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Begomovirus-associated epidemics currently threaten tomato production worldwide due to the emergence of highly pathogenic virus species and the proliferation of a whitefly B biotype vector that is adapted to tomato. To generate an efficient defence against begomovirus, we modulated the activity of the immune defence receptor nuclear shuttle protein (NSP)-interacting kinase (NIK) in tomato plants; NIK is a virulence target of the begomovirus NSP during infection. Mutation of T474 within the kinase activation loop promoted the constitutive activation of NIK-mediated defences, resulting in the down-regulation of translation-related genes and the suppression of global translation. Consistent with these findings, transgenic lines harbouring an activating mutation (T474D) were tolerant to the tomato-infecting begomoviruses ToYSV and ToSRV. This phenotype was associated with reduced loading of coat protein viral mRNA in actively translating polysomes, lower infection efficiency and reduced accumulation of viral DNA in systemic leaves. Our results also add some relevant insights into the mechanism underlying the NIK-mediated defence. We observed that the mock-inoculated T474D-overexpressing lines showed a constitutively infected wild-type transcriptome, indicating that the activation of the NIKmediated signalling pathway triggers a typical response to begomovirus infection. In addition, the gain-of-function mutant T474D could sustain an activated NIK-mediated antiviral response in the absence of the virus, further confirming that phosphorylation of Thr-474 is the crucial event that leads to the activation of the kinase. [ABSTRACT FROM AUTHOR]

Whitefly-transmitted begomoviruses are the most important limiting factor for tomato cultivation in Oman, particularly in the Al-Batinah region, the major agricultural area of the country. Commercial farms in the Al-Batinah region were surveyed during January-March 2013. Samples of tomato showing leaf curl disease symptoms typical of begomoviruses were collected and analysed. Full-length sequences of five clones were shown to have relatively low percentage identity values to known begomoviruses, with the highest (886%) to isolates of Tomato leaf curl Oman virus (ToLCOMV), a begomovirus previously reported in Oman, indicating that these represent a newly identified species, for which the name Tomato leaf curl Barka virus (ToLCBrV) is proposed. Four isolates of ToLCBrV were found associated with Tomato leaf curl betasatellite (ToLCB). The five isolates of ToLCBrV characterized in this study were shown to be recombinants, with ToLCOMV as the major parent, and a fragment of Croton yellow vein virus (CrYVV) spanning the 3' half of the replication-associated protein. The significance of these findings is discussed. [ABSTRACT FROM AUTHOR]

The biological and molecular characterization of six isolates of a new Cowpea mild mottle virus strain ( CPMMV; Carlavirus, Betaflexiviridae) are reported. Soybean plants with mosaic and stem necrosis were collected in Bahia, Goiás, Mato Grosso and Minas Gerais states, Brazil. Complete genomes of the CPMMV isolates are 8180-8198 nucleotides (nt) long, excluding the 3′-polyadenylated tail, and have 67-68% nt sequence identity with a Ghana isolate of CPMMV, the only CPMMV isolate for which the genome has previously been sequenced. The replicase has only 60-61% nt sequence identity with the Ghana CPMMV isolate, and the coat protein ( CP) is highly conserved (79% nt sequence identity and 95-96% amino acid sequence identity). The high CP identity and the phylogenetic analyses supported the classification of the Brazilian isolates as CPMMV. Biological and molecular differences with the Ghana CPMMV isolate were found and indicated that the six isolates represent a distinct CPMMV strain denominated as CPMMV- BR. Furthermore, it is shown that recombination occurred mainly in the polymerase gene, and may occur less frequently in other regions of the CPMMV genome. [ABSTRACT FROM AUTHOR]

A survey of begomoviruses infecting leguminous weeds (family Fabaceae) was carried out in four states of northeastern Brazil. A total of 26 full-length begomovirus components (19 DNA-A and seven DNA-B, with three pairs of cognate A and B components) were amplified using rolling-circle amplification, then cloned and sequenced. Sequence analysis indicated the presence of six species, four of them novel. In phylogenetic analysis five of the viruses clustered with other Brazilian begomoviruses, but one of them ( Euphorbia yellow mosaic virus, EuYMV) clustered with viruses from other countries in Central and South America. Evidence of recombination was found among isolates of Macroptilium yellow spot virus (MaYSV). The MaYSV population had a high degree of genetic variability. Macroptilium lathyroides was revealed as a common host for several of these viruses, and could act as a mixing vessel from which recombinant viruses could emerge. The results indicate that leguminous weeds are reservoirs of several begomoviruses in Brazil, and could play a significant role in begomovirus epidemics, both as inoculum sources and as sources of emerging novel viruses. [ABSTRACT FROM AUTHOR]

