Characterization of Cucurbit Aphid-Borne Yellows Virus (CABYV) from Passion Fruit in Brazil: Evidence of a Complex of Species within CABYV Isolates.

High-throughput sequencing (HTS) has been an important tool for the discovery of plant viruses and their surveillance. In 2015, several virus-like symptoms were observed in passion fruit (PF) plants in Bahia state, Brazil. Using HTS technology, bioinformatics tools, RT-PCR, and Sanger sequencing, we identified the cucurbit aphid-borne yellows virus (CABYV, Polerovirus, Solemoviridae) in co-infection with cowpea aphid-borne mosaic virus (CABMV, Potyvirus, Potyviridae) in PF, in green manure, and spontaneous plants in several localities in Bahia. Complete genomes of CABYV-PF isolates were determined and analyzed with other CABYV isolates available in GenBank that have been identified in various countries. Phylogenetic analysis and pairwise identity comparison with CABYV isolates showed that CABYV-PFs are more closely related to French and Spanish isolates. Overall, analyses of all the CABYV genomes revealed that these could represent ten distinct species, and we thus proposed reclassifying these CABYV as isolates into ten species, tentatively named "Polerovirus curcubitaeprimum" to "Polerovirus curcubitaenonum", and "Polerovirus melo". CABYV-PF is a member of "Polerovirus curcubitaeprimum".

A Capsid Protein Fragment of a Fusagra-like Virus Found in Carica papaya Latex Interacts with the 50S Ribosomal Protein L17.

Papaya sticky disease is caused by the association of a fusagra-like and an umbra-like virus, named papaya meleira virus (PMeV) and papaya meleira virus 2 (PMeV2), respectively. Both viral genomes are encapsidated in particles formed by the PMeV ORF1 product, which has the potential to encode a protein with 1563 amino acids (aa). However, the structural components of the viral capsid are unknown. To characterize the structural proteins of PMeV and PMeV2, virions were purified from Carica papaya latex. SDS-PAGE analysis of purified virus revealed two major proteins of ~40 kDa and ~55 kDa. Amino-terminal sequencing of the ~55 kDa protein and LC-MS/MS of purified virions indicated that this protein starts at aa 263 of the deduced ORF1 product as a result of either degradation or proteolytic processing. A yeast two-hybrid assay was used to identify Arabidopsis proteins interacting with two PMeV ORF1 product fragments (aa 321-670 and 961-1200). The 50S ribosomal protein L17 (AtRPL17) was identified as potentially associated with modulated translation-related proteins. In plant cells, AtRPL17 co-localized and interacted with the PMeV ORF1 fragments. These findings support the hypothesis that the interaction between PMeV/PMeV2 structural proteins and RPL17 is important for virus-host interactions.

Current Scenario of Exogenously Induced RNAi for Lepidopteran Agricultural Pest Control: From dsRNA Design to Topical Application.

Invasive insects cost the global economy around USD 70 billion per year. Moreover, increasing agricultural insect pests raise concerns about global food security constraining and infestation rising after climate changes. Current agricultural pest management largely relies on plant breeding-with or without transgenes-and chemical pesticides. Both approaches face serious technological obsolescence in the field due to plant resistance breakdown or development of insecticide resistance. The need for new modes of action (MoA) for managing crop health is growing each year, driven by market demands to reduce economic losses and by consumer demand for phytosanitary measures. The disabling of pest genes through sequence-specific expression silencing is a promising tool in the development of environmentally-friendly and safe biopesticides. The specificity conferred by long dsRNA-base solutions helps minimize effects on off-target genes in the insect pest genome and the target gene in non-target organisms (NTOs). In this review, we summarize the status of gene silencing by RNA interference (RNAi) for agricultural control. More specifically, we focus on the engineering, development and application of gene silencing to control Lepidoptera through non-transforming dsRNA technologies. Despite some delivery and stability drawbacks of topical applications, we reviewed works showing convincing proof-of-concept results that point to innovative solutions. Considerations about the regulation of the ongoing research on dsRNA-based pesticides to produce commercialized products for exogenous application are discussed. Academic and industry initiatives have revealed a worthy effort to control Lepidoptera pests with this new mode of action, which provides more sustainable and reliable technologies for field management. New data on the genomics of this taxon may contribute to a future customized target gene portfolio. As a case study, we illustrate how dsRNA and associated methodologies could be applied to control an important lepidopteran coffee pest.

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.

Diverse genomoviruses representing twenty-nine species identified associated with plants.

Genomoviruses (family Genomoviridae) are circular single-stranded DNA viruses that have been mainly identified through metagenomics studies in a wide variety of samples from various environments. Here, we describe 98 genomes of genomoviruses found associated with members of 19 plant families from Australia, Brazil, France, South Africa and the USA. These 98 genomoviruses represent 29 species, 26 of which are new, in the genera Gemykolovirus (n = 37), Gemyduguivirus (n = 9), Gemygorvirus (n = 8), Gemykroznavirus (n = 6), Gemycircularvirus (n = 21) and Gemykibivirus (n = 17).

