The Application of Nicotiana benthamiana as a Transient Expression Host to Clone the Coding Sequences of Plant Genes

Coding sequences (CDS) are commonly used for transient gene expression, in yeast two-hybrid screening, to verify protein interactions and in prokaryotic gene expression studies. CDS are most commonly obtained using complementary DNA (cDNA) derived from messenger RNA (mRNA) extracted from plant tissues and generated by reverse transcription. However, some CDS are difficult to acquire through this process as they are expressed at extremely low levels or have specific spatial and/or temporal expression patterns in vivo. These challenges require the development of alternative CDS cloning technologies. In this study, we found that the genomic intron-containing gene coding sequences (gDNA) from Arabidopsis thaliana, Oryza sativa, Brassica napus, and Glycine max can be correctly transcribed and spliced into mRNA in Nicotiana benthamiana. In contrast, gDNAs from Triticum aestivum and Sorghum bicolor did not function correctly. In transient expression experiments, the target DNA sequence is driven by a constitutive promoter. Theoretically, a sufficient amount of mRNA can be extracted from the N. benthamiana leaves, making it conducive to the cloning of CDS target genes. Our data demonstrate that N. benthamiana can be used as an effective host for the cloning CDS of plant genes.

Structural and Functional Insights into an Arabidopsis NBS-LRR Receptor in Nicotiana benthamiana

Nucleotide-binding site leucine-rich repeat receptors (NBS-LRR/NLRs) are crucial intracellular immune proteins in plants. Previous article reported a novel NLR protein SUT1 (SUPPRESSORS OF TOPP4-1, 1), which is involved in autoimmunity initiated by type one protein phosphatase 4 mutation (topp4-1) in Arabidopsis, however, its role in planta is still unclear. This study employed Nicotiana benthamiana, a model platform, to conduct an overall structural and functional analysis of SUT1 protein. The transient expression results revealed that SUT1 is a typical CNL (CC-NBS-LRR) receptor, both fluorescence data and biochemical results showed the protein is mainly anchored on the plasma membrane due to its N-terminal acylation site. Further truncation experiments announced that its CC (coiled-coil) domain possessed cell-death-inducing activity. The outcomes of point mutations analysis revealed that not only the CC domain, but also the full-length SUT1 protein, whose function and subcellular localization are influenced by highly conserved hydrophobic residues. These research outcomes provided favorable clues for elucidating the activation mechanism of SUT1.

Transient Expression of BYDV-MP in Nicotiana benthamiana

[Objective]The aim of this study was to identify transient expression of movement protein （MP） gene in Nicotinana benthaminana rapidly and further investigate the function of this exogenous gene. [Method]The movement protein gene of barley yellow dwarf virus （BYDV） was cloned into potato virus X （PVX） viral vector of pGR107,and PVX-recombinant vector was obtained. After electroporation of Agrobacterium tumefaciens,PVX was inoculated into the lower leaves of tobacco by Agrobacterium infiltration assay to observe the infection of virus on tobacco. [Result]After infection for 7 days,upper non-inoculated leaves of tobacco infected by the PVX-recombinant vector showed the virus infection symptoms,while the control group had no viral infection phenomenon. Daily follow-up observations for two groups revealed that tobacco infected by PVX-recombinant vector had severe symptoms of virus infection and curling leaves,or even led to necrosis both in infiltrated and systemic leaves in late period. However,tobacco infected by PVX vector had only slight symptoms of virus infection and could recover from infection. RT-PCR of the infected tobacco indicated that exogenous gene BYDV-MP had a normal transcription and expression in tobacco. [Conclusion]As a determinant factor for viral disease,BYDV-MP promotes the systemic infection rate of PVX and its symptom. In addition,it is feasible to express exogenous MP gene in Nicotiana benthaminan via PVX expression vector.

