Comparative transcriptome analysis of lipid biosynthesis in seeds and non-seed tissues of sea buckthorn

Abstract

Sea buckthorn (Hippophae L.) is a woody crop with an unusual ability to thrive in very dry, nutrient-poor habitats. Seeds and berry pulp are rich in bioactive compounds with powerful medicinal properties, and are being used worldwide to an increasing extent. However, genomic information is still lacking for this crop, which limits the possibilities of raise the oil quality and yield with advanced breeding program. In this study, (1) sea buckthorn de novo transcriptome libraries for seeds, pulp, leaf, stem and root tissues were first constructed simultaneously, and 62,166 unigenes were assembled. Sixty-six differential expression genes (e-value cutoff <1 × 10⁻³⁰) were found to be involved in lipid biosynthesis pathway, (2) based on the comparative transcriptome data, we first revealed the differentially expressed genes of oil biosynthesis and accumulation in seeds and berry pulp, and the high unigene expression of source gene 'GPD1' (3.61) contributed to synthesis more G3P of TAG precursor in pulp, and the high expression of sink genes 'DGAT1 and DGAT2' (14.57 and 12.57, respectively) accelerated high TAG accumulation in pulp, compared to their expressions in seeds (0, 1.24 and 6.85, respectively). The oil content in pulp (36.90%) was also higher than that in seed (14.15%), (3) qRT-PCR verification results showed the expressions of GPD1, DGAT1 and DGAT2 genes (1.46, 0.93 and 2.13 fold change, respectively) in pulp were also higher than those in seeds (0.47, 0.21 and 1.02 fold change, respectively). Our results suggest that the high coordinated expression of source 'GPD1' and sink 'DGAT1 and DGAT2' genes resulted in strong oil biosynthesis and accumulation in the pulp with high-oil pulp, compared to its seed with low-oil seeds. These transcriptome data provide genomic information for identification of genetic regulation system for sea buckthorn, especially understanding lipid biosynthesis mechanism in seeds and pulp. The detection of these three source and sink genes of lipid biosynthesis provided scientific basis for improving low oil contents in seeds and pulp of sea buckthorn berries.

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