Bringing PIPs to root tips

Tiny hairs on Arabidopsis thaliana roots elongate via tip growth, in which new membrane is added specifically at the root hair tip. Vincent et al. (page 801) now show that a phosphatidylinositol transfer protein (PITP) related to yeast Sec14p is critical for this polarized growth, suggesting that PIP₂ may be the start of the polarity cascade in this system.The authors show that Arabidopsis has a large family of these PITPs. One such PITP is AtSfh1p, which, along with its downstream product PIP₂, localized to the tip plasma membrane and on post-Golgi vesicles that accumulate at the hair tips.

AtSfh1p mutation disrupted several aspects of polarity normally found in wild-type hairs and culminated in the loss of tip-directed membrane secretion. These...