Caulimoviridae (Plant Pararetroviruses)

Hull, Roger

doi:10.1002/9780470015902.a0000746.pub2

Cited by 7 publications

(6 citation statements)

References 29 publications

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“…observ.). This pattern is coherent with the one observed in the transmission and spread of viruses from families Potyviridae , Caulimoviridae and other plant infecting families that cause mosaic and breaking patterns in plants ( McKay and Warner 1933 ; McWhorter 1938 ; Andret-Link and Fuchs 2005 ; Hull 2007 ; Valverde et al 2012 ). Thus, in the present study, striped specimens of T. subg.…”

Section: Resultssupporting

confidence: 83%

WITHDRAWN: Wandering throughout South America: Taxonomic revision of Tradescantia subg. Austrotradescantia (D.R.Hunt) M.Pell. (Commelinaceae)

Moo

2018

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I present the first taxonomic revision for T. subg. Austrotradescantia, based on extensive field, cultivation and herbaria studies. I accept 13 species, three of them (i.e. T. atlantica, T. hertweckii and T. tucumanensis) being described as new in the present study. I provide an identification key to the species, distribution maps, descriptions, comments, conservation assessments and illustrations for all species. The troublesome weed T. fluminensis has its specific limits clarified and its native range is presented so it can serve as a basis to better understanding its ecological requirements and to help control it throughout its invasive range. Furthermore, I highlight that T. mundula, a commonly neglected species closely related to T. fluminensis, might also represent a troublesome weed. Tradescantia mundula has been widely introduced in cultivation under the name T. albiflora and seems to have also escaped from cultivation. However, due to the hitherto poorly understood specific limits of T. fluminensis, T. mundula has been treated as a mere cultivar of T. fluminensis s.s.

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Section: Resultssupporting

confidence: 83%

WITHDRAWN: Wandering throughout South America: Taxonomic revision of Tradescantia subg. Austrotradescantia (D.R.Hunt) M.Pell. (Commelinaceae)

Moo

2018

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“…Cauliflower mosaic virus (CaMV) and Rice tungro bacilliform virus (RTBV) belong to distinct genera of Caulimoviridae , Caulimovirus and Tungrovirus , which differ in host range, insect vector and virion architecture [56]. Both viruses have 8 kb circular dsDNA genome that replicates via reverse transcription of pregenomic (pg)RNA.…”

Section: Plant Viruses and The Pti- And Eti-based Defense Systemmentioning

confidence: 99%

“…Some pararetrovirus genera including Tungrovirus and Badnavirus do not possess a TAV homolog [56], suggesting that other viral protein(s) may have effector activity. Alternatively, these viruses employ a different strategy to evade silencing and innate immune responses.…”

Section: Rna Silencing-based Antiviral Defense and Viral Silencingmentioning

confidence: 99%

“…CaMV virions contain open-circular dsDNA with a gap in the minus strand marking the start of reverse transcription primed by Met-tRNA and two gaps in the plus strand marking initiation sites of plus strand DNA synthesis. At each replication cycle, virions release viral DNA into the nucleus where the gaps are repaired and the resulting covalently-closed dsDNA is transcribed by Pol II [56,57]. The 35S transcript covers the whole genome with a 200 nt terminal repeat.…”

Section: Rna Silencing-based Antiviral Defense and Viral Silencingmentioning

confidence: 99%

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Silencing and Innate Immunity in Plant Defense Against Viral and Non-Viral Pathogens

Zvereva

Pooggin

2012

Viruses

189

125

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The frontline of plant defense against non-viral pathogens such as bacteria, fungi and oomycetes is provided by transmembrane pattern recognition receptors that detect conserved pathogen-associated molecular patterns (PAMPs), leading to pattern-triggered immunity (PTI). To counteract this innate defense, pathogens deploy effector proteins with a primary function to suppress PTI. In specific cases, plants have evolved intracellular resistance (R) proteins detecting isolate-specific pathogen effectors, leading to effector-triggered immunity (ETI), an amplified version of PTI, often associated with hypersensitive response (HR) and programmed cell death (PCD). In the case of plant viruses, no conserved PAMP was identified so far and the primary plant defense is thought to be based mainly on RNA silencing, an evolutionary conserved, sequence-specific mechanism that regulates gene expression and chromatin states and represses invasive nucleic acids such as transposons. Endogenous silencing pathways generate 21-24 nt small (s)RNAs, miRNAs and short interfering (si)RNAs, that repress genes post-transcriptionally and/or transcriptionally. Four distinct Dicer-like (DCL) proteins, which normally produce endogenous miRNAs and siRNAs, all contribute to the biogenesis of viral siRNAs in infected plants. Growing evidence indicates that RNA silencing also contributes to plant defense against non-viral pathogens. Conversely, PTI-based innate responses may contribute to antiviral defense. Intracellular R proteins of the same NB-LRR family are able to recognize both non-viral effectors and avirulence (Avr) proteins of RNA viruses, and, as a result, trigger HR and PCD in virus-resistant hosts. In some cases, viral Avr proteins also function as silencing suppressors. We hypothesize that RNA silencing and innate immunity (PTI and ETI) function in concert to fight plant viruses. Viruses counteract this dual defense by effectors that suppress both PTI-/ETI-based innate responses and RNA silencing to establish successful infection.

