In the dark, Arabidopsis seedlings follow a skotomorphogenetic progam and develop long hypocotyls. When they are exposed to light, seedlings switch to photomorphogenetic development, and hypocotyl cell elongation is inhibited. On pages 1623-1636 of this issue, Sidler et al. demonstrate that an ABC transporter encoded by the AtPGP1 gene mediates hypocotyl cell elongation in the light. They also show that this process is independent of the skotomorphogenetic cell elongation program that operates in the dark. The AtPGP1 gene is expressed predominantly in shoot and root apices, and the AtPGP1 protein is thought to be targeted to the plasma membrane. This point is highlighted on the cover, which depicts a false-color image of a leaf cell from a transgenic Arabidopsis plant constitutively expressing a c-Myc epitopetagged AtPGP1 protein. c-Myctagged AtPGP1 is visualized in green; the cell wall, stained with calcofluor white, appears purple; and chloroplasts autofluoresce red.