ABC (
ATP-binding cassette) subfamily D transporters are found in all eukaryotic kingdoms and are known to play essential roles in mammals and plants; however, their number, organization and physiological contexts differ. Via cross-kingdom expression experiments, we have explored the conservation of targeting, protein stability and function between mammalian and plant
ABCD transporters. When expressed in tobacco epidermal cells, the mammalian
ABCD proteins ALDP (
adrenoleukodystrophy protein), ALDR (
adrenoleukodystrophy-related
protein) and PMP70 (70 kDa peroxisomal
membrane protein) targeted faithfully to peroxisomes and P70R (PMP70-related protein) targeted to the ER (endoplasmic reticulum), as in the native host. The Arabidopsis thaliana
peroxin AtPex19_1 interacted with human peroxisomal
ABC transporters both in vivo and in vitro, providing an explanation for the fidelity of targeting. The fate of
X-linked adrenoleukodystrophy disease-related mutants differed between fibroblasts and plant cells. In fibroblasts, levels of ALDP in some '
protein-absent' mutants were increased by low-temperature culture, in some cases restoring function. In contrast, all mutant ALDP
proteins examined were stable and correctly targeted in plant cells, regardless of their fate in fibroblasts. ALDR complemented the seed germination defect of the Arabidopsis cts-1 mutant which lacks the peroxisomal ABCD transporter CTS (
Comatose), but neither ALDR nor ALDP was able to rescue the defect in
fatty acid β-oxidation in establishing seedlings. Taken together, our results indicate that the mechanism for trafficking of peroxisomal
membrane proteins is shared between plants and mammals, but suggest differences in the sensing and turnover of mutant
ABC transporter proteins and differences in substrate specificity and/or function.