A dual role for cell plate-associated PI4Kß in endocytosis and phragmoplast dynamics during plant somatic cytokinesis.

ABSTRACT

Plant cytokinesis involves membrane trafficking and cytoskeletal rearrangements. Here, we report that the phosphoinositide kinases PI4Kß1 and PI4Kß2 integrate these processes in Arabidopsis thaliana (Arabidopsis) roots. Cytokinetic defects of an Arabidopsis pi4kß1 pi4kß2 double mutant are accompanied by defects in membrane trafficking. Specifically, we show that trafficking of the proteins KNOLLE and PIN2 at the cell plate, clathrin recruitment, and endocytosis is impaired in pi4kß1 pi4kß2 double mutants, accompanied by unfused vesicles at the nascent cell plate and around cell wall stubs. Interestingly, pi4kß1 pi4kß2 plants also display ectopic overstabilization of phragmoplast microtubules, which guide membrane trafficking at the cell plate. The overstabilization of phragmoplasts in the double mutant coincides with mislocalization of the microtubule-associated protein 65-3 (MAP65-3), which cross-links microtubules and is a downstream target for inhibition by the MAP kinase MPK4. Based on similar cytokinetic defects of the pi4kß1 pi4kß2 and mpk4-2 mutants and genetic and physical interaction of PI4Kß1 and MPK4, we propose that PI4Kß and MPK4 influence localization and activity of MAP65-3, respectively, acting synergistically to control phragmoplast dynamics.