Universiteit Leiden

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Dissertation

Novel factors modulating AGC kinase signaling-controlled polar auxin transport

The PID-directed shift in PIN polarity has been broadly accepted as one of the essential mechanisms for the regulation of auxin transport polarity.

Author
Xiao, Y.
Date
10 December 2019
Links
Thesis in Leiden Repository

The PID-directed shift in PIN polarity has been broadly accepted as one of the essential mechanisms for the regulation of auxin transport polarity. We verified that both PID functionality and its subcellular localization do not depend on PDK1 function. However, by detailed analysis on these phenotypes and the expression of the auxin response reporter, we found the pdk1 pdk2 double mutant to be impaired in auxin transport in vascular tissues. Together with other mutant phenotypes, we suspect that PDK1 may be the master regulator of AGC1 kinases. The pdk1 pdk2 short root phenotype caused by phloem differentiation defects phenocopied the pax mutant. Complementation results of wild type and phosphomimic PAX in the pdk1 pdk2 background suggest that PDK1-dependent PAX phosphorylation and activation are essential for its full biological function. We also explain the molecular basis of PDK1 basal localization and the unnecessity of this polarity for vascular development. In addition, we investigated downstream action after PID phosphorylation. Several conserved tyrosine residues close to serine phosphorylation sites in the PIN1 and PIN2 HLs are mutated. Two of these tyrosines redundantly affected PIN polarity. However, PID mediated phosphorylation and tyrosine-based PIN trafficking are independent processes.

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