キウイフルーツのデンプン分解と成熟を促進する低温誘導性ユビキチン化制御転写因子

Kiwifruit (Actinidia spp.) ripening is highly sensitive to ethylene, yet reliance on exogenous ethylene often results in over-softening, greatly reducing their shelf life. Here, we uncovered a cool temperature (CT, 5-10°C)-induced pathway that, under conditions of ethylene perception inhibition by 1-methylcyclopropene (1-MCP), directly orchestrates starch-to-sugar conversion in kiwifruit. Transcriptomic and metabolomic profiling revealed AcBAM3.3, a β-amylase gene specifically induced by CT but not by ambient temperature. A CT-inducible ERF transcription factor, AcCTS1 (CT Specific factor 1), was found to directly bind the promoters of AcBAM3.3 and AcBAM3.5 and activate their transcription, as validated by dual-luciferase assays, EMSA, and yeast one-hybrid assays. Moreover, we identified an E3 ubiquitin ligase, AcPUB11, which targets AcCTS1 for 26S proteasomal degradation, thereby repressing starch degradation at room temperature. Under CT, reduced AcPUB11 abundance allows for AcCTS1 accumulation, driving AcBAM3.3 and AcBAM3.5 expression and promoting ripening. Functional validation via overexpression, RNAi, and CRISPR-Cas9 in both callus and fruit confirmed the AcPUB11-AcCTS1-AcBAM3s module as the central regulator of CT-induced starch metabolism. Our findings define a ubiquitination-controlled transcriptional regulatory module that mediates fruit adaptation to cool environments, providing a mechanistic foundation for temperature-controlled starch degradation during ripening.