-
甘油脂包括甘油磷脂和甘油糖脂,是细胞膜及信号分子的重要组成部分,参与广泛的生理生化过程,在植物生长发育过程中发挥重要作用[1−5]。在高等植物中,甘油脂的合成涉及2条途径,即在质体外进行真核合成途径和质体中进行原核合成途径[6−7]。在原核合成途径中,由ATS1基因编码的3-磷酸甘油酰基转移酶(glycerol-3-phosphate acyltransferases,GPAT)催化甘油脂生物合成途径的第一步酰化反应,该反应被认为是关键的限速步骤[8−10]。
有关质体中ATS1基因的克隆与功能已有较多研究[11−13]。随着现代分子生物学的发展,人们已从南瓜Cucurbita moschata、红花Carthamus tinctorius、向日葵Helianthus annuus和油菜Brassica napus等植物中分离鉴定了多个与拟南芥Arabidopsis thaliana ATS1同源的基因[14−17]。这些ATS1基因表现出多种生理功能,在植物生长发育和抗逆性中发挥着重要作用。如YAN 等[18]研究发现:在烟草Nicotiana tabacum中异源表达甜椒Caspsicum frutescens质体ATS1基因可增强转基因烟草对高温胁迫的耐受性。KANG等[17]报道甘蓝型油菜BnATS1的过表达增加了细胞膜中多不饱和脂肪酸的积累,从而促进了甘蓝型油菜在低温条件下的生长。另有研究表明:ATS1在植物高盐和低磷等非生物胁迫中具有重要作用[19−20]。
然而,ATS1在植物正常生长发育中的功能并不完全清楚。KUNST等[21]利用EMS诱变创制了多个拟南芥ats1突变体,尽管这些突变体叶片的质体中脂肪酸组分发生了急剧变化,但是ATS1基因上的点突变并未对种子发育产生明显影响。相反,在高于28 ℃的温度条件下,突变体的生长速度比野生型略快。与上述ats1表型不一致的是,ATS1基因的T-DNA插入纯合突变体呈现败育现象, 并且发现运用RNAi干扰技术下调ATS1基因的表达会导致植株变小、胚胎发育受阻、种子结实率下降[9]。目前,尚不清楚造成这种不一致性的真正原因,但一种可能原因是,转基因植株中的T-DNA可能会干扰其插入位点或上下游基因的功能,从而对表型产生某种影响。
为了进一步明确ATS1在拟南芥正常生长发育中的功能,本研究利用现代基因编辑技术,采用优化后的CRISPR/Cas9基因编辑载体对ATS1基因进行定点编辑,创建功能丧失型突变体,并分析 ATS1基因功能的丧失对拟南芥生长发育的影响,有助于进一步了解高等植物中甘油脂原核合成途径在植物生长发育过程中的作用。
-
运用农杆菌介导法将含ATS1靶序列的CRISPR/Cas9基因编辑载体(含mCherry报告基因)转到拟南芥中,并筛选带荧光的T1代转基因种子(图1A)。随后,采用聚丙烯酰胺凝胶电泳法鉴定转基因阳性植株中 ATS1 基因编辑产物的PCR扩增片段特性(图1B)。经连续多代筛选,从不同转基因株系的后代分离群体中获得 3个纯合且稳定遗传的突变体,分别命名为ats1-1、ats1-2、ats1-3。同时,对这些突变体的自交后代进行连续多代的PCR检测与荧光观察,获得不含任何外源T-DNA插入片段的突变体,这些突变体中既不含Cas9基因,也不带荧光蛋白报告基因(mCherry)。
图 1 转基因拟南芥的mCherry荧光蛋白鉴定与ATS1编辑产物的聚丙烯酰胺凝胶电泳鉴定
Figure 1. Screening of transgenic plants carrying the mCherry fluorescent protein and those with CRISPR/Cas9-edited ATS1 gene product
进而,对这些突变体的靶位点附近序列进行测序分析,结果显示这些突变体的突变位点均位于第 1 个外显子上(图2)。在ats1-1突变体中,ATS1基因的92~314 bp (相对起始密码子ATG的位置)处发生215 bp 碱基缺失和8 bp 碱基替换。在ats1-2中,ATS1基因在2个位置发生1 bp 碱基插入,分别位于91 和293 bp 处。在ats1-3中,ATS1基因的91~92 bp之间存在7 bp 碱基插入,而在275~289 bp 间发生11 bp 碱基缺失和4 bp 碱基替换(表1)。上述这些突变大多位于 PAM 序列(NGG)的切割位点附近,其特点是ATS1基因的第1个外显子的碱基数呈非3的倍数的插入或缺失,从而导致移码突变或翻译提前终止,且由之产生的蛋白不含酰基转移酶保守结构域。这些结果表明,上述3个ATS1基因突变体均属功能丧失型突变体。这些突变体可成为ATS1基因功能研究的理想遗传材料。
图 2 不同ats1突变体中ATS1基因的突变位点序列
Figure 2. Sequences of mutational sites in ATS1 gene in different ats1 mutants
表 1 不同ats1突变体名称及其相应突变位点序列信息
Table 1. Designation of different ats1 mutants and the sequences of corresponding mutational sites
突变体 突变位点 ats1-1 92~314 bp:215 bp缺失;8 bp替换 ats1-2 91~92 bp:插入1 bp;293~294 bp:插入1 bp ats1-3 91~92 bp:7 bp插入;275~289 bp:11 bp缺失,
4 bp替换 -
