Reassortment of infectious clones of radish mosaic virus shows that systemic necrosis in Nicotiana benthamiana is determined by RNA1

Authors: HU, WENXING - Chungnam National University; SEO, EUN-YOUNG - Chungnam National University; CHO, IN-SOOK - National Institute Of Horticultural & Herbal Science (NIHHS); KIM, JUNG-KYU - Chungnam National University; SONG, ZHENGXING - Chungnam National University; KIM, GANG-HEE - Chungnam National University; EOM, WON-SEOB - Chungnam National University; JUNG, SUNG-HOON - Chungnam National University; Hammond, John; LIM, HYOUN-SUB - Chungnam National University

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2021
Publication Date: 5/2/2022
Citation: Hu, W., Seo, E., Cho, I., Kim, J., Song, Z., Kim, G., Eom, W., Jung, S., Hammond, J., Lim, H. 2022. Reassortment of infectious clones of radish mosaic virus shows that systemic necrosis in Nicotiana benthamiana is determined by RNA1. Phytopathology. https://doi.org/10.1094/PHYTO-04-21-0172-R.
DOI: https://doi.org/10.1094/PHYTO-04-21-0172-R

Interpretive Summary: Virus infections cause reductions of yield and quality in many crops, while changes in climate and crop production practices may result in alterations in the distribution of viruses and their vectors. Radish (Raphanus sativus) is a major vegetable crop in Korea; radish mosaic virus (RaMV) infection of this crop in Korea was first reported on Jeju Island in 2009, and has since spread to mainland Korea, causing significant crop damage. ARS and Korean scientists collaborated to understand variation in the virus population and disease severity between isolates of RaMV from Jeju Island and mainland Korea. Three distinct isolates were used to examine differences in disease severity in radish, Chinese cabbage, and the model host Nicotiana benthamiana. Disease severity was shown to depend upon the isolate from which a particular region of the viral genome was derived. This caused either severe mosaic and necrosis in radish but relatively mild symptoms in the model host, or milder disease in radish and more severe disease in the model host. In contrast, symptoms in Chinese cabbage were similar for all three isolates. Further analysis of the new Korean isolates, and comparison to other isolates from the USA, Europe, Japan and Taiwan suggest that evolution of RaMV isolates occurs largely by exchange of genome segments between isolates. These findings may be useful to plant breeders to aid identification and breeding of varieties with resistance to RaMV infection.

Technical Abstract: Three infectious clones of radish mosaic virus (RaMV) were generated from isolates collected in mainland Korea (RaMV-Gg) and Jeju Island (RaMV-Aa and RaMV-Bb). These isolates differed in sequences and pathogenicity. Examination of the wildtype isolates and reassortants between the genomic RNA1 and RNA2 of these three isolates revealed that severe symptoms were associated with RNA1 of isolates Aa or Gg causing systemic necrosis in Nicotiana benthamiana, or with RNA1 of isolate Bb for induction of veinal necrosis and severe mosaic symptoms in radish. Sequence analysis and phylogenetic analysis including previously characterized isolates from the USA, Europe, Japan, and Taiwan suggest possible recombination within RNA1, while analysis of concatenated RNA1+RNA2 sequences indicates that reassortment of RNA1 and RNA2 has been more important in evolution of RaMV isolates than recombination. Korean isolate Aa is a potential reassortant between Japanese and Taiwanese isolates, while isolate Bb may have evolved from reassortment between American and Japanese isolates. The Korean isolates were shown to also be able to infect Chinese cabbage, raising concerns that RaMV may spread from radish fields to the Chinese cabbage crop in Korea, causing further economic losses.