Results .Gravitropic defects induced by metazachlor are dependent upon PI4P synthesis at the TGN . In Arabidopsis root epidermal cells, PI4P mainly resides at the plasma membrane (PM) and sparsely at the TGN/EEs24 , 27. At the TGN, local synthesis of PI4P partly occurs through the TGN-localized PI4-Kinase β1 (PI4Kβ1), which acts redundantly with PI4Kβ213 , 26 , 28. To test the hypothesis of a crosstalk between sphingolipids and PI4P at the TGN we treated either wild-typ...