<scp>MdARF2</scp> ‐mediated <scp>ABA</scp> signaling orchestrates malate biosynthesis and transport via repression of <i>MdcyMDH</i> and <i>MdMATEL1</i> in apple

Abscisic acid (ABA) is a crucial regulator of plant growth, while vacuolar malate accumulation is pivotal for determining fruit taste and flavor. However, the relationship between ABA signaling and malate metabolism remains poorly understood. Here, we show that the ABA-modulated auxin response factor 2 (ARF2)-multidrug and toxic compound extrusion protein like 1 (MdMATEL1)/cytosolic NAD-dependent malate dehydrogenase (MdcyMDH) network regulates malate accumulation in apple fruit. Auxin response factor MdARF2 exhibits evolutionary conservation and negatively regulates malate accumulation through analysis of high-acid and low-acid orthogonal/reciprocal progenies derived from 'Gala' and 'Mato 1' apple varieties. Further functional validation using two-electrode voltage-clamp analysis in Xenopus laevis oocytes confirmed that MdMATEL1 acts as a malate transporter and positively regulates malate accumulation. Biochemical assays demonstrated that MdARF2 directly binds to the promoters of MdMATEL1 and MdcyMDH, repressing their transcription in response to ABA and thereby reducing malate levels in apple. Taken together, our findings unveil a novel regulatory mechanism in which MdARF2, under ABA signaling, modulates the expression of MdcyMDH and MdMATEL1 (a malate transporter), ultimately suppressing malate synthesis and vacuolar transport.