Genome-Wide Identification and Expression Analysis of Mitochondrial Dicarboxylate Carriers (DICs) in Medicago Under...

Aluminum (Al) is solubilized as phytotoxic Al³⁺ in acidic soils, rapidly inhibiting root elongation. To detoxify Al, plant roots secrete organic acids that chelate the ion. The transcription factor SENSITIVE-TO-PROTON-RHIZOTOXICITY1 (STOP1) regulates the export, distribution and metabolism of organic acids, which is crucial for Al resistance. Plant DICARBOXYLATE-CARRIERs (DICs) located in the inner mitochondrial membrane are presumed to exchange the dicarboxylates. However, whether Al or STOP1 modulates DIC expression to coordinate the organic acid shuttle remains unclear. Here, in the model legume Medicago truncatula, we identified three DIC genes and twelve in tetraploid Medicago sativa. Phylogenetic analysis places all Medicago DICs in a clade with Arabidopsis AtDIC1 and AtDIC2, whereas AtDIC3 lacks an ortholog in M. truncatula. Mining RNA-seq datasets followed by qRT-PCR validation showed that MtDIC2 is upregulated by Al in roots in a MtSTOP1-dependent manner. Consistently, STOP1-binding motifs exist in the MtDIC2 promoter, and MtSTOP1 binds to the MtDIC2 promoter in yeast. Furthermore, MsDIC2.4 shows an increase under Al treatment. Our study provides a genome-wide characterization of Medicago DICs and identifies MtDIC2 as a candidate target of MtSTOP1, whose Al-responsive induction may enhance organic acid flux across the mitochondrial membrane.