Aluminum (Al) toxicity is a major limitation to crop production on acid soils, which comprise up to 50% of the world’s potentially arable lands. The development of cultivars adapted to acid soils is a key aspect in securing sustainable crop production. Al-activated release of Al-binding ligands (organic acids) from roots is a major Al tolerance mechanism in plants. We recently cloned the gene underlying a major maize Al tolerance QTL, ZmMATE1, which encodes a plasma membrane transporter from the MATE (multidrug and toxic compound extrusion) family, and mediates Al-activated citrate release in maize roots. [14C]citrate efflux experiments in oocytes demonstrate that ZmMATE1 is a citrate transporter. ZmMATE1 is expressed in roots at significantly higher levels in Al-tolerant genotypes, and this expression is upregulated by Al. Increased ZmMATE1 expression plays an important role in differential Al tolerance in maize. Therefore, we are investigating the mechanisms that regulate ZmMATE1 expression, and will present here our most recent results. To identify elements involved in increased expression as well as upregulation by Al, expression QTL (eQTL) mapping is being performed both in control conditions and under Al stress. For the eQTL mapping, a high-density marker set was generated via GBS (genotyping-by-sequencing). In addition, we are using a BAC library generated from the Al-tolerant parent of our mapping population to determine the genomic organization of ZmMATE1 and identify cis regulatory elements. Lastly, we have demonstrated that ZmMATE1 transcripts undergo extensive alternative splicing, and are currently investigating how this mechanism contributes to regulating transcript abundance.