Length of poly(A) tail affects transcript infectivity of three ZYMV symptom variants differing at only five amino acid positions

Authors: KIM, BORAM - Chungnam National University; CHO, IN-SOOK - Rural Development Administration - Korea; KIM, IK-HYUN - Chungnam National University; CHOI, GOWOON - Chungnam National University; JU, HYEKYUNG - Chungnam National University; HU, WEN-XING - Chungnam National University; OH, JUNPYO - Chungnam National University; KIM, JUNG-KYU - Chungnam National University; SEO, EUNYOUNG - Chungnam National University; Domier, Leslie; Hammond, John; LIM, HYOUN-SUB - Chungnam National University

Submitted to: Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2019
Publication Date: 5/24/2019
Citation: Kim, B., Cho, I., Kim, I., Choi, G., Ju, H., Hu, W., Oh, J., Kim, J., Seo, E., Domier, L.L., Hammond, J., Lim, H. 2019. Length of poly(A) tail affects transcript infectivity of three ZYMV symptom variants differing at only five amino acid positions. Journal of Plant Pathology. 101:1187-1193. https://doi.org/10.1007/s42161-019-00316-4.
DOI: https://doi.org/10.1007/s42161-019-00316-4

Interpretive Summary: Plant viruses cause reductions in yield and quality in many crops and may be spread within the crop by horticultural operations, or by insects or other vectors. New virus isolates may arise by mutation, or by movement into the crop from external sources, often resulting from long-distance movement by windblown insect vectors, or via seed transmission. Several viruses affecting crops in both China and Korea are spread both by insect vectors and seed transmission. Three new isolates of Zucchini mosaic virus, an important virus causing losses in cucurbit crops, were obtained from zucchini crops in Korea and shown to differ in pathogenicity. Molecular analysis indicated that these isolates differed by only five amino acids located within four distinct genes. A new method of establishing infection in zucchini was demonstrated, paving the way for utilizing molecules from these isolates to screen multiple zucchini and other cucurbit varieties for resistance to infection, and to determine the contribution of each of the variant amino acids towards symptom differences and pathogenicity.

Technical Abstract: Cucurbitaceous vegetables are very important sources of dietary nutrients in Korea. The incidence of plant virus diseases infecting cucurbitaceous vegetables has increased in Korea as new isolates have been introduced, associated with warming temperatures and vector movement caused by climate change. To develop new tools to study viral disease in cucurbitaceous vegetables, we investigated zucchini yellow mosaic virus (ZYMV) isolates in Korea and developed methods to inoculate the model plant Nicotiana benthamiana with ZYMV expressed from a binary vector including both the 35S and T7 promoters. For this purpose, we identified three new ZYMV isolates and generated full-length infectious clones downstream of either T7, or 35S and T7 promoters. Sequence analysis indicated three isolates, BR1(MH042024), BR2(MH042025), and BR3(MH042026), which are all closely related to ZYMV isolates recently reported from Spain. The nucleotide sequences of the three isolates showed 99% pair-wise identity and differed at only five amino acid positions located in HC-Pro, CI, 6K2, and NIb. In vitro RNA transcripts from the three full-length cDNAs were infectious in presence of 60 nt, but not 30 nt, poly(A) tails. As an alternative to in vitro transcription, N benthamiana leaves were sucessfully inoculated with ZYMV full-length clones by agroinfiltration. Even though ZYMV did not move systemically in N. benthamiana, sap from agroinfiltrated leaves could be used as inoculum for cucurbitaceous vegetables.