Transmission of the Bean-Associated Cytorhabdovirus by the Whitefly Bemisia tabaci MEAM1

The knowledge of genomic data of new plant viruses is increasing exponentially; however, some aspects of their biology, such as vectors and host range, remain mostly unknown. This information is crucial for the understanding of virus–plant interactions, control strategies, and mechanisms to prevent outbreaks. Typically, rhabdoviruses infect monocot and dicot plants and are vectored in nature by hemipteran sap-sucking insects, including aphids, leafhoppers, and planthoppers. However, several strains of a potentially whitefly-transmitted virus, papaya cytorhabdovirus, were recently described: (i) bean-associated cytorhabdovirus (BaCV) in Brazil, (ii) papaya virus E (PpVE) in Ecuador, and (iii) citrus-associated rhabdovirus (CiaRV) in China. Here, we examine the potential of the Bemisia tabaci Middle East-Asia Minor 1 (MEAM1) to transmit BaCV, its morphological and cytopathological characteristics, and assess the incidence of BaCV across bean producing areas in Brazil. Our results show that BaCV is efficiently transmitted, in experimental conditions, by B. tabaci MEAM1 to bean cultivars, and with lower efficiency to cowpea and soybean. Moreover, we detected BaCV RNA in viruliferous whiteflies but we were unable to visualize viral particles or viroplasm in the whitefly tissues. BaCV could not be singly isolated for pathogenicity tests, identification of the induced symptoms, and the transmission assay. BaCV was detected in five out of the seven states in Brazil included in our study, suggesting that it is widely distributed throughout bean producing areas in the country. This is the first report of a whitefly-transmitted rhabdovirus.

Genetically Engineered Crops: Importance of Diversified Integrated Pest Management for Agricultural Sustainability

As the global population continues to expand, utilizing an integrated approach to pest management will be critically important for food security, agricultural sustainability, and environmental protection. Genetically engineered (GE) crops that provide protection against insects and diseases, or tolerance to herbicides are important tools that complement a diversified integrated pest management (IPM) plan. However, despite the advantages that GE crops may bring for simplifying the approach and improving efficiency of pest and weed control, there are also challenges for successful implementation and sustainable use. This paper considers how several GE traits, including those that confer protection against insects by expression of proteins from Bacillus thuringiensis (Bt), traits that confer tolerance to herbicides, and RNAi-based traits that confer resistance to viral pathogens, can be key elements of a diversified IPM plan for several different crops in both developed and developing countries. Additionally, we highlight the importance of community engagement and extension, strong partnership between industry, regulators and farmers, and education and training programs, for achieving long-term success. By leveraging the experiences gained with these GE crops, understanding the limitations of the technology, and considering the successes and failures of GE traits in IPM plans for different crops and regions, we can improve the sustainability and versatility of IPM plans that incorporate these and future technologies.

Double-Stranded RNA High-Throughput Sequencing Reveals a New Cytorhabdovirus in a Bean Golden Mosaic Virus-Resistant Common Bean Transgenic Line

Using double-strand RNA (dsRNA) high-throughput sequencing, we identified five RNA viruses in a bean golden mosaic virus (BGMV)-resistant common bean transgenic line with symptoms of viral infection. Four of the identified viruses had already been described as infecting common bean (cowpea mild mottle virus, bean rugose mosaic virus, Phaseolus vulgaris alphaendornavirus 1, and Phaseolus vulgaris alphaendornavirus 2) and one is a putative new plant rhabdovirus (genus Cytorhabdovirus), tentatively named bean-associated cytorhabdovirus (BaCV). The BaCV genome presented all five open reading frames (ORFs) found in most rhabdoviruses: nucleoprotein (N) (ORF1) (451 amino acids, aa), phosphoprotein (P) (ORF2) (445 aa), matrix (M) (ORF4) (287 aa), glycoprotein (G) (ORF5) (520 aa), and an RNA-dependent RNA polymerase (L) (ORF6) (114 aa), as well as a putative movement protein (P3) (ORF3) (189 aa) and the hypothetical small protein P4. The predicted BaCV proteins were compared to homologous proteins from the closest cytorhabdoviruses, and a low level of sequence identity (15⁻39%) was observed. The phylogenetic analysis shows that BaCV clustered with yerba mate chlorosis-associated virus (YmCaV) and rice stripe mosaic virus (RSMV). Overall, our results provide strong evidence that BaCV is indeed a new virus species in the genus Cytorhabdovirus (family Rhabdoviridae), the first rhabdovirus to be identified infecting common bean.

