J Agric Food Chem. 2019 Feb 20;67(7):1877-1888. doi: 10.1021/acs.jafc.8b06138. Epub 2019 Feb 8.
The seeds of Torreya grandis (Cephalotaxaceae) are rich in tocopherols, which are essential components of the human diet as a result of their function in scavenging reactive oxygen and free radicals. Different T. grandis cultivars (10 cultivars selected in this study were researched, and their information is shown in Table S1 of the Supporting Information) vary enormously in their tocopherol contents (0.28-11.98 mg/100 g). However, little is known about the molecular basis and regulatory mechanisms of tocopherol biosynthesis in T. grandis kernels. Here, we applied single-molecule real-time (SMRT) sequencing to T. grandis (X08 cultivar) for the first time and obtained a total of 97 211 full-length transcripts. We proposed the biosynthetic pathway of tocopherol and identified eight full-length transcripts encoding enzymes potentially involved in tocopherol biosynthesis in T. grandis. The results of the correlation analysis between the tocopherol content and gene expression level in the 10 selected cultivars and different kernel developmental stages of the X08 cultivar suggested that homogentisate phytyltransferase coding gene ( TgVTE2b) and γ-tocopherol methyltransferase coding gene ( TgVTE4) may be key players in tocopherol accumulation in the kernels of T. grandis. Subcellular localization assays showed that both TgVTE2b and TgVTE4 were localized to the chloroplast. We also identified candidate regulatory genes similar to WRI1 and DGAT1 in Arabidopsis that may be involved in the regulation of tocopherol biosynthesis. Our findings provide valuable genetic information for T. grandis using full-length transcriptomic analysis, elucidating the candidate genes and key regulatory genes involved in tocopherol biosynthesis. This information will be critical for further molecular-assisted screening and breeding of T. grandis genotypes with high tocopherol contents.
香榧的种子富含生育酚，由于其清除活性氧和自由基的功能，生育酚是人类饮食的重要组成部分。不同的香榧品种（本研究选择了 10 个品种，其信息见支持信息表 S1）在生育酚含量方面差异很大（0.28-11.98mg/100g）。然而，关于香榧种仁生育酚生物合成的分子基础和调控机制知之甚少。在这里，我们首次应用单分子实时（SMRT）测序技术对香榧（X08 品种）进行了研究，共获得了 97211 条全长转录本。我们提出了生育酚的生物合成途径，并在香榧中鉴定了 8 个全长转录本编码的酶，这些酶可能参与生育酚的生物合成。对 10 个选定品种和 X08 品种不同种仁发育阶段的生育酚含量与基因表达水平的相关性分析结果表明，生育酚质体转移酶编码基因（ TgVTE2b）和γ-生育酚甲基转移酶编码基因（ TgVTE4）可能是香榧种仁生育酚积累的关键基因。亚细胞定位实验表明，TgVTE2b 和 TgVTE4 均定位于叶绿体。我们还鉴定了与拟南芥中 WRI1 和 DGAT1 相似的候选调控基因，它们可能参与生育酚生物合成的调控。我们的研究结果通过全长转录组分析为香榧提供了有价值的遗传信息，阐明了参与生育酚生物合成的候选基因和关键调控基因。这些信息对于进一步进行分子辅助筛选和培育高生育酚含量的香榧基因型将是至关重要的。
