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

ZHANG, CHENG; DE MARCOS SERRANO, ALBERTO; ZHIPONOVA, MIROSLAVA K.; EECKHOUT, DOMINIQUE; BETTI, CAMILLA; MENA, MONTAÑA; RUSSINOVA, EUGENIA; HOUBAERT, ANAXI; WANG, KUN; URS, MOUNASHREE J.; VANHOUTTE, ISABELLE; KARIMI, MANSOUR; FENOLL, CARMEN; DE JAEGER, GEERT; TIWARI, MANISH; SAVATIN, DANIEL V.; GUDESBLAT, GUSTAVO E.; BOEREN, SJEF; JACOBS, THOMAS; DE VRIES, SACCO

NATURE

NATURE PUBLISHING GROUP

Año: 2018 vol. 563 p. 574 - 578

0028-0836

Stomatal cell lineage is an archetypal example of asymmetric cell division (ACD), which is necessary for plant survival 1?4 . In Arabidopsis thaliana, the GLYCOGEN SYNTHASE KINASE3 (GSK3)/SHAGGY-like kinase BRASSINOSTEROID INSENSITIVE 2 (BIN2) phosphorylates both the mitogen-activated protein kinase (MAPK) signalling module 5,6 and its downstream target, the transcription factor SPEECHLESS (SPCH) 7 , to promote and restrict ACDs, respectively, in the same stomatal lineage cell. However, the mechanisms that balance these mutually exclusive activities remain unclear. Here we identify the plant-specific protein POLAR as a stomatal lineage scaffold for a subset of GSK3-like kinases that confines them to the cytosol and subsequently transiently polarizes them within the cell, together with BREAKING OF ASYMMETRY IN THE STOMATAL LINEAGE (BASL), before ACD. As a result, MAPK signalling is attenuated, enabling SPCH to drive ACD in the nucleus. Moreover, POLAR turnover requires phosphorylation on specific residues, mediated by GSK3. Our study reveals a mechanism by which the scaffolding protein POLAR ensures GSK3 substrate specificity, and could serve as a paradigm for understanding regulation of GSK3 in plants.