Cloning and Gentic Transformation of NbDAD1 Gene from Nicotiana benthamiana

[Objective] The aim was to clone NbDAD1 gene from Nicotiana benthami- ana and study its genetic transformation. [Method] NbDAD1 gene was isolated from N. benthamiana by using RT-PCR technology and over-expression vectors were con- structed to obtain NbDADl-overexpression resistant plants and NbDADl-overexpres- sion resistant plants carrying HA tag. [Result] The 351 bp long NbDAD1 gene was cloned from N. benthamiana; recombinant plasmids pCAMBIA1301-NbDAD1 and pCAMBIA1301-NbDAD1HAtag were constructed successfully; 50T0-generation N. ben- thamiana Hyg-resistant transgenic lines of three genotypes were obtained, including 23 positive transgenic plants. [Conclusion] This study laid the foundation for investi- gating the specific functions of NbDAD1 gene in N. benthamiana and exploring the possible functional mechanism of DAD1 protein in programmed cell death of plants.

A TOM1 homologue is required for multiplication of Tobacco mosaic virus in Nicotiana benthamiana

The AtTOM1 gene of Arabidopsis thaliana had been shown to be essential for the efficient multiplication of Tobacco mosaic virus(TMV) in A.thaliana.In this study,we cloned an AtTOM1-like gene from Nicotiana benthamiana named as NbTOM1.Sequence alignment showed that NbTOM1 is closely related to AtTOM1 homologues of N.tabacum and Lycopersicon esculentum with 97.2% and 92.6% nucleotide sequence identities,respectively.Silencing of NbTOM1 by a modified viral satellite DNA-based vector resulted in complete inhibition of the multiplication of TMV in N.benthamiana.The result suggests that inhibition of NbTOM1 via RNA silencing is a potentially useful method for generating TMV-resistant plants.

Sugarcane mosaic virus infection of model plants Brachypodium distachyon and Nicotiana benthamiana

Sugarcane mosaic virus (SCMV;genus Potyvirus, family Potyviridae) is a causal pathogen of sugarcane mosaic disease, and it is widespread in regions where sugarcane (Saccharum spp. hybrids) is grown. It is difficult to investigate the molecular mechanism of pathogen infection in sugarcane because of limited genomic information. Here, we demonstrated that SCMV strain FZ1 can systemically infect Brachypodium distachyon inbred line Bd21 and Nicotiana benthamiana through inoculation, double antibody sandwich enzyme-linked immunosorbent, transmission electron microscopy, and reverse transcription PCR assays. The leaves of Bd21 developed mosaic symptoms, while the leaves of N. benthamiana showed no obvious symptoms under the challenge of SCMV-FZ1. We concluded that B. distachyon inbred line Bd21 is a promising experimental model plant compared with N. benthamiana for study on the infectivity of SCMV. This is the first report on the SCMV infection of model plants B. distachyon inbred line Bd21 and N. benthamiana, which will shed light on the mechanism of SCMV infection of sugarcane and benefit sugarcane breeding against sugarcane mosaic disease.

High-quality assembled and annotated genomes of Nicotiana tabacum and Nicotiana benthamiana reveal chromosome evolution and changes in defense arsenals

Nicotiana tabacum and Nicotiana benthamiana are widely used models in plant biology research.However,genomic studies of these species have lagged.Here we report the chromosome-level reference genome assemblies for N.benthamiana and N.tabacum with an estimated 99.5%and 99.8%completeness,respec-tively.Sensitive transcription start and termination site sequencing methods were developed and used for accurate gene annotation in N.tabacum.Comparative analyses revealed evidence for the parental origins and chromosome structural changes,leading to hybrid genome formation of each species.Interestingly,theantiviral silencinggenesRDR1,RDR6,DCL2,DCL3,andAGO2were lost from one or both subgenomes in N.benthamiana,while both homeologs were kept in N.tabacum.Furthermore,the N.benthamiana genome encodes fewer immune receptors and signaling components than that of N.tabacum.These find-ings uncover possible reasons underlying the hypersusceptible nature of N.benthamiana.We developed the user-friendly Nicomics(http:/lifenglab.hzau.edu.cn/Nicomics/)web server to facilitate better use of Nicotiana genomic resources as well as gene structure and expression analyses.

