Required for aluminum (Al) resistance/tolerance, probably by translocating Al from sensitive tissues such as growing roots to tissues less sensisitive to the toxic effects of Al. Expressed in roots, leaves, stems, and flowers. By Al, primarily in leaf hydathodes and the phloem throughout the plant, along with the root cortex. Regulated positively by STOP1. ALS3 transcripts are mobile in the phloem sap. Belongs to the UPF0014 family. Was originally (PubMed:18299247) thought to belong to the ABC transporter family. Lacks the conserved ABC domain, which is one of the features of the ABC transporter family.