Abstract
Yellow horn (Xanthoceras sorbifolium Bunge) is an endemic oil-rich shrub that has been widely cultivated in northern China for bioactive oil production. However, little is known regarding the molecular mechanisms that contribute to oil content in yellow horn. Herein, we measured the oil contents of high- and low-oil yellow horn embryo tissues at four developmental stages and investigated the global gene expression profiles through RNA-seq. The results found that at 40, 54, 68, and 81 days after anthesis, a total of 762, 664, 599, and 124 genes, respectively, were significantly differentially expressed between the high- and low-oil lines. Gene ontology (GO) enrichment analysis revealed some critical GO terms related to oil accumulation, including acyl-[acyl-carrier-protein] desaturase activity, pyruvate kinase activity, acetyl-CoA carboxylase activity, and seed oil body biogenesis. The identified differentially expressed genes also included several transcription factors, such as, AP2-EREBP family members, B3 domain proteins and C2C2-Dof proteins. Several genes involved in fatty acid (FA) biosynthesis, glycolysis/gluconeogenesis, and pyruvate metabolism were also up-regulated in the high-oil line at different developmental stages. Our findings indicate that the higher oil accumulation in high-oil yellow horn could be mostly driven by increased FA biosynthesis and carbon supply, i.e. a source effect.
Highlights
Yellow horn (Xanthoceras sorbifolium Bunge), belonging to the Sapindaceae family, is an endemic oil-rich shrub widely distributed in northern China and grows well in barren lands with a dry climate
The expression profiles generated identified two genes encoding accC, with significantly higher expression levels noted in HO compared to LO at 40 daa, implying that the increased expression levels of accC genes are correlated with increased oil content in the yellow horn embryos examined
It is proposed that two up-regulated accC genes may promote fatty acid (FA) biosynthesis at the early stage of embryonic development, which further promote oil accumulation in developing yellow horn embryos, resulting in higher oil content in the high-oil line (Figure 5)
Summary
Yellow horn (Xanthoceras sorbifolium Bunge), belonging to the Sapindaceae family, is an endemic oil-rich shrub widely distributed in northern China and grows well in barren lands with a dry climate. Yellow horn seeds are abundant in oil (55–70%), which is comprised of 85–93% unsaturated fatty acids (FAs), mainly including oleic acid, linoleic acid, gondoic acid and nervonic acid [1,2]. This woody oil-bearing tree species has been deemed suitable for cultivation in deserts and arid and semi-arid zones within northern China. When studying the molecular mechanisms of oil biosynthesis in yellow horn via functional expressional analysis of XsSAD in Escherichia coli and Arabidopsis, a correlation between XsSAD expression and FA accumulation was noted [6]. XsSAD was found to determine the synthesis of oleic acid and contributed to unsaturated FA accumulation in yellow horn seeds
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