Biotechnological approaches to determine the impact of viruses in the energy crop plant Jatropha curcas

Isolation and sequence characterization of DNA-A genome of a new begomovirus strain associated with severe leaf curling symptoms of Jatropha curcas L

Begomoviruses belong to the family Geminiviridae are associated with several disease symptoms, such as mosaic and leaf curling in Jatropha curcas. The molecular characterization of these viral strains will help in developing management strategies to control the disease. In this study, J. curcas that was infected with begomovirus and showed acute leaf curling symptoms were identified. DNA-A segment from pathogenic viral strain was isolated and sequenced. The sequenced genome was assembled and characterized in detail. The full-length DNA-A sequence was covered by primer walking. The genome sequence showed the general organization of DNA-A from begomovirus by the distribution of ORFs in both viral and anti-viral strands. The genome size ranged from 2844 bp-2852 bp. Three strains with minor nucleotide variations were identified, and a phylogenetic analysis was performed by comparing the DNA-A segments from other reported begomovirus isolates. The maximum sequence similarity was observed with Euphorbia yellow mosaic virus (FN435995). In the phylogenetic tree, no clustering was observed with previously reported begomovirus strains isolated from J. curcas host. The strains isolated in this study belong to new begomoviral strain that elicits symptoms of leaf curling in J. curcas. The results indicate that the probable origin of the strains is from Jatropha mosaic virus infecting J. gassypifolia. The strains isolated in this study are referred as Jatropha curcas leaf curl India virus (JCLCIV) based on the major symptoms exhibited by host J. curcas.

Molecular characterization of a new begomovirus associated with leaf yellow mosaic disease of Jatropha curcas in India

During a survey in June 2011, severe leaf yellow mosaic disease was observed on about 45 % plants of Jatropha curcas growing in the Katerniaghat wildlife sanctuary in India. An association of a begomovirus with disease was detected in 15 out of 20 samples by PCR using begomovirus genus-specific primers and total DNA isolated from symptomatic leaf samples. For identification of the begomovirus, the complete genome was amplified using a Phi-29 DNA-polymerase-based rolling-circle amplification kit and total DNA from five representative samples and then digested with BamHI. The linearized RCA products were cloned and sequenced. Their GenBank accession numbers are JN698954 (SKRK1) and JN135236 (SKRK2). The sequences of the two begomovirus isolates were 97 % identical to each other and no more than 86 % to those of jatropha mosaic India virus (JMIV, HM230683) and other begomoviruses reported worldwide. In phylogenetic analysis, SKRK1 and SKRK2 clustered together and showed distant relationships to jatropha mosaic India virus, Jatropha curcas mosaic virus, Indian cassava mosaic virus, Sri Lankan cassava mosaic virus and other begomoviruses. Based on 86 % sequence identities and distant phylogenetic relationships to JMIV and other begomoviruses and the begomovirus species demarcation criteria of the ICTV (<89 % sequence identity of complete DNA-A genome), the begomovirus isolates associated with leaf yellow mosaic disease of J. curcas were identified as members of a new begomovirus species and provisionally designated as jatropha leaf yellow mosaic Katerniaghat virus (JLYMKV). Agroinfectious clones of the DNA molecule of the begomovirus isolate were also generated, and the fulfillment of Koch's postulates was demonstrated in J. curcas plants.

Characterization of a novel begomovirus associated with yellow mosaic disease of three ornamental species of Jatropha grown in India

