A potato cDNA encoding a homologue of mammalian multidrug resistant P-glycoprotein

A homologue of the multidrug resistance (MDR) gene was obtained while screening a potato stolen tip cDNA expression library with S-35-labeled calmodulin. The mammalian MDR gene codes for a membrane-bound P-glycoprotein (170-180 kDa) which imparts multidrug resistance to cancerous cells. The potato cDNA (PMDR1) codes for a polypeptide of 1313 amino acid residues (ca. 144 kDa) and its structural features are very similar to the MDR P-glycoprotein. The N-terminal half of the PMDR1-encoded protein shares striking homology with its C-terminal half, and each half contains a conserved ATP-binding site and six putative transmembrane domains. Southern blot analysis indicated that potato has one or two MDR-like genes. PMDR1 mRNA is constitutively expressed in all organs studied with higher expression in the stem and stolen tip. The PMDR1 expression was highest during tuber initiation and decreased during tuber development.