ATS1是甘油脂原核合成途径中参与第一步酰化反应的关键酶,过去的研究表明,ATS1基因突变会改变膜脂组分及脂肪酸组分,特别是质体中的C16:3含量急剧下降[6]。对生长 4周的拟南芥植株叶片进行脂肪酸组分分析显示:与野生型相比,3个突变体(ats1-1、ats1-2和ats1-3)中不饱和脂肪酸C16:3的含量急剧下降,而不饱和脂肪酸C18:3的含量显著增加(表2),这与过去基于EMS诱变产生的ATS1突变体的脂肪酸组分变化完全一致[6]。因为质体外的甘油脂不含C16:3,其通常存在于质体中的单半乳糖基二酰基甘油 (monogalactosyldiacylglycerol,MGDG)骨架的sn-2位置[6, 21],因此,ats1-1、ats1-2和ats1-3中C16:3的大幅降低,印证了这些突变体中参与甘油脂原核合成途径中第一步酰化反应的ATS1基因的功能丧失。
表 2 野生型拟南芥与ats1突变体叶片的脂肪酸组分
Table 2. Leaf fatty acid composition of ats1 mutants and wild-type A. thaliana
脂肪酸 脂肪酸组分含量/% C16:0 C16:1 C16:3 C18:0 C18:1 C18:2 C18:3 WT 14.91±0.73 a 7.35±0.53 a 11.56±0.38 a 6.17±1.55 a 4.37±0.59 b 14.89±1.30 b 38.50±3.04 b ats1-1 11.91±0.65 b 5.55±0.69 b 0.70±0.15 b 3.89±0.87 a 8.65±0.75 a 18.61±0.54 a 49.14±2.24 a ats1-2 11.20±0.18 b 5.93±0.89 ab 0.65±0.15 b 4.67±0.32 a 8.89±1.06 a 18.67±0.98 a 48.31±1.68 a ats1-3 12.29±0.81 b 6.00±0.93 ab 0.57±0.18 b 6.02±1.62 a 9.08±1.02 a 18.28±0.88 a 46.04±1.45 a 说明:WT为野生型对照,n=3,不同小写字母表示不同株系间显著差异(P<0.05)。 -
如图3 A所示:在营养生长期,与野生型相比,突变体(ats1-1、ats1-2和ats1-3)有时会出现叶片略微变黄的现象,但植株叶片发育与野生型相比无明显差异。对植株地上部生物量检测结果显示:与野生型相比,突变体植株地上部生物量无显著差异(图3 B)。对植株叶片叶绿素检测结果显示:与野生型相比,突变体植株叶绿素a/b约上升29.5%(图3 C)。拟南芥果荚生长分析显示:与野生型一样,突变体株系的种子发育正常,无败育现象出现(图3 D和E),这一结果不支持XU等[9]的研究结果。本研究结果表明在正常生长条件下ATS1 基因的功能丧失对拟南芥种子发育并不产生可见影响。
Loss-of-function mutations in ATS1 reveal its dispensable role in normal seed development of Arabidopsis thaliana
-
摘要:
目的 甘油脂是生物膜的重要组成成分,植物中的ATS1催化甘油脂原核合成途径的第1步酰化反应,但目前ATS1在植物正常生长发育中的功能并不完全清楚。本研究运用反向遗传学手段剖析ATS1功能丧失对植物生长发育的影响。 方法 运用CRISPR/Cas9基因编辑技术,构建拟南芥Arabidopsis thaliana ATS1基因功能丧失型突变体,并比较分析突变体与野生型在整个生育期的表型差异。 结果 分子鉴定显示:多个突变体中ATS1基因的第1个外显子碱基数呈非3的倍数的缺失或插入,从而导致移码突变或翻译提前终止。这些突变体的叶片中多不饱和脂肪酸C16:3的含量急剧下降,而C18:3 含量则显著增加。相随的表型分析显示:ATS1基因功能丧失有时会使叶片略显黄色,但对种子发育未产生可见影响。 结论 在正常生长条件下,ATS1并非拟南芥种子发育所必需的。图3表2参25 Abstract:Objective Glycerolipids are the main constituents of biological membranes. ATS1 catalyzes the first acylation reaction in the prokaryotic pathway of glycerolipid synthesis. However, the function of ATS1 in normal plant growth and development is not completely understood. The present study was intended to dissect the effect of loss of function of ATS1 on plant growth and development by taking a reverse genetic approach. Method Loss-of-function mutants of the ATS1 gene were constructed by using CRISPR/Cas9 gene editing technology. Then, comparative analysis was conducted on phenotypic difference between the mutants and wild type Arabidopsis thaliana during the entire growth phase. Result Molecular characterization of multiple mutants revealed that the number of base pairs inserted or deleted in the first exon of the ATS1 