Comparative transcriptome analysis of the genes involved in lipid biosynthesis pathway and regulation of oil body formation in Torreya grandis kernels

Abstract Torreya grandis (T. grandis) is an important economic tree species because of the high content of unsaturated fatty acids in its kernel oil. However, different T. grandis landraces vary significantly in their fatty acid and oil contents, and their molecular regulatory mechanisms remain unclear. To investigate the molecular basis of the fatty acid biosynthesis pathway and oil body formation in T. grandis kernels, transcriptome sequencing were performed based on the Illumina platform in ten different T. grandis landraces. In total, 112,699 unigenes were identified, among them, 175 unigenes related to lipid biosynthesis were found, including 126 unigenes for fatty acid biosynthesis, 37 unigenes for triacylglycerol assembly and 12 unigenes for oil body proteins. The correlation analysis between the oil content and the expression levels of unigenes suggested that biotin carboxylase, acyl-ACP thioesterase A and lysophosphatidic acid acyltransferase may play key roles in oil accumulation. Three candidate genes (TgOLEO1, TgCLO1 and TgSLO1) encoding oil body-associated proteins were further identified through phylogenetic analysis and amino acid sequence alignment. Further subcellular localization assay indicated that all of the proteins were localized in both of endoplasmic reticulum and oil body. Compared with wild type, oil body proteins transiently over-expressed tobacco leaves had a higher abundance of oil bodies. Furthermore, the candidate regulatory genes (including TgWRI1, TgFUS3, etc.) that may be involved in the regulation of lipid biosynthesis were also identified. This study will be critical for the molecular assisted screening and breeding of high content of oil and unsaturated fatty acids cultivars for T. grandis.