A multipartite single-stranded negative-sense RNA virus is the putative agent of fig mosaic disease

Abstract

Several dsRNA bands (approx. 0.6-7 kbp in size) were recovered from tissues of mosaicdiseased fig seedlings which contained the enveloped round structures known as double membrane bodies (DMBs). BLAST analysis of a 4353 and a 1120 nt sequence from the two largest RNA segments showed homology with the polymerase and the putative glycoprotein precursor genes of negative-sense single-stranded RNA viruses of the family Bunyaviridae. Negative-and positive-sense riboprobes designed from both RNA segments hybridized to two bands of approximately 7 and 2.3 kbp in Northern blots of dsRNAs. Thus, these segments were identified as putative RNA-1 and RNA-2 of a novel virus for which the name fig mosaic virus (FMV) is proposed. Identity levels of predicted amino acids of the protein encoded by FMV RNA-1 with those of species of the family Bunyaviridae and European mountain ash ringspot-associated virus (EMERaV) were 28 and 54 %, respectively. RNA-2 showed 38 % identity at the amino acid level only with EMARaV. RNA-1 segment contained five conserved motifs (A-E) and an endonucleolytic centre of comparable genes of L RNA of bunyaviruses and EMARaV RNA-1. In a phylogenetic tree constructed with RdRp sequences, EMARaV grouped with FMV in a clade distinct from those of all bunyavirus genera. The consistent association of DMBs with mosaic symptoms and the results of molecular investigations strongly indicate that DMBs are particles of FMV, the aetiological agent of fig mosaic disease.

Emaravirus-specific degenerate PCR primers allowed the identification of partial RNA-dependent RNA polymerase sequences of Maize red stripe virus and Pigeonpea sterility mosaic virus

“…Comparison of the nucleotides and predicted amino acid sequence of all RNA segments of Emaravirus-like viruses with their homologue showed that RNA1 is the most conserved segments among all others analyzed, for which that of FMV, EMARaV, RLBV, RRV and RYRV revealed the presence of five highly conserved regions denoted as motifs (A-E) in the RdRp gene, similarly to what has been previously reported with FMV and EMARaV by Elbeaino et al, (2009aElbeaino et al, ( , 2009b. Computer-assisted analysis showed that among all five analyzed regions, the pre-motif A, motifs A and C were the most conserved ones (data not shown) (Fig.…”

“…Leaf vein tissues (10 g) from infected plant materials were used to recover dsRNAs by phenol/chloroform extraction and chromatography through cellulose CF-11 column in the presence of 17% ethanol (Elbeaino et al, 2009a). Extracts were followed by selective digestion by DNase and RNase (Dodds, 1993).…”

“…The genus deems its' acronym to the European mountain ash ringspot-associated virus (EMARaV), firstly identified and is the type species of this genus, which has a genome composed of four RNA segments (Mielke and Muehlbach, 2007). Fig mosaic virus (FMV) is an another approved species (Adams and Carstens, 2012) of the recently established genus Emaravirus with a genome composed of six single-stranded negative-sense RNA that has recently been recognised as the causal agent of fig mosaic disease (FMD) (Elbeaino et al, 2009a;2009b. Intracellular DMBs were identified as particles of the putative causal agents of fig mosaic and of the ringspot disease of European mountain ash (Mielke and Muehlbach, 2007;Elbeaino et al, 2009a;2009b).…”

“…Fig mosaic virus (FMV) is an another approved species (Adams and Carstens, 2012) of the recently established genus Emaravirus with a genome composed of six single-stranded negative-sense RNA that has recently been recognised as the causal agent of fig mosaic disease (FMD) (Elbeaino et al, 2009a;2009b. Intracellular DMBs were identified as particles of the putative causal agents of fig mosaic and of the ringspot disease of European mountain ash (Mielke and Muehlbach, 2007;Elbeaino et al, 2009a;2009b). In addition, the same structures were also observed in infected cells of mosaic-diseased plants of pigeonpea (Cajanus cajan L.), maize (Zea mays L.) and wheat (Triticum aestivum L.), thought to be induced by Pigeonpea sterility mosaic virus (PPSMV) and Maize red stripe virus (MRSV) (Kumar et al, 2002;Ahn et al, 1998;Jensen et al, 1996).…”

“…Members of genus Emaravirus, an unassigned genus to any family of plant viruses, share some distant similarities with viruses belonging to the family Bunyaviridae and the genus Tenuivirus (Elbeaino et al, 2009a(Elbeaino et al, , 2009b. However, the number of genome segments (at least four) distinguishes the genus Emaravirus from bunyaviruses and sequence analyses do not allow classification within either the family Bunyaviridae or the genus Tenuivirus (Muehlbach and Mielke-Ehret, 2011).…”