大豆种子蛋白和油脂含量调控的研究进展

作为重要的粮油饲兼用作物,大豆为世界膳食提供高达约71%的蛋白质和29%的油脂。随着人口不断增长和大豆消费需求的不断提高,在有限的耕地面积和单产条件下,大豆品质的遗传改良则更具重要意义。该文综述了大豆种子蛋白和油脂含量两个重要品质性状调控的研究进展,总结了调控大豆蛋白和油脂合成的关键酶和转录因子及因子间的相互作用,并根据蛋白和油脂合成代谢调控途径中关键酶和转录因子作用机制,绘制了大豆蛋白和油脂合成代谢的分子调控网络。此外,该文还讨论了当前大豆种子蛋白油脂含量调控研究存在的瓶颈及对策,以期为大豆种子品质的遗传改良和高产品种培育提供参考。     

植物C_2H_2型锌指蛋白的研究进展

锌指蛋白是转录因子的一种,对真核生物的生长发育及逆境胁迫的耐受能力都有着重要关系,而植物C2H2型锌指蛋白是研究较多、较为明确的一种锌指蛋白,该蛋白大部分锌指结构具有一段高度保守的氨基酸序列QALGGH,这是植物中独有的特征,且据报道该C2H2型锌指蛋白与逆境胁迫是相关的。本文主要综述了植物C2H2型锌指蛋白的分类、结构和功能,植物C2H2型锌指蛋白与DNA、RNA和蛋白质的相互作用,以及概述了与盐胁迫、低温胁迫、干旱胁迫、氧胁迫和光胁迫等逆境胁迫相关的植物C2H2型锌指蛋白,最后还对其进一步的深入研究进行了展望,这就为日后利用基因工程技术改良作物品质、提高作物的抗逆性提供了有利条件。     

RNAi技术在作物品质改良中的应用

RNA干涉(RNAi)是由同源性内源或外源dsRNA引起的序列特异性基因沉默现象,在动、植物和真菌中广泛存在并被证实。目前已应用RNAi技术在改善油脂的品质、改良淀粉品质、提高营养物质或降低有害物质含量、提高抗褐化能力、提高果实耐贮性、进行代谢调控以获得目的次生代谢物等方面进行了作物品质改良研究。作为一种下调表达技术,该技术在研究植物基因功能和改良作物品质等领域有良好的应用前景。本文重点从上述六个方面对近年来应用RNAi技术在作物品质改良研究方面进行了回顾并对其存在的问题作了初步探讨。     

食用植物油脂的代谢工程

植物种子油可提供人类营养所需的多种脂肪酸,也是工业用油的原料之一。文章结合我们对植物种子发育、脂肪酸生物合成途径和大豆油脂遗传改良的研究,重点论述参与脂肪酸合成及其调控的一些关键酶的基因、代谢工程改良植物油脂营养价值的技术策略及其研究进展,分析目前应用油料作物种子作为“生物反应器”规模化生产有重要营养价值和特殊用途的脂肪酸的问题及技术“瓶颈”,讨论未来植物脂肪酸代谢工程主攻方向以及在培育可再生资源和推动人类社会及经济可持续发展中的应用前景。     

种子特异表达异源DGAT1基因提高大豆种子含油量和营养品质

为提高大豆Glycine max种子含油量和营养品质,文中以二酰甘油酰基转移酶1(Diacylglycerol acyltransferase 1,DGAT1)基因为遗传修饰靶标。将来自高油植物斑鸠菊Vernonia galamensis L.编码DGAT1酶蛋白的c DNA克隆Vg DGAT1A在大豆种子特异超表达。连续选择获得高代(T7)Vg DGAT1A转基因大豆株系。转基因株系表型鉴定显示,在大豆种子发育中期(30–45 DAF),Vg DGAT1A高表达,相应地DGAT酶活性是非转基因野生型和空载体转化对照的7.8倍。转基因成熟种子含油量比对照提高了5.1%,淀粉含量比对照减少2%–3%,蛋白质含量与对照无显著差异。此外,转基因大豆种子百粒重(14.5 g)和种子萌发率(95.6%)与对照亦无明显差异。种子油脂脂肪酸成分分析显示,转基因大豆种子油中抗氧化的油酸(C18:1Δ9)含量比对照提高8.2%,相应地易氧化的亚油酸(C18:2Δ9,12)和亚麻酸(C18:3Δ9,12,15)分别减少6%和2%。这些数据表明,种子特异超表达外源Vg DGAT1A基因,打破了大豆种子含油量和蛋白质含量的负连锁,显著提高种子含油量且未导致蛋白含量降低。转基因大豆种子重量和萌发率亦未显负效应,而且种子油脂抗氧化性和营养品质得以改善。研究表明应用这一高酶活性Vg DGAT1A的基因工程是提高种子含油量和改善油脂品质的一条有效途径。     

植物NAC转录因子的研究进展

NAC转录因子是近些年来新发现的植物特有的转录调控因子,其N端含有高度保守的NAC结构域,在植物的生长发育、器官建成、逆境胁迫以及作物的品质改良中具有重要作用.主要介绍了植物NAC转录因子结构特点、生物学功能、作用机制等方面的最新研究进展进行综述.     

