Polycipiviridae: a proposed new family of polycistronic picorna-like RNA viruses

Solenopsis invicta virus 2 is a single-stranded positive-sense picorna-like RNA virus with an unusual genome structure. The monopartite genome of approximately 11 kb contains four open reading frames in its 5′ one third, three of which encode proteins with homology to picornavirus-like jelly-roll fold capsid proteins. These are followed by an intergenic region, and then a single long open reading frame that covers the 3′ two thirds of the genome. The polypeptide translation of this 3′ open reading frame contains motifs characteristic of picornavirus-like helicase, protease and RNA-dependent RNA polymerase domains. Inspection of public transcriptome shotgun assembly sequences revealed five related apparently nearly complete virus genomes isolated from ant species and one from a dipteran insect. By high-throughput sequencing and in silico assembly of RNA isolated from Solenopsis invicta and four other ant species, followed by targeted Sanger sequencing, we obtained nearly complete genomes for four further viruses in the group. Four further sequences were obtained from a recent large-scale invertebrate virus study. The 15 sequences are highly divergent (pairwise amino acid identities as low as 17% in the non-structural polyprotein), but possess the same overall polycistronic genome structure distinct from all other characterized picorna-like viruses. Consequently we propose the formation of a new virus family, Polycipiviridae, to classify this clade of arthropod-infecting polycistronic picorna-like viruses. We further propose that this family be divided into three genera: Chipolycivirus (2 species), Hupolycivirus (2 species), and Sopolycivirus (11 species), with members of the latter infecting ants in at least three different subfamilies.This work was supported by a Wellcome Trust grant [106207] and a European Research Council (ERC) European Union's Horizon 2020 research and innovation programme grant [646891] to A.E.F

The coat protein of Alfalfa mosaic virus interacts and interferes with the transcriptional activity of the bHLH transcription factor ILR3 promoting salicylic acid-dependent defence signalling response

[EN] During virus infection, specific viral component-host factor interaction elicits the transcriptional reprogramming of diverse cellular pathways. Alfalfa mosaic virus (AMV) can establish a compatible interaction in tobacco and Arabidopsis hosts. We show that the coat protein (CP) of AMV interacts directly with transcription factor (TF) ILR3 of both species. ILR3 is a basic helix-loop-helix (bHLH) family member of TFs, previously proposed to participate in diverse metabolic pathways. ILR3 has been shown to regulate NEET in Arabidopsis, a critical protein in plant development, senescence, iron metabolism and reactive oxygen species (ROS) homeostasis. We show that the AMV CP-ILR3 interaction causes a fraction of this TF to relocate from the nucleus to the nucleolus. ROS, pathogenesis-related protein 1 (PR1) mRNAs, salicylic acid (SA) and jasmonic acid (JA) contents are increased in healthy Arabidopsis loss-of-function ILR3 mutant (ilr3.2) plants, which implicates ILR3 in the regulation of plant defence responses. In AMV-infected wild-type (wt) plants, NEET expression is reduced slightly, but is induced significantly in ilr3.2 mutant plants. Furthermore, the accumulation of SA and JA is induced in Arabidopsis wt-infected plants. AMV infection in ilr3.2 plants increases JA by over 10-fold, and SA is reduced significantly, indicating an antagonist crosstalk effect. The accumulation levels of viral RNAs are decreased significantly in ilr3.2 mutants, but the virus can still systemically invade the plant. The AMV CP-ILR3 interaction may down-regulate a host factor, NEET, leading to the activation of plant hormone responses to obtain a hormonal equilibrium state, where infection remains at a level that does not affect plant viability.F.A. was the recipient of a contract Ramon y Cajal (RYC-2010-06169) program of the Ministerio de Educacion, Cultura y Deporte of Spain. We thank L. Corachan for excellent technical assistance. This work was supported by Grants BIO2014-54862-R from the Spanish grant agency Direccion General de Investigacion Cientifica y Tecnica (DGICT) the Prometeo Program GV2015/010 from the Generalitat Valenciana and PAID-06-10-1496 from the Universitat Politecnica de Valencia (Spain).Aparicio Herrero, F.; Pallás Benet, V. (2017). The coat protein of Alfalfa mosaic virus interacts and interferes with the transcriptional activity of the bHLH transcription factor ILR3 promoting salicylic acid-dependent defence signalling response. 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