Polar transport of auxin is important for plant growth and development.The directional auxin flow depends on the polar subcellular localization of PIN auxin efflux regulators in plant.Overexpression of the PINOID protein kinase induces a basal-topical shift in PIN localization,resulting in the loss of auxin gradients and strong defects in embryo and seedling roots.In this study,the phosphorylated peptides in seedlings of 35S::PID and wide type Arabidopsis were analyzed using solid metal affinity chromatography and dimethyl tag-based quantification mass spectrometry approaches.