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椰子(Cocos nucifera L.)是许多热带国家最重要的经济作物[1]。椰子属于棕榈科椰子属,基因组大小约为2.4 Gb[2-3]。根据植物形态和繁殖类型,椰子可以分为2种类型:typica (tall)和nana (dwarf)[4]。椰子根据进化起源可以分为2个亚群——印度洋种群和太平洋种群[5-6]。高种椰子异花授粉,基因型表现为一定程度的杂合,而矮种椰子自花授粉,基因型纯合。矮种椰子生长缓慢、植株矮小、树冠较小、果小而多、椰肉厚度薄、开花时间较早,通常在种植4~6 a后开花,株高10~15 m[7-9]。高种椰子耐寒,果实大,能够适应更广泛的环境,株高20~30 m,初次开花时间晚(种植8~10 a后开花)。在中国,椰子主要种植在海南和云南等地区,海南地区的高种椰子“Hainan Tall”有着36 000 hm2的种植面积[10],高种椰子耐盐碱和高温,但对低温敏感。目前普遍认为矮种椰子经高种椰子驯化而来[4],且矮种椰子更易受不利环境的影响。椰油占椰肉重量的65%[8,11],与其他植物油相比,椰油具有独特的理化性质和药用价值。椰子油富含饱和脂肪酸(93%),主要成分是己酸(C6)、辛酸(C8)、癸酸(C10)、月桂酸(C12)、肉豆蔻酸(C14)、棕榈酸(C16)、硬脂酸(C18)和花生酸(C20),其中85%是中链脂肪酸(medium-chain fatty acids, MCFA)。据报道,月桂酸在棕榈科中的主要来源是椰子和油棕,两者都仅限于在热带和亚热带气候中生长[11-14]。月桂酸能够提高氧化稳定性,具有低熔点,能产生稳定的乳液,这对食品和化学工业应用具有重要意义[11]。目前月桂酸在医药和食品工业等各个领域都具有广泛的应用,包括用于制造肥皂、洗涤剂、纺织品、油漆、清漆、化妆品、药品等。肉豆蔻酸在食品工业中常用作调味剂和食品添加剂[15]。肉豆蔻酸有一定的药理活性,相较于其他饱和脂肪酸,肉豆蔻酸有更强的抗氧化活性[16],肉豆蔻酸还可以降低血糖[17]。除了饱和脂肪酸以外,椰子油还含有少量不饱和脂肪酸,如油酸(C18:1)、棕榈油酸(C18:1)和亚麻酸(C18:3)。目前有报道使用椰子油可以降低阿尔茨海默病的患病风险[13-14],抑制肿瘤生长、抑制氧化应激和神经炎症,以及消除抗肿瘤药甲氨蝶呤引起的脑神经毒性[18-24]。植物脂肪酸代谢途径在其他物种中已有广泛报道[25-34],但目前在椰子中罕有报道。不同类型椰子品种在脂肪酸积累和合成调控途径是否存在差异,仍有待阐明。椰肉作为脂肪酸积累的主要部位,是研究脂肪酸合成调控的理想场所。本研究利用非靶向代谢组学,比较了海南高种、黄矮椰子和绿矮椰子的脂肪酸积累水平,研究表明,高种椰子的脂肪酸含量最高,黄矮椰子其次,绿矮椰子最低。结合转录组学数据,重建了椰子脂肪酸代谢途径,研究发现,相较于矮种椰子而言,脂肪酸途径的基因大多在高种椰子中高表达。WGCNA结果表明,“Melightyellow”模块中的基因与差异积累的脂肪酸有着相似的变化趋势,在此基础上结合模块中结构基因启动子区的cis-element,预测并构建了完整的脂肪酸调控网络。本研究通过组学策略探究了不同类型椰子品种脂肪酸差异的分子机理,预测并构建了完整的椰子脂肪酸调控网络,为后续椰子脂肪酸合成调控的进一步解析提供了可用资源,为高油脂椰子品种的选育提供了理论依据。
Elucidation of the fatty acid regulatory network for different coconut varieties by integrating transcriptome and metabolome
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摘要: 为了探究不同类型椰子中脂质种类和含量的差异,本研究利用非靶向代谢组学方法对海南高种和矮种椰子椰肉组织的代谢物进行了分析,共检测到12 579种代谢信号,其中鉴定了564种代谢物,包括氨基酸、脂肪酸、类黄酮等。定量分析表明高种椰子的脂质总体含量高于矮种椰子,其中绿矮椰子脂质含量最低。甘油脂、鞘脂和脂肪酰是不同类型椰子中主要的差异物质。转录组数据结果表明,不同类型椰子中的差异基因主要参与脂肪酸代谢、α-亚麻酸代谢、木质素代谢和苯丙烷代谢。基于表达模式的不同将差异基因划分为20个不同的模块,其中“Melightyellow”模块与差异积累的脂肪酸高度相关。通过分析模块中脂质途径结构基因启动子区的cis-element,发现大多数脂质途径基因的启动子区存在多个MYB家族的结合位点及大量的激素信号响应元件。结果表明,MYB家族的转录因子可能在脂质的合成调控中发挥重要作用,并且激素可能作为一种信号分子参与到脂质的合成调控中。本研究通过组合策略对不同品种椰肉组织脂质差异的分子机理进行分析,并进一步构建了转录因子−结构基因−代谢物的合成调控网络,为后续解析脂质合成调控的分子机制提供了资源,为油脂椰子品种选育提供了依据。