INVOLVEMENT OF AN ABC TRANSPORTER IN A DEVELOPMENTAL PATHWAY REGULATING HYPOCOTYL CELL ELONGATION IN THE LIGHT

In the dark, plant seedlings follow the skotomorphogenetic development al program, which results in hypocotyl cell elongation. When the seedl ings are exposed to light, a switch to photomorphogenetic development occurs, and hypocotyl cell elongation is inhibited. We have manipulate d the expression of the AtPGP1 (for Arabidopsis thaliana P glycoprotei n1) gene in transgenic Arabidopsis plants by using sense and antisense constructs. We show that within a certain light fluence rate window, overexpression of the AtPGP1 gene under the control of the cauliflower mosaic virus 35S promoter causes plants to develop longer hypocotyls, whereas expression of the gene in antisense orientation results in hy pocotyls shorter than those occurring in the wild type. In the dark, h ypocotyls of transgenic and wild-type plants are indistinguishable. Be cause the AtPGP1 gene encodes a member of the superfamily of ATP bindi ng cassette-containing (ABC) transporters, these results imply that a transport process is involved in a hypocotyl cell elongation pathway a ctive in the light. The AtPGP1 transporter is localized in the plasmal emma, as indicated by immunohistochemical techniques and biochemical m embrane separation methods. Analysis of the AtPGP1 expression pattern by using reporter gene constructs and in situ hybridization shows that in wild-type seedlings, AtPGP1 is expressed in both the root and shoo t apices.