High-throughput RNA sequencing analysis of Mallotus japonicus revealed novel polerovirus and amalgavirus.

High-throughput RNA sequencing (RNA-seq) analysis of samples from Mallotus japonicus, a traditional medicinal plant, yielded two novel RNA viruses tentatively named Mallotus japonicus virus A (MjVA) and Mallotus japonicus virus B (MjVB). The MjVA and MjVB genomes encode proteins showing amino acid sequence similarities to those of poleroviruses (the genus Polerovirus, the family Solemoviridae) and amalgaviruses (the genus Amalgavirus, the family Amalgaviridae), respectively. The MjVA genome contains seven highly overlapping open reading frames, which are translated to seven proteins through various translational mechanisms, including -1 programmed ribosomal frameshifting (PRF) at the slippery motif GGGAAAC, non-AUG translational initiation, and stop codon readthrough. The MjVB genome encodes two proteins; one of which is translated by +1 PRF mechanism at the slippery motif UUUCGN. The abundance analysis of virus-derived RNA fragments revealed that MjVA is highly concentrated in plant parts with well-developed phloem tissues as previously demonstrated in other poleroviruses, which are transmitted by phloem feeders, such as aphids. MjVB, an amalgavirus generally transmitted by seeds, is distributed in all samples at low concentrations. Thus, this study demonstrates the effectiveness and usefulness of RNA-seq analysis of plant samples for the identification of novel RNA viruses and analysis of their tissue distribution. Keywords: Polerovirus; Amalgavirus; Mallotus japonicus; RNA virus; viral genome; programmed ribosomal frameshifting.