The 30th International Conference on Arabidopsis Research (ICAR 2019)

568 / 2019-03-29 03:56:11

POLAR-guided signaling complex assembly and localization drive asymmetric cell division

Polar,Asymmetric cell division,GSK3

Plenary track > Cell Biology

Stomatal cell lineage is a prime example of asymmetric cell division (ACD) necessary for plant survival. In Arabidopsis thaliana, the GLYCOGEN SYNTHASE KINASE3 (GSK3)/SHAGGY kinase BRASSINOSTEROID INSENSITIVE2 (BIN2) phosphorylates both the mitogen-activated protein kinase (MAPK) signaling module and its downstream target, the transcription factor SPEECHLESS (SPCH) to promote and restrict ACDs, respectively, in the same stomatal lineage cell. Yet, the mechanisms allowing for the coexistence of such mutually exclusive activities remain unclear. Here, we identified the plant-specific protein POLAR as a stomatal lineage scaffold for a subset of GSK3-like kinases, confining them to the cytosol and, subsequently transiently polarizing them together with BREAKING OF ASYMMETRY IN THE STOMATAL LINEAGE (BASL) prior to the ACD. As a result, the MAPK signaling is attenuated allowing for SPCH to drive ACD in the nucleus. Moreover, GSK3-mediated phosphorylation of POLAR was required for its turnover. Our study uncovers an unknown mechanism, by which a scaffolding protein ensures GSK3 substrate specificity that might serve as a paradigm for understanding GSK3 regulation in plants.