Abstract: Coconut (Cocos nucifera L.), as an important oil crop, is one of the sources of high-quality vegetable oil in the world. In order to explore the differences of lipid species and their contents in different types of coconuts, non-targeted metabolomics method was used to analyze the metabolites in coconut meat tissue of tall and dwarf coconuts in Hainan. A total of 12 579 metabolic signals were detected, among which 564 metabolites were identified, including fatty acids, amino acids, and flavonoids, etc. Quantitative analysis showed that the lipid content of tall coconut was generally higher than that of dwarf coconut, and that the lipid content of green dwarf coconut was the lowest. Glycerolipids, sphingolipids and fatty acylides were the main differentiating substances in different types of coconuts. Transcriptome data showed that the differential genes in three types of coconuts were mainly involved in fatty acid metabolism, α-linolenic acid metabolism, lignin metabolism and phenylpropane metabolism. The differential genes were divided into 20 modules based on expression patterns, among which "Melightyellow" module was highly correlated with differential accumulation of fatty acids. Analysis of the cis-elements in the promoter regions of lipid pathway structural genes in the module showed that there were multiple MYB family transcription factors binding sites and a large number of hormone signal response elements. These results suggested that MYB transcription factors may play an important role in the regulation of lipid synthesis, and that hormones may be involved in the regulation of lipid synthesis as signaling molecules. In this study, the molecular mechanism of lipid differences in meat tissues of different coconut varieties was analyzed through a combination strategy, and a synthetic regulatory network of transcription factors-structural genes-metabolites was further constructed. This study not only provided resources for the subsequent analysis of the molecular mechanism of lipid synthesis regulation, but also provided a basis for the breeding of high-fat coconut varieties.
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Key words:
- coconut /
- metabolome /
- transcriptome /
- WGCNA /
- lipid
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图 4 加权共表达分析鉴定与脂肪酸合成相关的基因
A:模块基因与差异脂肪酸的相关性热图;B:“Melightyellow”模块中与脂肪酸合成相关的基因调控网络;C:LPC 18:1在LPCAT基因的作用下与油酸结合生成Phosphatidylcholine (18:1/18:1);D:不同椰子品种中20-Oxoarachidonic acid (Cnm05349)和Phosphatidylcholine (18:1/18:1)的含量分布。HT表示高种椰子,YD表示黄矮椰子,GD表示绿矮椰子;E: ADH和LPCAT基因在不同椰子品种中的转录水平;F: ADH和LPCAT基因的qRT-PCR结果。
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