Development of an event-specific hydrolysis probe quantitative real-time polymerase chain reaction assay for Embrapa 5.1 genetically modified common bean (Phaseolus vulgaris)

A genetically modified (GM) common bean event, namely Embrapa 5.1, resistant to the bean golden mosaic virus (BGMV), was approved for commercialization in Brazil. Brazilian regulation for genetically modified organism (GMO) labeling requires that any food containing more than 1% GMO be labeled. The event-specific polymerase chain reaction (PCR) method has been the primary trend for GMO identification and quantitation because of its high specificity based on the flanking sequence. This work reports the development of an event-specific assay, named FGM, for Embrapa 5.1 detection and quantitation by use of SYBR Green or hydrolysis probe. The FGM assay specificity was tested for Embrapa 2.3 event (a noncommercial GM common bean also resistant to BGMV), 46 non-GM common bean varieties, and other crop species including maize, GM maize, soybean, and GM soybean. The FGM assay showed high specificity to detect the Embrapa 5.1 event. Standard curves for the FGM assay presented a mean efficiency of 95% and a limit of detection (LOD) of 100 genome copies in the presence of background DNA. The primers and probe developed are suitable for the detection and quantitation of Embrapa 5.1.

Populational survey of arthropods on transgenic common bean expressing the rep gene from Bean golden mosaic virus

Genetically modified (GM) crops is considered the fastest adopted crop technology in the history of modern agriculture. However, possible undesirable and unintended effects must be considered during the research steps toward development of a commercial product. In this report we evaluated effects of a common bean virus resistant line on arthropod populations, considered as non-target organisms. This GM bean line (named M1/4) was modified for resistance against Bean golden mosaic virus (BGMV) by expressing a mutated REP protein, which is essential for virus replication. Biosafety studies were performed for a period of three years under field conditions. The abundance of some species was significantly higher in specific treatments in a particular year, but not consistently different in other years. A regular pattern was not observed in the distribution of insects between genetically modified and conventional treatments. Data analyses showed that minor differences observed can be attributed to random variation and were not consistent enough to conclude that the treatments were different. Therefore the present study indicates that the relative abundance of species are similar in transgenic and non-transgenic fields.

Development of plasmid DNA reference material for the quantification of genetically modified common bean embrapa 5.1

The genetically modified (GM) common bean Embrapa 5.1 was recently approved for commercialization. The reliable detection and quantification of GM organisms is strongly dependent on validated methods as well as calibration systems. This work presents the development of a calibrant plasmid for Embrapa 5.1 common bean detection. The reaction parameters were determined and compared for both the plasmid DNA (pDNA) and the genomic DNA (gDNA). PCR efficiencies for pDNA were 81% for the construction-specific assays and 76% for the taxon-specific assay, whereas for gDNA efficiencies were 94 and 93%, respectively. The limits of detection (LOD) in both qPCR assays were 10(2) and 10(3) copies of gDNA and pDNA per PCR reaction, respectively. This is sufficient to detect 0.067 and 0.67% of GM common bean in 100 ng of DNA, respectively, which is in agreement with detecting the 1% GM content required by the Brazilian legislation.

Primers and probes development for specific PCR detection of genetically modified common bean (Phaseolus vulgaris) Embrapa 5.1

The genetically modified common bean Embrapa 5.1, developed by Brazilian Agricultural Research Corporation (Embrapa), is the first commercial GM plant produced in Latin America. It presents high resistance to the Bean golden mosaic virus. In this work, primers and probes targeting a taxon-specific reference DNA sequence for the common bean (Phaseolus vulgaris L.) and a construct-specific DNA sequence of Embrapa 5.1 GM common bean were successfully developed. The primers and probes showed high specificity for the target detection. Both methods showed suitable efficiency and performance to be used as an endogenous target for detection of common bean DNA and for construct-specific detection of GM common bean Embrapa 5.1, respectively. Both real-time PCR assays proved to be valuable for future assessment of interlaboratory studies.

