identified conserved rapid auxin-dependent phosphorylation changes in proteins involved in multiple cellular processes. Interestingly, most of this auxin-dependent phosphorylation occurs independently of all reported auxin receptors, indicating that the auxin signal is perceived by an unknown receptor. Additional mutant analysis showed that cytoplasmic Phox Bem1 (PB1) domain-containing MAP kinases (PB1-MAPKs, named MARKs) are critical for signal transduction in all tested plant species. Mammalian PB1-MAPKs form large supramolecular protein complexes, named ‘signalosomes’, via PB1-mediated protein polymerization which is crucial for signal integration. Preliminary result suggest that MARK in Marchantia polymorpha can also form signalosomes. However, both the signalosome composition and its activation mechanism remain elusive. I hypothesize that auxin-dependent MARK-signalosome activation occurs upon the perception of auxin by an unknown cell-surface receptor. Combining comparative evolutionary biology, proteomics and structural biology with genetics, cell biology and biochemical analysis of auxin action and auxin binding by receptor proteins, I aim to elucidate the molecular mechanism by which MARK perceives and transduces the auxin signal as well as understanding the physiological role of Rapid Auxin-induced Phosphorylation pathway In Diverse Outputs (RAPIDO). If you would be interested in thesis project please contact prof. Dolf Weijers for current specific projects.