Begomovirus Inoculation in Arabidopsis and Cassava

The use of infectious clones to inoculate plant viruses allows for controlled studies that lead to a better understanding of plant-virus interactions. The main methods used for laboratory inoculation of geminiviruses are agroinoculation and biolistics. We describe how to successfully inoculate geminiviruses, focusing on Arabidopsis as a model plant and cassava as a crop.

Field and agroinoculation screening of national collection of urd bean (Vigna mungo) germplasm accessions for new sources of mung bean yellow mosaic virus (MYMV) resistance

Yellow mosaic disease (YMD) is a major problem in Urd bean (Vigna mungo L.) in India, which causes huge yield losses. Breeding for wide spectrum and durable Mungbean yellow mosaic virus (MYMV) resistance and cultivating resistant cultivars is the most appropriate and effective approach. However, the task has become challenging with the report of at least two species of the virus, viz., Mungbean yellow mosaic virus (MYMV) and Mungbean yellow mosaic India virus (MYMIV) and their recombinants; the existence of various isolates of these species with varied virulence and rapid mutations noted in the virus as well as in the whitefly vector population. Thus the present study was carried out to identify and characterize novel and diverse sources of YMV resistance and develop linked molecular markers for breeding durable and broadspectrum resistant urdbean cultivars against YMV. Towards this goal, we have screened 998 accessions of urdbean national collection of germplasm against YMD Hyderabad isolate both in a field under the natural level of disease incidence and through agro inoculation in the laboratory using viruliferous clones of the same isolate. Ten highly resistant accessions identified through repeated testing have been characterized in terms of reported linked markers. We attempted to see diversity among the ten resistant accessions reported here using earlier reported resistance-linked SCAR marker YMV1 and SSR CEDG180 marker. SCAR marker YMV1 did not amplify with any of the 10 accessions. But with CEDG180, results suggested that 10 accessions shortlisted through field and laboratory tests do not carry PU31 allele and this shows that it may be likely to carry novel gene(s). Further studies are needed to genetically characterize these new sources.

Molecular Epidemiology of Begomoviruses Infecting Mungbean from Yellow Mosaic Disease Hotspot Regions of India

The major threat to mungbean (Vigna radiata L.) cultivation in the Indian subcontinent is yellow mosaic diseases (YMD), caused by Begomovirus containing bipartite genomes (DNA-A and DNA-B). In the current study, we address the epidemiology of begomoviruses infecting mungbean plants in three YMD hotspot regions of India. Full-length genomic components of the viruses from the symptomatic leaves were cloned by rolling circle amplification (RCA) and sequenced. Mungbean yellow mosaic virus (MYMV) was detected in Bihar and mungbean yellow mosaic India virus (MYMIV) in Assam and Orissa. Furthermore, we studied the population structure and genetic diversity of MYMV and MYMIV isolates of Vigna species reported to date from India. Interestingly, based on phylogenetics, we observed independent evolution of DNA-A and coevolution of DNA-B of MYMV and MYMIV. This finding is supported by the high mutation rate and recombination events in DNA-B, particularly in BV1 and BC1 genes over DNA-A, with high transition/transversion bias (R) for DNA-A over DNA-B. To investigate the effect of Begomovirus infection in plants, we constructed infectious clones (i.e. MYMV and MYMIV) and inoculated them to eight mungbean genotypes, cowpea (Vigna unguiculata L.) and tobacco (Nicotiana benthamiana) through agroinfiltration. The infected plants developed varying degrees of typical YMD symptoms. Based on the disease severity score and viral titre, mungbean genotypes were categorized as highly susceptible to MYMV (ML267) and MYMIV (K851) and immune to MYMV (PDM139, SML668) and MYMIV (Pusa Vishal). Conclusively, our findings may help prevent an epidemic of YMD in Vigna species and develop mungbean genotypes resistant to YMD via breeding programs.

