The regulation of cell polarity by lipid transfer proteins of the SEC14 family

- SEC14 proteins are key regulators of phosphoinositide (PIP) metabolism.
- SEC14-Nlj16 protein AtSFH1 controls root hair polarity.
- Polybasic motifs in Nlj16 domains contribute to PIP binding specificity.
- AtSFH1 couples synthesis and lateral organization of PIPs in membrane microdomains.

SEC14 lipid transfer proteins are important regulators of phospholipid metabolism. Structural, genetic and cell biological studies in yeast suggest that they help phosphatidylinositol (PtdIns)/phosphoinositide (PIP) kinases to overcome their intrinsic inefficiency to recognize membrane-embedded substrate, thereby playing a key role in PIP homeostasis. Genomes of higher plants encode a high number and diversity of SEC14 proteins, often in combination with other domains. The Arabidopsis SEC14-Nlj16 protein AtSFH1, an important regulator of root hair development, plays an important role in the establishment of PIP microdomains. Key to this mechanism is a highly specific interaction of the Nlj16 domain with PtdIns(4,5)P2 and an interaction-triggered oligomerization of the protein. Nlj16/PtdIns(4,5)P2 interaction depends on a polybasic motif similar to those identified in other regulatory proteins.