Severe yellow mosaic disease was observed in three ornamental species of Jatropha: J. integerrima, J. podagrica and J. multifida grown in gardens at Lucknow, India, during a survey in 2013. The causal pathogen was successfully transmitted from diseased to healthy plants of these species by whitefly (Bemisia tabaci). The infection of begomovirus was initially detected in naturally infected plant samples by PCR using begomovirus universal primers. The begomovirus was characterized having a monopartite genome based on sequence analyses of the cloned ∼2.9kb DNA-A genome amplified by rolling circle amplification using Phi-29 DNA polymerase. The genome contained 2844 nucleotides that could be translated into seven potential open reading frames. The nucleotide sequences of DNA-A genome of the begomovirus isolates: JI (KC513823), JP (KF652078) and JM (KF652077) shared 94-95% identities together and 93-95% identities with an uncharacterized begomovirus isolated from J. curcas (the only sequences available in GenBank database as GU451249 and EU798996 under the name jatropha leaf curl virus). These shared highest identity of 61% and highly distant phylogenetic relationships with other begomoviruses reported worldwide. Based on 61% sequence identities (much less than 89%, the species demarcation criteria for a new begomovirus) the isolates under study were identified as members of a new Begomovirus species for which the name was proposed as "Jatropha mosaic Lucknow virus (JMLV)". The recombination analysis also suggested that JMLV was not a recombinant species, hence considered as unidentified Begomovirus species. Koch's postulates were also established by agroinfiltration assay of agroinfectious clone of JMLV. Characterization of JMLV associated with yellow mosaic disease of J. integerrima, J. podagrica and J. multifida is being reported for the first time.

Jatropha (Jatropha curcas L.)

The seed oil of Jatropha (Jatropha curcas L.) as a source of biodiesel fuel is gaining worldwide importance. Commercial-scale exploration of Jatropha has not succeeded due to low and unstable seed yield in semiarid lands unsuitable for the food production and infestation to diseases. Genetic engineering is promising to improve various agronomic traits in Jatropha and to understand the molecular functions of key Jatropha genes for molecular breeding. We describe a protocol routinely followed in our laboratory for stable and efficient Agrobacterium tumefaciens-mediated transformation of Jatropha using cotyledonary leaf as explants. The 4-day-old explants are infected with Agrobacterium tumefaciens strain EHA105 harboring pBI121 plant binary vector, which contains nptII as plant selectable marker and gus as reporter. The putative transformed plants are selected on kanamycin, and stable integration of transgene(s) is confirmed by histochemical GUS assay, polymerase chain reaction, and Southern hybridization.

Molecular identification of a new begomovirus associated with leaf crumple disease of Jatropha curcas L. in India

Association of a new begomovirus with leaf crumple disease of Jatropha curcas was identified based on sequence analysis of cloned ~2.7-kb viral DNA genomes from three representative samples amplified by RCA using phi-29 DNA polymerase. Sequence analysis of these isolates SKJ1 (KM066975), SKJ2 (KM189818) and SKJ3 (KM189819)--showed the presence of a monopartite begomovirus-like genome of 2,735 to 2,738 nucleotides containing seven ORFs: V3, V2 and V1 in virion sense and C3, C2, C1 and C4 in the complementary sense. Pairwise alignment showed 99 % nucleotide sequence similarity to each other and less than 81 % identity to other begomoviruses reported worldwide. Based on begomovirus species demarcation criteria for a new species (sequence identity <89 %), the begomovirus isolates were identified as the members of a new Begomovirus species and provisionally designated as Jatropha leaf crumple India virus (JLCrIV).

The complete genome sequence of New World jatropha mosaic virus

Full-length sequences of a bipartite begomovirus were obtained from a plant of Jatropha multifida in Florida showing symptoms of foliar mosaic, distortion and necrosis. Sequences of four clones each of a DNA-A and DNA-B were obtained, which showed very low sequence diversity among themselves. The clones were infectious when biolistically inoculated to J. multifida, Phaseolus vulgaris and Nicotiana tabacum, but not to J. curcas. The DNA-A sequences had less than 89 % pairwise identity scores with the DNA-A of other begomoviruses. The DNA-A appeared to be a recombinant in that 18 % of the DNA-A (470 nt) had a pairwise identity score of 91.98 % with RhRGMV, indicating that this portion most likely originated from a virus closely related to RhRGMV. The remaining 82 % of the DNA-A had lower identity scores with TbMoLCV (87.84 %) and RhRGMV (87.46 %), which suggests that this part of the component originated from an undescribed virus. There was no evidence for recombination in the DNA-B. Equivalent sequences of the DNA-A had the highest identity score (94.18 %) with a 533-nt sequence obtained from J. multifida from Puerto Rico in 2001 (GenBank accession no. AF058025). Pairwise comparison, recombination and phylogenetic analysis, and biology suggest that these clones are those of jatropha mosaic virus first reported from Puerto Rico. This is the first report of the complete genome sequence of jatropha mosaic virus.