植物种子a-亚麻酸形成及调控机理研究进展

a-亚麻酸是人体必需但不能自身合成的ω-3系列多不饱和脂肪酸,主要来源于植物油脂。由于大宗油料作物种子油脂中ALA含量普遍较低,所以探寻新的种质资源,了解a-亚麻酸形成及调控机理,对于油脂营养膳食健康及植物油脂改良具有重要意义。种子中富含a-亚麻酸的陆生植物资源有紫苏、亚麻、杜仲、油用牡丹、奇亚、藿香、香薷、猕猴桃、星油藤等。在植物中,ω-3FAD是催化LA转化生成ALA的关键酶,ω-3FAD由在质体中FAD3及在内质网中的FAD7及FAD8组成。目前通过基因组及转录组研究已极大的丰富了ω-3FAD基因家族的鉴定及研究。其中,FAD3基因是种子ALA合成的关键基因,其表达受多个转录因子的调控,bZIP、WRI1、LEC、ABI3、FUS3、ASIL1和PKL等转录因子通过相互作用调控FAD3基因表达,决定油料作物种子中a-亚麻酸的含量。本文综述了高含量a-亚麻酸油料植物资源分布,以及主要油料植物种子中油脂脂肪组成及ALA的含量,种子ALA生物合成基本途径及关键基因,植物ω-3脂肪酸脱饱和酶类型及功能以及ω-3FAD的关键调控因子,以期为高ALA植物新资源的利用,以及油料植物脂肪酸成分改良等相关研究提供理论依据。     

植物中DREBs类转录因子及其在非生物胁迫中的作用

低温、干旱、高盐等非生物胁迫能够严重影响植物的生长及作物的产量。最近发现了许多调控多种与逆境相关基因表达的转录因子, 其中DREBs类转录因子能够通过与含有DRE/CRT顺式作用元件的抗逆相关基因启动子区相互作用, 进而调控一系列抗逆基因的表达, 使植物品质得到综合改良从而提高植物对非生物胁迫耐受力。文章通过对DREBs的结构、表达调控、作用方式及机理进行总结, 并结合其在植物胁迫信号通路中的作用以及提高转基因植株胁迫耐受性的最新研究成果加以综述, 并对其在农业生产中的应用前景进行展望。     

植物NAC转录因子家族在抗逆响应中的功能

NAC转录因子是植物特有的一类转录因子,其共同特点是在N端含有一段高度保守的约150个氨基酸组成的NAC结构域,而C端为高度多样化的转录调控区。NAC转录因子是具有多种生物功能的新型转录因子,在植物细胞次生壁的生长、植物顶端分生组织形成、植物侧根发育等生长发育过程以及作物的品质改良中具有重要作用。此外,研究表明NAC转录因子在植物抗逆反应中也具有重要的调控作用。本文综述了近年来NAC转录因子家族在植物抗逆中的研究进展。     

丹波黑大豆GmbHLH30转录因子耐铝功能初步研究

铝毒是酸性土壤作物生长的主要限制因素。前期研究发现,铝胁迫下,耐铝型丹波黑大豆SSH(suppression subtractive hybridization,SSH)cDNA文库中bHLH30转录因子基因上调表达,推测该基因与丹波黑大豆耐铝性相关。克隆GmbHLH30基因,构建GmbHLH30植物表达载体pK2-35S-GmbHLH30,并在烟草中过量表达获得转GmbHLH30的转基因烟草植株。在铝胁迫下,转GmbHLH30的转基因烟草相对根伸长率比野生型烟草大,可溶性糖和脯氨酸含量高,H2O2水平低。表明GmbHLH30基因的过量表达可以增强植物的耐铝能力,暗示GmbHLH30转录因子参与调控植物的耐铝特性。     

Mutant alleles of <Emphasis Type="Italic">FAD2-1A</Emphasis> and <Emphasis Type="Italic">FAD2-1B</Emphasis>combine to produce soybeans with the high oleic acid seed oil trait

Background  

The alteration of fatty acid profiles in soybean [Glycine max (L.) Merr.] to improve soybean oil quality is an important and evolving theme in soybean research to meet nutritional needs and industrial criteria in the modern market. Soybean oil with elevated oleic acid is desirable because this monounsaturated fatty acid improves the nutrition and oxidative stability of the oil. Commodity soybean oil typically contains 20% oleic acid and the target for high oleic acid soybean oil is approximately 80% of the oil; previous conventional plant breeding research to raise the oleic acid level to just 50-60% of the oil was hindered by the genetic complexity and environmental instability of the trait. The objective of this work was to create the high oleic acid trait in soybeans by identifying and combining mutations in two delta-twelve fatty acid desaturase genes, FAD2-1A and FAD2-1B.     

