Oil Accumulation Rule And Transcriptomics Analyses Of An Woody Oil Plant Idesia Polycarpa During Fruit Development

Idesia polycarpa is a deciduous tree, whose fruits are rich in oil. Linoleic acid content could reach up to 80% or above. Its oil is widely used in the fields of food, medicine, chemical industry and biomass energy, thus it is an excellent woody oil tree and energy tree species. However, Idesia polycarpa still remain wild or semi-wild. A lack of excellent strains severely restrict the promotion of it. Therefore, the breeding of excellent strains of Idesia polycarpa will help to develop and promote new varieties.In this study, the oil content of 73 fruiting trees from Huanggang base is evaluated first. The 11 trees whose oil contents are above 40% were selected. In order to analyze the oil accumulation rule of Idesia polycarpa, line 76 A is chosen to be determined its oil content at different developmental stages. The pericarp of its fruit also contains oil. Surprisingly, the oil content in pericarp is higher than that in seed, and the two tissues are significantly different in fatty acid component. hi order to study on the molecular mechanism of oil synthesis in seed and pericarp, RNA-seq is conducted during the period of oil accumulation. The result of RNA-seq not only provide its genetic information, but also lay the foundation for genetic engineering.The main results are as follows:(1) The oil content and water content of Idesia polycarpa show "S" type change at different developmental stages. The oil content increases and the water content decreases gradually. Both of them show dramatic changes during 40-80DAP. Oil accumulation in seed occurred in the early stage of fruit development, and oil accumulation of pericarp is later than that of seed. In the latter period of fruit development the oil content of seed shows a slightly decrease. Oil bodies are easily observed in seed, but they are not found in pericarp.(2) 120126 unigenes are assembled from 356707894 clean reads and then annotated in public databases. Among them,198 unigenes which relate to lipid metabolism show differential expression between seed and pericarp, with 136 up in pericarp and 52 up in seed.(3) FAD2 shows highly expression in seed and pericarp could explain the high content of linoleic acid in the two tissues. Oil body associated protein genes show high expression in seed and low expression in pericarp. In addition, the expression of oil synthesis associated transcriptional factor WRI1 in pericarp is higher than in seed, and other transcriptional factors LEC1, LEC2, ABI4, ABI3 and FUS3 are only expressed in seed. All these differential expression indicates that the existence of different mechanisms in the regulation of lipid synthesis and oil assembling in seed and pericarp.