gene is not a multiple of three, resulting in frameshift mutations or premature translation termination. Consistent with this, the content of polyunsaturated fatty acid C16:3 in the leaves of these mutants decreased sharply, concomitant with significant increases in the content of C18:3. Meanwhile, phenotypic analysis showed that loss of ATS1 gene function sometimes made the leaves turn slightly yellow, while having no visible effect on seed development. Conclusion The above results strongly indicate that ATS1 is dispensable for A. thaliana seed development under normal growth conditions. [Ch, 3 fig. 2 tab. 25 ref.] -
Key words:
- Arabidopsis thaliana /
- ATS1 /
- gene editing /
- ats1 mutant
-
表 1 不同ats1突变体名称及其相应突变位点序列信息
Table 1. Designation of different ats1 mutants and the sequences of corresponding mutational sites
突变体 突变位点 ats1-1 92~314 bp:215 bp缺失;8 bp替换 ats1-2 91~92 bp:插入1 bp;293~294 bp:插入1 bp ats1-3 91~92 bp:7 bp插入;275~289 bp:11 bp缺失,
4 bp替换表 2 野生型拟南芥与ats1突变体叶片的脂肪酸组分
Table 2. Leaf fatty acid composition of ats1 mutants and wild-type A. thaliana
脂肪酸 脂肪酸组分含量/% C16:0 C16:1 C16:3 C18:0 C18:1 C18:2 C18:3 WT 14.91±0.73 a 7.35±0.53 a 11.56±0.38 a 6.17±1.55 a 4.37±0.59 b 14.89±1.30 b 38.50±3.04 b ats1-1 11.91±0.65 b 5.55±0.69 b 0.70±0.15 b 3.89±0.87 a 8.65±0.75 a 18.61±0.54 a 49.14±2.24 a ats1-2 11.20±0.18 b 5.93±0.89 ab 0.65±0.15 b 4.67±0.32 a 8.89±1.06 a 18.67±0.98 a 48.31±1.68 a ats1-3 12.29±0.81 b 6.00±0.93 ab 0.57±0.18 b 6.02±1.62 a 9.08±1.02 a 18.28±0.88 a 46.04±1.45 a 说明:WT为野生型对照,n=3,不同小写字母表示不同株系间显著差异(P<0.05)。 -
[1] MURATA N, TASAKA Y. Glycerol-3-phosphate acyltransferase in plants [J]. Biochimica et Biophysica Acta (BBA)-Lipids and Lipid Metabolism, 1997, 1348(1/2): 10 − 16. [2] CHEN Xue, SNYDER C L, TRUKSA M, et al. Sn-glycerol-3-phosphate acyltransferases in plants [J]. Plant Signaling &Behavior, 2011, 6(11): 1695 − 1699. [3] 韩妮莎, 丁硕, 郑月萍, 等. 植物甘油脂合成途径第一步酰化反应的研究进展[J]. 中国油料作物学报, 2022, 44(4): 699 − 711. HAN Nisha, DING Shuo, ZHENG Yueping, et al. Advance in studies on the initial step of the glycerolipid biosynthetic pathway in plants [J]. Chinese Journal of Oil Crop Sciences, 2022, 44(4): 699 − 711. [4] GAN Yi, SONG Yu, CHEN Yadong, et al. Transcriptome analysis reveals a composite molecular map linked to unique seed oil profile of Neocinnamomum caudatum (Nees) Merr [J/OL]. BMC Plant Biology, 2018, 18(1): 303[2022-11-10]. doi:10.1186/s12870-018-1525-9. [5] ZHENG Zhifu, XIA Qun, DAUK M, et al. Arabidopsis AtGPAT1, a member of the