SUMMARY Cassava mosaic disease (CMD) caused by cassava mosaic geminiviruses (CMGs) is one of the most devastating crop diseases and a major constraint for cassava cultivation. CMD has been reported only from the African continent and Indian subcontinent despite the large-scale cultivation of cassava in Latin America and several South-East Asian countries. Seven CMG species have been reported from Africa and two from the Indian subcontinent and, in addition, several strains have been recognized. Recombination and pseudo-recombination between CMGs give rise not only to different strains, but also to members of novel virus species with increased virulence and a new source of biodiversity, causing severe disease epidemics. CMGs are known to trigger gene silencing in plants and, in order to counteract this natural host defence, geminiviruses have evolved suppressor proteins. Temperature and other environmental factors can affect silencing and suppression, and thus modulate the symptoms. In the case of mixed infections of two or more CMGs, there is a possibility for a synergistic interaction as a result of the presence of differential and combinatorial suppressor proteins. In this article, we provide the status of recent research findings with regard to the CMD complex, present the molecular biology knowledge of CMGs with reference to other geminiviruses, and highlight the mechanisms by which CMGs have exploited nature to their advantage.

Cassava mosaic geminiviruses: actual knowledge and perspectives.

Viruses of the genus Begomovirus (family Geminiviridae) have genomes consisting of either one or two genomic components. The component of bipartite begomoviruses known as DNA-A is homologous to the genomes of all geminiviruses and encodes proteins required for replication, control of gene expression, overcoming host defenses, encapsidation and insect transmission. The second component, referred to as DNA-B, encodes two proteins with functions in intra- and intercellular movement in host plants. The origin of the DNA-B component remains unclear. The study described here was initiated to investigate the relationship between the DNA-A and DNA-B components of bipartite begomoviruses with a view to unraveling their evolutionary histories and providing information on the possible origin of the DNA-B component. Comparative phylogenetic and exhaustive pairwise sequence comparison of all DNA-A and DNA-B components of begomoviruses demonstrates that the two molecules have very distinct molecular evolutionary histories and likely are under very different evolutionary pressures. The analysis highlights that component exchange has played a far greater role in diversification of begomoviruses than previously suspected, although there are distinct differences in the apparent ability of different groups of viruses to utilize this "sexual" mechanism of genetic exchange. Additionally we explore the hypothesis that DNA-B originated as a satellite that was captured by the monopartite progenitor of all extant bipartite begomoviruses and subsequently evolved to become the integral (essential) genome component that we recognize today. The situation with present-day satellites associated with begomoviruses provides some clues to the processes and selection pressures that may have led to the "domestication" of a wild progenitor of the DNA-B component. The analysis has highlighted the greater genetic variation of DNA-B components, in comparison to the DNA-A components, and that component exchange is more widespread than previously demonstrated and confined to viruses from the Old World. Although the vast majority of New World and some Old World begomoviruses show near perfect co-evolution of the DNA-A and DNA-B components, this is not the case for the majority of Old World viruses. Genetic differences between Old and New World begomoviruses and the cultivation of exotic crops in the Old World are likely factors that have led to this dichotomy.

/pdf/distinct-evolutionary-histories-of-the-dna-a-and-dna-b-41u9pprd9l.pdf

Distinct evolutionary histories of the DNA-A and DNA-B components of bipartite begomoviruses

Although single stranded (ss) DNA viruses that infect humans and their domesticated animals do not generally cause major diseases, the arthropod borne ssDNA viruses of plants do, and as a result seriously constrain food production in most temperate regions of the world. Besides the well known plant and animal-infecting ssDNA viruses, it has recently become apparent through metagenomic surveys of ssDNA molecules that there also exist large numbers of other diverse ssDNA viruses within almost all terrestrial and aquatic environments. The host ranges of these viruses probably span the tree of life and they are likely to be important components of global ecosystems. Various lines of evidence suggest that a pivotal evolutionary process during the generation of this global ssDNA virus diversity has probably been genetic recombination. High rates of homologous recombination, non-homologous recombination and genome component reassortment are known to occur within and between various different ssDNA virus species and we look here at the various roles that these different types of recombination may play, both in the day-to-day biology, and in the longer term evolution, of these viruses. We specifically focus on the ecological, biochemical and selective factors underlying patterns of genetic exchange detectable amongst the ssDNA viruses and discuss how these should all be considered when assessing the adaptive value of recombination during ssDNA virus evolution.

/pdf/recombination-in-eukaryotic-single-stranded-dna-viruses-2480cx3uqs.pdf

Recombination in eukaryotic single stranded DNA viruses.

Geminiviruses are often associated with subviral agents called DNA satellites that require proteins encoded by the helper virus for their replication, movement and encapsidation. Hitherto, most of the single-stranded DNA satellites reported to be associated with members of the family Geminiviridae have been associated with monopartite begomoviruses. Cassava mosaic disease is known to be caused by viruses belonging to nine different begomovirus species in the African continent and the Indian subcontinent. In addition to these species, several strains have been recognized that exhibit contrasting phenotypes and infection dynamics. It is established that Sri Lankan cassava mosaic virus can trans-replicate betasatellites and can cross host barriers. To extend these studies further, we carried out an exhaustive investigation of the ability of geminiviruses, selected to represent all cassava-infecting geminivirus species, to trans-replicate betasatellites (DNA-β) and to interact with alphasatellites (nanovirus-like components; previously called DNA-1). Each of the cassava-infecting geminiviruses showed a contrasting and differential interaction with the DNA satellites, not only in the capacity to interact with these molecules but also in the modulation of symptom phenotypes by the satellites. These observations could be extrapolated to field situations in order to hypothesize about the possibility of acquisition of such DNA satellites currently associated with other begomoviruses. These results call for more detailed analyses of these subviral components and an investigation of their possible interaction with the cassava mosaic disease complex.

Differential interaction between cassava mosaic geminiviruses and geminivirus satellites.

The in vitro replication of the Torque teno virus (TT virus) tth8 full-length genome and particle formation in a Hodgkin's lymphoma-derived cell line after transfection with cloned viral DNA were demonstrated. Analyses of the transcription patterns of tth8 and tth7 TT virus isolates in a number of lymphoma and T-cell leukemia cell lines indicated differential additional splicing events and intragenomic rearrangement generating open reading frames which could not be deducted from the genomic sequence. We also demonstrated the presence of rearranged TT virus genomes in vivo in sera taken from pregnant mothers whose children later developed childhood leukemia, as well as sera from control mothers. Control experiments using religated cloned genomic tth8 DNA mixed with cellular DNA did not result in such subviral molecules. These subviral isolates ranged from 172 bp to full-length TT virus genomes. Possible in vivo selection for specific rearranged molecules was indicated by the presence of one isolate (561 bp) in 11 serum samples. It remains to be clarified whether selected rearranged subviral components resulting from specific TT virus types may contribute to the initiation of disease. These data demonstrate new features of TT viruses suggesting possible similarities to plant viruses of the family Geminiviridae, as well as raise questions about the documented plurality and diversity of anelloviruses.

In Vivo and In Vitro Intragenomic Rearrangement of TT Viruses

Deletion and recombination events between the DNA-A and DNA-B components of Indian cassava-infecting geminiviruses generate defective molecules in Nicotiana benthamiana.

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

Nitin Dutt

Author Tools

Chat about Author

Papers

Deletion and recombination events between the DNA-A and DNA-B components of Indian cassava-infecting geminiviruses generate defective molecules in Nicotiana benthamiana.