Transcriptome-based analysis of oil accumulation pattern and key gene screening in Gardenia jasminoides fruits

<i>Gardenia jasminoides</i> fruit is a highly promising woody oil resource, characterized by high oil content and a lipid profile enriched in unsaturated fatty acids with pharmacological activities such as cholesterol-lowering and antioxidant effects. To elucidate the molecular mechanisms underlying its oil accumulation, we systematically investigated fruit morphology, oil content, fatty acid composition, and oil body structure during development, and performed transcriptomic analyses at five key stages: 15, 45, 75, 105, and 150 DAF. These analyses revealed the developmental progression of the fruit, the patterns of oil accumulation, and the dynamic changes in fatty acid composition. DEGs analysis further elucidated the oil biosynthesis pathway and identified several key candidate genes. The results showed that <i>G. jasminoides</i> fruit development comprises three major stages: a rapid expansion stage (15~60 DAF), a color-transition stage (60~150 DAF), and a maturation stage (150~180 DAF). The fruit color gradually changed from green to orange-yellow and finally to orange-red, reaching morphological maturity at 150 DAF. Oil content exhibited an S-shaped growth pattern, reaching its maximum of 16.7% at 180 DAF. In mature fruits, the dominant fatty acids were linoleic acid (C18:2) and oleic acid (C18:1), with average relative contents of 55.2% and 20.6%, respectively, and unsaturated fatty acids accounting for 75.8% of main fatty acids. Oil body diameter displayed a distinct developmental pattern, increasing rapidly from 15 to 150 DAF, stabilizing between 150 and 180 DAF, and reaching a maximum of 29.8 μm at 180 DAF. Integrating fatty acid dynamics with DEG analysis, we screened <i>ACC</i>, <i>SAD</i>, <i>FATA</i>, <i>FAD2</i>, <i>DGAT2</i>, and <i>LACS2</i> as key candidate genes involved in oil biosynthesis in <i>G. jasminoides</i> fruit. Together, the transcriptomic analyses uncovered the molecular regulatory mechanisms of oil accumulation and enabled the construction of a metabolic pathway model for oil biosynthesis in <i>G. jasminoides</i>. These findings provide important theoretical insights and practical implications for enhancing oil yield and improving oil quality in <i>G. jasminoides</i>.