Molecular and biological characterization of the begomovirus isolate BR:LNS2:Pas:01, obtained from yellow passionfruit plants in Livramento de Nossa Senhora, Bahia state, Brazil, was carried out. Sequence analysis demonstrated that the BR:LNS2:Pas:01 DNA-A had highest nucleotide sequence identity with Tomato chlorotic mottle virus (77%) and had five ORFs corresponding to the genes cp, rep, trap, ren and ac4. The DNA-B had highest nucleotide sequence identity with Tomato yellow spot virus (74%) and two ORFs corresponding to the genes mp and nsp. These identity values indicate that this isolate represents a new begomovirus species, for which the name Passionfruit severe leaf distortion virus (PSLDV), is proposed. Phylogenetic analysis clustered the PSLDV DNA-A and -B in a monophyletic branch with Brazilian tomato-infecting begomoviruses. The isolate’s host range was restricted to species from the Passifloraceae and Solanaceae. PSLDV-[BR:LNS2:Pas:01] was capable of forming pseudorecombinants with tomato-infecting begomoviruses, reinforcing its close relationship with these viruses and suggesting a possible common origin. However, the virus was not capable of infecting tomato. [ABSTRACT FROM AUTHOR]

In contrast to the accumulated data on nuclear transport mechanisms of macromolecules, little is known concerning the regulated release of nuclear-exported complexes and their subsequent trans-cytoplasmic movement. The bipartite begomovirus nuclear shuttle protein (NSP) facilitates the nuclear export of viral DNA and cooperates with the movement protein (MP) to transport viral DNA across the plant cell wall. Here, we identified a cellular NSP-interacting GTPase (NIG) with biochemical properties consistent with a nucleocytoplasmic transport role. We show that NIG is a cytosolic GTP-binding protein that accumulates around the nuclear envelope and possesses intrinsic GTPase activity. NIG interacts with NSP in vitro and in vivo (under transient expression), and redirects the viral protein from the nucleus to the cytoplasm. We propose that NIG acts as a positive contributor to geminivirus infection by modulating NSP nucleocytoplasmic shuttling and hence facilitating MP–NSP interaction in the cortical cytoplasm. In support of this, overexpression of NIG in Arabidopsis enhances susceptibility to geminivirus infection. In addition to highlighting the relevance of NIG as a cellular co-factor for NSP function, our findings also have implications for general nucleocytoplasmic trafficking of cellular macromolecules. [ABSTRACT FROM AUTHOR]

A viral complex causing golden mosaic and leaf distortion (rugosity) in tomato plants was obtained from viruliferous whiteflies, and named TGV-Ub1. This complex was sap-transmitted from tomato to Nicotiana benthamiana. PCR amplification using universal begomovirus primers yielded two distinct fragments for DNA-A, suggesting that the TGV-Ub1 complex comprised at least two distinct viruses. Clones corresponding to full-length viral genomes were obtained from tomato plants infected with TGV-Ub1. Comparisons of the complete sequences of clones pUb1-49 (DNA-A), pUb1-62 and pUb1-81 (both DNA-B) indicated that they constitute novel western hemisphere begomoviruses. Clones pUb1-49 and pUB1-81 have identical common regions, thus representing the cognate DNA-A and -B of a novel begomovirus, named Tomato rugose mosaic virus (ToRMV). Clone pUb1-62 has a distinct common region from ToRMV and all other geminiviruses. A cognate DNA-A for pUb1-62 was not found. Clones containing 1·8 copies of the genomic components were constructed. Infectivity assays of these clones in tomato and N. benthamiana demonstrated that the clones corresponding to ToRMV systemically infected both hosts. Symptoms were analogous to those observed when using the pure isolates obtained in this study. The combination of pUb1-49 and -62 did not result in systemic infection, indicating that these components do not form a viable virus. ToRMV was sap-transmitted from N. benthamiana to N. benthamiana, and by grafting to Solanum tuberosum and Datura stramonium. ToRMV-A and ToRMV-B were detected in plants of Nicandra physaloides and Phaseolus vulgaris, respectively, growing in nearby tomato fields, in association with distinct DNA components. [ABSTRACT FROM AUTHOR]

‘Meleira’, or ‘sticky disease’, is currently the most damaging papaya disease in the mid-eastern Brazilian growing regions. Consistent disease transmission via latex injection, presence of similar isometric particles in the laticiferous vessels of diseased plants, and detection of double-stranded DNA in naturally and experimentally infected papaya trees suggest that a virus is the causal agent. Conclusive evidence for viral aetiology was previously lacking, mostly because every attempt to purify the putative virus from infected papayas had failed. Following the successful purification and partial characterization of the meleira virus, healthy papaya seedlings injected with purified virus particles later developed typical symptoms of the disease. Negatively stained, isometric, full and ‘empty’ purified virus particles measured 42 and 38 nm, respectively. The viral genome was a single dsRNA molecule of about 12 kbp. Several capsid proteins, ranging in size from 14·4 to 45 kDa, were consistently revealed by PAGE. Papaya meleira virus (PMeV) appears to represent a novel group of viruses, with no known similar counterpart among known plant-, vertebrate-, invertebrate- or prokaryote-infecting viruses. [ABSTRACT FROM AUTHOR]