The Transcription Factor StStop1–3 Activates StALMT10 Expression to Enhance Aluminum Tolerance by Promoting Malate Secretion in Potato ( Solanum tuberosum L.)

Acidic soils, occupying roughly one-third of arable land, restrict root growth through soluble Al3+ below pH 5.5. Malate exudation chelates Al3+ in the rhizosphere and confers Al tolerance, yet its transcriptional control in potato remains uncharacterized. Here, StSTOP1–3 was identified as a direct activator of the malate transporter gene StALMT10. StALMT10 was root-predominant, encoded a plasma-membrane protein enriched in root tips, and its CRISPR/Cas9 knockout caused Al3+ hypersensitivity, root-tip Al accumulation, and reduced malate exudation. Among three potato STOP1 paralogs, only StSTOP1–3 was rapidly induced by Al3+ and localized to the nucleus. Yeast one-hybrid, dual-luciferase, and DNA pull-down assays confirmed that StSTOP1–3 binds the StALMT10 promoter and activates its transcription. StSTOP1–3 knockout lines showed an even stronger malate-secretion defect than StALMT10 mutants, implying additional downstream targets. Thus, the StSTOP1–3–StALMT10 module confers Al tolerance through root malate secretion, supporting marker-assisted breeding on acidic soils.