membrane-bound glycerol-3-phosphate acyltransferase gene family, is essential for tapetum differentiation and male fertility [J]. The Plant Cell, 2003, 15(8): 1872 − 1887. [6] KUNST L, BROWSE J, SOMERVILLE C. Altered regulation of lipid biosynthesis in a mutant of Arabidopsis deficient in chloroplast glycerol-3-phosphate acyltransferase activity [J]. Proceedings of the National Academy of Sciences of the United States of America, 1988, 85(12): 4143 − 4147. [7] OHLROGGE J, BROWSE J. Lipid biosynthesis [J]. The Plant Cell, 1995, 7(7): 957 − 970. [8] NISHIDA I, TASAKA Y, SHIRAISHI H, et al. The gene and the RNA for the precursor to the plastid-located glycerol-3-phosphate acyltransferase of Arabidopsis thaliana [J]. Plant Molecular Biology, 1993, 21(2): 267 − 277. [9] XU Changcheng, YU Bin, CORNISH A J, et al. Phosphatidylglycerol biosynthesis in chloroplasts of Arabidopsis mutants deficient in acyl-ACP glycerol-3-phosphate acyltransferase [J]. The Plant Journal, 2006, 47(2): 296 − 309. [10] KIM H U, HUANG A H. Plastid lysophosphatidyl acyltransferase is essential for embryo development in Arabidopsis [J]. Plant Physiology, 2004, 134(3): 1206 − 1216. [11] 陈娜, 郭尚敬, 颜坤, 等. 甜椒甘油-3-磷酸酰基转移酶基因的克隆与表达分析[J]. 园艺学报, 2005, 32(5): 58 − 62. CHEN Na, GUO Shangjing, YAN Kun, et al. Cloning and expression analysis of glycerol-3-phosphate acyltransferase gene from sweet pepper [J]. Acta Horticulturae Sinica, 2005, 32(5): 58 − 62. [12] FRITZ M, HEINZ E, WOLTER F P. Cloning and sequencing of a full-length cDNA coding for sn-glycerol-3-phosphate acyltransferase from Phaseolus vulgaris [J]. Plant Physiology, 1995, 107(3): 1039 − 1040. [13] WEBER S, WOLTER F P, BUCK F, et al. Purification and cDNA sequencing of an oleate-selective acyl-ACP: sn-glycerol-3-phosphate acyltransferase from pea chloroplasts [J]. Plant Molecular Biology, 1991, 17(5): 1067 − 1076. [14] NISHIDA I, SUGIURA M, ENJU A, et al. A second gene for acyl-(acyl-carrier-protein): glycerol-3-phosphate acyltransferase in squash, Cucurbita moschata cv. Shirogikuza(*), codes for an oleate-selective isozyme: molecular cloning and protein purification studies [J]. Plant Cell Physiology, 2000, 41(12): 1381 − 1391. [15] BHELLA R S, MACKENZIE S L. Nucleotide sequence of a cDNA from Carthamus tinctorius encoding a glycerol-3-phosphate acyl transferase [J]. Plant Physiology, 1994, 106(4): 1713 − 1714. [16] PAYA-MILANS M, VENEGAS-CALERON M, SALAS J J, et al. Cloning, heterologous expression and biochemical characterization