Tian Bo, Lu Tianquan, Xu Yang, Wang Ruling, Chen Guanqun
1Key Laboratory of Tropical Plant Resource and Sustainable Use, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Kunming, 650223 China.
2Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB T6G 2P5 Canada.
Biotechnol Biofuels. 2019 Jan 21;12:16. doi: 10.1186/s13068-019-1358-2. eCollection 2019.
Ricinoleic acid is a high-value hydroxy fatty acid with broad industrial applications. seed oil contains a high amount of ricinoleic acid (~ 80%) and represents an emerging source of this unusual fatty acid. However, the mechanism of ricinoleic acid accumulation in is yet to be explored at the molecular level, which hampers the exploration of its potential in ricinoleic acid production.
To explore the molecular mechanism of ricinoleic acid biosynthesis and regulation, seeds were harvested at five developing stages (13, 16, 19, 22, and 25 days after pollination) for lipid analysis. The results revealed that the rapid accumulation of ricinoleic acid occurred at the early-mid-seed development stages (16-22 days after pollination). Subsequently, the gene transcription profiles of the developing seeds were characterized via a comprehensive transcriptome analysis with second-generation sequencing and single-molecule real-time sequencing. Differential expression patterns were identified in 12,555 transcripts, including 71 enzymes in lipid metabolic pathways, 246 putative transcription factors (TFs) and 124 long noncoding RNAs (lncRNAs). Twelve genes involved in diverse lipid metabolism pathways, including fatty acid biosynthesis and modification (hydroxylation), lipid traffic, triacylglycerol assembly, acyl editing and oil-body formation, displayed high expression levels and consistent expression patterns with ricinoleic acid accumulation in the developing seeds, suggesting their primary roles in ricinoleic acid production. Subsequent co-expression network analysis identified 57 TFs and 35 lncRNAs, which are putatively involved in the regulation of ricinoleic acid biosynthesis. The transcriptome data were further validated by analyzing the expression profiles of key enzyme-encoding genes, TFs and lncRNAs with quantitative real-time PCR. Finally, a network of genes associated with ricinoleic acid accumulation in was established.
This study was the first step toward the understating of the molecular mechanisms of ricinoleic acid biosynthesis and oil accumulation in seeds and identified a pool of novel genes regulating ricinoleic acid accumulation. The results set a foundation for developing into a novel ricinoleic acid feedstock at the transcriptomic level and provided valuable candidate genes for improving ricinoleic acid production in other plants.
蓖麻油酸是一种具有广泛工业应用价值的高价值羟基脂肪酸。蓖麻种子油含有大量的蓖麻油酸（约80%），是这种特殊脂肪酸的一个新兴来源。然而，蓖麻油酸在蓖麻中积累的分子机制尚未在分子水平上进行探索，这阻碍了对其在蓖麻油酸生产中潜力的挖掘。
为了探究蓖麻油酸生物合成与调控的分子机制，在五个发育阶段（授粉后13、16、19、22和25天）收获蓖麻种子进行脂质分析。结果表明，蓖麻油酸在种子发育的中早期阶段（授粉后16 - 22天）快速积累。随后，通过第二代测序和单分子实时测序的综合转录组分析对发育种子的基因转录谱进行了表征。在12555个转录本中鉴定出差异表达模式，包括脂质代谢途径中的71种酶、246个假定的转录因子（TFs）和124个长链非编码RNA（lncRNAs）。12个参与多种脂质代谢途径的基因，包括脂肪酸生物合成与修饰（羟基化）、脂质转运、三酰甘油组装、酰基编辑和油体形成，在发育种子中表现出高表达水平和与蓖麻油酸积累一致的表达模式，表明它们在蓖麻油酸生产中起主要作用。随后的共表达网络分析鉴定出57个TFs和35个lncRNAs，推测它们参与蓖麻油酸生物合成的调控。通过定量实时PCR分析关键酶编码基因、TFs和lncRNAs的表达谱，进一步验证了转录组数据。最后，建立了一个与蓖麻中蓖麻油酸积累相关的基因网络。
本研究是了解蓖麻种子中蓖麻油酸生物合成和油脂积累分子机制的第一步，并鉴定出一批调控蓖麻油酸积累的新基因。这些结果为在转录组水平上将蓖麻开发成一种新型蓖麻油酸原料奠定了基础，并为提高其他植物中蓖麻油酸的产量提供了有价值的候选基因。
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