The invention relates to the genetic manipulation of organisms, particularly to the expression of P-glycoprotein genes in transformed plants and other organisms. Nucleotide sequences for the P-glycoprotein genes, particularly the Dw3 gene of sorghum, and methods for their use are provided. The sequences find use in modifying the growth of organisms, particularly plants. Additionally, the invention provides methods for producing stable dwarf crop plants, particularly stable dwarf sorghum plants.