Transcriptome analysis reveals the potential molecular mechanism involved in fatty acids biosynthesis of Sunflower

Background Sunflower ( Helianthus annuus ) is one of the most important oilseed crops worldwide. To reveal the molecular mechanism of biosynthesis and accumulation of major fatty acid components in sunflower, and to clarify the primary and secondary relationships between temperature, genes, and fatty acid synthesis in sunflower. In this study, as our study materials, we chose the sunflower inbred lines J9 and P50 with high and low oleic acids, respectively. Sampling at the same period of sowing at different periods (S-test) and sampling at different periods of sowing at the same time (A-test) were used to determine the fatty acid fractions and contents of different samples of seeds after pollination, respectively; and RNA-Seq technology was utilized to sequence the different samples to obtain the gene expression data related to fatty acid synthesis for each sample. Results Five main fatty acids were detected, including Oleic acid, linoleic acid, stearic acid, linolenic acid, palmitic acid, and the relative contents of oleic acid and linoleic acid were negatively correlated, while the relative contents of linolenic acid and palmitic acid were lower and showed a continuous decreasing trend during seed development. The crucial turning point in sunflower fatty acid synthesis occurs at 20 days after flowering (DAF), and fatty acid fractions and contents of high oleic sunflower lines were little affected by temperature, while low oleic lines were susceptible to temperature. A total of 81,676 unigenes were obtained by transcriptome sequencing. There were 15885 and 18220 genes obtained in the S dataset and A dataset, respectively, were annotated in the GO and KEGG functional databases. Based on the KEGG database, a total of 19 pathways associated with lipid metabolism, with a cumulative enrichment of 29 DEGs. Through the analysis of metabolic pathways, a total of 42 differentially expressed genes (DEGs) directly related to sunflower fatty acid metabolism were identified. These DEGs belong to 22 different types of enzymes, including PIGT, KCS, ACC, SAD, MFP, ACX, ACP, and FAB, which are key genes involved in the biosynthesis of unsaturated fatty acids and oil accumulation in sunflowers. Conclusions We predicted that PIGT, KCS, ACC, SAD, MFP, ACX, ACP, and FAB were the key enzymes, regulating their genes in the fatty acid biosynthesis and oil accumulation in sunflower seed. This study provides the first comprehensive genomic resources characterizing sunflowers seed gene expression at the transcriptional level. These data lay the foundation for elucidating the molecular mechanisms of fatty acid biosynthesis and oil accumulation for sunflower.