A vicinal oxygen chelate protein facilitates viral infection by triggering the unfolded protein response in Nicotiana benthamiana

Vicinal oxygen chelate(VOC)proteins are members of an enzyme superfamily with dioxygenase or non-dioxygenase activities.However,the biological functions of VOC proteins in plants are poorly understood.Here,we show that a VOC in Nicotiana benthamiana(NbVOC1)facilitates viral infection.NbVOC1 was significantly induced by infection by beet necrotic yellow vein virus(BNYVV).Transient overexpression of NbVOC1 or its homolog from Beta vulgaris(BvVOC1)enhanced BNYVV infection in N.benthamiana,which required the nuclear localization of VOC1.Consistent with this result,overexpressing NbVOC1 facilitated BNYVV infection,whereas,knockdown and knockout of NbVOC1 inhibited BNYVV infection in transgenic N.benthamiana plants.NbVOC1 interacts with the basic leucine zipper transcription factors bZIP17/28,which enhances their self-interaction and DNA binding to the promoters of unfolded protein response(UPR)-related genes.We propose that bZIP17/28 directly binds to the NbVOC1 promoter and induces its transcription,forming a positive feedback loop to induce the UPR and facilitating BNYVV infection.Collectively,our results demonstrate that NbVOC1 positively regulates the UPR that enhances viral infection in plants.

SNARE-RNAi Results in Higher Terpene Emission from Ectopically Expressed Caryophyllene Synthase in Nicotiana benthamiana

Plants produce numerous terpenes and much effort has been dedicated to the identification and charac- terization of the terpene biosynthetic genes. However, little is known about how terpenes are transported within the cell and from the cell into the apoplast. To investigate a putative role of vesicle fusion in this pro- cess, we used Agrobacterium tumefaciens-mediated transient coexpression in Nicotiana benthamiana of an MtVAMP721e-RNAi construct （Vi） with either a caryophyllene synthase or a linalool synthase, respec- tively. Headspace analysis of the leaves showed that caryophyllene or linalool emission increased about five-fold when N. benthamiana VAMP72 function was blocked. RNA sequencing and protein ubiquitination analysis of the agroinflltrated N. benthamiana leaf extracts suggested that increased terpene emissions may be attributed to proteasome malfunction based on three observations： leaves with TPS＋Vi showed （1） a higher level of a DsRed marker protein, （2） a higher level of ubiquitinated proteins, and （3） coordinated induced expression of multiple proteasome genes, presumably caused by the lack of proteasome- mediated feedback regulation. However, caryophyllene or linalool did not inhibit proteasome-related pro- tease activity in the in vitro assays. While the results are not conclusive for a role of vesicle fusion in terpene transport, they do show a strong interaction between inhibition of vesicle fusion and ectopic expression of certain terpenes. The results have potential applications in metabolic engineering.

Nicotiana benthamiana LRR-RLP Nb EIX2 mediates the perception of an EIX-like protein from Verticillium dahliae

Verticillium wilt diseases caused by the soil-borne fungus Verticillium dahliae result in devastating yield losses in many economically important crops annually. Here, we identified a novel ethyleneinducing xylanase(EIX)-like protein, VdEIX3, from V. dahliae, which exhibits immunity-inducing activity in Nicotiana benthamiana. In vitro-purified VdEIX3 can induce strong oxidative burst, activate the expression of defense-related genes, and increase resistance against oomycete and fungal pathogens in N. benthamiana. VdEIX3 orthologs of other Verticillium pathogens also induce cell death in N. benthamiana, which form a new type of EIX protein family that is distinct from the known EIX proteins. A leucine-rich repeat receptor-like protein, NbEIX2, regulates the perception of VdEIX3 in N. benthamiana. Our results demonstrate that VdEIX3 is a novel EIX-like protein that can be recognized by N. benthamiana NbEIX2, and also suggest that NbEIX2 is a promising receptor-like protein that is potentially applicable to transgenic breeding for improving resistance to Verticillium wilt diseases.

Insight into Function and Subcellular Localization of a Type III-Secreted Effector in Pseudomonas syringae pv. tomato DC3000

Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) is a bacterial pathogen of tomato and of the model plants Arabidopsis and Nicotiana benthamiana (N. benthamiana). Like numerous Gram-negative bacterial pathogens of animals and plants, Pst DC3000 exploits the conserved type III secretion system (TTSS) to deliver multiple virulence effectors directly into the host cells. Type III effectors (T3Es) collectively participate in causing disease, by mechanisms that are not well clarity. Elucidating the virulence function of individual effector is fundamental for understanding bacterial infection of plants. Here, we focused on studying one of these effectors, HopAA1-1, and analyzed its potential function and subcellular localization in N. benthamiana. Using an Agrobacterium-mediated transient expression system, we found that HopAA1-1 can trigger domain-dependent cell death in N. benthamiana. The observation using confocal microscopy showed that the YFP-tagged HopAA1-1 localizes to diverse cellular components containing nucleus, cytoplasm and cell membrane, which was demonstrated through immunoblot analysis of membrane fractionation and nuclear separation. Enforced HopAA1-1 subcellular localization, by tagging with a nuclear localization sequence (NLS) or a nuclear export sequence (NES), shows that HopAA1-1-induced cell death in N. benthamiana is suppressed in the nucleus but enhanced in the cytoplasm. Our research is lay a foundation for revealed the molecular pathogenesis of Pseudomonas syringae pv. tomato.

Screening and Identifying of Interaction Protein AtL5 in Arabidopsis thaliana

Research background: The Arabidopsis-resistance protein L5 (AT1G12290) can trigger cell death in Nicotiana benthamiana, which is a characteristic function of an NBS-LRR (Nucleotide-Binding Sites and Leucine-Rich Repeat) protein activation. Purpose: To explore the function and molecular regulatory network of L5. Method: We employed yeast two-hybrid technology to search for interacting proteins of L5, combined with laser confocal microscopy to observe the subcellular localization of these candidate proteins, and analyzed the impact of these proteins on L5 function using an Agrobacterium mediated transient expression system. Results: Seven candidate interacting proteins were identified from the Arabidopsis cDNA library, including PPA1 (AT1G01050), RIN4 (AT3G25070), LSU1 (AT3G49580), BZIP24 (AT3G51960), BOI (AT4G19700), RING/U (AT4G22250) and PPA3 (AT2G46860). Functional analysis of these candidate interacting proteins showed that they participated in multiple pathways, including biological and abiotic stress, programmed cell death, protein degradation, material metabolism and transcriptional regulation. The results of laser confocal microscopy manifested that RIN4 was only localized on the plasma membrane (PM), and RING/U was mainly associated with the PM. PPA1, PPA3, LSU1, BZIP24, and BOI all emerged nuclear and cytoplasmic localization. The results of the transient assay proclaimed that both BOI and RING/U can inhibit cell death caused by L5. Conclusions: These results indicate that L5 immune receptors may participate in various pathways, and their protein levels and activities are strictly regulated at multiple levels, providing a basis for elucidating the mechanism of L5 immune receptors in Arabidopsis resistance.

磷脂酶Dα1在TuMV激活叶绿素降解相关基因表达中的功能分析

【目的】研究磷脂酶Dα1(phospholipase Dα1)及其产物磷脂酸(phosphatidic acid,PA)在芜菁花叶病毒(turnip mosaic virus,TuMV)促进植物叶绿素降解相关基因表达过程中的作用。【方法】通过UV-2800紫外分光光度计检测TuMV对本氏烟叶绿素含量的影响。利用Real-time qPCR检测TuMV侵染或瞬时表达6K2蛋白对本氏烟叶绿素降解相关基因NbNYE1(Nicotiana benthamiana NON-YELLOWING1)、NbNYE2(Nicotiana benthamiana NON-YELLOWING2)和NbPAO(Nicotiana benthamiana pheide a oxygense)mRNA相对表达水平的影响。敲除NbPLDα1(Nicotiana benthamiana phospholipase D alpha 1)或正丁醇降低磷脂酶D产生的磷脂酸含量,检测对TuMV诱导的NbNYE1、NbNYE2和NbPAO mRNA相对表达水平的影响。体外喷施磷脂酸对NbNYE1、NbNYE2和NbPAO mRNA相对表达水平的影响。【结果】TuMV侵染导致野生型本氏烟叶片叶绿素含量下降48%。TuMV侵染的野生型本氏烟中NbNYE1、NbNYE2和NbPAO表达量分别为健康野生型本氏烟的7.61、15.80和5.19倍。TuMV侵染的NbPLDα1敲除突变体本氏烟中NbNYE1、NbNYE2和NbPAO表达量分别为健康野生型本氏烟的2.35、7.83和1.29倍。正丁醇处理后,TuMV侵染的野生型本氏烟NbNYE1、NbNYE2和NbPAO表达量与健康野生型本氏烟无明显差异。喷施磷脂酸的叶片中NbNYE1、NbNYE2和NbPAO表达量分别为清水处理野生型本氏烟的12.39、3.64和8.26倍。此外,瞬时表达6K2蛋白叶片中NbNYE1、NbNYE2和NbPAO表达量分别为瞬时表达GFP野生型本氏烟的5.64、4.67和3.45倍。【结论】TuMV促进叶绿素降解相关基因表达依赖磷脂酶Dα1及其产物磷脂酸,病毒编码的6K2蛋白是促进叶绿素降解相关基因的关键致病因子。

