Jasmonate‐responsive MdMYC2/MdMED25 complex regulates malic acid accumulation in apples through the miR858– MdMYB73 module

ABSTRACT Malic acid is a crucial determinant of apple ( Malus domestica ) fruit quality, influencing acidity and flavor. While transcriptional regulation of malic acid metabolism is well‐studied, post‐transcriptional control and the role of jasmonate (JA) remain largely unexplored. We identify a novel regulatory pathway involving JA signaling, a microRNA (miRNA), and vacuolar transport regulators that control malic acid accumulation in apple fruit. We show that mdm‐miR858, which increases during fruit maturation, directly targets and cleaves MdMYB73 transcripts. MdMYB73 is a known positive regulator of vacuolar H + ‐pumping and malate transport, activating genes like MdVHA‐A , MdVHP , and MdALMT9 . Overexpression of mdm‐miR858 suppressed MdMYB73 , thereby reducing MdVHA‐A , MdVHP , and MdALMT9 expression and malic acid content in apple calli, fruits, and GL‐3 plantlets, while silencing mdm‐miR858 had opposite effects. Crucially, the JA‐responsive transcription factor MdMYC2, the expression of which increases during fruit maturation, directly binds the mdm‐miR858 promoter and activates its expression. Furthermore, the Mediator complex subunit MdMED25 interacts with MdMYC2, enhancing this activation. Manipulating MdMYC2 or MdMED25 expression altered mdm‐miR858 levels, MdMYB73 expression, and malic acid accumulation, mirroring exogenous methyl jasmonate (MeJA) treatment effects. A miR858‐resistant MdMYB73 variant confirmed the miRNA‐target interaction's specificity and functional significance. Our findings reveal a novel JA–MdMYC2/MdMED25–miR858– MdMYB73 regulatory cascade controlling malic acid accumulation in apple, providing a mechanistic link between hormonal signaling and post‐transcriptional regulation of fruit acidity. This discovery offers new targets for manipulating fruit quality.