Gene flow from transgenic common beans expressing the bar gene

Gene flow is a common phenomenon even in self-pollinated plant species. With the advent of genetically modified plants this subject has become of the utmost importance due to the need for controlling the spread of transgenes. This study was conducted to determine the occurrence and intensity of outcrossing in transgenic common beans. In order to evaluate the outcross rates, four experiments were conducted in Santo Antonio de Goiás (GO, Brazil) and one in Londrina (PR, Brazil), using transgenic cultivars resistant to the herbicide glufosinate ammonium and their conventional counterparts as recipients of the transgene. Experiments with cv. Olathe Pinto and the transgenic line Olathe M1/4 were conducted in a completely randomized design with ten replications for three years in one location, whereas the experiments with cv. Pérola and the transgenic line Pérola M1/4 were conducted at two locations for one year, with the transgenic cultivar surrounded on all sides by the conventional counterpart. The outcross occurred at a negligible rate of 0.00741% in cv. Pérola, while none was observed (0.0%) in cv. Olathe Pinto. The frequency of gene flow was cultivar dependent and most of the observed outcross was within 2.5 m from the edge of the pollen source. Index terms: Phaseolus vulgaris, outcross, glufosinate ammonium.

Three distinct begomoviruses associated with soybean in central Brazil

We report the complete nucleotide sequences of geminiviruses of the genus Begomovirus infecting soybean (Glycine max) in central Brazil. Samples obtained from soybean plants collected at Santo Antonio de Goiás, Goiás State, showing typical symptoms of viral infection, were analyzed. Infection was confirmed by PCR-based amplification of a DNA-A fragment with universal begomovirus primers. Total DNA from infected plants was then subjected to rolling-circle amplification (RCA), and 2.6-kb molecules were cloned into plasmid vectors. Sequencing of the three DNA-A and two DNA-B clones thus obtained confirmed infection by three distinct begomoviruses: bean golden mosaic virus, Sida micrantha mosaic virus and okra mottle virus, the last of which was reported recently to be a novel virus infecting okra plants in Brazil. Begomovirus infection of soybean plants has been reported sporadically in Brazil and has generally not been considered to be of economic relevance.

RNAi-mediated resistance to Bean golden mosaic virus in genetically engineered common bean (Phaseolus vulgaris)

Bean golden mosaic virus (BGMV) is transmitted by the whitefly Bemisia tabaci in a persistent, circulative manner, causing the golden mosaic of common bean (Phaseolus vulgaris L.). The characteristic symptoms are yellow-green mosaic of leaves, stunted growth, or distorted pods. The disease is the largest constraint to bean production in Latin America and causes severe yield losses (40 to 100%). Here, we explored the concept of using an RNA interference construct to silence the sequence region of the AC1 viral gene and generate highly resistant transgenic common bean plants. Eighteen transgenic common bean lines were obtained with an intron-hairpin construction to induce post-transcriptional gene silencing against the AC1 gene. One line (named 5.1) presented high resistance (approximately 93% of the plants were free of symptoms) upon inoculation at high pressure (more than 300 viruliferous whiteflies per plant during the whole plant life cycle) and at a very early stage of plant development. Transgene-specific small interfering RNAs were detected in both inoculated and non-inoculated transgenic plants. A semiquantitative polymerase chain reaction analysis revealed the presence of viral DNA in transgenic plants exposed to viruliferous whiteflies for a period of 6 days. However, when insects were removed, no virus DNA could be detected after an additional period of 6 days.

Transgene elimination in genetically modified dry bean and soybean lines

Transgene elimination is a poorly studied phenomenon in plants. We made genetic and molecular studies of a transgenic dry bean line immune to bean golden mosaic geminivirus and a soybean line. In both lines, the transgenes were stable during the vegetative phase but were eliminated during meiosis. Due to its potential biotechnological value, this transgenic line was micropropagated by grafting and the vegetative copies were studied for more than two years. More than 300 plants of progeny were obtained during this period, demonstrating that the phenomenon of elimination was consistently repeated and offering an opportunity for detailed study of transgene elimination, including the characterization of the integration sites. Cloning and sequencing of the transgenic loci, reciprocal crosses to untransformed plants, genomic DNA blots, and GUS assays were performed in the transgenic lines. Based on the molecular and genetic characterization, possible mechanisms involved in transgene elimination include intrachromosomal recombination, genetic instability resulting from the tissue culture manipulations, and co-elimination of transgenes, triggered by a process of genome defense.