Tobacco rattle virus-induced VcANS gene silencing in blueberry fruit

Blueberry (Vaccinium corymbosum L.), a woody perennial bush in the genus Vaccinium, is an economically important and popular fruit crop worldwide. Development the superior cultivars, which including excellent fruit traits, not only means higher yielding and economic efficiency, but also produce fruit that to meet the preferences of different consumers. Excavating fruit quality-related genes, studying their functions, and using transgenic or molecular-assisted breeding are beneficial to the development of excellent blueberry varieties. Genetic transformation is an excellent way to study the function of genes in plants, however, it is a labor-intensive and time-consuming process to genetically transform many woody plants, including blueberry. Virus-induced gene silencing (VIGS) provides an efficient approach to knock-down the expression of target genes for functional analysis. In this study, tobacco rattle virus induced genes silencing (TRV-VIGS) was established in blueberry fruits using the VcANS gene as a reporter. The silenced sector of the skin of blueberry fruits injected with pTRV2 (plasmid Tobacco Rattle Virus, TRV-RNA2)::VcANS remained green or white at 25 days after agroinfiltration. In agroinfiltrated materials, the VcANS transcript levels were much lower in fruits with phenotypic changes (delayed color change) than in those infiltrated with the pTRV2 empty vector. Silencing of VcANS also affected the expression of other genes involved in the anthocyanin synthesis pathway. The experimental results support that VcANS can be used as an effective marker gene for VIGS system. In addition, the TRV-VIGS system has been successfully established in blueberry fruits, which provided an effective verification method for functional identification of unknown genes in blueberry fruits.

RTBV-Based VIGS Vector for Functional Genomics in Rice: Methodology, Advances, Challenges, and Future Implications

The availability of protocols for virus-induced gene silencing (VIGS) in rice has opened up an important channel for the elucidation of gene functions in this important crop plant. Here, we present an updated protocol of a VIGS system based on Rice tungro bacilliform virus (RTBV) for gene silencing in rice. We present complete updated protocols for VIGS in rice, compare the system with other existing ones for monocots, identify some of the challenges faced by this system and discuss ways in which the vector could be improved for better silencing efficiency.

Achieving maximum efficiency of Mungbean yellow mosaic India virus infection in mungbean by agroinoculation

Mungbean is one of the important food legumes in the Indian-sub-continent. Yellow mosaic disease, caused by Mungbean yellow mosaic virus and Mungbean yellow mosaic India virus (MYMIV) poses a severe threat to its production. Agroinoculation has been the most preferred way to test the function of genomic components of these viruses. However, the available inoculation methods are not as efficient as whitefly transmission, thereby limiting their usage for screening and biological studies. We hereby report an efficient and reproducible agroinoculation method for achieving maximum (100%) efficiency using tandem repeat infectious agro-constructs of DNA A and DNA B of MYMIV. The present study targeted wounding of various meristematic tissues of root, shoot, parts of germinating seeds and also non-meristematic tissue of stem to test the suitable tissue types for maximum infection. Among the various tissues selected for, the inoculation on the epicotyl region showed maximum infectivity. Further, to enhance the infectivity of MYMIV, different concentrations of acetosyringone, incubation time and Agrobacterium cell density were also standardized. The incubation of wounded sprouted seeds in 1.0 OD of agroculture containing repeat construct of MYMIV for 2-4 h without acetosyringone followed by sowing in soil showed maximum infection of MYMIV within 10-12 days on the first trifoliate leaf. This standardized method is reproducible and has potential to screen germplasm lines and will be useful in mungbean biological/virological studies and breeding programmes.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03088-w.

Molecular analysis, infectivity and host range of Tomato leaf curl Karnataka virus associated with Corchorus yellow vein mosaic betasatellite

