Abstract
BackgroundPerilla frutescens is well known for its high α-linolenic acid (ALA) accumulation in seeds and medicinal values as well as a source of edible and general-purpose oils. However, the regulatory mechanisms of the biosynthesis of fatty acid in its seeds remain poorly understood due to the lacking of sequenced genome. For better understanding the regulation of lipid metabolism and further increase its oil content or modify oil composition, time-course transcriptome and lipid composition analyses were performed.ResultsAnalysis of fatty acid content and composition showed that the α-linolenic acid and oleic acid accumulated rapidly from 5 DAF to 15 DAF and then kept relatively stable. However, the amount of palmitic acid and linoleic acid decreased quickly from 5 DAF to 15DAF. No significant variation of stearic acid content was observed from 5 DAF to 25DAF. Our transcriptome data analyses revealed that 110,176 unigenes were generated from six seed libraries at 5, 10, 20 DAF. Of these, 53 (31 up, 22 down) and 653 (259 up, 394 down) genes showed temporal and differentially expression during the seed development in 5 DAF vs 10 DAF, 20 vs 10 DAF, respectively. The differentially expressed genes were annotated and found to be involved in distinct functional categories and metabolic pathways. Deep mining of transcriptome data led to the identification of key genes involved in fatty acid and triacylglycerol biosynthesis and metabolism. Thirty seven members of transcription factor family AP2, B3 and NFYB putatively involved in oil synthesis and deposition were differentially expressed during seed development. The results of qRT-PCR for selected genes showed a strong positive correlation with the expression abundance measured in RNA-seq analysis.ConclusionsThe present study provides valuable genomic resources for characterizing Perilla seed gene expression at the transcriptional level and will extend our understanding of the complex molecular and cellular events of oil biosynthesis and accumulation in oilseed crops.
Highlights
Perilla frutescens is well known for its high α-linolenic acid (ALA) accumulation in seeds and medicinal values as well as a source of edible and general-purpose oils
Major fatty acid content and composition differ from developing seeds To obtain time-series of oil content variation during seed development, Perilla seeds at 5, 15 and 25 days after flowering (DAF) were selected for oil content and composition measurements
The content variation of major compositions in mid-developing stage (15 DAF) and latedeveloping stage (25 DAF) was not significant, which provides a platform to elucidate how fatty acid biosynthesized in Perilla seeds
Summary
Perilla frutescens is well known for its high α-linolenic acid (ALA) accumulation in seeds and medicinal values as well as a source of edible and general-purpose oils. The regulatory mechanisms of the biosynthesis of fatty acid in its seeds remain poorly understood due to the lacking of sequenced genome. Frutescens seed has potential application in pharmaceutical and food industry due to the high accumulation of unsaturated acids, such as α-linolenic acid (ALA, 18:3) (> 60% of total FA in seeds) [4, 5]. High ALA content in Perilla seeds, ranging from 60 to 70% depending on the varieties, is beneficial to human health and important for stress responses, pathogen defense-related signaling and cell maturation processes. It is a good model plant to dissect the biosynthesis pathways of unsaturated fatty acids. Few genes encoding enzymes involved in fatty acid biosynthesis, such as FAD3, 3-ketoacyl-ACP synthases, KAS (I, II, and III), have been characterized in Perilla [10, 11], the
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