Auxin and cell polarity: the emergence of AXR4.

Polar localization of the Arabidopsis auxin influx facilitator protein AUX1 in certain cell types is essential for normal root gravitropism and lateral root formation. Sunethra Dharmasiri and colleagues recently reported that this polar localization requires the activity of the AXR4 gene. The sequence of the AXR4 gene suggests that novel mechanisms could be important for targeting certain proteins to specific cellular locations.