Severe leaf curl disease of tomato (ToLCD) was noticed recently in the central parts of India and is an emerging threat to the cultivation of tomato. The genomic components of the begomovirus isolate, DNA A and betasatellite associated with ToLCD were cloned by rolling circle amplification method and sequenced. The sequence analysis revealed that the DNA A (2766 nt) of this isolate had the nucleotide identity of >91% with other strains of Tomato leaf curl Karnataka virus (ToLCKV), hence this isolate is proposed as a strain of ToLCKV, named as ToLCKV-Raipur. Similarly, the betasatellite molecule (1355 nt) had the highest identity of 91.1% with Corchorus yellow vein mosaic betasatellite (CoYVMB) and named as CoYVMB-Raipur. The full-length dimerized clones of these two genomic components were agroinoculated on natural (tomato), experimental (Nicotiana benthamiana) hosts and other 20 plant species belong to six different families. The severe leaf curl symptoms appeared only in the hosts, N. benthamiana, and in tomato inoculated with ToLCKV-Raipur alone and ToLCKV-Raipur with CoYVMB-Raipur after 8 and 16-18 days inoculation, respectively. This isolate was also transmissible to healthy tomato plants by whitefly from the tomato plant agroinoculated with ToLCKV-Raipur alone and with CoYVMB-Raipur and produced symptoms within 14-16 days after inoculation. Interestingly, this isolate infects horse gram and chilli by whitefly transmission and both the hosts showed positive for DNA A alone but not for betasatellite. Quantification of the genomic components of this isolate with the agroinoculated N. benthamiana samples by qRT-PCR results showed that the quantity of ToLCKV-Raipur was enhanced by three-fold while inoculated with CoYVMB-Raipur compared to ToLCKV-Raipur alone inoculated plants. However, CoYVMB-Raipur did not enhance the levels of ToLCKV-Raipur in the agroinoculated tomato plants. This is the first evidence of the natural co-occurrence of ToLCKV with betasatellite, CoYVMB causing ToLCD.

Development of a method to rapidly assess resistance/susceptibility of Micro-Tom tomatoes to Tomato yellow leaf curl virus via agroinoculation of cotyledons

Objective

Tomato yellow leaf curl virus (TYLCV) is one of the pathogens severely damaging tomato crops. Therefore, methods to treat or prevent TYLCV infection need to be developed. For this purpose, a method to conveniently and quickly assess infection of tomatoes by TYLCV is desired. In the present study, we established a quick method to evaluate TYLCV infection using cotyledons of Micro-Tom, a miniature tomato cultivar.

Results

First, we constructed a binary plasmid harboring 1.5 copies of the TYLCV genome and transformed Agrobacterium with the plasmid. By injecting agroinoculum from the resulting transformant into the branches of Micro-Tom, we confirmed the susceptibility of Micro-Tom to TYLCV. To shorten the evaluation process of TYLCV infection further, we agroinoculated cotyledons of Micro-Tom 10 days after sowing seeds. We consistently observed typical symptoms of TYLCV infection on true leaves 10 days after agroinoculation. Molecular analysis detected TYLCV progeny DNA in all leaves demonstrating symptoms 6 days after agroinoculation. Therefore, our new protocol enabled assessment of TYLCV infection within 20 days after sowing seeds. Thus, agroinoculation of Micro-Tom cotyledons will accelerate the process of screening TYLCV-resistant Micro-Toms and enable screening of larger numbers of plants more quickly, contributing to the development of TYLCV-resistant tomatoes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13104-021-05651-3.

Transcriptional reprogramming caused by the geminivirus Tomato yellow leaf curl virus in local or systemic infections in Nicotiana benthamiana

BACKGROUND

Viruses have evolved to create a cellular environment permissive for viral replication in susceptible hosts. Possibly both enabling and resulting from these virus-triggered changes, infected hosts undergo a dramatic transcriptional reprogramming, the analysis of which can shed light on the molecular processes underlying the outcome of virus-host interactions. The study of the transcriptional changes triggered by the plant DNA viruses geminiviruses is potentially hampered by the low representation of infected cells in the total population, a situation that becomes extreme in those cases, like that of Tomato yellow leaf curl virus (TYLCV), in which the virus is restricted to phloem companion cells.

