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First Report of Bean common mosaic virus in Cudrania tricuspidata in Korea

Cudrania tricuspidata (Moraceae) is a deciduous tree widely distributed in East Asia, including China, Korea, and Japan. It produces delicious fruit, and its cortex and root bark have been used as a traditional medicine to treat neuritis and inflammation. As C. tricuspidata has become known as a functional food, its cultivation area and production gradually have increased in Korea. However, information of viral disease in C. tricuspidata is very limited. In September 2012, open-field-grown C. tricuspidata trees showing virus-like symptoms of mosaic, yellowing, and distortion on the leaves were found in Naju, Korea. The fruit production in the diseased trees decreased to 20 to 40% of that in healthy trees. To identify causal agent(s), total RNA was isolated from the symptomatic leaves and used to generate a transcriptome library using the TruSeq Stranded Total RNA with Ribo-Zero Plant kit (Illumina, San Diego, CA) according to the manufacturer's instruction. The transcriptome library was analyzed by next-generation sequencing (NGS) using an Illumina HiSeq2000 sequencer. NGS reads were quality filtered and de novo assembled by the Trinity pipeline, and the assembled contigs were analyzed against the viral reference genome database in Genbank by BLASTn and BLASTx searches (3). The entire NGS procedure was perofrmed by Macrogen Inc. (Seoul, South Korea). Among the analyzed contigs, one large contig (10,043 bp) was of viral origin. Nucleotide blast searches showed that the contig has a maximum identity of 89% (with 100% coverage) to the isolate MS1 (Genbank Accession No. EU761198) of Bean common mosaic virus (BCMV), which was isolated from Macroptilium atropurpureum in Australia. The presence of BCMV was confirmed by a commercially available double-antibody sandwich (DAS)-ELISA kit (Agdia, Elkhart, IN). To confirm the BCMV sequence obtained by NGS, two large fragments covering the entire BCMV genome were amplified by reverse transcription-polymerase chain reaction (RT-PCR) using two sets of specific primers (5′-AAAATAAAACAACTCATAAAGACAAC-3′ and 5′-AGACTGTGTCCCAGAGCATTTC-3′ to amplify the 5′ half of the BCMV genome; 5′-GCATCCTGAGATTCACAGAATTC-3′ and 5′-GGAACAACAAACATTGCCGTAG-3′ to amplify the 3′ half of the BCMV genome) and sequenced. To obtain the complete genome sequence, the 5′ and 3′ terminal sequences were analyzed by the 5′ and 3′ rapid amplification of cDNA ends (RACE) method as described previously (1). The assembled full-length sequence of BCMV isolated from C. tricuspidata was 10,051 nucleotides in length without a poly(A) tail. It was deposited in Genbank under the accession number KM076650. BCMV, a member of the genus Potyvirus, is one of the most common viruses naturally infecting legumes, including Phaseolus vulgaris (2). In general, BCMV is known to have a restricted host range outside legume species (2). Therefore, the identification of BCMV from C. tricuspidata in this report is very exceptional. Because BCMV is easily transmitted by various aphids like other potyviruses, a large-scale survey may be required for exact investigation of the BCMV incidence in C. tricuspidata to prevent rapid spread of the virus. To the best of our knowledge, this is the first report of BCMV in C. tricuspidata.

References: (1) H.-R. Kwak et al. Plant Pathol. J. 29:274, 2013. (2) M. Saiz et al. Virus Res. 31:39, 1994. (3) S.-E. Schelhorn et al. PLoS Comput. Biol. 9:e1003228, 2013.