imported>Lcovelli at 12:00, 15 March 2010

2010-03-15T12:00:18Z

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{{Element
|genbank=[http://www.ncbi.nlm.nih.gov/entrez/viewer.fcgi?db=nucleotide&val=3183634 3183634]
|type=
|genus= Badnavirus
|subfamily= Class 2
|family= Caulimoviridae
|group= LTR retroelements
|description=''Banana streak virus'' (BSV), the causal agent of viral "leaf streak disease" of banana and plantain (''Musa'' spp.) ([[Literature:100630|Lockhart, 1986]]), is a member of the plant pararetrovirus genus ''Badnavirus'' of [[Caulimoviridae|''Caulimoviridae'']] family (''International Committee on the Taxonomy of Viruses'' -ICTV- [[Literature:100589|Fauquet ''et al''. 2005]]). Several isolated have been studied, one of which is BSOLV infecting a triploid plantain cultivar “Obino L'Ewai” (used as the female parent in the production of improved tetraploid hybrids, [[Literature:100632|Harper and Hull 1998]]). According to [[Literature:100596|Llorens ''et al''. 2009]], BSOLV belongs to ''Badnavirus'' genus within Class 2 of the ''Caulimoviridae'' family.

The analyzed BSOLV (Nigerian isolate) has bacilliform particles of 30 x 150 nm in size containing a circular double-stranded DNA genome of about 7.3 kb in size (7389 bp long) which three Open reading frames (ORFs I, II, III) potentially coding for proteins ([[Literature:100632|Harper and Hull 1998]]). The first two ORFs encode two small proteins: the ORF I-product reveals sequence similarity to the virion associated protein (VAP) present in mainly of caulimoviruses, while the function of ORF II is not yet well known. The third large ORF III encodes a polyprotein containing regions with homologies to a movement protein, a ''gag''-RNA binding domain, to an aspartic protease (AP), reverse transcriptase (RT) and RNase H (RH) domains typical of the badnavirus species ([[Literature:100632|Harper and Hull 1998]]). The plant pararetrovirus consensus RNA-binding sequence associated to the putative ''gag'' region is larger than the related retroelement consensus RNA-binding sequence (C-X2-C-X4-H-X4-C) as it includes a large region rich in zinc finger (CCHC) array duplications (only preserved in Badna and Tungroviruses) similarly to those of several LTR retroelement nucleocapsids ([[Literature:100605|Hull 1996]]; [[Literature:8054|Bouhida ''et al.'' 1993]]; [[Literature:100596|Llorens ''et al''. 2009]]).

The viral "leaf streak disease" was first described in Ivory Coast, Africa in 1968 ([[Literature:100631|Lassoudiere 1974]]), but now is probably distributed worldwide in cultivated banana and plantain crops. The symptomatology is correlated with variations in virus concentration. The symptoms may vary from faint broken chlorotic lines to necrosis of young leaves, internal necrosis of the pseudostem and plant death. The bunch size and fruit quality are also compromised ([[Literature:100630|Lockhart, 1986]]). The virus is transmitted naturally by the two mealybug vectors (''Pseudococcidae'') ''Planococcus citri'' and ''Saccharicoccus sacchari'' (both of which colonize banana), as well as by seed, even if the vegetative propagation is the principal method of virus spread.

Unlike the petuvirus ''Petunia vein clearing virus'' (PVCV, [[Literature:63308|Richert-Pöggeler and Shepherd 1997]]), no obvious integrase motif could be identified in the BSV sequence ([[Literature:100632|Harper and Hull 1998]]). However, multiple BSV-DNAs were found to be integrated into the nuclear genome of the cultivar (cv) Obino l’Ewaï ([[Literature:100635|Harper ''et al.'' 1999]]; [[Literature:100633|Geering ''et al.'' 2005]]) as well as in that of other ''Musa'' cvv. ([[Literature:100608|Ndowora ''et al.'' 1999]]; [[Literature:100635|Harper ''et al.'' 1999]]; [[Literature:89695|Gayral ''et al.'' 2008]]; [[Literature:89696|Gayral and Iskra-Caruana 2009]]). Two types of BSV-Endogenous pararetrovirus (EPRVs) sequences have been described in banana. The first type sequences, defined as noninfectious (with nonfunctional viral ORFs and/or incomplete viral genomes), are present in the two most common ''Musa'' species ''Musa acuminata'' (denoted A) and ''Musa balbisiana'' (denoted B) that, together to ''Musa schizocarpa'' (denoted S) are the wild progenitors of the domesticated banana ([[Literature:100633| Geering ''et al.'' 2005]]). The second EPRV sequences, so-called infectious type, contain the complete functional viral genome and have been detected in some ''Musa'' genotypes (i.e AAB and BB groups, [[Literature:100633| Geering ''et al.'' 2005]] ; [[Literature:89695|Gayral ''et al.'' 2008]]).
In particular, the BSOLV-integrant sequence appeared particularly complex: it consists of two segments (which together constitute the full complement of the virus genome) separated by a "scrambled region" containing non-contiguous and inverted viral sequences ([[Literature:100608|Ndowora ''et al.'' 1999]]; [[Literature:100633| Geering ''et al.'' 2005]]).
Interestingly, the absence of episomal BSV in the "mother plants" before the tissue culture procedure and the presence of viral sequences into the propagated material strongly suggest for an integrated origin of the episomal forms detected during the proliferation stage ([[Literature:100634|Dallot ''et al.'' 2001]]; [[Literature:89695|Gayral ''et al.'' 2008]]). Indeed, it has been demonstrated that ''in vitro'' micropropagation procedure could play a possible effect on BSV expression in healthy plants (episomal BSV-free) carrying EPRV sequences and that the proliferation stage is clearly determinant in the appearance of episomal BSV ([[Literature:100634|Dallot ''et al.'' 2001]]).
The high degree of sequence conservation between the integrated and episomal form of the virus indicates a recent integration event ([[Literature:89695|Gayral ''et al.'' 2008]]). Moreover, recent independent integration events occurred after the divergence of the three banana species (A, B and S), also indicate that viral integration is a recent and frequent phenomenon [[Literature:89696|Gayral and Iskra-Caruana 2009]]).
|structure=BSOLV.png
|host=Musa sp
|hostpic=Musa_sp.gif
|literature=
|picowner=[http://www.biotechvana.com Image, Carlos Llorens, Copyright, GyDB, Biotech Vana]
}}
[[Category:Element]]

Element:BSOLV - Revision history

imported>Lcovelli at 12:00, 15 March 2010