Resumen de Functional implication of protein kinase ck2 in f-actin dynamics and in the cross-talk between auxin and salicylic acid signalling pathways in arabidopsis thaliana
The aim of this thesis was the study of the role of protein kinase CK2 in three plant biological processes, using Arabidopsis thaliana as a model: plant phototropisms, regulation of salicylic acid and auxin signalling pathways, and dynamic of actin cytoskeleton. A loss-of-function mutant of CK2 (CK2mut), obtained by former members of the laboratory and that showed phenotype traits linked to alterations in auxin dependent processes, was used as the main tool for our studies. In the present work we show that CK2mut seedlings exhibit loss of the hypocotyl phototropic response and increase of the root phototropic curvature under blue light treatments. Moreover, PIN2 internalization into vacuolar compartments after transferring CK2mut seedlings to darkness did not occur when CK2 activity was depleted, although PIN2 recycling to the plasma membrane was not affected.
In order to better understand auxin-signalling regulation in CK2-defective plants we studied the stability of AUX/IAA proteins, which are repressors of auxin signalling pathways and modulate responses to auxin. We performed histochemical and fluorimetric assays and we demonstrated that inhibition of CK2 resulted in over-stabilization of the AXR3 repressor. As CK2mut seedlings contain high levels of salicylic acid (SA), we then studied the cross-talk between auxin and SA pathways and we demonstrated that the over-stabilization of AXR3 in CK2-defective plants is mediated by SA.
In vivo confocal imaging of actin architecture was performed by using the actin reporter GFP-FABD2. CK2-depleted seedlings showed strong disorganization of the actin network and collapse of F-actin bundles. Studies of actin turnover in Arabidopsis seedlings confirmed that the lack of CK2 activity strongly affects polymerisation of actin filaments. F-actin turnover is regulated by actin binding proteins, among them the family of actin depolymerisation factors (ADFs). In our study, we found some putative predicted phosphorylation sites for CK2 in ADF4. Thus, we can speculate that CK2 might be involved in the regulation of the ADF4 actin filament disassembly activity.