RESULTS

In order to gain insight into how different the transcriptional landscapes of TYLCV-infected cells or whole tissues of TYLCV-infected plants might be, here we compare the transcriptional changes in leaf patches infected with TYLCV by agroinfiltration or in systemic leaves of TYLCV-infected plants in Nicotiana benthamiana. Our results show that, in agreement with previous works, infection by TYLCV induces a dramatic transcriptional reprogramming; the detected changes, however, are not equivalent in local and systemic infections, with a much larger number of genes differentially expressed locally, and some genes responding in an opposite manner. Interestingly, a transcriptional repression of the auxin signalling pathway and a transcriptional activation of the ethylene signalling pathway were detected in both local and systemically infected samples. A transcriptional activation of defence was also detectable in both cases. Comparison with the transcriptional changes induced by systemic infection by the geminivirus Tobacco curly shoot virus (TbSV) shows common subsets of up- and down-regulated genes similarly affected by both viral species, unveiling a common transcriptional repression of terpenoid biosynthesis, a process also suppressed by the geminivirus Tomato yellow leaf curl China virus.

CONCLUSIONS

Taken together, the results presented here not only offer insight into the transcriptional changes derived from the infection by TYLCV in N. benthamiana, but also demonstrate that the resolution provided by local and systemic infection approaches largely differs, highlighting the urge to come up with a better system to gain an accurate view of the molecular and physiological changes caused by the viral invasion.

Quantification of a legume begomovirus to evaluate soybean genotypes for resistance to yellow mosaic disease

Mungbean yellow mosaic India virus (MYMIV) infecting soybean and other legumes causes yellow mosaic disease (YMD). Evaluation of soybean genotypes for YMD resistance involves field screening at disease hot spots or in a protected environment using infectious clones or viruliferous whiteflies as sources of virus inocula. Development of efficient virus inoculation and quantification protocols to screen soybean genetic stocks against YMD is imperative for breeding resistant varieties. Binary plasmids harbouring complete, tandem dimeric genomic components DNA A and DNA B of MYMIV-soybean isolate were engineered. The infectivity of the clones was demonstrated in soybean genotypes JS335 and UPSM534 that display contrasting YMD resistance. As a follow-up, soybean germplasm lines, breeding lines, and representative cultivars that were initially screened at an YMD hot-spot were then subjected to Agrobacterium-based infection with MYMIV. Quantitative real time polymerase chain reaction (qRT-PCR) based copy number analysis of MYMIV genomic components allowed soybean genotypes to be classified into three discrete categories; resistant, moderately resistant and susceptible to the viral infection. Thus, a soybean germplasm disease screening system based on agro-infection and qRT-PCR based quantification of MYMIV was developed to facilitate breeding YMD resistant soybean. The implications of this study for obtaining YMD resistant soybean cultivars are discussed.

Optimal systemic grapevine fanleaf virus infection in Nicotiana benthamiana following agroinoculation

One of the greatest hindrances to the study of grapevine fanleaf virus (GFLV) is the dearth of robust protocols for reliable, scalable, and cost-effective inoculation of host plants, especially methods which allow for rapid and targeted manipulation of the virus genome. Agroinoculation fulfills these requirements: it is a relatively rapid, inexpensive, and reliable method for establishing infections, and enables genetic manipulation of viral sequences by modifying plasmids. We designed a system of binary plasmids based on the two genomic RNAs [RNA1 (1) and RNA2 (2)] of GFLV strains F13 (F) and GHu (G) and optimized parameters to maximize systemic infection frequency in Nicotiana benthamiana via agroinoculation. The genomic make-up of the inoculum (G1-G2 and reassortant F1-G2), the identity of the co-infiltrated silencing suppressor (grapevine leafroll associated virus 2 p24), and temperature at which plants were maintained (25 °C) significantly increased systemic infection, while high optical densities of infiltration cultures (OD600nm of 1.0 or 2.0) increased the consistency of systemic infection frequency in N. benthamiana. In contrast, acetosyringone in the bacterial culture media, regardless of concentration, had no effect. Plasmids in this system are amenable to rapid and reliable manipulation by one-step site-directed mutagenesis, as shown by the creation of infectious RNA1 chimeras of the GFLV-F13 and GHu strains. The GFLV agroinoculation plasmids described here, together with the optimized protocol for bacterial culturing and plant maintenance, provide a robust system for the establishment of systemic GFLV infection in N. benthamiana and the rapid generation of GFLV mutants, granting a much-needed tool for investigations into GFLV-host interactions.

