Arabidopsis D6PK is a lipid domain-dependent mediator of root epidermal planar polarity

Abstract

Development of diverse multicellular organisms relies on coordination of single-cell polarities within the plane of the tissue layer (planar polarity). Cell polarity often involves plasma membrane heterogeneity generated by accumulation of specific lipids and proteins into membrane subdomains. Coordinated hair positioning along Arabidopsis root epidermal cells provides a planar polarity model in plants, but knowledge about the functions of proteo-lipid domains in planar polarity signalling remains limited. Here we show that Rho-of-plant (ROP) 2 and 6, phosphatidylinositol-4-phosphate 5-kinase 3 (PIP5K3), DYNAMIN-RELATED PROTEIN (DRP) 1A and DRP2B accumulate in a sterol-enriched, polar membrane domain during root hair initiation. DRP1A, DRP2B, PIP5K3 and sterols are required for planar polarity and the AGCVIII kinase D6 PROTEIN KINASE (D6PK) is a modulator of this process. D6PK undergoes phosphatidylinositol-4,5-bisphosphate- and sterol-dependent basal-to-planar polarity switching into the polar, lipid-enriched domain just before hair formation, unravelling lipid-dependent D6PK localization during late planar polarity signalling.

Phospholipid composition and a polybasic motif determine D6 PROTEIN KINASE polar association with the plasma membrane and tropic responses

“…Similarly to the reported internalization of YFP:D6PK in root hair cells of pip5k3 mutants, we noted reduced YFP:D6PK plasma membrane association in the root epidermal cells of the pip5k1 pip5k2 double mutant (Fig. 2F,G) (Stanislas et al, 2015). Thus, the reported alterations of PtdIns(4,5)P 2 levels in pip5k1 pip5k2 mutants might exert an influence on the plasma membrane targeting of D6PK (Ischebeck et al, 2013;Tejos et al, 2014).…”

“…D6PK binding was strongest to PtdIns3P when using TRIS-buffered saline and to PtdOH when using PBS ( phosphate-buffered saline) of comparable ionic strengths (188 mM and 181 mM) (Fig. 1A) (Stanislas et al, 2015). D6PK did not bind to phospholipids with neutral headgroups, namely PtdCho ( phosphatidylcholine) and PtdEtn ( phosphatidylethanolamine), or to phospholipids with monoacidic headgroups such as PtdIns and phosphatidylserine (PtdSer; Fig.…”

“…D6PK associates also with root hair tips following root hair initiation (Stanislas et al, 2015). PINs, the established D6PK substrates, are reportedly absent from root hair tips and D6PK might have other phosphorylation substrates and PIN-independent roles at this plasma membrane region (Stanislas et al, 2015).…”

“…PINs, the established D6PK substrates, are reportedly absent from root hair tips and D6PK might have other phosphorylation substrates and PIN-independent roles at this plasma membrane region (Stanislas et al, 2015). The association of D6PK with the root hair initiation site is dependent on PIP5K3 and, reciprocally, D6PK can bind phospholipids in vitro (Stanislas et al, 2015). A basic sequence stretch noted in several AGCVIII kinases is a good candidate region for phospholipid interactions (Zegzouti et al, 2006).…”

Auxin and ROP GTPase Signaling of Polar Nuclear Migration in Root Epidermal Hair Cells

“…The localization of ROP2, ROP4, and ROP6 to the root hair initiation site (Molendijk et al, 2001;Jones et al, 2002;Stanislas et al, 2015) suggests the involvement of at least three ROPs in nuclear migration in trichoblasts compared with at least ROP8 in the female gametophyte (Kawashima et al, 2014). Therefore, we resorted to loss-of-function mutants in positive and Table I.…”