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“…Based on the genome organization, protein functions, and other features, BSV is classified into genus Badnavirus (bacilliform DNA virus) of the family Caulimoviridae. This family comprises nine genera of plant pararetroviruses that replicate via reverse transcription of pregenomic RNA (pgRNA) and encapsidate open circular doublestranded (ds) genomic DNA into bacilliform or icosahedral virions (30,31). According to an interpretation based mostly on extensive studies of CaMV from genus Caulimovirus (31,32), the viral life cycle begins with a release of viral double-stranded DNA (dsDNA) from virions into the nucleus, where the gaps on both strands remaining after reverse transcription are repaired and the resulting covalently closed dsDNA associates with histones to form a minichromosome (episome).…”

mentioning

confidence: 99%

Evasion of Short Interfering RNA-Directed Antiviral Silencing in Musa acuminata Persistently Infected with Six Distinct Banana Streak Pararetroviruses

Rajeswaran

Séguin

Chabannes

et al. 2014

J Virol

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Vegetatively propagated crop plants often suffer from infections with persistent RNA and DNA viruses. Such viruses appear to evade the plant defenses that normally restrict viral replication and spread. The major antiviral defense mechanism is based on RNA silencing generating viral short interfering RNAs (siRNAs) that can potentially repress viral genes posttranscriptionally through RNA cleavage and transcriptionally through DNA cytosine methylation. Here we examined the RNA silencing machinery of banana plants persistently infected with six pararetroviruses after many years of vegetative propagation. Using deep sequencing, we reconstructed consensus master genomes of the viruses and characterized virus-derived and endogenous small RNAs. Consistent with the presence of endogenous siRNAs that can potentially establish and maintain DNA methylation, the banana genomic DNA was extensively methylated in both healthy and virus-infected plants. A novel class of abundant 20-nucleotide (nt) endogenous small RNAs with 5=-terminal guanosine was identified. In all virus-infected plants, 21-to 24-nt viral siRNAs accumulated at relatively high levels (up to 22% of the total small RNA population) and covered the entire circular viral DNA genomes in both orientations. The hotspots of 21-nt and 22-nt siRNAs occurred within open reading frame (ORF) I and II and the 5= portion of ORF III, while 24-nt siRNAs were more evenly distributed along the viral genome. Despite the presence of abundant viral siRNAs of different size classes, the viral DNA was largely free of cytosine methylation. Thus, the virus is able to evade siRNA-directed DNA methylation and thereby avoid transcriptional silencing. This evasion of silencing likely contributes to the persistence of pararetroviruses in banana plants. IMPORTANCEWe report that DNA pararetroviruses in Musa acuminata banana plants are able to evade DNA cytosine methylation and transcriptional gene silencing, despite being targeted by the host silencing machinery generating abundant 21-to 24-nucleotide short interfering RNAs. At the same time, the banana genomic DNA is extensively methylated in both healthy and virus-infected plants. Our findings shed light on the siRNA-generating gene silencing machinery of banana and provide a possible explanation why episomal pararetroviruses can persist in plants whereas true retroviruses with an obligatory genome-integration step in their replication cycle do not exist in plants. V iruses are often described as causing acute and persistent infections: acute virus infections cause severe disease symptoms and, in many cases, kill the host plant, whereas persistent virus infections normally cause mild symptoms and allow the host to recover from the disease; persistent virus infections can sometimes be beneficial for plant physiology (1). Depending on the environmental conditions and host plant species, the viral disease symptoms can oscillate from severe to nonvisible (recovery) and back. The molecular mechanisms underlying such oscillations in pers...

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Caulimoviridae (Plant Pararetroviruses)

Cited by 7 publications

References 29 publications

WITHDRAWN: Wandering throughout South America: Taxonomic revision of Tradescantia subg. Austrotradescantia (D.R.Hunt) M.Pell. (Commelinaceae)

WITHDRAWN: Wandering throughout South America: Taxonomic revision of Tradescantia subg. Austrotradescantia (D.R.Hunt) M.Pell. (Commelinaceae)

Silencing and Innate Immunity in Plant Defense Against Viral and Non-Viral Pathogens

Evasion of Short Interfering RNA-Directed Antiviral Silencing in Musa acuminata Persistently Infected with Six Distinct Banana Streak Pararetroviruses

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