Evaluation of a series of turnip mosaic virus (TuMV) chimeric clones reveals two amino acid sites critical for systemic infection in Chinese cabbage

Authors: SONG, ZHENGXING - Chungnam National University; HU, WEN-XING - Chungnam National University; SEO, EUN-YOUNG - Chungnam National University; KIM, JUNG-KYU - Chungnam National University; KANG, JUN-SEONG - Chungnam National University; Hammond, John; LIM, HYOUN-SUB - Chungnam National University

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2023
Publication Date: 6/1/2023
Citation: Song, Z., Hu, W., Seo, E., Kim, J., Kang, J., Hammond, J., Lim, H. 2023. Evaluation of a series of turnip mosaic virus (TuMV) chimeric clones reveals two amino acid sites critical for systemic infection in Chinese cabbage. Phytopathology. https://doi.org/10.1094/PHYTO-01-23-0013-R.
DOI: https://doi.org/10.1094/PHYTO-01-23-0013-R

Interpretive Summary: Plant virus infections commonly cause losses of both yield and quality in commercial crops, and the best means of avoiding such losses is to avoid the introduction of the virus to the crop, preferably through the utilization of virus-resistant cultivars. However, many crop varieties lack effective virus resistance genes, and sources of resistance must be identified to aid selection of future virus-resistant crop varieties. Turnip mosaic virus causes economic damage to many vegetable crops, including Chinese cabbage. Scientists at Chungnam National University in Korea identified two isolates of turnip mosaic virus that differed in their ability to infect four Korean varieties of Chinese cabbage, and the viral determinants responsible for overcoming the host plant resistance were identified. Two of the Chinese cabbage varieties showed increased resistance to infection by the virus. In addition, two variants of the virus were identified which can be used to screen additional breeding lines of Chinese cabbage to aid selection of other virus-resistant cultivars. These results will be of value to plant breeders and to plant pathologists studying mechanisms of plant virus resistance.

Technical Abstract: In this study, two TuMV infectious clones with differential infectivity in Chinese cabbage (Brassica rapa subsp. pekinensis) were obtained. Both infected Nicotiana benthamiana systemically and induced similar symptoms, whereas only KBC-8 infected Chinese cabbage systemically. To identify the determinants affecting infectivity on Chinese cabbage, chimeric clones were constructed by restriction fragment exchange, and tested on several Chinese cabbage cultivars. Chimeric clones 1N8C and 8N1C demonstrated that the C-terminal portion of the polyprotein determines systemic infection of Chinese cabbage despite only three amino acid differences in this region, located in the cylindrical inclusion (CI), viral protein genome-linked (VPg) and coat protein (CP), respectively. Both of a second pair of hybrid constructs, HindIII-1N8C and HindIII-8N1C, failed to infect cultivars CR Victory and Jinseonnorang systemically, yet HindIII-1N8C caused HR-like lesions on the local leaves of these cultivars, and could systemically infect cultivars CR Chusarang and Jeongsang;, this indicates that R genes effective against TuMV may exist in the first two cultivars but not the latter two. All constructs with single amino acid changes in both VPg (K2045E) and CP (Y3095H) failed to infect Chinese cabbage, which implies that at least one of these two amino acid substitutions is essential for the successful infection on Chinese cabbage. Successful infection by mutant KBC-8-CP-H and no infection with mutant HJY1-VPg-E suggested that VPg (2045K) is the residue required for infection of Chinese cabbage, and likely involved in the interaction between VPg and the eukaryotic initiation factor eIF(iso)4E, confirmed by yeast two-hybrid assay.