Construction of an Agroinfectious Clone of a Korean Isolate of Sweet Potato Symptomless Virus 1 and Comparison of Its Infectivity According to Agrobacterium tumefaciens Strains in Nicotiana benthamiana

Sweet potato symptomless virus 1 (SPSMV-1) is a single-stranded circular DNA virus, belonging to the genus Mastrevirus (family Geminiviridae) that was first identified on sweet potato plants in South Korea in 2012. Although SPSMV-1 does not induce distinct symptoms in sweet potato plants, its co-infection with different sweet potato viruses is highly prevalent, and thus threatens sweet potato production in South Korea. In this study, the complete genome sequence of a Korean isolate of SPSMV-1 was obtained by Sanger sequencing of polymerase chain reaction (PCR) amplicons from sweet potato plants collected in the field (Suwon). An infectious clone of SPSMV-1 (1.1-mer) was constructed, cloned into the plant expression vector pCAMBIA1303, and agro-inoculated into Nicotiana benthamiana using three Agrobacterium tumefaciens strains (GV3101, LBA4404, and EHA105). Although no visual differences were observed between the mock and infected groups, SPSMV-1 accumulation was detected in the roots, stems, and newly produced leaves through PCR. The A. tumefaciens strain LBA4404 was the most effective at transferring the SPSMV-1 genome to N. benthamiana. We confirmed the viral replication in N. benthamiana samples through strand-specific amplification using virion-sense- and complementary-sense-specific primer sets.