A novel <Emphasis Type="Italic">FAD2</Emphasis>-<Emphasis Type="Italic">1 A</Emphasis> allele in a soybean plant introduction offers an alternate means to produce soybean seed oil with 85% oleic acid content

The alteration of fatty acid profiles in soybean to improve soybean oil quality has been a long-time goal of soybean researchers. Soybean oil with elevated oleic acid is desirable because this monounsaturated fatty acid improves the nutrition and oxidative stability of soybean oil compared to other oils. In the lipid biosynthetic pathway, the enzyme fatty acid desaturase 2 (FAD2) is responsible for the conversion of oleic acid precursors to linoleic acid precursors in developing soybean seeds. Two genes encoding FAD2-1A and FAD2-1B were identified to be expressed specifically in seeds during embryogenesis and have been considered to hold an important role in controlling the seed oleic acid content. A total of 22 soybean plant introduction (PI) lines identified to have an elevated oleic acid content were characterized for sequence mutations in the FAD 2-1A and FAD2-1B genes. PI 603452 was found to contain a deletion of a nucleotide in the second exon of FAD2-1A. These important SNPs were used in developing molecular marker genotyping assays. The assays appear to be a reliable and accurate tool to identify the FAD 2-1A and FAD2-1B genotype of wild-type and mutant plants. PI 603452 was subsequently crossed with PI 283327, a soybean line that has a mutation in FAD2-1B. Interestingly, soybean lines carrying both homozygous insertion/deletion mutation (indel) FAD2-1A alleles and mutant FAD2-1B alleles have an average of 82–86% oleic acid content, compared to 20% in conventional soybean, and low levels of linoleic and linolenic acids. The newly identified indel mutation in the FAD2-1A gene offers a simple method for the development of high oleic acid commercial soybean varieties.     

Soybean Aphid Infestation Induces Changes in Fatty Acid Metabolism in Soybean

The soybean aphid (Aphis glycines Matsumura) is one of the most important insect pests of soybeans in the North-central region of the US. It has been hypothesized that aphids avoid effective defenses by inhibition of jasmonate-regulated plant responses. Given the role fatty acids play in jasmonate-induced plant defenses, we analyzed the fatty acid profile of soybean leaves and seeds from aphid-infested plants. Aphid infestation reduced levels of polyunsaturated fatty acids in leaves with a concomitant increase in palmitic acid. In seeds, a reduction in polyunsaturated fatty acids was associated with an increase in stearic acid and oleic acid. Soybean plants challenged with the brown stem rot fungus or with soybean cyst nematodes did not present changes in fatty acid levels in leaves or seeds, indicating that the changes induced by aphids are not a general response to pests. One of the polyunsaturated fatty acids, linolenic acid, is the precursor of jasmonate; thus, these changes in fatty acid metabolism may be examples of “metabolic hijacking” by the aphid to avoid the induction of effective defenses. Based on the changes in fatty acid levels observed in seeds and leaves, we hypothesize that aphids potentially induce interference in the fatty acid desaturation pathway, likely reducing FAD2 and FAD6 activity that leads to a reduction in polyunsaturated fatty acids. Our data support the idea that aphids block jasmonate-dependent defenses by reduction of the hormone precursor.     

High-Oleic Peanut Oils Produced by HpRNA-Mediated Gene Silencing of Oleate Desaturase

The quality of peanut oil largely depends on the quantity of oleic (18:1) and linoleic acids (18:2). These two acids comprise more than 80% of the total fatty acids in peanuts. The oleate desaturase (FAD2) gene is important for maintaining high oleic acid content. A partial conservative sequence of the FAD2 gene from peanut was selected. The sense and antisense 260-bp fragments were amplified and subcloned into pFGC1008 binary expression vectors. A total of 21 transgenic plants were obtained via Agrobacterium-mediated transformation. The resulting down-regulation of the FAD2 gene resulted in a 70% increase in oleic acid content in the seeds of transformed plants compared with a 37.93% increase in untransformed plants. The results demonstrated that the target genes were likely suppressed by hpRNA interference, a pathway capable of achieving phenotypic changes. The silencing of FAD2 enabled the development of peanut oils having novel combinations of oleic acid content that can be used in high-value applications, making this approach a reliable technique for the genetic modification of seed quality and the potential for enhancement of other traits as well.     

Overexpression of <Emphasis Type="Italic">FAD2</Emphasis> promotes seed germination and hypocotyl elongation in <Emphasis Type="Italic">Brassica napus</Emphasis>

The enzyme fatty acid desaturase 2 (FAD2) transforms oleic acid (C18:1) to linoleic acid (C18:2) in plants and as such is involved in fatty acid synthesis. It is also involved in plant development and self-defense, such as seed germination, leaf expansion and cold resistance. We have cloned the full coding region of the Brassica napus FAD2 gene and ectopically expressed it in B. napus expressing low levels of FAD2. Overexpression of FAD2 under the control of the CaMV 35S promoter resulted in an up-regulated FAD2 mRNA level in B. napus as expected. Further analysis revealed that the FAD2 transgenic lines varied greatly in terms of their physiological characteristics, such as enhanced seed germination and increased hypocotyl length, compared to non-transgenic plants, suggesting that up-regulated FAD2 can promote seed germination and hypocotyl elongation in B. napus. Our results demonstrate the possible roles of FAD2 in plant development and also provide a platform for further analysis of fatty acid synthesis in plants.