The mechanism of high contents of oil and oleic acid revealed by transcriptomic and lipidomic analysis during embryogenesis in Carya cathayensis Sarg.

BACKGROUND: Hickory (Carya cathayensis Sarg.) accumulates more than 70% oil and 90% unsaturated fatty acids with considerably high oleic acid in its mature embryo. The concurrent global trancriptomic and lipidomic analyses provided a framework for better understanding of glycerolipid biosynthesis and metabolism in the hickory nut.

RESULTS: The synthetical regulation of numerous leading lipid-related genes harmonized with the oil accumulation and fatty acid conversion in embryo development. The high level of ACCase correlated positively with fatty acids de novo synthesis, and the synergy of DGAT2 and PDAT promoted the TAG assembly, and oleosins, caleosins and steroleosins were transcribed considerably high for timely energy reserve in oil body. Glycolysis possibly provided sufficient precursors and energy for lipid synthesis. The perfect harmonization of the high level of SAD with low level of FAD2 facilitated the oleic acid accumulation. And the ratio of FATA/FATB or SAD/FATB was proposed for determining the saturated degree of oil. The gene multi-copy event was generated probably for accommodating various survival environments. A thermotolerant defense system including TAG hydrolysis determinants, heat shock proteins, and high ratio of MUFA to PUFA constrained the lipid degradation and provided a guarantee for high lipid content. A batch of potential genes recruited from the co-expression network helps us to understand the lipid synthesis and the response to high temperature better.

CONCLUSIONS: The high transcriptional levels of key genes in lipid synthesis promoted the oil accumulation, and the harmonious expression of key ones for unsaturated fatty acids led oleic acid to high levels.