Data_Sheet_2_Comparative de novo Transcriptome Analysis of Two Cultivars With Contrasting Content of Oil and Fatty Acids During Kernel Development in Torreya grandis.xlsx

Vegetable oil is an indispensable nutritional resource for human health and mainly characterized by the composition and content of fatty acids (FAs). As a commercial species of gymnosperm, Torreya grandis produces oil-rich nuts with high unsaturated fatty acids content in the mature kernels. In this study, two cultivars, T. grandis ‘Xifei’ and T. grandis ‘Dielsii,’ with distinct oil content were employed to compare the profiles of FAs accumulation during kernel development. The accumulation rate of oil content was significantly different between ‘Xifei’ and ‘Dielsii.’ Besides, the final oil content of ‘Xifei’ (52.87%) was significantly higher than that of ‘Dielsii’ (41.62%) at maturity. The significant differences in main FAs were observed at almost each kernel development stages between the two cultivars. C16:0, C18:1, and C20:3 FA exhibited different accumulation patterns between cultivars. The content and the initiation of accumulation of C20:3 FA were different between the two cultivars. To explore the molecular mechanism associated with different content of oil and FAs between two cultivars, de novo transcriptome of kernels was compared between ‘Xifei’ (high oil) and ‘Dielsii’ (low oil) at three stages of oil accumulation, respectively. Totally 142,213 unigenes were assembled and 16,379 unigenes with a length of over 1,000 nt were successfully annotated, including 139 unigenes related to FA biosynthesis, elongation, and metabolism. Compared with ‘Dielsii,’ totally 1,476, 2,140, and 1,145 differentially expressed genes (DEGs) were upregulated in ‘Xifei’ at the stage of the initiative, the rapid rise, and the stationary oil accumulation, respectively; the number of downregulated DEGs reached 913, 1,245, and 904, respectively. Relative expressions of 11 DEGs involved in FAs biosynthesis and metabolism were confirmed by RT-qPCR. Abundant differentially expressed transcription factors and pathway DEGs were correlated to oil and FAs according to Pearson’s correlation analysis between transcriptome and metabolites (oil and FAs), suggesting their contributions to the differential oil and FAs between the two cultivars during kernel development of T. grandis. To conclude, our findings can provide novel insights into the developmental differences in metabolites and de novo transcriptome correlated to lipid accumulation and FA synthesis of kernels between cultivars with contrasting oil deposits and demystify the regulatory mechanism of high oil accumulation in T. grandis.

植物油是维系人体健康不可或缺的营养资源，其品质核心特征为脂肪酸（Fatty Acids, FAs）的组成与含量。作为裸子植物经济栽培树种，榧树（Torreya grandis）的成熟种仁富含油脂，且不饱和脂肪酸含量较高。本研究选取两个油脂含量差异显著的榧树栽培品种——‘西妃’与‘迪尔斯’，对其种仁发育过程中的脂肪酸积累特征开展比较分析。两个品种的油脂积累速率存在显著差异；成熟时，‘西妃’的最终油脂含量达52.87%，显著高于‘迪尔斯’的41.62%。二者的主要脂肪酸含量在几乎所有种仁发育阶段均存在显著差异。棕榈酸（C16:0）、油酸（C18:1）与二十碳三烯酸（C20:3）在两个品种间展现出截然不同的积累模式，且二十碳三烯酸的积累起始时间与最终含量亦存在显著差异。为探究两个品种油脂与脂肪酸含量差异的分子调控机制，本研究分别选取油脂积累过程中的三个关键阶段，对高油品种‘西妃’与低油品种‘迪尔斯’的种仁进行从头转录组（de novo transcriptome）比较分析。本次组装共获得142,213条单基因簇（unigenes），其中16,379条长度超过1000 nt（nucleotide）的单基因簇得到成功注释，包含139条与脂肪酸生物合成、延伸及代谢相关的单基因簇。与‘迪尔斯’相比，‘西妃’在油脂积累起始期、快速上升期与平台期的上调差异表达基因（Differentially Expressed Genes, DEGs）分别为1476、2140与1145条，下调差异表达基因则分别为913、1245与904条。本研究通过实时定量聚合酶链反应（Reverse Transcription Quantitative Polymerase Chain Reaction, RT-qPCR）验证了11个参与脂肪酸生物合成与代谢的差异表达基因的相对表达量。通过转录组与代谢物（油脂与脂肪酸）的皮尔逊相关分析（Pearson’s correlation analysis）发现，大量差异表达转录因子及通路相关差异表达基因与油脂及脂肪酸含量显著相关，表明这些基因在榧树种仁发育过程中参与调控两个品种间油脂与脂肪酸的含量差异。综上，本研究结果为解析油脂含量差异显著的榧树栽培品种间种仁脂质积累与脂肪酸合成相关的代谢物及从头转录组发育差异提供了新视角，同时阐明了榧树高油脂积累的调控机制。