of plastidial sn-glycerol-3-phosphate acyltransferase from Helianthus annuus [J]. Phytochemistry, 2015, 111: 27 − 36. [17] KANG Huiling, JIA Chenxi, LIU Ni’an, et al. Plastid glycerol-3-phosphate acyltransferase enhanced plant growth and prokaryotic glycerolipid synthesis in Brassica napus [J/OL]. International Journal of Molecular Sciences, 2020, 21(15): 5325[2022-11-20]. doi:10.3390/ijms21155325. [18] YAN Kun, CHEN Na, QU Yanyan, et al. Overexpression of sweet pepper glycerol-3-phosphate acyltransferase gene enhanced thermotolerance of photosynthetic apparatus in transgenic tobacco [J]. Journal of Integrative Plant Biology, 2008, 50(5): 613 − 621. [19] 李昊根. ATS1异位表达对拟南芥甘油脂合成及磷胁迫响应的影响[D]. 杭州: 浙江农林大学, 2019. LI Haogen. Effects of Ectopic Expression of ATS1 on Glycerolipid Biosynthesis and Response to Phosphorus Stress in Arabidopsis thaliana [D]. Hangzhou: Zhejiang A&F University, 2019. [20] BAHIELDIN A, SABIR J S M, RAMADAN A, et al. Control of glycerol biosynthesis under high salt stress in Arabidopsis [J]. Functional Plant Biology, 2013, 41(1): 87 − 95. [21] KUNST L, BROWSE J, SOMERVILLE C. Altered chloroplast structure and function in a mutant of Arabidopsis deficient in plastid glycerol-3-phosphate acyltransferase activity [J]. Plant Physiology, 1989, 90(3): 846 − 853. [22] WANG Zhiping, XING Huili, DONG Li, et al. Egg cell-specific promoter-controlled CRISPR/Cas9 efficiently generates homozygous mutants for multiple target genes in Arabidopsis in a single generation [J/OL]. Genome Biology, 2015, 16: 144[2022-11-10]. doi:10.1186/s13059-015-0715-0. [23] 朱丽颖, 郑月萍, 徐雪珍, 等. 一种准确、简便测定CRISPR/Cas9基因编辑效率的方法[J]. 江苏农业学报, 2020, 36(2): 299 − 305. ZHU Liying, ZHENG Yueping, XU Xuezhen, et al. A convenient and accurate method for determining the efficiency of CRISPR/Cas9-based gene editing [J]. Jiangsu Academy of Agricultural Sciences, 2020, 36(2): 299 − 305. [24] 李丹丹, 林蓉, 李新国, 等. AtJAR1 基因在拟南芥耐盐性中的功能分析[J]. 浙江农林大学学报, 2022, 39(5): 998 − 1009. LI Dandan, LIN Rong, LI Xinguo, et al. Functional analysis of AtJAR1 gene in salt tolerance of Arabidopsis thaliana [J]. Journal of Zhejiang A&F University, 2022, 39(5): 998 − 1009. [25] 徐雪珍, 郑月萍, 张夏婷, 等. 拟南芥AtFAD6 基因突变体的构建[J]. 江苏农业学报, 2021, 37(5): 1125 − 1130. XU Xuezhen, ZHENG Yueping, ZHANG Xiating, et al. Construction of Arabidopsis AtFAD6 gene mutant [J]. Jiangsu Academy of Agricultural Sciences, 2021, 37(5): 1125 − 1130. -
链接本文:
https://zlxb.zafu.edu.cn/article/doi/10.11833/j.issn.2095-0756.20220738