Engineering geminivirus resistance in Jatropha curcus

BACKGROUND

Jatropha curcus is a good candidate plant for biodiesel production in tropical and subtropical regions. However, J. curcus is susceptible to the geminivirus Indian cassava mosaic virus (ICMV), and frequent viral disease outbreaks severely limit productivity. Therefore the development of J. curcus to carry on durable virus resistance remains crucial and poses a major biotechnological challenge.

RESULTS

We generated transgenic J. curcus plants expressing a hairpin, double-stranded (ds) RNA with sequences homologous to five key genes of ICMV-Dha strain DNA-A, which silences sequence-related viral genes thereby conferring ICMV resistance. Two rounds of virus inoculation were conducted via vacuum infiltration of ICMV-Dha. The durability and heritability of resistance conferred by the dsRNA was further tested to ascertain that T1 progeny transgenic plants were resistant to the ICMV-SG strain, which shared 94.5% nucleotides identity with the ICMV-Dha strain. Quantitative PCR analysis showed that resistant transgenic lines had no detectable virus.

CONCLUSIONS

In this study we developed transgenic J. curcus plants to include a resistance to prevailing geminiviruses in Asia. These virus-resistant transgenic J. curcus plants can be used in various Jatropha breeding programs.

First report of a complete genome sequence for a begomovirus infecting Jatropha gossypifolia in the Americas

Jatropha gossypifolia is a weed that is commonly found with yellow mosaic symptoms growing along the roadside and in close proximity to cultivated crops in many farming communities in Jamaica. For the first time, the complete genome sequence of a new begomovirus, designated jatropha mosaic virus-[Jamaica:Spanish Town:2004] (JMV-[JM:ST:04]), was determined from field-infected J. gossypifolia in the western hemisphere. DNA-A nucleotide sequence comparisons showed closest identity (84 %) to two tobacco-infecting viruses from Cuba, tobacco mottle leaf curl virus-[Cuba:Sancti Spiritus:03] (TbMoLCV-[CU:SS:03]) and tobacco leaf curl Cuba virus-[Cuba:Taguasco:2005] (TbLCuCUV-[CU:Tag:05]), and two weed-infecting viruses from Cuba and Jamaica, Rhynchosia rugose golden mosaic virus-[Cuba:Camaguey:171:2009] (RhRGMV- [CU:Cam:171:09]) and Wissadula golden mosaic St. Thomas virus-[Jamaica:Albion:2005] (WGMSTV-[JM:Alb:05]). Phylogenetic analysis revealed that JMV-[JM:ST:04] is most closely related to tobacco and tomato viruses from Cuba and WGMSTV-[JM:Alb:05], a common malvaceous-weed-infecting virus from eastern Jamaica, and that it is distinct from begomoviruses infecting Jatropha species in India and Nigeria.

Virus versus host plant microRNAs: who determines the outcome of the interaction?

