Citrate transporter critical for aluminum tolerance. Responsible for citrate exudation into the rhizosphere to protect roots from aluminum toxicity. Expressed in roots, but not in shoots (PubMed:18826429, PubMed:22413742). Detected in the mature regions of the root, extending from above the root-hair region to the root-shoot junction (PubMed:22413742). Up-regulated by aluminum (PubMed:18826429, PubMed:22413742). The STOP1 transcription factor is required for MATE expression (PubMed:18826429). No visible phenotype when grown under normal conditions. Strong reduction of aluminum-activated citrate release and small decrease in aluminum tolerance. Acts in parallel but independently of ALMT1, an aluminum-activated root malate transporter. May be due to a competing donor splice site. Aberrant spliced mRNA with a premature translation termination codon (PTC) that could be the target of the NMD degradation pathway. Belongs to the multi antimicrobial extrusion (MATE) (TC 2.A.66.1) family.