Transcriptomic insights into ABA- and ethephon-mediated regulation of flavonoid biosynthesis during pericarp coloration in Litchi chinensis cv. Deshi

Pericarp coloration heavily dictates the economic value of Litchi chinensis Sonn., yet commercial cultivars like 'Deshi' often suffer from poor pigmentation. While hormonal application is known to influence fruit ripening, the integrated transcriptional hierarchy governing anthocyanin accumulation remains poorly understood under field conditions. This study investigated the physiological, biochemical, and transcriptomic responses of 'Deshi' litchi to exogenous abscisic acid (150 mg/L ABA), ethephon (500 µL/L ETH), and their combination. Field results demonstrated that ABA significantly outperformed ETH in enhancing red pigmentation and total anthocyanin accumulation. High-throughput RNA-Seq (10.10 million reads) revealed that ABA-induced coloration is driven by a robust, multi-tiered transcriptional cascade. Exogenous ABA effectively activated the canonical PYR/PYL-PP2C-SnRK2 signaling module, leading to the targeted upregulation of key MYB and bHLH transcription factors. This regulatory complex subsequently activated the complete flavonoid biosynthetic pathway, notably upregulating critical late-stage structural genes ( LcDFR, LcANS, LcUFGT ). Conversely, combined ETH and ABA treatments were less effective than ABA alone, suggesting distinct hormonal antagonism where ethylene signaling potentially induces ERF repressors that block late biosynthetic genes. These findings establish ABA as the primary mechanistic driver of pericarp coloration in 'Deshi' litchi and offer precision molecular targets for post-harvest quality improvement.