Transcriptome comparative analysis of two Camellia species reveals lipid metabolism during mature seed natural drying

Abstract

Key messageThe molecular mechanisms of fatty acid biosynthesis and accumulation duringCamellia meiocarpa andCamellia oleifera seed natural drying are characterized through transcriptome analyses.Camellia seed oil has been used as high quality and healthy food for over two thousand years. Seed drying affects oil quality and quantity; however, the molecular mechanisms of fatty acid biosynthesis and accumulation during the drying process remain unknown. In this study, the transcriptomes of Camellia meiocarpa and C. oleifera seed were characterized at five moisture content levels (10–50%) to identify the major processes and reveal genes affecting lipid metabolism in response to natural drying. We found a total of 111,156 unigenes by de novo assembled from RNA-Seq libraries of five moisture content levels during after-ripening of C. meiocarpa (74,016) and C. oleifera (76,374). Ten pathways were closely linked to changes in oil content and composition with 244 genes involved in fatty acid synthesis and accumulation. Gene ontology enrichment of differentially expressed genes (DEGs) indicated that fatty acid synthesis and accumulation are essential in C. meiocarpa while fatty acid accumulation in C. oleifera during natural drying process. Comparative analyses of DEGs between any two consecutive moisture contents identified six and three key unigenes in C. meiocarpaand C.oleifera seeds, respectively, and one additional unigene responsible for the difference between the two species’ fatty acid synthesis and accumulation. Natural drying has improved the quality and quantity of the camellia seed oil. The study provided: (a) global transcriptional profiles at five moisture content levels during seed natural drying, (b) highlighting transcripts putatively involved in the regulation of gene expression program and in specific processes likely essential for lipid metabolism, and (c) discovery of genes associated with oil seed quantity and quality improvement for the studied two camellia species.