Variability in Geminivirus Isolates Associated with Phaseolus spp. in Brazil

ABSTRACT Bean golden mosaic geminivirus (BGMV) is the single most devastating virus of common beans in the tropical and subtropical Americas and the Caribbean Basin. The BGMV from Brazil, named BGMV-BZ, is considered distinct from BGMV-PR isolates from Puerto Rico, Guatemala, and the Dominican Republic because of DNA sequence data, the ability to form pseudorecombinants, and mechanical transmissibility properties. In bean-growing areas of Brazil, samples were collected from beans, lima beans, and the weed Leonurus sibiricus displaying typical symptoms of infection by geminiviruses. Viral DNA fragments comprising part of the rep gene, the common region, and part of the cp gene were amplified by polymerase chain reaction, cloned, and sequenced. The bean samples had geminivirus with sequences nearly identical to that of BGMV-BZ collected in Goiânia, state of Goiás, in 1986. The sample from lima bean contained a new species of geminivirus that induces symptoms similar to those induced by BGMV-BZ and was named lima bean golden mosaic virus (LBGMV-BR). While all sequences from bean samples clustered with BGMV-BZ, the sequence from the lima bean isolate stood alone. A mixed infection with abutilon mosaic geminivirus was also found in a single sample from the state of São Paulo. DNA sequence comparisons indicate that the virus isolate from L. sibiricus represents a new geminivirus species, designated here as leonurus mosaic virus.

Widespread Occurrence of Tomato Geminiviruses in Brazil, Associated with the New Biotype of the Whitefly Vector

Although tomato golden mosaic virus (TGMV) was reported in Brazil more than 20 years ago (3), tomato-infecting geminiviruses have not been of economic significance in the country until recently. However, a sharp increase in the incidence of geminivirus-like symptoms in tomatoes has been reported in several areas of Brazil since 1994. This has coincided with the appearance of the B biotype of Bemisia tabaci, which, as opposed to the A biotype, readily colonizes solanaceous plants (2). We have isolated geminiviruses from symptomatic tomato plants in the Federal District, in two different areas of the state of Minas Gerais, and in the state of Pernambuco. Tomato plants in these areas showed a variety of symptoms, including yellow mosaic, severe leaf distortion, down-cupping, and epinasty. Whitefly infestation was high in all fields sampled, and in some fields, particularly in Pernambuco, incidence of virus-like symptoms was close to 100%, and no tomatoes of commercial value were harvested (1). Using primer pairs PAL1v1978/PAR1c496 and PCRc1/PBL1v2040 (4), DNA-A and -B fragments were polymerase chain reaction (PCR)-amplified from total DNA extracted from diseased plants, cloned, and sequenced. Sequence comparisons of the PCR fragments indicated the existence of at least six different geminiviruses. The nucleotide sequence homologies for DNA-A fragments ranged from 67 to 80% for the 5' end of the cp gene, and from 44 to 80% for the 5' end of the rep gene. Data base comparisons indicated the viruses are most closely related to TGMV, bean golden mosaic virus from Brazil (BGMV-Br), and tomato yellow vein streak virus (ToYVSV), although homologies were less than 80% for the fragments compared. A similar lack of a close relationship with each other and other geminiviruses was obtained with two DNA-B component PCR products compared, corresponding to the 5' end of the BC1 open reading frame. Infectious, full-length genomic clones from the tomato viruses are being generated for biological and molecular characterization. References: (1) I. C. Bezerra et al. Fitopatol. Bras. 22:331, 1997. (2) F. H. França et al., Ann. Soc. Entomol. Bras. 25:369, 1996. (3) J. C. Matyis et al. Summa Phytopathol. 1:267, 1975. (4) M. R. Rojas et al. Plant Dis. 77:340, 1993.