转基因本氏烟草中CtDXR基因拷贝数及耐盐耐高温功能的初步分析

评估转基因本氏烟草中CtDXR基因的拷贝数,并初步分析其耐盐与耐高温能力。首先利用Southern Blot技术确定野生型本氏烟草中Actin基因的拷贝数,并以Actin基因为内参基因,以转CtDXR基因本氏烟草为材料,采用实时荧光定量PCR方法,检测转基因植株中CtDXR基因的拷贝数。最后,初步分析转基因植株的耐盐与耐高温能力。基于PCR方法,随机检测10株T1代转基因本氏烟草植株均能扩增出目的条带,表明它们均已成功转入目的基因CtDXR;Actin基因在本氏烟草基因组中为单拷贝基因;以Actin基因为内参基因,最终确定80%的转CtDXR基因植株为单拷贝或低拷贝株系;盐胁迫下,转CtDXR基因植株的株高(P<0.01)、侧根数(P<0.01)与鲜重(P<0.001)优于野生型植株,高温胁迫下,转CtDXR基因植株的株高(P<0.01)、叶片数(P<0.01)与鲜重优于野生型植株,表明转基因植株具有更强的耐盐和耐高温能力。利用研究建立的转基因本氏烟草外源基因拷贝数的检测方法,对转CtDXR基因植株完成外源基因拷贝数的鉴定,且初步鉴定了CtDXR基因具有耐盐与耐高温功能。

小麦miRNA靶基因的体外实验验证

miRNA是一类内源非编码单链小RNA,广泛存在于动植物中,主要通过切割靶基因或者抑制靶基因表达参与细胞分化、生长和发育等多种生物学调控。目前缺少一种快速简便验证miRNA靶基因的方法。本研究基于前期筛选到的小麦特有的miRNA——Tae-miR9666a,合成其前体及前体突变体,并连接到表达载体上,构建含有GFP(绿色荧光蛋白)标记的靶基因过表达载体,共转化烟草,通过观察GFP的荧光亮度判断靶基因的切割情况,以此来验证miRNA与靶基因的相互作用。结果发现,共转miRNA前体的烟草叶片的荧光亮度较低,表明靶基因被miRNA切割,其后的GFP无法正常表达;共转miRNA前体突变体的烟草叶片的荧光亮度与单转靶基因的相当,表明miRNA前体突变体未切割靶基因,导致GFP正常表达。本实验有效证明了miRNA的靶基因切割情况,也表明利用烟草验证miRNA与靶基因相互作用是可行的。

本氏烟NbGAD1蛋白的原核表达及多克隆抗体制备

γ-氨基丁酸(GABA)作为一种非蛋白质氨基酸,普遍存在于植物体内,在植物生长发育和抗胁迫方面发挥着重要作用。谷氨酸脱羧酶(GAD)是合成GABA的关键蛋白酶,目前关于GAD介导GABA调控植物防御病毒侵染的分子机制尚不清楚。利用RT-PCR克隆本氏烟NbGAD1基因,并与原核表达载体pET-28a连接,构建重组载体pET-28a-NbGAD1,诱导产生重组蛋白,经Ni-NTA柱纯化蛋白后免疫新西兰白兔,最终获得抗血清。结果表明:成功构建原核表达载体pET-28a-NbGAD1,经大肠埃希菌诱导纯化后获得分子量约57 ku的重组蛋白NbGAD1。免疫制备的抗血清经Western blot检测显示,抗血清效价达1∶100000,抗血清稀释2000倍仍能检测到浓度为0.005 mg·mL^(-1)的重组蛋白,且能检测到本氏烟中内源表达的NbGAD1蛋白,说明该抗血清特异性强、灵敏度高,为今后深入探究GAD在植物病毒侵染过程中的作用机制奠定了基础。

