The transcriptional regulatory module MdERF2-MdSCR11 promotes ABA-mediated apple fruit ripening through synergistic repression of MdABA4-2

Abstract

The phytohormone abscisic acid (ABA) plays a pivotal role in regulating the ripening processes of both climacteric and non-climacteric fruits, including apple (Malus domestica). However, the underlying regulatory mechanisms remain elusive. In this study, exogenous ABA treatment markedly enhanced ethylene production, decreased fruit firmness, and accelerated ripening in ‘Red Delicious’ apples. Intriguingly, exogenous ethylene increased endogenous ABA levels and biosynthetic enzyme activities in ‘Golden Delicious’ fruit, whereas 1-MCP treatment suppressed ABA accumulation and delayed ripening. Subsequently, we identified two ABA-responsive transcription factors, MdERF2 and MdSCR11, that directly trans-repress the promoter of MdABA4–2, which shows a negative correlation with ABA accumulation. Notably, MdSCR11 physically interacts with MdERF2 and synergistically represses MdABA4–2 transcriptional activity. Furthermore, transient overexpression of MdABA4–2 in apple fruit significantly reduced ABA content and ethylene production, delaying ripening, whereas MdSCR11 overexpression suppressed MdABA4–2 expression and accelerated ripening. Finally, complementary evidence from transgenic calli confirmed that MdABA4–2 negatively regulates ABA biosynthesis while MdSCR11 positively modulates ABA accumulation through MdABA4–2 suppression. Our findings establish a novel transcriptional regulatory module wherein ABA promotes apple fruit ripening through MdERF2-MdSCR11-mediated repression of MdABA4–2, providing mechanistic insights into hormone crosstalk during climacteric fruit maturation.