Transcriptome analysis of Chelidonium majus elaiosomes and seeds provide insights into fatty acid biosynthesis

Background: Elaiosomes are specialized fleshy and edible seed appendages dispersed by ants. Lipids are the primary components of elaiosomes. Chelidonium majus is a well-known plant, the seeds of which are dispersed by ants. Previous studies have identified the presence of primary fatty acids in its elaiosomes and seeds. However, the molecular mechanisms underlying fatty acid biosynthesis in elaiosomes remain unknown. Methods: In order to gain a comprehensive transcriptional profile of the elaiosomes and seeds of C. majus, and understand the expression patterns of genes associated with fatty acid biosynthesis, four different developmental stages, including the flower-bud (Ch01), flowering (Ch02), young seed (Ch03), and mature seed (Ch04) stages, were chosen to perform whole-transcriptome profiling through the RNA-seq technology (Illumina NGS sequencing). Results: A total of 63,064 unigenes were generated from 12 libraries. Of these, 7,323, 258, and 11,540 unigenes were annotated with 25 Cluster of Orthologous Groups, 43 Gene Ontology terms, and 373 Kyoto Encyclopedia of Genes and Genomes pathways, respectively. In addition, 322 genes were involved in lipid transport and metabolism, and 508 genes were involved in the lipid metabolism pathways. A total of 41 significantly differentially expressed genes (DEGs) involved in the lipid metabolism pathways were identified, most of which were upregulated in Ch03 compared to Ch02, indicating that fatty acid biosynthesis primarily occurs during the flowering to the young seed stages. Of the DEGs, acyl-ACP thioesterases, acyl carrier protein desaturase (DESA I), and malonyl CoA-ACP transacylase were involved in palmitic acid synthesis; stearoyl-CoA desaturase and DESA1 were involved in oleic acid synthesis, and aryl-lipid omega-6 desaturase was involved in linoleic acid synthesis.