Battle of Three: The Curious Case of Papaya Sticky Disease.

Among the most serious problems in papaya production are the viruses associated with papaya ringspot and papaya sticky disease (PSD). PSD concerns producers worldwide because its symptoms are extremely aggressive and appear only after flowering. As no resistant cultivar is available, several disease management strategies have been used in affected countries, such as the use of healthy seeds, exclusion of the pathogen, and roguing. In the 1990s, a dsRNA virus, papaya meleira virus (PMeV), was identified in Brazil as the causal agent of PSD. However, in 2016 a second virus, papaya meleira virus 2 (PMeV2), with an ssRNA genome, was also identified in PSD plants. Only PMeV is detected in asymptomatic plants, whereas all symptomatic plants contain both viral RNAs separately packaged in particles formed by the PMeV capsid protein. PSD also affects papaya plants in Mexico, Ecuador, and Australia. PMeV2-like viruses have been identified in the affected plants, but the partner virus(es) in these countries are still unknown. In Brazil, PMeV and PMeV2 reside in laticifers that promote spontaneous latex exudation, resulting in the affected papaya fruit's sticky appearance. Genes modulated in plants affected by PSD include those involved in reactive oxygen species and salicylic acid signaling, proteasomal degradation, and photosynthesis, which are key plant defenses against PMeV complex infection. However, the complete activation of the defense response is impaired by the expression of negative effectors modulated by the virus. This review presents a summary of the current knowledge of the Carica papaya-PMeV complex interaction and management strategies.

Sequence and genome organization of papaya meleira virus infecting papaya in Brazil.

Papaya sticky disease ('meleira') was first observed in Brazil at the beginning of the 1980s. The disease is characterized by intense latex exudation from the fruit surface that becomes dark as it oxidizes, which makes it difficult to sell. The causal agent, which has been called papaya meleira virus (PMeV), has been identified as an isometric virus particle, approximately 50 nm in diameter, with a double-stranded RNA genome. Here, we report the first complete sequence and organization of the 8.7-kb viral dsRNA genome. Two ORFs coding for a putative coat protein and RNA-dependent RNA polymerase (RdRp) were predicted. In silico analysis revealed that the translated ORF2 contains the conserved domains characteristic of an RdRp protein (pfam02123:RdRP 4), which is a family that includes RdRps from members of the genera Luteovirus, Totivirus and Rotavirus. Evolutionary analysis with amino acid sequences with the RdRps from members of the family Totiviridae and some dsRNA viruses showed that PMeV RdRp did not root itself in any genus.

Isolation and characterization of a myo-inositol-1-phosphate synthase gene from yellow passion fruit (Passiflora edulis f. flavicarpa) expressed during seed development and environmental stress.

BACKGROUND AND AIMS: Myo-inositol-1l-phosphate synthase (MIPS) catalyses the conversion of d-glucose 6-phosphate to 1-l-myo-inositol-1-phosphate, the first and rate-limiting step in the biosynthesis of all inositol-containing compounds. Inositol phospholipids play a vital role in membrane trafficking and signalling pathways, auxin storage and transport, phytic acid biosynthesis, cell wall biosynthesis and production of stress-related molecules. In the present study, an MIPS cDNA from developing Passiflora edulis f. flavicarpa seeds was characterized and an investigation made into its spatial and differential expression, as well as changes in its transcription during exposure of growing plants to cold and heat stresses. METHODS: The MIPS-encoding gene was isolated by polymerase chain reaction (PCR) methods, and transcript levels were examined using semi-quantitative reverse transcription-PCR (RT-PCR) during seed development and in response to heat and cold stress. In addition, the copy number of the cloned PeMIPS1 gene in the genome of Passiflora edulis, P. eichleriana, P. caerulea, P. nitida and P. coccinea was determined by Southern blot analyses. KEY RESULTS: A full-length cDNA clone of the PeMIPS1 from P. edulis was isolated and characterized. Southern blot analyses indicated that the genomic DNA might have diverse sequences of MIPS-encoding genes and one copy of the cloned PeMIPS1 gene in the genomes of P. edulis, P. eichleriana, P. caerulea, P. nitida and P. coccinea. RT-PCR expression analyses revealed the presence of PeMIPS1 transcripts in ovules, pollen grains and leaves, and during the seed developmental stages, where it peaked at 9 d after pollination. The PeMIPS1 gene is differentially regulated under cold and heat stress, presenting a light-responsive transcription. CONCLUSIONS: Experimental data suggest that PeMIPS1 transcription plays an important role in the establishment of developmental programmes and during the response of plants to environmental changes. The PeMIPS1 is differentially transcribed during cold and heat stress, presenting a light response pattern, suggesting that it is important for environmental stress response.