An ABC‐transporter of Arabidopsis thaliana has both glutathione‐conjugate and chlorophyll catabolite transport activity

An ABC-transporter of Arabidopsis thaliana exhibiting high sequence similarity to the human (MRP) and yeast (YCF) glutathione-conjugate transporters has been analysed and used to complement a cadmium-sensitive yeast mutant (DTY68) that also lacks glutathione-conjugate transport activity. Comparison of the hydrophobicity plots of this A. thaliana MRP-like protein with MRP and YCF demonstrates that the transmembrane domains are conserved, even at the N-terminus where sequence identity is low. Cadmium resistance is partially restored in the complemented ycf mutant, and glutathione-conjugate transport activity can be observed as well. The kinetic properties of the A. thaliana MRP-like protein (AtMRP3) are very similar to those previously described for the vacuolar glutathione-conjugate transporter of barley and mung bean. Furthermore, a hitherto undescribed ATP-dependent transport activity could be correlated with the gene product, i.e. vesicles isolated from the complemented yeast, but not from DTY68 or the wild type, take up the chlorophyll catabolite Bn-NCC-. The results indicate that the product of the MRP-like gene of A. thaliana is capable of mediating the transport of the two different classes of compounds.