Journal
VIRUSES-BASEL
Volume 13, Issue 8, Pages -Publisher
MDPI
DOI: 10.3390/v13081552
Keywords
odontoglossum ringspot virus (ORSV); cymbidium mosaic virus (CymMV); viral synergism; RNA silencing; viral suppressor of RNA silencing (VSR); Phalaenopsis
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Funding
- Institute of Plant and Microbial Biology, Academia Sinica, Taiwan
- Innovative Translational Agricultural Research Program [AS-109-ITAR-L02]
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Synergistic interactions among viruses, hosts, and transmission vectors during mixed infection can change viral titers, symptom severity, or host range, with VSRs being one contributing factor. ORSV and CymMV exhibit unilateral enhancement in Phalaenopsis orchids, revealing the VSR function of ORSV's replicase P126 in enhancing CymMV cell-to-cell movement. Mutagenesis analysis showed that the VSR and protein function of P126 might be prerequisites for this enhancement.
Synergistic interactions among viruses, hosts and/or transmission vectors during mixed infection can alter viral titers, symptom severity or host range. Viral suppressors of RNA silencing (VSRs) are considered one of such factors contributing to synergistic responses. Odontoglossum ringspot virus (ORSV) and cymbidium mosaic virus (CymMV), which are two of the most significant orchid viruses, exhibit synergistic symptom intensification in Phalaenopsis orchids with unilaterally enhanced CymMV movement by ORSV. In order to reveal the underlying mechanisms, we generated infectious cDNA clones of ORSV and CymMV isolated from Phalaenopsis that exerted similar unilateral synergism in both Phalaenopsis orchid and Nicotiana benthamiana. Moreover, we show that the ORSV replicase P126 is a VSR. Mutagenesis analysis revealed that mutation of the methionine in the carboxyl terminus of ORSV P126 abolished ORSV replication even though some P126 mutants preserved VSR activity, indicating that the VSR function of P126 alone is not sufficient for viral replication. Thus, P126 functions in both ORSV replication and as a VSR. Furthermore, P126 expression enhanced cell-to-cell movement and viral titers of CymMV in infected Phalaenopsis flowers and N. benthamiana leaves. Taking together, both the VSR and protein function of P126 might be prerequisites for unilaterally enhancing CymMV cell-to-cell movement by ORSV.
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