The plant hormone auxin regulates plant growth and development through polar cell-to-cell transport-generated maxima and minima. PIN FORMED (PIN) auxin efflux carriers determine the direction of... Show moreThe plant hormone auxin regulates plant growth and development through polar cell-to-cell transport-generated maxima and minima. PIN FORMED (PIN) auxin efflux carriers determine the direction of this auxin flow through their asymmetric placement on the plasma membrane (PM). In Arabidopsis thaliana (Arabidopsis), the PM-associated protein kinase PINOID (PID) regulates PIN localisation and thereby auxin transport polarity by phosphorylating these carriers in their central cytoplasmic loop. PID in turn interacts with the calmodulin-like protein TOUCH3 (TCH3) in response to elevated cytosolic calcium, which dissociates PID from the PM and inhibits its kinase activity. In this thesis, we show that PID also interacts with 10 other CALMODULIN/CALMODULIN-LIKE proteins, which together with TCH3 form a confined clade in the CaM/CML family. The CaM/CML binding domain in PID was found to map to an amphipathic alpha-helix inserted in the catalytic kinase core. Disruption of this alpha-helix did not affect PID kinase activity, but impaired both its PM association and the interaction with the CaM/CMLs, making the kinase “untouchable”. Expression of “untouchable” PID versions in the pid mutant background revealed that proper calcium-CaM/CML-PID signalling is essential to maintain the robust spiral phyllotaxis that is typical for the Arabidopsis inflorescence. Show less
The Jacobaea hybrid system has been proved to be a good tool to study the interaction between PA variation and herbivore resistance. Based on this hybrid system, we have explored how the biotic and... Show moreThe Jacobaea hybrid system has been proved to be a good tool to study the interaction between PA variation and herbivore resistance. Based on this hybrid system, we have explored how the biotic and abiotic factors influence the PA diversity. All the herbivore tests were integrated to draw the general conclusion that the selection pressures from different herbivores contribute to the diversity in PA composition and that generalist and specialist herbivores exert a divergent selection pressure on PA concentrations. The PAs showed seasonal variation within each genotype and the relative differences between genotypes remained constant over time, which was the first study to report the seasonal variation of SMs. The application of MeJA can lead to a shift in PA composition and primary metabolites. Importantly the shift in metabolite diversity induced by MeJA application can conversely affect the feeding of chewing herbivores and cell-content feeders. However, SA application did not lead to significant changes in PAs and the metabolite profile changes detected by NMR rendered J. aquatica more resistance to piercing-sucking herbivore thrips, showing that PAs did not affect thrips resistance. Several metabolites detected by NMR were found to be correlated with resistance and susceptibility to thrips F. occidentalis. Show less