A New Geminivirus Associated with Tomato in the State of São Paulo, Brazil

The apical growth of about 20% of young tomato plants in observed fields near Campinas, State of São Paulo, Brazil, had yellow streaking of veins. Leaf symptoms developed into patches of yellow mosaic and the leaves became wavy. The whitefly Bemisia tabaci Genn. transmitted a pathogen from the infected tomato plants to healthy tomato and potato plants, reproducing the original symptoms in tomato. The apical leaves of infected potatoes showed yellow or green mottle that developed into leaf distortion with yellow blotches, symptoms indistinguishable from potato-deforming mosaic disease (2). DNA was extracted from these tomato and potato plants (1). Using DNA from the infected tomato plant, polymerase chain reaction (PCR) with the degenerate primer pair PAC1v1978/ PAV1c715 (1), which amplifies part of the rep gene (AC1 ORF), the common region (CR), and part of the cp gene (AV1 ORF), and with the primer pair PBC1v2039/PBV1c800, which amplifies part of BC1 ORF, CR, and part of BV1 ORF, gave virus-specific DNA fragments of the sizes expected from a whitefly-transmitted geminivirus. These were cloned and the complete nucleotide (sequences for DNA-A (pToYA, GenBank accession no. U79998) and DNA-B (pToYB, GenBank accession no. U80042) fragments obtained. Nucleotide identity between the CRs (184 nucleotides) was 90%, strongly indicating that those fragments correspond to a bipartite subgroup III geminivirus. PCR with the DNA from infected potato gave the expected size fragment for DNA-A. The partial sequence of the rep gene was 100% identical to the homologous sequence from the PCR fragment from the infected tomato. A search in the GenBank, EMBL, DDBJ, and PDB databases, using the BLAST program, found no identical geminivirus. The highest identity for the CR was 75% to tomato mottle geminivirus-Florida (ToMoV) and 74% to bean golden mosaic virus-Brazil. For the rep gene, the highest identity was 73% to tomato yellow leaf curl virus-Israel, an Old World geminivi-rus, followed by 71% to tomato golden mosaic virus-Brazil (TGMV) and ToMoV. For the cp gene, the highest identity was 86% to TGMV, followed by 83% to squash leaf curl geminivirus. Therefore, we propose the name tomato yellow vein streak geminivirus (ToYVSV) for this distinct virus (2). References: (1) M. R. Rojas et al. Plant Dis. 77:340, 1993. (2) J. A. C. Souza-Dias et al. Summa Phytopathol. 22:57, 1996.

Inheritance of foreign genes in transgenic bean (Phaseolus vulgaris L.) co-transformed via particle bombardment

Exploiting the biolistic process we have generated stable transgenic bean (Phaseolus vulgaris L.) plants with unlinked and linked foreign genes. Co-transformation was conducted using plasmid constructions containing a fusion of the gus and neo genes, which were co-introduced with the methionine-rich 2S albumin gene isolated from the Brazil nut and the antisense sequence of AC1, AC2, AC3 and BC1 genes from the bean golden mosaic geminivirus. The results revealed a co-transformation frequency ranging from 40% to 50% when using unlinked genes and 100% for linked genes. The introduced foreign genes were inherited in a Mendelian fashion in most of the transgenic bean lines. PCR and Southern blot hybridization confirmed the integration of the foreign genes in the plant genome.

Factors influencing transient gene expression in bean (Phaseolus vulgaris L.) using an electrical particle acceleration device

The parameters influencing transient expression of the betaglucuronidase gene in bean embryonic axes, cotyledons, apical meristems and leaves were evaluated after gene delivery with an electrical particle acceleration device. A calciumspermidine procedure for coating gold particles with DNA resulted in higher levels of GUS expression with lower concentrations of gold particles compared with a calcium phosphate procedure. The DNA concentration, distance between the discharge chamber and the retaining screen and the vacuum in the apparatus also influenced gene delivery. Sections prepared for light and electron microscopy showed the localisation, within target cells, of gold particles used to deliver the DNA. Immunolocalization of foreign gene expression within cells confirmed an even distribution of gene product throughout the cell cytoplasm.