Integrative Analysis of Transcriptome and Metabolome Reveals Regulatory Networks Associated with Flavonoids in Leaves of Rhododendron hainanense Under High-Temperature Stress

Heat stress severely impairs normal plant growth and yield, which significantly limits the horticultural and productive application of most <i>Rhododendron</i> species. In contrast, <i>Rhododendron hainanense</i> exhibits considerable heat tolerance due to its unique growing environment; however, the molecular mechanisms underlying its response to heat stress remain poorly understood. In this study, <i>R. hainanense</i> plants were subjected to heat stress treatment. Combined transcriptomic and metabolomic analyses identified 5454 differentially expressed genes and 152 differential metabolites. The results demonstrated that heat stress significantly induced the accumulation of flavonoids in <i>R. hainanense</i>. Notably, derivatives of myricetin, quercetin, and kaempferol were abundantly accumulated, suggesting their potential role in aiding plant defense against heat stress. The significant up-regulation of specific <i>Rh4CL</i> and <i>RhFLS</i> genes under high-temperature stress, coupled with the substantial accumulation of their flavonoid products (myricetin, quercetin, and kaempferol), indicates a potential role for these metabolites in the thermotolerance of <i>Rhododendron hainanense</i>. These findings provide novel insights into the heat stress response and flavonoid biosynthesis regulation in <i>R. hainanense</i>, highlighting the critical role of flavonoids in plant adaptation to heat stress. This study offers valuable references for the genetic improvement of <i>Rhododendron</i> cultivars with high stress resistance.