Full-Length Transcriptome Analysis of the Genes Involved in Tocopherol Biosynthesis in Torreya grandis.

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.

New sights into lipid metabolism regulation by low temperature in harvested Torreya grandis nuts.

BACKGROUND: Torreya grandis, a large evergreen coniferous tree with oil-rich nuts, undergoes a crucial ripening stage after harvest that results in oil accumulation, finally giving rise to the nut that is edible in roasted form. To understand lipid metabolism in T. grandis nuts during the post-harvest ripening period, the effects of low temperature on lipid content, fatty acid composition, lipid biosynthesis and degradation were investigated. RESULTS: The lipid content increased during ripening at room temperature and a low temperature slowed down this increase. Linoleic acid content increased at low temperature, which was accompanied by an increase in the microsomal oleate desaturase (FAD2) activity and FAD2 expression. Furthermore, a low temperature attenuated lipid peroxidation as indicated by lower contents of malondialdehyde, hydroperoxide and total free fatty acid in T. grandis nuts during the ripening stage, as well as the down-regulation of gene expression of lipid degradation-related enzymes such as phospholipase D and lipoxygenases. CONCLUSION: The findings of the present study indicate that a low temperature increased polyunsaturated fatty acid contents by increasing FAD2 biosynthesis and decreasing lipid peroxidation, thereby improving the oil yield in T. grandis nuts during the post-harvest ripening period. © 2019 Society of Chemical Industry.