Auxin-regulated gene expression in intact soybean hypocotyl and excised hypocotyl sections

A library of complementary DNA (cDNA) clones has been prepared from polyadenylated RNA (poly(A)(+)RNA) from auxin (2,4-dichlorophenoxyacetic acid)-treated soybean (Glycine max (L.) Merr. cv. Wayne) seedlings. Using differential hybridization, four clones were selected as auxin-responsive, and characterized. The levels of the RNA sequences homologous to the cDNA clones were examined in the hypocotyl of the intact seedling and in excised hypocotyl sections before and after auxin treatment, using RNA blot hybridization analysis. RNA levels are rapidly increased (within 0.25-0.5 h) following auxin treatment and the response in the hypocotyl of the intact seedling is transient, reaching maximum RNA levels 2-4 h after auxin application. Increases in RNA levels were also observed with the auxins indole 3-acetic acid and 2,4,5-trichlorophenoxyacetic acid, but not with the ethylene-producing compound, Ethephon (2-chloroethylphosphonic acid). Hybridization analysis of in-vitro transcription products made in nuclei isolated from untreated and auxin-treated soybean primary leaves and excised hypocotyl sections indicates that, for the two cDNA clones analyzed, the increased RNA levels in auxin-treated organs are at least partially the result of increased transcriptional activity of specific DNA sequences.