Infectivity of cloned begomoviral DNAs: an appraisal

Infectivity of cloned begomoviral DNAs is an important criterion to establish the etiology of the disease it causes, to study viral gene functions and host-virus interactions. Three main methods have been employed to study infectivity; mechanical inoculation with cloned viral DNA using abrasives, Agrobacterium-mediated inoculation (agroinoculation) of cloned viral DNA and bombardment using microprojectiles coated with cloned viral DNA (biolistics). Each method has its own advantages and disadvantages and the adoption of one over the other for demonstrating infectivity depends on various factors. This review compares the various features associated with the above three methods.

Cassava geminivirus agroclones for virus-induced gene silencing in cassava leaves and roots

AIM

We report the construction of a Virus-Induced Gene Silencing (VIGS) vector and an agroinoculation protocol for gene silencing in cassava (Manihot esculenta Crantz) leaves and roots. The African cassava mosaic virus isolate from Nigeria (ACMV-[NOg]), which was initially cloned in a binary vector for agroinoculation assays, was modified for application as VIGS vector. The functionality of the VIGS vector was validated in Nicotiana benthamiana and subsequently applied in wild-type and transgenic cassava plants expressing the uidA gene under the control of the CaMV 35S promoter in order to facilitate the visualization of gene silencing in root tissues. VIGS vectors were targeted to the Mg2+-chelatase gene in wild type plants and both the coding and promoter sequences of the 35S::uidA transgene in transgenic plants to induce silencing. We established an efficient agro-inoculation method with the hyper-virulent Agrobacterium tumefaciens strain AGL1, which allows high virus infection rates. The method can be used as a low-cost and rapid high-throughput evaluation of gene function in cassava leaves, fibrous roots and storage roots.

BACKGROUND

VIGS is a powerful tool to trigger transient sequence-specific gene silencing in planta. Gene silencing in different organs of cassava plants, including leaves, fibrous and storage roots, is useful for the analysis of gene function.

RESULTS

We developed an African cassava mosaic virus-based VIGS vector as well as a rapid and efficient agro-inoculation protocol to inoculate cassava plants. The VIGS vector was validated by targeting endogenous genes from Nicotiana benthamiana and cassava as well as the uidA marker gene in transgenic cassava for visualization of gene silencing in cassava leaves and roots.

CONCLUSIONS

The African cassava mosaic virus-based VIGS vector allows efficient and cost-effective inoculation of cassava for high-throughput analysis of gene function in cassava leaves and roots.

Phenotyping of VIGS-mediated gene silencing in rice using a vector derived from a DNA virus

Target genes in rice can be optimally silenced if inserted in antisense or hairpin orientation in the RTBV-derived VIGS vector and plants grown at 28 °C and 80% humidity after inoculation. Virus induced gene silencing (VIGS) is a method used to transiently silence genes in dicot as well as monocot plants. For the important monocot species rice, the Rice tungro bacilliform virus (RTBV)-derived VIGS system (RTBV-VIGS), which uses agroinoculation to initiate silencing, has not been standardized for optimal use. Here, using RTBV-VIGS, three sets of conditions were tested to achieve optimal silencing of the rice marker gene phytoene desaturase (pds). The effect of orientation of the insert in the RTBV-VIGS plasmid (sense, antisense and hairpin) on the silencing of the target gene was then evaluated using rice magnesium chelatase subunit H (chlH). Finally, the rice Xa21 gene, conferring resistance against bacterial leaf blight disease (BLB) was silenced using RTBV-VIGS system. In each case, real-time PCR-based assessment indicated approximately 40-80% fall in the accumulation levels of the transcripts of pds, chlH and Xa21. In the case of pds, the appearance of white streaks in the emerging leaves, and for chlH, chlorophyll levels and F _v/F _m ratio were assessed as phenotypes for silencing. For Xa21, the resistance levels to BLB were assessed by measuring the lesion length and the percent diseased areas of leaves, following challenge inoculation with Xanthomonas oryzae. In each case, the RTBV-MVIGS system gave rise to a discernible phenotype indicating the silencing of the respective target gene using condition III (temperature 28 °C, humidity 80% and 1 mM MES and 20 µM acetosyringone in secondary agrobacterium culture), which revealed the robustness of this gene silencing system for rice.

