XVI International Botanical Congess

In the dark, plant seedlings develop elongated hypocotyl cells. Whenexposed to light, seedlings switch to photomorphogenetic development and hypocotyl cell elongation is inhibited. We show that overexpression of the AtPGP1 gene, which encodes an ABC transporter, in transgenic Arabidopsis causes seedlings to develop longer hypocotyls in the light, whereas AtPGP1 antisense plants develop shorter hypocotyls in the light than the wild type. In darkness, wild-type and transgenic seedlings are indistinguishable. This indicates that a transport process mediated by the AtPGP1 transporter is involved in a hypocotyl cell elongation pathway that is active in the light. The AtPGP1 gene is expressed predominantly in the root and shoot apices and the protein product is localized in the plasmalemma.