抗菌肽和几丁质酶基因提高烟草对黑胫病菌和赤星病菌的抗性研究

通过农杆菌介导法将加信号肽修饰的人工合成杂合抗菌肽CEMA基因(SPCEMA),苜蓿防御素基因(AFP),苦瓜几丁质酶基因(CHI)以及SPCEMA-CHI、AFP-CHI、AFP-SPCEMA双价基因导入本明烟(Nicotianabenthamiana),并对转基因烟草T0和T1代进行了抗病性检测,比较了不同转基因植株的抗病效果。研究结果表明,转基因烟草对黑胫病菌(Phytoph-thoraparasiticavar.nicotianae)、赤星病菌(Alternariaalternata)的抗性均强于非转基因烟草,病情指数差异达极显著水平,其中转AFP-CHI双价基因烟草具有较强的抗性,与单价转基因烟草的抗性差异达显著水平。但各单价转基因以及双价转基因烟草之间对上述病菌并未表现出显著的抗病性差异。结果表明植物源的抗菌肽基因与几丁质酶基因在抗植物真菌病害中具有协同增效作用。

烟草DREB转录因子新基因的克隆与功能分析

采用同源克隆及cDNA末端快速扩增法(rapid amplification of cDNA ends,RACE),从烟草中克隆到1个新的烟草DREB基因,命名为NbDREB2 a.序列分析表明该基因全长1191 bp,编码330个氨基酸,具有典型的DREB转录因子保守的AP2结构域.实时RT-PCR分析表明,该基因能在烟草的根、茎、叶中表达,受低温、干旱和高盐诱导.酵母转录激活实验证明,该基因可以特异性结合DRE顺式作用元件,并能激活报告基因的表达.为了研究该基因在植物抗逆反应中的功能,利用农杆菌介导法,将该基因转化到模式生物拟南芥中,筛选到了单拷贝插入的、纯合的拟南芥株系;对获得的转基因拟南芥进行干旱及高盐处理,结果表明,与对照相比,超量表达该基因能够明显地提高拟南芥对干旱及高盐的抗性.

镉胁迫对烟草生理特性的影响

为探明镉胁迫对烟草生理特性的影响,选用本生烟草(Nicotiana benthamiana)为材料,采用盆栽试验,挑选了生长4周健壮的烟草苗进行不同浓度镉胁迫处理(0,50,250和500μg·L-1),并于处理后一周分别取样并进行相关生理指标(叶绿素含量、丙二醛含量、超氧化物歧化酶、过氧化物酶和过氧化氢酶活性)的测定。结果表明:随着镉浓度的增加,本生烟草叶片叶绿素含量、超氧化物歧化酶和过氧化氢酶活性呈下降趋势,过氧化物酶活性呈先升后降趋势,丙二醛含量呈上升趋势。试验数据表明低浓度的镉胁迫下烟草会出现自我保护现象,但浓度超过250μg·L-1的镉胁迫一周会明显抑制烟草叶绿素合成及氧化酶系活性,进而对烟草细胞产生伤害。

利用病毒载体在烟草中瞬时表达融合HBsAg基因

利用马铃薯PVX病毒载体构建了外源人工融合乙肝表面抗原HBsAg基因的表达载体,在烟草中利用农杆菌介导进行瞬时表达,以快速鉴定外源基因瞬时表达的状况以及重组蛋白的免疫活性。利用PCR技术从含有人工融合HBsAg基因的表达载体中分别扩增出LP+PreS1+PreS2+S、PreS1+PreS2+S、PreS2+S序列,将其分别与PVX病毒载体pgR106连接,构建成PVX-LP、PVX-S1和PVX-S2等3个转化载体,并将此载体导入农杆菌菌株GV3101中用于侵染烟草植株叶片。感染植株经RT-PCR、RNA Dot blotting和HBsAg蛋白的ELISA检测显示,3个人工融合的HBsAg基因均可在植物体内得到转录,翻译成具有活性的蛋白。结果表明,外源融合HB-sAg基因经过植物病毒载体瞬时表达系统可以在植物系统中正常转录和翻译。