Structure of an mdr-like gene from Arabidopsis thaliana. Evolutionary implications.

Multidrug resistance of mammalian tumor cells is caused by the enhanced expression of P-glycoproteins. These proteins are encoded by mdr genes and mediate the energy-dependent efflux of a variety of lipophilic drugs from cells. To test whether in plants mdr-like genes might be involved in certain cases of cross-resistance to different herbicides, we have cloned and characterized a gene from Arabidopsis thaliana, atpgp1, encoding a putative P-glycoprotein homologue. Like the mammalian P-glycoproteins, with which it shares extensive sequence homology and a similar organization in structural domains, this protein is internally duplicated. Seven of the nine introns in the atpgp1 gene match introns in the mammalian mdr genes to within a few nucleotides, and the positions of these suggest that P-glycoprotein genes evolved by duplication and subsequent fusion of an intron-containing primordial gene prior to the evolutionary separation of plants and mammals. The atpgp1 gene gives rise to transcripts present in all plant parts but particularly abundant in inflorescence axes.