Dual resistance of transgenic plants against Cymbidium mosaic virus and Odontoglossum ringspot virus

Ting-Yu Chen,Yau-Heiu Hsu,Shu-Chuan Lee,Tzu-Tung Lin,Fu-Chen Hsu,Na-Sheng Lin,Chih-Hao Chang,Liang-Yu Hou,Hsuan Pai

doi:10.1038/s41598-019-46695-7

Abstract

Taxonomically distinct Cymbidium mosaic potexvirus (CymMV) and Odontoglossum ringspot tobamovirus (ORSV) are two of the most prevalent viruses worldwide; when co-infecting orchids, they cause synergistic symptoms. Because of the huge economic loss in quality and quantity in the orchid industry with virus-infected orchids, virus-resistant orchids are urgently needed. To date, no transgenic resistant lines against these two viruses have been reported. In this study, we generated transgenic Nicotiana benthamiana expressing various constructs of partial CymMV and ORSV genomes. Several transgenic lines grew normally and remained symptomless after mixed inoculation with CymMV and ORSV. The replication of CymMV and ORSV was approximately 70–90% lower in protoplasts of transgenic lines than wild-type (WT) plants. Of note, we detected extremely low or no viral RNA or capsid protein of CymMV and ORSV in systemic leaves of transgenic lines after co-infection. Grafting experiments further revealed that CymMV and ORSV trafficked extremely inefficiently from co-infected WT stocks to transgenic scions, presumably due to RNA-mediated interference. This study reports the first successful creation of dual resistant transgenic lines against CymMV and ORSV. Our studies shed light on the commercial development of transgenic orchid production to combat the global viral threat.

Highlights

The Orchidaceae is the largest and most diverse family of flowering plants, about 28,000 species, distributed in about 763 genera[1]
Given that the accumulation of Cymbidium mosaic potexvirus (CymMV) and Odontoglossum ringspot tobamovirus (ORSV) in protoplasts and inoculated leaves (IL) was significantly lower in resistant transgenic lines than WT plants and almost no virus was detectable in systemic leaves (SL) of transgenic lines (Table 1 and Fig. S1), we considered that viral trafficking may be limited in transgenic lines
More resistant lines against the two viruses were generated from transgenic lines with the pH7W-COCP transgene (Fig. 1B,C), which has a hairpin structure containing the full-length capsid protein (CP) genes of CymMV and ORSV under control of the 35S promoter

Summary

Introduction

The Orchidaceae is the largest and most diverse family of flowering plants, about 28,000 species, distributed in about 763 genera[1]. Orchids are susceptible to virus infection; at least 50 different viruses have been reported[2]. Cymbidium mosaic virus (CymMV) and Odontoglossum ringspot virus (ORSV) are the two most prevalent and economically important viruses affecting orchids worldwide[2]. Mixed infection with CymMV and ORSV commonly occurs worldwide and induces synergistic severe symptoms, including necrotic ringspots in leaves and mottling, ridging, curling and distortion of flowers[3,4,5], leading to diminished flower size, quality and great economic loss. The CPs of CymMV and ORSV are expressed from their respective subgenomic RNAs. In addition, the CP of Potexvirus has been found required for cell-to-cell movement[9], whereas that of Tobamovirus is a host-specific determinant of long-distance movement in plants[10]. No insect vector has been reported in the field, we lack efficient measures to control virus diseases as compared with other pests and pathogens

Methods

Results

Conclusion