The MdERF17–MdbHLH149 Module Mediates Ethylene‐Induced Starch Degradation Through the Transcriptional Repression of α‐Amylase <i>MdAMY1</i> in Apple

The ripening of climacteric fruits is characterised by a sharp increase in ethylene production, coinciding with the conversion of starch into soluble sugars. However, the regulatory interplay between ethylene and starch degradation in apple remains largely unclear. Here, we report a negative correlation between starch accumulation and ethylene levels during late fruit development. Integrated transcriptomic analysis identified the α-amylase gene MdAMY1 as a key component of the ethylene-starch regulatory pathway. Functional characterisation confirmed that MdAMY1, an ethylene-responsive gene, acts as a positive regulator of starch-to-sugar conversion. Biochemical assays showed that the basic helix-loop-helix (bHLH) transcription factor MdbHLH149 directly represses MdAMY1 transcription. Furthermore, MdERF17-a negative regulator in ethylene signalling-interacts with MdbHLH149 and synergistically enhances this repression. A combination of GUS staining, quantitative enzyme activity assays and VIGS-based transient transformation demonstrated that the MdERF17-MdbHLH149-MdAMY1 module acts downstream of ethylene signalling to control starch degradation. Collectively, these findings establish that ethylene facilitates starch degradation by negatively regulating the MdERF17-MdbHLH149-MdAMY1 repression module.