Regulation of Rop-mediated signal transduction during cell division and cell polarity establishment by a small RopGAP subfamily

01/01/2019 to 31/12/2021

The establishment of cell polarity, an unequal distribution of cellular content, is a prerequisite of cellular morphogenesis. Cell polarity is under genetic control and coordinated at the cell-, tissue- and organ level, to ensure the stereotypic reproduction of functional plant organs. The evolutionarily conserved family of Rho of plant (ROP) small cytosolic GTPases serves as molecular switches in cell polarity signaling and orchestrate the spatiotemporal distribution of cellular content. Regulatory proteins enable the switching between activity and inactivity of the small Rho-GTPases. The Guanine nucleotide exchange factors (RopGEF), replace guanosine diphosphate (GDP) for guanosine triphosphate (GTP) to promote ROP activation. On the contrary, GTPase activating proteins (RopGAP) accelerate the intrinsically slow hydrolysis of GTP and render the respective target ROPs inactive. Little is known about the regulation of ROPinactivation. Our previous work on ROP inactivation by the PHGAP subfamily of RopGAPs implicated them in cell division. They localize to the plasma membrane and the division site and require the motor protein kinesin-12 POK for retention at that site. We hypothesise that PHGAPs act in the inactivation of specific ROPs to set up the division site/actin depleted zone to ensure normal cell division. We will gain further insights into the regulation and cellular dynamic of PHGAPs during cell division. We will clarify which ROPs are inactivated by PHGAPs and we will identify novel interaction partners to investigate how PHGAP protein function is regulated. In addition, we will establish transient reconstitution assays to recreate ROP-signaling modules and investigate their spatiotemporal regulation.