Abstract
Background Arctium species (Asteraceae) are distributed worldwide and are used as food and rich sources of secondary metabolites for the pharmaceutical industry, e.g., against avian influenza virus. RNA silencing is an antiviral defense mechanism that detects and destroys virus-derived double-stranded RNA, resulting in accumulation of virus-derived small RNAs (21–24 nucleotides) that can be used for generic detection of viruses by small-RNA deep sequencing (SRDS).Methodology/Principal FindingsSRDS was used to detect viruses in the biennial wild plant species Arctium tomentosum (woolly burdock; family Asteraceae) displaying virus-like symptoms of vein yellowing and leaf mosaic in southern Finland. Assembly of the small-RNA reads resulted in contigs homologous to Alstroemeria virus X (AlsVX), a positive/single-stranded RNA virus of genus Potexvirus (family Alphaflexiviridae), or related to negative/single-stranded RNA viruses of the genus Emaravirus. The coat protein gene of AlsVX was 81% and 89% identical to the two AlsVX isolates from Japan and Norway, respectively. The deduced, partial nucleocapsid protein amino acid sequence of the emara-like virus was only 78% or less identical to reported emaraviruses and showed no variability among the virus isolates characterized. This virus—tentatively named as Woolly burdock yellow vein virus—was exclusively associated with yellow vein and leaf mosaic symptoms in woolly burdock, whereas AlsVX was detected in only one of the 52 plants tested.Conclusions/SignificanceThese results provide novel information about natural virus infections in Acrtium species and reveal woolly burdock as the first natural host of AlsVX besides Alstroemeria (family Alstroemeriaceae). Results also revealed a new virus related to the recently emerged Emaravirus genus and demonstrated applicability of SRDS to detect negative-strand RNA viruses. SRDS potentiates virus surveys of wild plants, a research area underrepresented in plant virology, and helps reveal natural reservoirs of viruses that cause yield losses in cultivated plants.
Highlights
Viruses occurring in communities of non-cultivated plants have gained limited attention as compared to those causing significant yield losses in cultivated plants [1]
When subjected to Basic Local Alignment Search Tool (BLAST), many contigs showed high identity to FMV, Fig mosaic-associated virus (FMAV), and European mountain ash ringspot-associated virus (EMARAV) representing multipartite, negative-strand single-stranded RNA (ssRNA) [(2)ssRNA] viruses that belong to the genus Emaravirus [35]
The greatest number of virus-derived siRNAs (vsiRNAs) mapped to the Alstroemeria virus X (AlsVX) genome regardless of vsiRNA length, and 37% of the genome sequence of AlsVX [31] was covered
Summary
Viruses occurring in communities of non-cultivated plants have gained limited attention as compared to those causing significant yield losses in cultivated plants [1]. Perennial and biennial plant species are potent virus reservoirs because they maintain viruses from one growing season to the next. Worldwide transport of cultivated plants can disseminate viruses over long distances [2,3] and causes a risk of introduction of viruses to new areas where some local wild species may become infected and serve as new virus reservoirs. Tens of native perennial or biennial wild species of genus Ipomoea (family Convolvulaceae) occur in Uganda where they are infected with the same viruses and virus strains as the cultivated sweetpotato (Ipomoea batatas Lam.) believed to have originated in Latin America. (family Fabaceae) is a virus reservoir with demonstrated potential to act as a source of virus infection of the cultivated legume Lupinus angustifolius L. RNA silencing is an antiviral defense mechanism that detects and destroys virus-derived double-stranded RNA, resulting in accumulation of virus-derived small RNAs (21–24 nucleotides) that can be used for generic detection of viruses by small-RNA deep sequencing (SRDS)
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