Genome characterization, infectivity assays of in vitro and in vivo infectious transcripts of soybean yellow mottle mosaic virus from India reveals a novel short mild genotype

Nucleotide sequence of a distinct soybean yellow mottle mosaic virusisolate from Vignaradiata (mungbean isolate, SYMMV-Mb) from India was determined and compared with othermembers of the family Tombusviridae. The complete monopartite single-stranded RNA genome of SYMMV-Mb consisted of 3974nt with six putative open reading frames and includes 5' and 3' untranslated regions of 35 and 254nt, respectively. SYMMV-Mb genome shared 75% nt sequence identity at complete genome level and 67-92% identity at all ORFs level with SYMMV Korean and USA isolates (soybean isolates) followed by CPMoV, whereas it shared very low identity with other tombusviridae members (5-41%). A full-length infectious cDNA clone of the SYMMV-Mb placed under the control of the T7 RNA polymerase and the CaMV35S promoters was generated and French bean plants on mechanical inoculation with in vitro RNA transcripts, p35SSYMMV-O4 plasmid and agroinoculation with p35SSYMMV-O4 showed symptoms typical of SYMMV-Mb infection. The infection was confirmed by DAC-ELISA, ISEM, RT-PCR and mechanical transmission to new plant species. Further testing of different plant species with agroinoculation of p35SSYMMV-O4 showed delay in symptoms but indistinguishable from mechanical sap inoculation and the infection was confirmed by DAC-ELISA, RT-PCR and mechanical transmission to new plants. The system developed here will be useful for further studies on pathogenecity, viral gene functions, plant-virus-vector interactions of SYMMV-Mb and to utilize it as a gene expression and silencing vector.

Plant Expression of Trans-Encapsidated Viral Nanoparticle Vaccines with Animal RNA Replicons

In this protocol, we outline how to produce a live viral nanoparticle vaccine in a biosafety level 1 (BSL1) environment. An animal viral vector RNA encapsidated with tobacco mosaic virus (TMV) coat protein can be fully assembled in planta. Agrobacterium cultures containing each component are inoculated together into tobacco leaves and the self-assembled hybrid nanoparticle vaccine is harvested 4 days later and purified with a simple PEG precipitation. The viral RNA delivery vector is derived from the BSL1 insect virus, Flock House virus (FHV), and replicates in human and animal cells but does not spread systemically. A polyethylene glycol purification protocol is also provided to collect and purify these vaccines for immunological tests.

The p22 RNA Silencing Suppressor of the Crinivirus Tomato chlorosis virus is Dispensable for Local Viral Replication but Important for Counteracting an Antiviral RDR6-Mediated Response during Systemic Infection

Among the components of the RNA silencing pathway in plants, RNA-dependent RNA polymerases (RDRs) play fundamental roles in antiviral defence. Here, we demonstrate that the Nicotiana benthamiana RDR6 is involved in defence against the bipartite crinivirus (genus Crinivirus, family Closteroviridae) Tomato chlorosis virus (ToCV). Additionally, by producing a p22-deficient ToCV infectious mutant clone (ToCVΔp22), we studied the role of this viral suppressor of RNA silencing in viral infection in both wild-type and RDR6-silenced N. benthamiana (NbRDR6i) plants. We demonstrate that p22 is dispensable for the replication of ToCV, where RDR6 appears not to have any effect. Furthermore, the finding that ToCV∆p22 systemic accumulation was impaired in wild-type N. benthamiana but not in NbRDR6i plants suggests a role for p22 in counteracting an RDR6-mediated antiviral response of the plant during systemic infection.

