First Report of Perilla Mosaic Emaravirus Infecting Perilla frutescens in South Korea

Abstract

Perilla mosaic virus (PerMV; the genus Emaravirus in the family Fimoviridae) has a multiple, negative-sense, single-stranded RNA genome (ICTV, 2018). PerMV has been reported in Japan, where it was transmitted by an eriophyid mite species (Acari: Eriophyidae) to Perilla frutescens (L.) Britton var. crispa (Kubota et al., 2020). In September 2021, typical symptoms of the virus including yellow flecks, mosaic symptoms, and malformation were observed in leaves of P. frutescens in a cultivated field in Iseo-myeon, Wanju, South Korea (Suppl. Fig. 1). Visual estimates indicated that symptom incidence reached 70%, and the top leaves of perilla plants exhibited more severe symptoms and leaf distortion. To identify the virus species accurately, total RNA was extracted from five symptomatic perilla leaves collected using the RNeasy Plant Mini Kit (Qiagen, Hilden, Germany) then cDNAs were amplified by reverse-transcription polymerase chain reaction (RT-PCR) using two pairs of primers to PerMV specific primer set designed to amplify 412- and 491-bp cDNAs of the nucleocapsid protein gene RNA 3 and movement protein gene RNA 4, respectively (Suppl. Table). Single-infection of PerMV in symptomatic Korean perilla plants was confirmed by high-throughput sequence (HTS) analysis and de novo transcriptome assembly using the Illumina HiSeq 4000 platform (Macrogen Inc., Seoul, Korea). The assembled sequences were aligned with viral reference genomes through searches performed using the BLASTn tool. Seven contigs (597–7,213 bp) revealed 92.09–97.37% nucleotide homology with RNAs of the isolate PerMV_Kochi_Nankoku_2011 (accession numbers LC496090 to LC496099) in the GenBank database. Other viruses including turnip mosaic virus and cucumber green mottle mosaic virus were not identified by HTS analysis (Cho et al., 2021; Park et al., 2020; Song et al., 2022). Seven RNA genomes of PerMV were confirmed by RT-PCR using specific primer sets designed to amplify part of each genome (Suppl. Table 1 and Fig. 2). The complete nucleotide sequences of PerMV (named IS isolate) RNA 1–7 were determined to be 7,177, 2,089, 1,094, 1,302, 1,079, 1,098, and 995 bp in length, respectively; these were deposited in GenBank (LC721296–LC721303). Sap from a symptomatic leaf sample confirmed for single infection was inoculated mechanically onto the leaves of 10 healthy P. frutescens seedlings, which developed the same PerMV symptoms within 3 weeks. These results indicate that PerMV is the causal agent of viral disease in Korean perilla plants cultivated in South Korea. To our knowledge, this is the first report of a perilla mosaic emaravirus infecting to Korean perilla, P. frutescens in South Korea.