MdARF2-mediated ABA signaling orchestrates malate biosynthesis and transport via repression of MdcyMDH and MdMATEL1 in apple

Authors: WANG, CHU-KUN - Shandong Agricultural University; XIAO, FAN - Shandong Agricultural University; WEI, MENG-MENG - Shandong Agricultural University; CHENG, LAILIANG - Cornell University; TSAI, YI-TSER - Cornell University; DU, LIAN-DA - Shandong Agricultural University; Pineros, Miguel; GU, KAI-DI - Shandong Agricultural University; LI, KE - Shandong Agricultural University; XIANG, YING - Shandong Agricultural University; MA, CHANG-NING - Shandong Agricultural University; HU, DA-GANG - Shandong Agricultural University

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2025
Publication Date: 5/29/2025
Citation: Wang, C., Xiao, F., Wei, M., Cheng, L., Tsai, Y., Du, L., Pineros, M., Gu, K., Li, K., Xiang, Y., Ma, C., Hu, D. 2025. MdARF2-mediated ABA signaling orchestrates malate biosynthesis and transport via repression of MdcyMDH and MdMATEL1 in apple. New Phytologist. 247(3):1263-1279. https://doi.org/10.1111/nph.70259.
DOI: https://doi.org/10.1111/nph.70259

Interpretive Summary: Malate accumulation in apple fruit cells is a key factor that determines the taste and flavor of the fruit. Despite its importance, the biological signals controlling malate levels remain largely unknown. In this study, we reveal a biological pathway where the plant hormone abscisic acid (ABA) regulates apple acidity. ABA activates a “switch” protein called ARF2, which suppresses the activity of two other proteins involved in malate production and transport in fruit cells. When ARF2 is active, it lowers malate levels, resulting in less tart apples. We characterized the transporter’s function and demonstrated that ARF2 directly interacts with and regulates the gene encoding this transporter, as well as another gene involved in malate metabolism. We confirmed these regulatory effects by comparing apple varieties with naturally high and low tartness levels. This work establishes a direct link between hormone signaling and apple fruit acidity, identifying a new target for breeders and growers to fine-tune apple flavor, improve taste for consumers, and support plant growth under changing environmental conditions.

Technical Abstract: 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.