Considering the importance of microRNAs (miRNAs) in the regulation of essential processes in plant pathogen interactions, it is not surprising that, while plant miRNA sequences counteract viral attack via antiviral RNA silencing, viruses in turn have developed antihost defense mechanisms blocking these RNA silencing pathways and establish a counter-defense. In the current study, computational and stem-loop Reverse Transcription – Polymerase Chain Reaction (RT-PCR) approaches were employed to a) predict and validate virus encoded mature miRNAs (miRs) in 39 DNA-A sequences of the bipartite genomes of African cassava mosaic virus (ACMV) and East African cassava mosaic virus-Uganda (EACMV-UG) isolates, b) determine whether virus encoded miRs/miRs* generated from the 5′/3′ harpin arms have the capacity to bind to genomic sequences of the host plants Jatropha or cassava and c) investigate whether plant encoded miR/miR* sequences have the potential to bind to the viral genomes. Different viral pre-miRNA hairpin sequences and viral miR/miR* length variants occurring as isomiRs were predicted in both viruses. These miRNAs were located in three Open Reading Frames (ORFs) and in the Intergenic Region (IR). Moreover, various target genes for miRNAs from both viruses were predicted and annotated in the host plant genomes indicating that they are involved in biotic response, metabolic pathways and transcription factors. Plant miRs/miRs* from conserved and highly expressed families were identified, which were shown to have potential targets in the genome of both begomoviruses, representing potential plant miRNAs mediating antiviral defense. This is the first assessment of predicted viral miRs/miRs* of ACMV and EACMV-UG and host plant miRNAs, providing a reference point for miRNA identification in pathogens and their hosts. These findings will improve the understanding of host- pathogen interaction pathways and the function of viral miRNAs in Euphorbiaceous crop plants.

DNA-A of a highly pathogenic Indian cassava mosaic virus isolated from Jatropha curcas causes symptoms in Nicotiana benthamiana

Jatropha curcas mosaic disease (JcMD) is a newly emerging disease that has been reported in Africa and India. Here, we report the complete nucleotide sequence of a new Indian cassava mosaic virus isolate (ICMV-SG) from Singapore. Infection of ICMV-SG showed more severe JcMD in Jatropha curcas and Nicotiana benthamiana than the other ICMV isolates reported previously, though ICMV-SG shares high sequence identity with the other ICMV isolates. Agroinfectious DNA-A alone sufficiently induced systemic symptoms in N. benthamiana, but not in J. curcas. Results from agroinfection assays showed that systemic infection of ICMV-SG in J. curcas required both DNA-A and DNA-B components.

A single-tube duplex and multiplex PCR for simultaneous detection of four cassava mosaic begomovirus species in cassava plants

A single-tube duplex and multiplex PCR was developed for the simultaneous detection of African cassava mosaic virus (ACMV), East African cassava mosaic Cameroon virus (EACMCV), East African cassava mosaic Malawi virus (EACMMV) and East African cassava mosaic Zanzibar virus (EACMZV), four cassava mosaic begomoviruses (CMBs) affecting cassava in sub-Saharan Africa. Co-occurrence of the CMBs in cassava synergistically enhances disease symptoms and complicates their detection and diagnostics. Four primer pairs were designed to target DNA-A component sequences of cassava begomoviruses in a single tube PCR amplification using DNA extracted from dry-stored cassava leaves. Duplex and multiplex PCR enabled the simultaneous detection and differentiation of the four CMBs, namely ACMV (940bp), EACMCV (435bp), EACMMV (504bp) and EACMZV (260bp) in single and mixed infections, and sequencing results confirmed virus identities according to the respective published sequences of begomovirus species. In addition, we report here a modified Dellapotra et al. (1983) protocol, which was used to extract DNA from dry and fresh cassava leaves with comparable results. Using the duplex and multiplex techniques, time was saved and amount of reagents used were reduced, which translated into reduced cost of the diagnostics. This tool can be used by cassava breeders screening for disease resistance; scientists doing virus diagnostic studies; phytosanitary officers checking movement of diseased planting materials, and seed certification and multipliers for virus indexing.

Molecular identification of a new begomovirus associated with mosaic disease of Jatropha curcas L. in Nigeria

We report the complete nucleotide sequence of DNA-A of a begomovirus naturally infecting Jatropha curcas L. in Nigeria. Symptoms observed on infected plants were severe mosaic, mottling and blistering of leaves. The virus, which we provisionally name "jatropha mosaic Nigeria virus" (JMNV), has a monopartite genome of 2,779 to 2,789 nucleotides. Pairwise comparisons of DNA-A sequences showed that JMNV had maximum nucleotide sequence identity (72%) with a strain of tomato yellow leaf curl virus. Since there are widespread infections of jatropha in Nigeria showing similar symptoms as those investigated in the present study, JMNV may represent a significant threat to a promising bioenergy crop.