Molecular characterization and construction of an infectious clone of a pepper isolate of Beet curly top Iran virus

Geminiviruses cause curly top disease, in dicotyledonous plants which constrains host crop production. Beet curly top Iran virus (BCTIV) is a widespread Becurtovirus (family Geminiviridae) in numerous areas within Iran. In this study, we isolated and analyzed a full-length genomic DNA of a new variant of BCTIV from pepper crops in the Kaftark region, east of Shiraz (proposed acronym: BCTIV-Kaf [IR: Kaf:2016:Pepper]). Infected pepper plants showed shortening of internodes, severe interveinal chlorosis, upward leaf rolling and leaf curling. Sequence and phylogenetic analysis showed this BCTIV variant grouped with sugar beet isolates of BCTIV and has the highest similarity to a sugar beet BCTIV isolate from Negar town in Kerman province, Iran. It was more distantly related to a bean isolate of BCTIV from northeast region of Iran. A tandem repeat partial dimmer of BCTIV was constructed and found to be infectious in pepper, tomato and Nicotiana benthamiana plants. Results of this study indicated that BCTIV-Kaf is a new variant of BCTIV infecting pepper plants in Shiraz and that geographic location rather than the type of host plant has more effect on genetic diversity of BCTIV in Iran.

A new transient expression system for large-scale production of recombinant proteins in plants based on air-brushing an Agrobacterium suspension

Plant transient expression using virus-based vectors is advantageous when high level of gene expression is desired within a short time. In this study, a new system, named “air-brush,” has been developed to facilitate a scale-up production of recombinant proteins in plants. GFP was expressed successfully in Nicotiana benthamiana (Nb) plants by air-brushing an Agrobacterium suspension that contained the TMV-based vector p35S-30B-GFP. Key factors influencing the gene expression were optimized, including the Agrobacterium cell density, seedling age, and the growth temperature of plant materials. In addition, the pharmaceutical protein human acidic fibroblast growth factor (ha FGF) was also expressed in Nb plants by the air-brush system. The results demonstrated that using this system is highly advantageous; it is convenient, quick, easily scaled-up, and has a higher expression efficiency than leaf infiltration.

Infectious cDNA clones of the crinivirus Tomato chlorosis virus are competent for systemic plant infection and whitefly-transmission

Tomato chlorosis virus (ToCV) (genus Crinivirus, family Closteroviridae) causes important emergent diseases in tomato and other solanaceous crops. ToCV is not transmitted mechanically and is naturally transmitted by whiteflies. The ToCV genome consists of two molecules of linear, positive-sense RNA encapsidated into long flexuous virions. We present the construction of full-length cDNA clones of the ToCV genome (RNA1 and RNA2) fused to the SP6 RNA polymerase promoter and under the control of the CaMV 35S promoter. RNA1 replicated in the absence of RNA2 in Nicotiana benthamiana and tomato protoplasts after inoculation with cDNA-derived in vitro transcripts. Agroinfiltration of RNA1 and RNA2 under the 35S promoter resulted in systemic infection in N. benthamiana plants. In addition, tomato plants were infected by grafting with agroinfected N. benthamiana scions, showing the typical ToCV symptoms. The viral progeny generated in tomato was transmissible by the whitefly Bemisia tabaci.

Engineering Resistance Against Mungbean yellow mosaic India virus Using Antisense RNA

Yellow mosaic disease of cultivated legumes in South-East Asia, is caused by Mungbean yellow mosaic India virus (MYMIV) and Mungbean yellow mosaic virus (MYMV) belonging to the genus Begomovirus of the family Geminiviridae. Efforts to engineer resistance against the genus Begomovirus are focused mainly on silencing of complementary-sense virus genes involved in virus replication. Here we have targeted a complementary-sense gene (ACI) encoding Replication initiation Protein (Rep) to develop resistance against soybean isolate of Mungbean yellow mosaic India virus-[India:New Delhi:Soybean 2:1999], a bipartite begomovirus prevalent throughout the Indian subcontinent. We show that the legume host plants co-agroinoculated with infectious constructs of soybean isolate of Mungbean yellow mosaic India virus [India:New Delhi:Soybean 2:1999] along with this antisense Rep gene construct show resistance to the virus.