Transcriptomic Insights into Heat-Induced Anthocyanin Suppression and Floral Color Fading in Chrysanthemum

High temperature (HT) is a crucial environmental factor influencing floral pigmentation and ornamental quality in chrysanthemum (Chrysanthemum morifolium) by modulating anthocyanin biosynthesis. In this study, comparative transcriptome profiling was performed in two F1 chrysanthemum lines (RO72 and RO99) under high-temperature stress to elucidate the molecular mechanisms behind heat-induced floral color fading. Analysis revealed extensive transcriptional reprogramming of genes associated with anthocyanin metabolism, hormonal signaling, and oxidative stress responses. While structural genes in the anthocyanin biosynthetic pathway (CHS, DFR, ANS, 3MAT and LDOX) were significantly downregulated, key glycosylation-related genes such as UFGT were upregulated, suggesting a compensatory mechanism that enhances pigment stabilization rather than de novo synthesis. This study identified a shift in the MYB–bHLH–WD40 regulatory complex, specifically the upregulation of transcriptional repressors (MYB62, MYB15) and downregulation of activators (MYB106, bHLH49), suggesting a suppressed anthocyanin accumulation. Simultaneously, genes associated with several signaling cascades such as ROS, ABA, and auxin–jasmonate signaling pathways were differentially expressed, suggesting that these alterations may contribute to the repression of pigment biosynthesis and color fading. Collectively, these results hypothesize that high temperature suppresses anthocyanin accumulation through a dual mechanism of transcriptional inhibition and hormonal modulation, while simultaneously promoting pigment stabilization via glycosylation. This study therefore provides fundamental insights into thermal regulation of floral pigmentation and identifies candidate genes and pathways potentially involved in heat-induced floral color fading in chrysanthemum.